fairing yacht hull

How To: Our top 5 tips for fairing a hull

Fairing a hull may seem like an overwhelming task but there are ways that you can make the process a lot easier, whilst also achieving a great smooth finish. Before using fairing boards for final fairing, why not try working with a grinder? You will need to be careful handling the device in order to control the removal, however this method can remove a substantial amount of material very quickly .

For safety, it’s probably a good idea at this stage to cut the corners of the square pad to a radius of 50mm and sand all the edges. It should end up looking something like this:

Drawing ‘glue’ and ‘sight’ lines Be careful to make sure you attach the foam exactly into the centre to avoid distortions. In order to do this, you can use a centre punch to mark the middle and then with a pencil compass or scriber, mark a circle the exact size of the pad’s diameter. This is the glue line. After this, make a concentric ring 3mm larger – this is the sight line. This is important because once the epoxy starts to squeeze out, the glue line may not easily be visible. Finally, ensure both surfaces have been abraded with sandpaper.

Applying epoxy to each surface Next, apply two thin, level coats of unthickened WEST SYSTEM epoxy on each surface, making sure that the surface beneath the square is flat. Your clamping system should be simply four 25mm x 100mm boards about 300mm long and 2kg lead weights. This passive clamping protects the foam from permanent distortion.

Make sure never to store the pad on its face with the machine attached, as this will distort the foam making it unusable.

• When using a variable speed machine, we recommend you start with a slower speed until you are comfortable using it. We find the optimum speed to be around 3,000 rpm.
• Avoid moving in a fore and aft direction on a waterline– it is crucial to use a continuous diagonal movement across the surface.
• Move your feet 3″ to 4″ for every pair of arm passes. Ensure that this constant motion is used across all areas including hard to reach areas– this can be a bit of a pain but it’s very important.
• We found that the best approach is to do multiple passes, removing small amounts of material each time. You will notice as you go that visible irregularities will disappear. Dust off the hull several times throughout this stage so you can inspect the progress thoroughly.
• You can use a pencil to mark any imperfections and it would also be a good idea to mark the entire surface as you go along, to keep track of the areas you’ve completed.

There you have it, our sanding tricks of the trade. Try them out next time you need to complete a hull fairing job to make the task a little easier for you.

Our thanks to Damian McLaughlin for his great ideas.

Visit West System International   for more tips on fairing and view the full range of WEST SYSTEM epoxy here.

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File / All you need to know about the fairing

Before starting the season or before launching your boat, it is essential to proceed with a refit, which consists of cleaning, inspecting, repairing and painting the hull. This step is crucial to guarantee the best performance of your boat.

The fairing is an important step in the maintenance of a boat, allowing to maintain its performance by minimizing the resistance of the hull in the water and guaranteeing a better speed and maneuverability. In addition, it prevents the accumulation of shells, algae and other marine organisms that can affect the speed and maneuverability of the boat .

After a period of immobilization, it is essential to clean the hull of your boat. The careening must be done every year, and can raise many questions about the steps to follow and the products to use. Whether you are looking for technical products for optimal gliding or resistant products for the whole season, there is something for everyone.

Even if it is not the most pleasant period for boaters, you should not make a mountain out of it. We offer you a complete file to make your careening a success.

Summary of the report

8 essential checks at the time of refit

Boat renovation: primer and epoxy undercoat

10 steps to a successful refit

Why do the hulls of our boats get dirty?

How to choose the right antifouling for your boat and your sailing program?

What is the essential equipment to apply antifouling?

Choose your antifouling paint, which matrix for which use of the boat?

Knowing the quantity of antifouling necessary for the careening of your boat

Is it necessary to apply antifouling to the propeller of his sailboat?

The method for applying antifouling, step by step

How do I know if I need to redo my erodible antifouling?

Designer's Notebook: Fairing by the "RABL Method"

Posted by Glen Witt on Dec 28th 2011

Most have never heard of Sam S. Rabl, a naval architect, author and innovator of small boat building methods. Sam was at the height of his career back in the mid-forties, when he wrote several books and numerous boatbuilding articles. Most of his works are now long gone, so why should you care about this man?

Sam developed a method of fairing a boat framework to accommodate sheet plywood that is simple and accurate; it takes the guesswork out of fairing. We call it the “Rabl Method”.

Sheet plywood boat planking is bent to the shape of a segment of a cylinder or a cone, a design process known as “conendric development”. Sam Rabl used this design method as the basis for his novel fairing method.

Most sheet plywood boat hulls are easy to fair in the aft section (incidentally, the word “fairing” means shaping a boat framework so the plywood will lay flat or mate to all members). Using the forward bottom of a typical sheet plywood hull as an example (see Plate 18-C) a series of equally spaced points are drawn along the curvature of the stem/keel and chine. The spaces are usually about a foot apart, although more points can be added if desired.

Starting at the stem/chine junction the points are labeled progressively "A”, “B”, “C”, etc., along both the stem/keel and chine. Use a straight-edge extending between points “A” on the stem and “A” on the chine to determine the amount of bevel required; file a notch in the respective members so the straight edge lies flat. Continue doing the same at each point, going aft until the bottom is flatter in section; the bevel at each frame is then filed in the keel and chine.

Use a plane sweeping between the points in a fair line and you have an accurate faired surface that the plywood planking will contact. The same method can be used to fair the surface for the side planking, but in practice using the frames as a guide and notching the chine or sheer will suffice.

As you sit back and admire your accurately faired hull give a thought to Sam Rabl, the guy who made it so easy.

Editor’s Note: A clever adaptation of the Rabl Method can be viewed in the Fairing Frames without Trouble video posted by Klaus Silbernagl immediately preceding this post in the Boatbuilders' Blog.

You can find dozens more "Designer's Notebook" articles by Glen L Witt in the arhives of the Glen-L WebLetters , the forerunner of the Boatbuilders' Blog.

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Hull Fairing And Development: Why And How

Remember how you might have created many things out of paper folding such as animals, flowers etc. back then you had actually learnt the concept of development of 3D dimensional objects starting with 2D laminas (e.g. paper). Now, let us think of something quite complex in three-dimensional terms but quite large in size. Yes, I’m talking about a ship’s hull.

How would you design a ship hull with all its curvatures and characteristic intricacies such that it doesn’t become too complex for production? Obviously, you would search for ways to break it down to smaller manageable pieces which can be easily processed in the workshop as the workshop has to find out practical ways to create a scaffolding/loft for bringing the desired hull shape to reality.

The concept of development of the hull plating for production is a very relevant one even in today’s CAD (Computer Aided Design) era. The ship hull is designed on a software platform which enables the user to visualise the 3D problem (Representation of the three-dimensional hull lines as 2D equivalents in various sections i.e. the sheer plan, half breadth plan and the body plans) in an intuitive manner. By making changes in any one of these sections, the user effectively manipulates the lines in 3D changing the other sections instantaneously.

Given this great advantage, we come to the actual problem of fairing a hullform while keeping the curvature developable with plating. Fairing often tends to get many definitions across literature, but it effectively serves certain purposes:

• Superior hydrodynamics: optimal vessel speed, low resistance, increased fuel efficiency, manoeuvrability, etc. • Aesthetics: appeal to the human senses, functionality after life cycle (e.g. conversion to resorts, display in museums, etc.)

However well built a vessel might be, it might serve its purpose very well, but the finishing and fairing job done reflects the shipbuilder’s attention to the tiniest of details and is often a matter of pride for them. Finishing and fairing are often considered among the finer arts of shipbuilding.

For a moment, think of you have the job of producing a smooth surface out of a body with a coarse surface, you have the option of removing away the high points on the surface until you reach a low level (something often done with wood), also you have the option of adding material to reach a higher level to maintain evenness (paints and surface applications) you could also take some material from the higher planes and deposit it on the lower planes to reach a degree of smoothness. Shipbuilding employs paint, surface preparation, and many other techniques to achieve the level of finishing of modern-day standards.

A ship hull is composed of numerous steel plates which are rolled or bent to give the characteristic shape at some section. Take a look here at a ship’s shell expansion plan:

This represents the developed surface of the plating used (at plate level) in the manufacture of a vessel and often gives an estimate of the steel to be used in manufacturing the ship. But since the development of a shell expansion plan comes quite later in to the ship’s design cycle, the designer is faced with the problem of ensuring that the hull surface is fairly developable. This is where software comes in. Advanced ship design productivity suites like MAXSURF or DELFTship provide fairing modules for this. The principle on which these are based is that the curvature of a certain ‘patch’ or element in the hull skin can either stand for single/multiple or positive/negative curvatures for the collection of points within it.

Certain typical representations of such curvature are as follows:

1.) In ship designs, the transverse curvature is particularly higher than the longitudinal curvature and so it might be helpful to exaggerate the transverse curvature in view to aid the designer in finding out the inconsistencies (if any) in the fairness of the model. For this reason, some programs allow this to be represented as one of the rendered forms.

2.) Another important tool allows us to modify particular waterline contours based a graphical representation of the curvature along the contour, often called curvature porcupines. Notice the radially outward emerging lines in grey? The height of these lines are proportional to the amount of curvature inherent at the location. Even a slight change in control point position alters these greatly and hence offer a better intuitive experience of fairing. In the event an outward emerging porcupine ends up inside the waterline, the section indicates a hollow in the hull surface and needs rectification. The porcupine curve which runs along the porcupines should be fairly smooth, if not, then there are options to change the stiffness of the control points used in the model.

3.) One popular and simple way of evaluating the fairness is by using the rendered hull using lighting highlights. This shows how light would bounce off the surface of the hull around the hull and often is useful in creating promotional and non-technical content too. This tool entirely depends upon the user’s perception and can only be used for major bumps/irregularities.

Read the full article on the Navisieger magazine here

This article is authored by  Sudripto Khasnabis  and was originally published at the inaugural issue of Navisieger. Navisieger is a magazine published by Learn Ship Design. It is a confluence of insights on the maritime technology sector taken from academic experts, naval architects, industry veterans in this field, in the form of articles and exclusive interviews. Learn Ship Design is the first student initiative in India that works towards enhancing industry-academia engagements in the maritime sector. 

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Hull fairing questions

Discussion in ' Boatbuilding ' started by laukejas , Nov 2, 2020 .

laukejas Senior Member

Hi guys, I have another question about some issues I've been having with fairing the hull on my new boat. It is a 4-meter open-transom sailing dinghy, built from 4mm okoume plywood. I am at the stage where the all the parts are in place, and it is now time for fairing and sanding. I want to do this before fiberglassing (boat will be glassed inside and out), because there are some surface irregularities, especially on the deck, that need to be faired before fiberglass is laid down, or else I will have to do it on top of fiberglass, and then it might crack over time. For fairing compound, I am using epoxy filled with microspheres, sometimes adding a little bit of fumed silica to prevent sagging. Today I faired the cockpit and the top deck. Before fairing: First, I wetted out all the surfaces to be faired with unthickened epoxy, and then started applying thickened epoxy, trying to put on a thin, consistent layer. At which I failed completely. After fairing: I spent 8 hours to get to what you see here. Just mixing epoxy, spreading it, trying to even out with a spreader, adding more to low spots, spreading again... And the result is still horrible. I used up 2 liters (half a gallon) of epoxy just to cover all these surfaces. I was trying to put down a layer as thin as possible, but if I go too thin, then the wood texture shines through, and I won't have a consistent-color surface when fairing, making it difficult to locate low and high spots. And besides that, turns out it is incredibly difficult to put down a thin layer without scraping it off completely. Especially over such a large area. I tried plastic spreaders, steel spatulas, flexible battens... None of these tools give a desired result unless the area to be faired is small and easily accessible. This is my first time fairing a hull, and I feel very disappointed at the result, especially considering the amount of epoxy I used up, most of which will be wasted when I sand it out. I thought of fairing only areas that are actually uneven, rather than fairing everything like I did. But there are 2 problems with that: 1. If only some areas have fairing compound applied to them, they will be harder than the surrounding bare plywood. And when I sand, it will be impossible to make the surface fair, because plywood will wear down faster than epoxy fairing compound. Even with microspheres, epoxy is just too damn hard. 2. It is extremely difficult to spot the low spots and high spots when the plywood is not painted in a uniform color. I tried using portable lights, battens slided over curved surfaces, feeling with my hand, but truth be told, none of these methods gets me close enough to a truly fair surface that would look good after it is painted. Only the paint seems to truly reveal these imperfections... Only it is too late by then. So my question is, what am I doing wrong here? How is that fairing supposed to be done without wasting such massive quantities of epoxy, not to mention time? Am I really supposed to cover ALL of the boat with fairing compound? If not, then how do I know where to add it, where the low spots are, before the boat is painted? And if I apply fairing compound only to selected places, how do I avoid having surfaces of different hardness when sanding? And most importantly, is there a way to give that plywood a consistent appearance that would show all the imperfections that I need to fill and sand? Some cheap, lightweight material (like paint), but one that will have no adhesion problems when epoxy/fiberglass is added on top of it? I mean, I have read quite a lot of boat plans, that include bill of materials... And on boats of comparable size, I have never ever seen such an amount of epoxy listed in the bill of materials that I have used! Surely I am doing something wrong here. You have reached the end of a this very long post. Thank you for your patience Please help!!  

jbo_c Junior Member

Are you using a board? If you aren’t, you’ll always just move the irregularities around. Also, use an indicator coat to help you know where to work. Jbo  

jbo_c said: ↑ Are you using a board? If you aren’t, you’ll always just move the irregularities around. Also, use an indicator coat to help you know where to work. Jbo Click to expand...

Blueknarr Senior Member

Feel your pain. Congratulations. You arrived at the two conclusions at 8 hours that it takes most 8 days or weeks to understand. Fairing can't be done with differential substrates. Pre sealing the wood was wise The late PAR have the best explation of fairing that I have read. Find and read it if you can. Going forward Block down what you applied. Sheath with glass. Add more micro balloon to peanut butter or mashed potatoes consistently Spread with a "V" notched trawel. Let harden Fill the grooves with more mashed peanuts Block Prime Paint What kind of sanding blocks do you have?  

BlueBell . . . _ _ _ . . . _ _ _

laukejas said: ↑ What is an indicator coat? Click to expand...

Blueknarr said: ↑ Feel your pain. Congratulations. You arrived at the two conclusions at 8 hours that it takes most 8 days or weeks to understand. Fairing can't be done with differential substrates. Pre sealing the wood was wise The late PAR have the best explation of fairing that I have read. Find and read it if you can. Going forward Block down what you applied. Sheath with glass. Add more micro balloon to peanut butter or mashed potatoes consistently Spread with a "V" notched trawel. Let harden Fill the grooves with more mashed peanuts Block Prime Paint What kind of sanding blocks do you have? Click to expand...

I meant “are you using a board for fairing?” An indicator coat is commonly something like a very light mist of spray paint that you put on before you start with the board so you see low spots easily when you’ve done some sanding. Then you know where to fill and where to stop sanding. Jbo  

That's the PAR . I don't know exactly where on his site the information you need is. Yes more fairing compound. You will need some after the cloth is pit down to fill the weave and wherever it overlaps. The 15inch longboard would be my choice for sanding the fairing compound. The notched trowel will give you the best chance of an eaven coat of compound. Practice with dry-wall mud on another surface. It is better to apply the second coat before the first fully cures.  

jbo_c said: ↑ I meant “are you using a board for fairing?” An indicator coat is commonly something like a very light mist of spray paint that you put on before you start with the board so you see low spots easily when you’ve done some sanding. Then you know where to fill and where to stop sanding. Jbo Click to expand...

Spray paint for a guide coat is common. It should only be a very fine mist, like overspray, NOT like you’re actually trying to color the surface. Jbo  

jbo_c said: ↑ Spray paint for a guide coat is common. It should only be a very fine mist, like overspray, NOT like you’re actually trying to color the surface. Jbo Click to expand...

Fairing compound is rarely listed in a materials list. Just like primers and paint. They are concerned "finishing" materials not "building" materials. It looks like you could have used much more balloons than you did. More balloons means less epoxy. Beware of Urine video of most coat. Most of the ones I have seen show bad techniques which will de-fair a surface. Watch one then remember that the goal is fair (flat) NOT removing the spray paint. Keep working the entire area NOT JUST where the mist coat remains. Focused sanding on a low spot covered with mist only creates a deaper valley. I recumend using the biggest, stiffest and firmest longboard you can manage.  

Barry Senior Member

FS 42070 E - Shipyard sander by Flexisander | NauticExpo https://www.nauticexpo.com/prod/flexisander/product-29251-307824.html This video really shows the ability of this sander. This is from Flexisand. They also have manual boards that apply pressure more evenly than a a "board" This one looks like you may just use your own grinder to power though I could not find a dedicated unit with the powered and board as one unit. I have seen them air powered or electric. The board in this case does do corners, though the air type that I have seen was longer  

Blueknarr said: ↑ Fairing compound is rarely listed in a materials list. Just like primers and paint. They are concerned "finishing" materials not "building" materials. It looks like you could have used much more balloons than you did. More balloons means less epoxy. Beware of Urine video of most coat. Most of the ones I have seen show bad techniques which will de-fair a surface. Watch one then remember that the goal is fair (flat) NOT removing the spray paint. Keep working the entire area NOT JUST where the mist coat remains. Focused sanding on a low spot covered with mist only creates a deaper valley. I recumend using the biggest, stiffest and firmest longboard you can manage. Click to expand...

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Correct. Stiffest possible but still able to flex into the desired curves. Too flexible and the board will simply conform to the un-fair surface The same with a too soft (squishy) board Lots of finding the momma bear's soup The hull will conform to a stiffer board, but a flexible board will conform to the hull The hull will conform to a harder board, but a squishy board will conform to the hull. The larger the board the more the hull will conform to it. But the harder it is to slide around.  

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• Practical Boat Owner
• Digital edition

16. Fairing the curves

• March 16, 2019

Casting a critical eye over the project boat’s lines, David Pugh and Ben Meakins set to work filling and fairing to make the hull smooth

In the previous article (Secret 20: Rounding the bilges) , we explained how we built up the chine panels on our project Secret 20 using cedar strip and epoxy.

See the full set of articles: Building the Secret 20 kit boat with PBO.

Aided by a little filler, this approach got us most of the way to completing the required curve, but they still needed fairing to get them to their final shape.

Other areas which still needed careful shaping were the angle between the keel and the bottom hull panels, the stem and the transition between the 6mm midships hull panels and the 4mm bow panels.

Additionally, the entire hull needed checking for high and low spots, and fairing as required.

Fairing is one of those jobs that can go on for ever, with endless rounds of filler and interminable sanding – and, to coin a phrase, you reach the ‘sod it and move on’ stage.

We’re not quite there yet – there are a few more rounds of filler to go – but it’s not far off!

Longboards made short work of fairing

How to spot highs and lows

By far the best tool for spotting irregularities is a critical eye. Get down low to the surface you’re examining and look at it from every angle and you’ll spot problems that evade a simple glance.

Hands work well too: when you’re sanding, run a hand over your work regularly to find small bumps and hollows.

There are ways you can help your eyes, however. The instructions which come with the boat kit suggest drawing a grid over the whole boat before using a longboard (sandpaper attached to – you’ve guessed it – a long board) to give the hull an initial sand.

The board will bridge across any high points, removing the grid, while leaving the marks untouched in any hollows.

Mike Pickles, foreman at Harbour Marine Services in Southwold and regular author of our ‘View from the Boatyard’ column, recommends simply scribbling over the area to be faired before using the longboard.

It’s the same idea, but easier than drawing a grid on the hull skin.

Another technique we found useful was a laser level. These project a long, straight line which when shone onto an irregular surface shows any lumps and bumps quite well.

We found it works best when the laser is angled obliquely to the surface.

A lower tech method is to use strips of tape, which just like the camber stripe on a sail help to show if a curve is fair or not.

A laser level shone obliquely showed up any lumps or depressions on the hull skin

Shaping the chines

A set of templates had got us close to the shape we needed, but there were still some areas which needed attention.

Approximately half way along the chine were some large flat spots owing to there being insufficient timber to completely build the curve, and a few other errors were apparent in other areas where we had been too enthusiastic with the plane.

Rather than adding more timber, we decided that the shape was close enough to allow us to make up the difference with fairing filler.

We used WEST SYSTEM low density microballoon blend in a stiff mix of epoxy to build up a layer of filler on the areas in question.

After letting it cure for 24 hours we sanded it back, first using a random orbital sander to remove obvious high points, followed by longboards and sandpaper pulled like a strap across the chine.

This was mostly successful, but we needed a further two applications of filler on the largest flat area. Building up smooth layers of epoxy is not easy – if you make the mix stiff enough to support thick layers of 10mm or more then you risk a rough surface and voids in the filler.

A less stiff mix gives a better finish, but you then need to build up layers and ensure the previous layer is clean and keyed to ensure good adhesion.

A random-orbit sander sped up the fairing of the chines

Smoothing the panels

Beyond general fairing, there were three main areas on the boat which needed special attention.

The first is the transition from the midships bottom panels, which are 6mm plywood , to the 4mm ply bow panels. This results in a 2mm step.

We removed the majority of the difference by using a long plane to taper the 6mm ply over a distance of around 40cm, before filling any hollows with fairing filler. The 4mm ply tends to scallop slightly around the fixings, so filler is inevitable.

Further aft, we had used two small 6mm panels to fill the gap between the midships panels and the aft bottom panel.

A longboard (sometimes known as a torture board!) was painful but effective

A longboard showed up areas that needed extra filling

As they were small it had proved impossible to make them continue the gentle bend of the bottom panels, so we glued them in place and used a plane to remove any high spots.

As they were mostly too high at the edges, we didn’t need much filler.

The third and final area was at the bow, where the bow panels meet the stem.

The ply had scalloped quite badly here where we had used screws to pull it into shape, so we cautiously planed the top of the bumps, taking care not to go through more than one laminate of plywood, and filled the hollows.

Masking tape stuck over the chines showed up any hollows or flats

Keel to hull joint

The kit provides two long mouldings to ease the gap between the keel and hull.

We first dry-fitted them, pulling them into place with long screws to check the fit before removing them and gluing them back into place with epoxy.

The mouldings provide most of the required curve, but as they don’t taper to a feather edge there’s some work required to fair them into the hull and keel on either side.

We found this was best done in two stages. The first was to make a tapered fillet on either side, for which the square end of a filleting stick proved ideal.

The angle was still too steep, however, so we used the back edge of a putty knife to form a curved transition on both sides using fairing filler.

The final shape to make was the lead into these mouldings at the forward edge of the keel.

We did this using more epoxy and fairing filler, formed to shape as best we could when wet.

We then finally shaped it using sandpaper in a roll to ensure the correct concave shape. The same technique was used to fair the fillets we had applied along the length of the keel.

We used a piping bag to pipe in a long fillet to secure and fair in the keel battens

A filleting stick smoothed the seam well

A mess of epoxy faired front of the keel…

…which could then be sanded smooth

Shaping the stem

This was possibly one of the most satisfying jobs on the boat so far. The stem, running down to meet the keel, had been left square while building the hull, so the challenge was to shape it to provide a pleasing angle between the two sides of the hull.

It also needed to be left square at the top in order to accept the bowsprit stemhead fitting.

We started by deciding the point at which the square would begin to taper, then set to work planing.

Using a long plane helped us to follow the angles set by the bow panels and did most of the work low down on the stem and along the forefoot, where we wanted a rounded shape between the two.

We used the plane to take the timber to a point, before rounding it off using a block plane and sandpaper.

Further up the stem we had to be more circumspect, so started off by carving a 45° angle into the stem using a spokeshave.

After continuing this a few inches down the stem, we drew a line from this to an estimated waterline and tapered the timber between the two points to match using a plane.

Once we had the shape we needed, we sanded the whole area to remove any irregularities, easing any sharp corners as we went to improve paint adhesion later on.

We also glued timber fillets in place at the top of the stem to make it wider, ready to acept the stemhead fitting.

A long plane to transfer the hull angle to stem

We used a spokeshave cut a ‘stopped arris’ on the stem

Fairing’s an odd sort of job, with much of what you do making the boat look worse rather than better as it starts to resemble a patchwork quilt. However, running your hand over the result is certainly rewarding as you feel a smooth, blemish-free surface beneath.

The most satisfying job by far, though, was planing the stem. Suddenly this rather agricultural, square timber took on new life as a shapely bow ready to carve its way through the water. It’s improved the aesthetics of the bow immensely, and is a reminder of what this boat’s meant to do – sail.

As published in the November 2017 issue of Practical Boat Owner magazine.

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Fair Through Hull Fittings: Essential to a Smooth Bottom

“She’s not very fast in light air. After all, she’s a cruising boat.” Are you still using that excuse for the poor light air performance of your boat? While you may never be able to turn the Seu Slug into Superboat there’s a good chance that you can measurably improve the light air perfor­mance of the typical production boat with little more than a fair amount of elbow grease. The secret is to pay attention to underwater fairness and smoothness.

In light air, a major portion of the total resistance of a sailboat derives from skin friction. To oversimplify, the smoother the boat’s “skin” — the submerged part of the vessel — the less power is required to drive it to a given speed. Put another way, given two boats identical in every way, including sail area, the boat with the smoother bot­tom will be slightly faster than a boat with a rough bottom in light air.

“Smooth’ and “rough” are, of course, relative terms. For practical purposes, the bottom of a displacement-type sailboat can be considered smooth if the surface varies no more than 2 mils — .002″! Before you throw up your hands in despair, it should be pointed out that a surface of this quality is not that hard to achieve. The base surface of the typical production fiberglass boat is this smooth when it comes from the mold. The smoothness begins to be compromised almost immediately, however, as through hull fittings, transducers, and bottom paint are added.

Most racing sailors have learned the value of a smooth bottom. Ironically, cruising sailors can benefit at least as much from the creation of a low-resistance bottom as racing sailors, although you rarely see a cruising or daysailing boat with a bottom to match that of a good racing boat. Why handicap a cruising boat, which is probably already underpowered in light air, by having a bottom which almost guarantees reduced performance in the lightest conditions? Almost any tub can be driven to hull speed with 20 knots of breeze, even if it has foot-long grass and an acre of barnacles on the bottom. But it takes a smooth bottom to help it along in a three knot zephyr.

You can begin along the path to a fast bottom by recess­ing or fairing in through hull fittings that protrude beyond the surface of the hull, particularly in the forward half of the boat. Typically, this means the head intake and discharge fittings.

Whether you decide to recess fittings or fair them in depends on the hull construction, the amount of money you want to spend, and the amount of time you want to spend.

The normal through hull, with rounded edges to the exter­nal flange which sits on the surface of the hull, is more suited to fairing in than to recessing. Through hull fittings specifically designed to be recessed have either a flange with vertical sides – sort of like the butt hinge designed to be recessed in the edge of a door -or they are beveled on the underside of the flange. If you want to spend the least amount of money and time, you’ll simply fair in the surface mounted through hulls. If you want the lowest resistance bottom, you’ll recess or replace them.

If you have a small boat with a fairly thin skin, it will probably be safer to fair in -building up material rather than to recess, which must inevitably remove some of the hull laminate. Likewise, if the hull is cored, and the outer laminate is thin, it is safer to fair in than to recess, unless the hull is solid laminate in the way of the through hull fittings. It’s fairly conservative to say that if the hull is less than 3/8” thick at the location of the through hull, you should fair in rather than recess the fitting.

Fairing in a fitting is pretty much the same, whatever the hull material. The only caveat is that with metal boats, you must not damage the barrier coats between metal and bottom paint. If you expose steel or aluminum, you must build up the barrier system again before fairing in. With metal boats, the adhesion of the fairing putty used is then limited to the strength of the barrier coat’s adhesion to the base metal,

Less care is required with a wood or fiberglass hull. Bottom paint surrounding the through hull to be faired in should be removed, and the gelcoat or wood sanded with medium grit paper in preparation for the application of fairing compound.

The larger the area over which you fair in the fitting, the more effective the job will be in terms of reducing drag. Obviously, at some point fairing in over an increasingly larger area simply doesn’t pay off. It becomes a lot of work without commensurate return on your time.

As a general rule, you should fair a through hull over the area of a circle whose radius is equal to about 4” for every 1/8” the fitting protrudes above the surface of the hull. For example, the typical 1 l/2” through hull for a head discharge sticks about 1/4” above the surface of the hull. Therefore, you should fair it in over an area that extends eight inches in all directions from the outside edge.

The actual fairing process is straightforward. Remember, bottom paint is removed and the surface given some “tooth” by sanding in the area to be faired. In addition, the bronze through hull must be sanded bright for adhesion of the fairing compound.

With a pencil, draw a circle on the hull around the fitting, the circle defining the area to be faired in. This area, and the outside of the through hull fitting, should receive a prime coat of clear epoxy resin to improve the bonding of the fairing compound.

The fairing putty should be epoxy based, using either microballoons or microspheres for thickening. Microspheres are slightly less dense, and their white color gives you a fairing putty that more or less matches the white bottom gelcoat of most boats. You can use a premixed putty such as Marinetex, but this is quite a bit more expensive than making your own from epoxy resin and fillers. In addition, making your own putty allows you to control the viscosity, making a putty as wet or dry as you need.

Using a trowel, wide putty knife, or flexible spatula of the type used in auto body work, trowel the putty onto the wet unfilled prime coat of resin. Smooth the mixture on the hull, tapering the thickness from the edge of the through hull out to the circle you’ve drawn on the hull. Get the fairing compound as smooth as you can, tapering as evenly as possible. The smoother you put it on in the initial application, the less sanding and spot filling you must do after the first coat has dried.

Putting on the fairing compound is trickier than it sounds. You must mix a putty of a consistency that is full-bodied enough not to sag off the hull while it dries, but is not so thick and dry that it can’t be smoothed with a trowel. A mixture the consistency of cake frosting is just about right.

Once the putty has set up, fair it in to the surrounding hull, making the transition as smooth as possible. Trowel on another coat of putty in any low spots, which can be detected by running a straightedge over the faired area. In any area where daylight shows under the straightedge, fill with more compound. Remember, the larger the area you fair in, the less disturbed will be the water flow over the hull.

Once you’re satisfied with the smoothness of the job, prime the area, including any adjacent gelcoat that has been sanded, with a two-part epoxy primer. Wet sand this smooth before bottom painting.

Although fairing in goes quickly and is just about minimum cost, it is really a second-best solution. Recessing the through hull flush with the skin of the boat is more effective in creating a low drag surface. Recessing is usually more work, however, and may cost more if you don’t already have the tools to do the job.

Special through hull fittings are made for flush mounting. Oddly enough, the ones we’ve seen are really a poor design for the job, because they’re fairly difficult to install, and have a flange that is too thick to use in the typical fiberglass production boat without reinforcement of the inside of the hull. The flush fittings work best if the hull skin is 5/8” thick or more, which means either a wooden boat, or a large fiberglass boat.

In addition, if you decide to replace your existing surface mounted fittings with flush fittings, you’ll have to lay out about $15 for a flush 3/4” through hull, and about $30 for a similar l1/2″ fitting.

Flush fittings are frequently used in fiberglass boats with cored hulls, since the total hull thickness is enough to accept then without weakening the layup excessively. However, the core material must be removed around the through hull, and solid glass laid up in its place. This is far easier to do in the original hull layup than in an existing hull, although it can be done if you’re a real masochist.

Cutting the mortise for a recessed through hull is the hardest job, because the mortise must be flat on the bottom, beveled on the edges. The accompanying illustration should make the problem more clear.

If you want to recess a through hull on a cored boat, take a deep breath and steel your nerves: here’s how to do it.

Remove the through hull and the seacock. Get your new flush-type through hull, and get a hole saw the diameter of the flange of the through hull fitting. Hole saws, designed to fit the chuck of a drill motor, are available at any large hardware store. Sizes are usually available in 1/16” increments. Note that a different size hole saw is required for every different size through hull fitting, so by now you’re going to have to spend some money. A hole saw arbor costs about $8, the hole saws about $8 to $12 each. A $2.99 multi-sized hole saw from the discount store may get you through one hole, if you never think you’re going to use it again.

Now comes the scary part. Cut a hole through the outer skin of the boat, concentric with the existing hole for the through hull, that is the size of the flange of the new flush through hull fitting. Don’t cut through the inner skin!

Next, dig out the core material around your cut for a distance of an inch or more, cutting back with a sharp knife or chisel. Clean the remains of the core material thoroughly from the inner surfaces of both fiberglass skins. What you are going to end up with is a solid glass section of hull in the way of the through hull fitting, and you want to remove all traces of core material that might inhibit the bond between the hull skins and the new glass you put in.

Test the fit of the through hull fitting in the holes you’ve cut in the hull. The through hull must be held in place while the new glass layup kicks off, and it must be held in place with as little movement as possible. A through hull retaining nut, which is designed to hold the fitting in place when it is installed without a seacock, will probably be adequate for securing the fitting during the critical cure period of the new fiberglass. It may, however, be necessary to physically hold things in place on the inside of the boat. A steady hand on the threaded tail of the through hull will do the job. Since the glass mixture may get hot, the steady hand should be gloved. To fill the cavity you’ve created by removing core material, you’ll need loose fiberglass fibers, or chopped strand mat, which easily pulls apart. Also required are rubber gloves, acetone, and polyester resin. Epoxy resin would work fine, but the cure time is longer and the cost greater.

Thoroughly wax the new through hull fitting, filling the threads as much as possible. Also wax the retaining nut that will be used to hold the fitting in place.

Because polyester resin will kick off quickly in the thick mixture you’re going to make, do a dry run before committing yourself to the job.

The idea is to pack the area where you’ve removed the  core material with a thick mixture of fibers and resin, then insert the through hull in place. When your glass mixture cures, you should have a perfect imprint of the through hull fitting in the hull, with solid fiberglass surrounding the fitting. The hull will be locally reinforced, and there will be no possibility of water penetrating the core.

This seemingly complicated process is basically the same method that boatbuilders use in original construction when flush fittings are installed in a cored hull, except that they have the advantage of doing it during the hull taking only a few minutes rather than the several hours you’ll have to spend.

-Work fast.

-Use the minimum amount of catalyst in your resin.

-Make the mixture dense -more fiber than resin.

-Brush the inside surfaces of the hull skins with unfilled resin before jamming the mix in, to seal the edges of the core.

-clean up resin overflow on the outside of the hull with acetone before the resin kicks off.

Mask off the areas of the outside of the hull adjacent to your work area, using polyethylene. Remove the masking immediately once everything is in place and spills are cleaned up.

To insure a perfectly flush fitting in the final installation, the through hull should actually be pulled slightly below the outer surface of the skin during the molding process. This allows a little room for bedding compound under the flange when the fitting is actually installed.

Because a lot of hands are required in the short time you have to work the catalyzed glass mixture, it’s helpful to have another person assisting at this stage. The helper will be most useful on the inside of the boat, installing the retaining nut and holding the through hull in position.

As soon as the resin mixture has kicked off, remove the through hull. Chances are that it will be lightly bonded in place, no matter how thoroughly you wax it. Light tapping with a wood or plastic mallet, or a hammer and a softwood block, should free it from the hull.

Before final installation of the through hull, heat it with a propane torch to remove the wax. Remember that paraffin is flammable, so hold the fitting with pliers or set it on the ground before heating. Obviously, this job should be done outdoors.

You should also round the edges of the transition between the bottom of the through hull flange mortise and the hole through the hull for the stem of the fitting to leave a space for bedding compound. It may also be necessary to cut the stem shorter to allow it to screw far enough into the seacock to be flush with the surface of the hull. Any glass dribbles on the inside of the hull should also be sanded or ground off before installing the seacock.

Recessing in Solid Hulls

Most uncored fiberglass hulls simply aren’t thick enough for the use of a standard flush fitting. If you want flush fittings on a thin solid hull, it will be necessary to lay up fiberglass on the inside of the hull, in effect building a glass backing block under the seacock at least as thick as the hull skin, preferably thicker. This is messy and a little time consuming.

Ideally, the buildup should cover an area no less than one foot square, and consist of alternating layers of mat and roving, with the resin carefully squeegeed out, just like laying up a hull. There is some risk of distoring the hull locally from the heat of laying up this fairly large patch, so it is best done a few layers at a time. Wax-free laminating resin must be used, or the interlaminar bond will be poor.

Once the backing block is laid up, you can cut for the flush fitting using the same method described for cored hulls. A fair amount of grinding and smoothing will be required on the inside of the hull after the interior layup is added, to make the job look clean and professional. If you don’t make it look clean and professional -and this goes for all work you do on the boat -the improvements may actually decrease the value of your boat, or make it difficult to sell.

Flush Fittings in Wood Hulls

Installing flush fittings in a single skin wood hull is easier than in any glass hull, since the planking is thick, there is no core to remove, and a backing block should already be in place under the seacock.

Two methods are acceptable. Using a hole saw and chisel, cut a circular mortise in the planking the depth of the through hull flange and the diameter of the inside surface of the through hull flange. The bevel can then be cut in with a sharp carving blade.

If you’re not skilled with carving tools, cut the mortise the size of the outside (larger) surface of the through hull flange, and fill in the gap between the beveled surface of the through hull and the bottom of the mortise with a mixture of epoxy and microballoons, using the same basic method required for molding the through hull recess in a cored fiberglass hull. Be sure to wax the fitting when doing this, or it will stick firmly -and permanently -to the hull. After the epoxy filler has kicked off, remove the fitting, dewax, and reinstall, using a bedding compound under the flange, just as in a glass boat.

Other Solutions

If installing the typical flush through hull fitting sounds like a big job, you can rest assured that it is. A much more easily installed flush fitting is made in Europe, but does not appear to be available in this country. The European fitting has a relatively small flange, and the edges of the flange are neither rounded, like a surface mount fitting, nor beveled on the underside, like the typical flush fitting. Rather, the edges are vertical sided. This means that cutting a mortise is a simple one-step operation, involving only a large spade bit or a hole saw and chisel to cut and finish the recess.

In addition, the flange is fairly thin, so that the mortise depth is shallow, allowing installation in fairly thin fiberglass hulls without heavy reinforcing on the inside of the hull.

If your hull is thick enough, or if you’re willing to do a little more work on the inside of the boat to locally strengthen the hull, you can flush recess a through hull designed for surface mounting, using the same method required for the European-type fitting.

Using a hole saw, cut a circle in the hull the depth and diameter of the through hull flange. Using a chisel, clean out the fiberglass within the circle you’ve cut, so that you end up with a circular mortise whose depth is equal to the thickness of the through hull flange. In practice, the mortise should be very slightly deeper than the flange thickness. This allows you to coat the inside of the mortise with a layer of resin to prevent any wicking of water in the laminate.

You need not glob resin in. Just use enough for a surface seal, being careful to keep the edges of the mortise free of standing resin. You don’t want to create a fillet of resin in the mortise that keeps the fitting from pulling in all the way.

As with all installations of through hulls, round the transition between the bottom of the mortise and the hole through the hull for the stem of the fitting. This rounded area will hold enough bedding compound to keep the fitting from leaking. Without it, it is easy to squeeze out all the compound under the fitting during installation, particularly if the through hull fitting is screwed into the seacock, rather than screwing the seacock onto the through hull fitting.

Once the fitting is installed, trowel the edges of the mortise with epoxy putty to smooth the transition between hull and through hull fitting. Sand the putty smooth, touch up any voids, and prime with epoxy primer. Wet sand perfectly smooth before applying bottom paint. The result is a perfectly recessed through hull, without replacing any existing fittings.

Several rules apply when recessing fittings, whether you use special flush fittings or regular surface mount through hull fittings:

-The depth of the mortise must not exceed half the skin thickness of the hull unless the inside of the hull is reinforced.

-Backing blocks are essential on the inside of the hull to help distribute load.

-No hull coring material should be left exposed. If you cannot meet these conditions, you must not recess through hull fittings. Rather, they must be faired in externally.

One the more tricky jobs in recessing any type of fitting is cutting a circular mortise that is perfectly concentric with the existing hole through the hull for the stem of the fitting. The simplest way, although its accuracy may not be perfect, is to carve a soft wood plug to fill the existing hole, then carefully locate the center by measuring for and drilling a small pilot hole in the center of the plug. The wood plug should be cut off flush with the outside of the hull before getting to the meat of the job. The plug is left in place during all the concentric cutting, then knocked out. Very slight error in concentricity can be eliminated by slight grinding of the edges of the through hull or the edges of the mortise, although the best course is to be very careful in locating the center before doing any cutting. Take your time.

Reducing the drag of through hull fittings is only the first step in creating a low resistance bottom. It can be a reasonably simple project if you take the short course fairing in but can quickly develop into a fairly time consuming job if you choose the more effective solution recessing the fittings flush to the surface of the boat.

You are not likely to notice an immediate improvement in the performance of the boat, since we’re talking about relatively small changes. However, they all add up. If you combine reducing through hull drag with other bottom improvements, such as careful attention to the application of bottom paint, you will be well on the way to measurable improvements in performance, without spending much money.

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Building, restoration, and repair with epoxy

Specialty Tools for Fairing

By  tom pawlak — gbi technical advisor, the fairing file.

My son Matt and I recently built a small stitch-and-glue boat. While fairing the bottom we discovered that hacksaw blades can be modified and used for fairing.

The buildup of fiberglass tape along the chine and keel had caused a low spot in the hull all along the edge of the fiberglass buildup. Filling the low spot with low-density filler was easy, but sanding the cured epoxy with sanding boards was slow work. Experimenting with a new hacksaw blade, we found it easily cut through the low-density filler and occasional high spots in the fiberglass.

The only problem was the blade was somewhat flexible and difficult to hang on to. To eliminate this shortcoming, we clamped the hacksaw blade between two ¼”-thick wooden strips. The result was a fairing tool that exceeded our expectations. The wooden strips added the required stiffness, yet were flexible enough to let the blade bend slightly with the hull. We rounded the corners of the wooden strips with sandpaper, making the tool comfortable to hang on to.

The first tools were held together with small wood screws. More recent versions have been held together with our G/5 Five Minute Adhesive. The key is to keep the glue out of the saw teeth while bonding the wooden strips to the saw blade. For fairing surfaces with lots of curve, a more flexible version can be made by adding thinner strips of wood to each side of the hacksaw blade. If it’s still too stiff, a few strokes of a hand plane on each side will fine tune flexibility.

It may be possible to use industrial hacksaw blades without adding wood. For example, power hacksaw blades are made with a thicker saw stock and may be stiff enough for fairing many projects. When doing a lot of fairing, it is helpful to have a variety of these tools, to allow a change of handholds to reduce fatigue.

Just like sandpaper, hacksaw blades offer differing abrasive qualities. A 6 to 10 TPI (teeth per inch) blade will offer good coarse fairing capability. A 16 to 20 TPI blade offers medium fairing capability and the 28 to 32 TPI offers fine fairing capability. Using one of each will reduce sandpaper usage and fairing time. Using quality bi-metal blades will dramatically extend the work life of the tool. Metal cutting band saw blades can also be used to build longer fairing files that will last and last.

To work this modified tool effectively, hold it so the saw teeth are against the surface to be faired. Lean the tool over slightly at a 10° to 20° angle and push the tool across the surface in a direction that is diagonal to the length of the tool. Avoid pushing in a direction parallel to the tool length, because the saw blade will cut a slot in the surface. Think of the modified saw as a file that is used in a diagonal direction to maximize the cut. To determine what works best, experiment with the angle at which you push or pull the tool across the surface.

These tools take a little getting used to, but once you discover the technique, it is easy to duplicate the effective motion. As with sandpaper, it is best to fair the surface in opposing directions on a diagonal. To do this, turn the saw around so the teeth are facing the other direction and repeat the fairing process working in the opposite direction. Fairing in opposing directions will quickly establish a fair surface and help to better maintain fairness.

The Flexible Sanding Board

Long, stiff sanding boards are often used for fairing large hulls and decks. These sanding tools are typically made from resawn lumber or plywood because these materials are stiff, reasonably light, and inexpensive. Ideally, the sanding boards are flexible enough along their length to curve with the hull, yet stiff enough to resist dipping into the low spots in the area being faired.

This kind of sanding board works well on gently curving structures. However, where surfaces become more tightly curved, very little of the sanding board will actually touch the surface. An example of this is near the bow of a boat hull, where the shape changes from gently rounded to tightly curved. Very little of the sandpaper along the length of the board touches in these areas, because the sanding board cannot flex across its width. If the surface is concave, only the edges of the sand paper touch the surface. If the surface is convex, the sanding board touches only in the middle across its width.

Believing that there must be a better sanding tool for fairing this kind of area, we searched through tool catalogs and visited several hardware stores. But no such tool existed. What we needed was a sanding board that was flat and stiff along its length, yet flexible across its width so more of it could contact the surface.

One creative employee decided to make such a tool. His sanding block was made by gluing 3/8″ thick redwood to conveyor belt material. He chose conveyor belt material because it was tough and flexible. He scuffed it up so it would bond well with our epoxy. After the glue cured, saw cuts were made parallel to the length of the redwood on ½” centers. The cuts were just deep enough to pass through the wood but not into the conveyor belt. This resulted in the appropriate sanding board.

This design worked so well that we made many versions of it. By varying the thickness of the wood and the distance between saw cuts, you can adjust the stiffness and edgewise flexibility of the tool.

One drawback to using this kind of sanding block is that when wet-sanding for long periods of time, the wood can swell causing the sanding block to bow along its length. An improved version can be made of two skins of flexible conveyor belting separated by a layer of low-density closed-cell foam core. The 1/16″ thick conveyor belting is held with epoxy to both sides of the foam core, creating a stiff laminate. Like the earlier wooden version, one of the sanding board surfaces has several deep saw cuts parallel to the length of the sanding board, going through the first skin but not into the second. These slits allow the sanding board to conform to concave or convex surfaces across the width of the sanding board while remaining stiff along the length.

We have experimented with various belting materials and core thicknesses to achieve different results for specific jobs. Fairing boards built here range in size from 1″ thick by 6″ wide by 36″ long, to much smaller versions ¼” thick by 1″ wide by 2″ long. A thickness that seems to work well for 1/3 to ½ sheet of sandpaper is ½” thick. It is made up of 3/8″ thick foam core separated by 2 layers of belting. These sanding blocks work particularly well with adhesive-backed sandpaper.

If you don’t have a source for closed-cell foam and conveyor belting, you can build a similar sanding board with more commonly available materials. Cloth-backed vinyl can be substituted for the belting. Open-cell seat cushion foam that has been wet out with epoxy will replace the closed-cell foam core. To make a sanding block like this you will need:

• a flat surface
• plastic sheathing or wax paper
• a smooth, flat piece of ¾”-thick plywood that is a few inches larger than the sanding block you’re about to build
• four ½” thick spacers
• ½”– ¾” thick open-cell seat cushion foam
• cloth backed vinyl for two sides of the sanding board
• WEST SYSTEM® epoxy

Cover the flat working surface with plastic sheathing. Cut one piece of foam and two pieces of vinyl into 4″ x 12″ shapes. Mix a small batch of 105 Resin and 206 Slow Hardener. Dip the seat cushion foam into the epoxy and wring it out like a sponge. Dip it again to be sure the epoxy is uniformly dispersed within the foam. Lightly squeeze the excess epoxy from the foam and set it aside for a moment.

Apply epoxy to the cloth side of both pieces of vinyl. Place one piece of vinyl, cloth side up, over the flat covered surface. On top of this, place the epoxy covered foam. Place the other vinyl piece, cloth side down, over the wet foam. Place ½” thick spacers just outside the four corners of the foam and vinyl stack. Cover the whole thing with plastic or wax paper. Place the piece of ¾” plywood on the stack, centering it over the ½” spacers. Place weights on the plywood to compress the foam, allowing the plywood to touch the ½” spacers. The spacers will determine the sanding block thickness and allow a uniformly thick sanding board.

Once the glue cures, trim the sanding block to size, then use your table saw to make cuts parallel to the length. Remember, the cuts should be just deep enough to pass through the foam/epoxy core but not into the vinyl fabric on the other side. Saw cuts can be spaced from ¼” to ½” apart. You can also use a hand saw to make cuts, as long as you use a guide to hold the saw straight while cutting into the sanding block.

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Hull Fairing and Stern Blocks

April 17, 2016

The next big step is to fair the hull.  This is an important step, because if not done correctly, the hull planking won’t lay flat.  Fortunately, it is a pretty straightforward process, so you just kind of ‘dive in’.

Basically, it is just a lot of sanding.

The goal of hull fairing is to bevel the edges of the bulkheads so that the hull planks lay flat.  If we didn’t do this, the planks would only hit the corners of the bulkheads.

The process is pretty simple:

• Hold or secure a hull plank against the bulkheads.
• Note where the plank doesn’t lie flat across the bulkhead edges.
• Sand until it does.

Using a sanding block that can span several bulkheads helps, since you can ‘rough in’ the bevel across multiple bulkheads.

Fairing the hull

Sometimes, a bulkhead will be too short, and there will be a gap between the bulkhead and the plank.  Rather than sanding down the surrounding bulkheads, you add a little strip of wood to fill it out.  I ended up adding two – one one each side of the ship (different bulkheads).

I also faired the deck, using a deck plank to ensure that the tops of the bulkheads were even and straight.

Overall fairing the hull took several hours.

The next step was the  horn timbers .  These are strips near the stern that run along the keel. They form the beams that planks will be attached to.  In the practicum I’ve got, and in some build logs, I see these installed flush with the surface of the keel, and the planking goes over the keel.  When I look at the plans, this looks wrong.  According to the hull planking plan, the planks in this area should sit flush with the keel.  The horn timbers should be recessed from the surface of the keel to allow for this.

Let’s go with what the plans do.  The horn timbers were cut, the ends were angled, and the pieces installed.  I used a piece of hull planking to verify the placement.

Planks should sit on the horn timbers and lie flush with the keel.

Next up are the stern blocks.  These are blocks of wood that are added at the very back of the ship to finish out the shape of the hull.  This requires you to take block of wood, cut it into two pieces, and shape it to fit.

These blocks of wood need to be heavily shaped to create the stern.

This took a while – probably 4-5 hours spread over two days.  If I had a scroll saw it might have gone faster, but I don’t have one.  The pieces were cut on a table saw to the right width.  I then traced the shape onto each piece and cut it out using a hand saw.

I’m adding a scroll saw to my wish list.

The pieces were then glued into place and shaped by hand.  I used a combination of my Dremel, a sanding block, and my Proxxon pen sander.

Once the bottoms were shaped, I flipped the ship back over and worked on the top.  It needed to be leveled out, as well has tapered in towards the back.  I traced the shape from the plans and made a template to be sure I tapered correctly.

Completed stern blocks.

So, my hull is faired, and the work at the stern is finished.  What’s next?

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FAIRING THE HULL FOR NEW PAINT!

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Good progress on the hull so far but there’s still more to the fairing process to get it perfect 😉 Next week should be the last of it then onto the painting using the new additive from Alexseal!

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VIDEO: LAYING THE FAIRING COMPOUND https://youtu.be/_8M9JYX_I90

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FILL, FAIR, RESHAPE, REPAIR

READY TO SAND IN 4 HOURS

NO SAGGING ON VERTICAL OR OVERHEAD SURFACES

EASY TO SAND SMOOTH WITH NO PINHOLES

TotalFair Epoxy Fairing Compound

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• Description
• Frequently Bought Together
• Specifications
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Easy to mix – green means it’s ready to go

With an improved formula for mixing, application, and sanding, TotalFair is the ideal solution for marine repairs, recreational vehicle improvements, fabrication, and woodworking. Ever had epoxy or fairing compound sag or go on like soggy sawdust because it wasn't mixed completely? That won’t happen with TotalFair because it's easy to see exactly when it's ready to use with color-coded components. The epoxy resin is yellow, and the hardener is blue (with some green expected from oxidation). Wearing protective gloves, mix the two parts together at a 1:1 ratio. Mix, fold, smear, scrape, repeat. Stop when you get a uniform, green-colored paste. That’s it. No complicated measuring or guessing. Just green. Once it's green and swirl-free, you’re ready to shape, fill, and fair dents, chips, gouges, cracks, and other unsightly things standing in the way of a gloriously smooth, ready-to-prime surface.

This fairing putty stays put

TotalFair is light and easy to work with to repair boats, kayaks, RVs, and trailers. The advanced, non-sagging formula formula spreads and hangs, staying where you put it. Even overhead, upside down, and sideways. Just pull or feather to a fine edge and a smoother surface.

Creates a smooth, hard, flexible finish

The TotalFair finish is smooth, even, and pinhole-free for strong, long-lasting bonds above or below the waterline . Make it even smoother by sanding after it cures. Which is quick – just 3 hours at 90°F. TotalFair has a high tolerance for flexing, especially on the hull. It adheres aggressively, distributes stress evenly, and it won’t crack or break free. To suit repairs ranging from a few minor cracks to a slew of imperfections, our marine fairing compound comes in pint, quart and gallon sizes.

TotalFair Details

• Lightweight, 2-part marine epoxy fairing compound
• New formula features thicker consistency for better control while scooping, mixing, and spreading
• Use above and below the waterline for reshaping, filling, fairing, and repairing.
• Works on horizontal, vertical, inclined, and overhead surfaces without sagging.
• No-mess, easy-mix, color-coded formula dries fast. Easy to sand once cured.
• Apply fairing compound to fiberglass, wood, steel, and aluminum.
• Sizes: Available in two-part Pint, Quart, and Gallon Kits. Each kit contains Resin Part A (yellow) and Hardener Part B (blue).
• 2-Pint kit includes one pint Part A & one pint Part B. 2-Quart kit includes one quart Part A & one quart Part B. Gallon kit includes half-gallon Part A & half-gallon Part B.
• IMPORTANT: TotalBoat Gelcoat should not be applied directly over TotalFair or the gelcoat will not cure properly. Instead, use TotalProtect over TotalFair, before applying Gelcoat.

Important Application Notes

• Some oxidation of the blue hardener is expected and does not impact the mixing or application of TotalFair. If hardener arrives with a light green oxidized tint, simply mix with the resin to achieve proper color and consistency.
• Gelcoat should not be applied directly over TotalFair or the gelcoat will not cure properly. Instead, apply TotalBoat TotalProtect Epoxy Barrier Coat Primer over TotalFair, and allow to cure fully before applying Gelcoat. Primers are sold separately.
• When filling holes or gouges: Filling holes up to 3/4" thick may need a second pass, once cured. When fairing a large gouge (maximum depth fill), a 6:1 width to depth ratio is recommended per application. For deep/narrow areas that exceed 6:1, just apply TotalFair in stages, building up each time.
• Do not apply TotalFair over 1-component previously painted surfaces. If you are not sure what the previous coating is, remove it before applying TotalFair.
• Storage below the recommended temperature range can cause crystallization of the resin and hardener. If TotalFair crystallizes, simply close the containers completely and set them in a sealed plastic bag, with no air. Place the sealed bag in a bowl of warm water (125-150°F) for a couple of hours. This action will undo the crystallization, and the product will be the proper consistency for use.
• In between uses, cover the remaining material in each container with plastic sheeting before securing the lids tightly. T his helps extend the shelf life and minimize further oxidation.

Safety Precautions

• Wear protective gloves when mixing TotalFair.
• Wear a proper respirator when sanding.

FREQUENTLY BOUGHT TOGETHER

TotalProtect Epoxy Barrier Coat Primer

Flexible Spreader Set

TECHNICAL DATA

• Application Method: Spreader, trowel
• Application Temperature: 50-100°F
• Working Time (150g mass, minimum): 15-20 minutes @ 90°F, 30 minutes @ 70°F, 45-60 minutes @ 50°F
• Tack-Free Time: 1 hour @ 90°F, 2 hours @ 70°F, 4 hours @ 50°F
• Dry Time to Sand: 3 hours @ 90°F, 6-8 hours @ 70°F, 12 hours @ 50°F
• Shelf Life: 1 year, minimum, if stored properly
• Mixed Appearance: Green paste
• Mix Ratio by Volume: 1A:1B (one part Part A Resin (yellow) to one part Part B Hardener (blue))
• Sag Resistance: >1" (Vertical Surface Test)
• Storage Temperature: 59-77°F
• Surface Prep Solvent: Fiberglass, Steel, and Previously Painted Surfaces - Acetone or denatured alchohol; Aluminum - TotalBoat Aluminum Boat Etch Wash; Oily Hardwoods - acetone
• Cleanup Solvent: Clean up with acetone before product is cured. Once cured, it must be removed mechanically.

• Composition:
• Substrates:
• Mixed/cured color:
• Application methods:
• Application temperature/RH:
• Working time:
• Sandable time:
• Finish/topcoat with...
• UV resistant?
• Units of measure:
• Best for: Reshaping, filling, fairing for boat building and repairs
• Composition: Epoxy-based fairing compound
• Substrates: Fiberglass, wood, aluminum, steel, and previously applied epoxy products or two-component urethanes in good condition
• Mix ratio: 1A:1B
• Mixed/cured color: Green
• Application methods: Spreader, Trowel
• Application temperature/RH: 50-100°F
• Working time: 150g mass, minimum - 15-20 minutes @ 90°F; 30 minutes @ 70°F; 45-60 minutes @ 50°F
• Sandable time: 3 hours @ 90°F; 6-8 hours @ 70°F; 12 hours @ 50°F
• Finish/topcoat with... Paint, primer, epoxy primer, or more TotalFair. DO NOT apply gelcoat directly to TotalFair. It will not cure properly. Before applying gelcoat, overcoat TotalFair with an epoxy barrier coat or epoxy surfacing primer.
• UV resistant? No
• BPA free? No
• Units of measure: 2 Pint Kit, 2 Quart Kit, Gallon Kit

FixWood Wood Repair Epoxy Putty

• High-strength, waterproof, permanent repairs to rotted or damaged wood
• Epoxy-based putty
• Shape by hand or using tools.
• 30-35 minutes @ 72°F
• Less than 6 hours @ 72°F
• Stain it or coat it with 1-part or 2-part polyurethane paint or varnish.
• 2 Pint Kit, 2 Quart Kit

Polyester Fairing Compound

• Fairing fiberglass decks and hulls (above the waterline only); cosmetic filling on composite surfaces to repair shallow dings, cracks, dents, and gouges; repairing fiberglass parts, molds, and plugs; filling print-through or porosity on composite surfaces; fairing joints in sheet metal
• Polyester resin-based fairing compound
• Fiberglass, gelcoat, composites, sheet metal
• For a proper cure, add 1-2% MEKP catalyst (included) to fairing compound.
• Spreader, Trowel
• 50-95°F; 0-90% RH
• Variable. At 77°F, adding 14-16 drops of MEKP to one ounce of TotalBoat Polyester Fairing Compound will provide a working time of 10-15 minutes, and will cure in 20-30 minutes.
• Depends on temperature, amount of catalyst, and mass of fairing compound. Example: 20-30 minutes @ 77°F for a 100g mass catalyzed with 1% MEKP.
• For UV protection, TotalBoat Polyester Fairing Compound must be finished with gelcoat, or primed and painted. For underwater applications where this fairing compound may be exposed to water, always barrier coat with TotalBoat TotalProtect, to prevent water intrusion.
• Quart Kit, Gallon Kit

Polyester Structural Marine Repair Putty

• Joining and filleting fiber-reinforced plastic (FRP) parts, bonding dissimilar materials such as metal and wood, radius forming, filling larger voids and cracks in composites, and fabricating composite parts
• Polyester resin-based repair putty
• FRP composites, core materials, wood
• Add 1-2% MEKP catalyst (included) to repair putty.
• For a 100g mass, catalyze with 1% MEKP for approximately 15-20 minutes of working time at 70°F (14 drops of MEKP catalyst per ounce of structural repair putty).
• For applications where this product will not be laminated over, a polyester resin air dry solution can be added at the rate of 1 ounce per quart of putty before catalyzing.
• Gelcoat with wax, Polyester Finishing Resin

YOU MAY ALSO LIKE

• TotalBoat TotalFair Technical Data
• Which Epoxy Should I Use for My Project?
• Recommended TotalBoat Epoxies Listed by Project Type

FREQUENTLY ASKED QUESTIONS

What applications is TotalFair most appropriate for?

Can i apply gelcoat over cured totalfair, can totalfair be applied over epoxy resin, can totalfair be applied over primers, does totalfair require an epoxy barrier coat when used below the waterline, or can you paint right over it, can totalfair be used to repair gelcoat chips and cracks, can totalfair be applied to aluminum boats, can totalfair be stained, what types of paint is this epoxy fairing compound compatible with, what is the temperature range for applying this epoxy fairing compound, the blue hardener has a green tint, is the formula impacted, is totalfair supposed to be green, once the 2 components are mixed, how long do i have to apply it, how long do i have to wait before sanding totalfair, what is the shelf life of totalfair once opened.

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