sailboat air draft

Calculate Clearance Under Bridges & Cables

• Post author: Noel Hutchinson
• Post published: October 25, 2019
• Post category: Uncategorized
• Post comments: 0 Comments

This article will show you how to calculate clearance under bridges & cables. We often need to do this in order to see if our vessel can fit underneath. Or we may have to work our when our vessel can fit underneath as it may need the tide to fall to a certain level.

When working out this puzzle, the first thing we need to do is find the charted height of the bridge or overhead obstruction. We can either find this on the chart itself or by looking up the information in an almanac or pilot book.

Overhead clearances under bridges & cables are measured above something called HAT or Highest Astronomical Tide. This is the highest a tide can rise due to influence of celestial bodies and weather. For a reminder of the different tide levels take a look at the image below or click through to the video.

So the next step is to find the height of HAT from the tide tables. Once we have done this we know the height of the bridge and the level above which it is measured.

The thing with HAT though is that it’s not that common. HAT is the highest a tide can be expected to rise. However, the tide often falls short of that level. This means that we often have some extra space. This space comes from the difference between the height of tide (HoT) on the day and HAT.

In order to find this extra bit of space we need to use a tidal curve or an App to get the height of tide. We can then take the height of tide off of HAT. This is our extra bit of space.

HAT – HoT = extra space

You can refresh yourself on tidal curves here if you need to:

How To Use Tidal Curves – watch the video

The Final Calculation

To calculate clearance under bridges & cables then, all you need to do is add the charted height and the extra bit of space together. This will then give you the total space available for a given time on a given day.

In order to see if you will fit under the bridge take the air draft of your vessel from the total space available. If the answer is positive then you can make your way underneath safely. The air draft is the height of the vessel from the waterline to the very top.

Here’s a summary of the steps to take:

• Get the charted height from the chart or almanac
• Get the level of HAT from the tide tables
• Calculate the height of tide (HoT) using the tidal curve (or use an App)
• Take the HoT from HAT to work out the extra space
• Add the extra space to the charted height for total clearance
• Take the air draft of the vessel from the total clearance to see if the vessel can fit

Calculate Clearance Under Bridges & Cables Cheat Sheet

As always, we have produced a free cheat sheet for you to use. It will make the steps super simple and help to keep you organised as well. We find the best thing to do is laminate it. Then you can use it again and again with a dry wipe marker pen or china-graph pencil ?

Please don’t forget to like, comment and share.

Our complete set of Knowledge Cards are available from our shop

Noel Hutchinson

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• You are here
• Everything Explained.Today
• A-Z Contents

Air draft explained

Air draft (or air draught ) is the distance from the surface of the water to the highest point on a vessel . This is similar to the deep draft of a vessel which is measured from the surface of the water to the deepest part of the hull below the surface. However, air draft is expressed as a height (positive upward), while deep draft is expressed as a depth (positive downward). [1]

Clearance below

The vessel's clearance is the distance in excess of the air draft which allows a vessel to pass safely under a bridge or obstacle such as power lines , etc. A bridge's "clearance below" is most often noted on charts as measured from the surface of the water to the underside of the bridge at the chart datum Mean High Water (MHW), [2] [3] a less restrictive clearance than Mean Higher High Water (MHHW).

In 2014, the United States Coast Guard reported that 1.2% of the collisions that it investigated in the recent past were caused by vessels attempting to pass under structures with insufficient clearance resulting in bridge strike s.

The Bridge of the Americas in Panama limits which ships can traverse the Panama Canal due to its height at 61.30NaN0 above the water. The world's largest cruise ships,, and the will fit within the canal's new widened locks , but they are too tall to pass under the bridge, even at low tide (the two first ships are 720NaN0, but do have lowerable funnels, enabling them to pass the 650NaN0 Great Belt Bridge in Denmark). New vessels are rarely built not clearing 650NaN0, a height which accommodates all but the largest cruise and container ship s.

The Suez Canal Bridge has a 700NaN0 clearance over the canal.

The Bayonne Bridge , an arch bridge connecting New Jersey with New York City, undertook a $1.7 billion modification to raise its roadbed to 660NaN0. [4]

• Structural clearance
• Structure gauge
• Cargo ship size categories Chart datum
• Bridge strike

Notes and References

• Book: 2104 Connecticut Boater's Guide . 60. State of Connecticut Department of Energy and Environmental Protection. 2015-02-15.
• https://charts.noaa.gov/PDFs/12335.pdf See: NOAA Navigation Chart #12335, Hudson and East Rivers, Governors Island to 67th Street, Revised October 1, 2019, "HEIGHTS: Heights in feet above Mean High Water"
• https://nauticalcharts.noaa.gov/publications/coast-pilot/files/cp5/CPB5_C08_WEB.pdf See: U.S. Coast Pilot 5, Chapter 8, p. 354, Structures across the Inner Harbor Navigation Canal, New Orleans , 15 December, 2019, "Vertical clearance measured at Mean High Water"
• https://www.silive.com/news/2019/06/bayonne-bridge-rededication-ceremony-marks-end-of-17-billion-project.html Bayonne Bridge rededication ceremony marks end of $1.7 billion project

This article is licensed under the GNU Free Documentation License . It uses material from the Wikipedia article " Air draft ".

Except where otherwise indicated, Everything.Explained.Today is © Copyright 2009-2024, A B Cryer, All Rights Reserved. Cookie policy .

Have you ever dreamed of leaving behind life on land and taking to the water for the adventure of a lifetime?  If so, a cruise around America’s Great Loop may be on your horizon. The Great Loop was once a route known only to lifelong boaters and hard-core long-distance cruisers, but the secret is out. “Looping” has become a passion for thousands who hope to one day navigate their boats on this 6,000-mile trip around eastern North America.

The first documented Great Loop completions date back to the late 1800s, but the popularity of the Great Loop increased with the opening of the Tennessee-Tombigbee Waterway in 1984, allowing “Loopers” to avoid the heavy commercial traffic on the Lower Mississippi and enter the Gulf of Mexico through Mobile Bay instead.

See the interactive Great Loop map .

The publishing of Honey, Let’s Get a Boat by Ron & Eva Stob in 1999 popularized the Great Loop in many boating circles, and the number of Loopers cruising and sharing their journey through letters back home, increased. But the rise of social media means instead of sharing the details of the trip with a handful of close friends and family members, today’s Loopers chronicle the adventure for hundreds (or even thousands) of followers. That exposure, coupled with articles in mainstream media outlets like The New York Times Magazine , The Wall Street Journal , USA Today and hundreds of local publications across the country have led to a rise in interest in the Great Loop.

Membership in America’s Great Loop Cruisers’ Association –an organization dedicated to helping Loopers with all facets of their high-adventure, low-risk, long-distance journey–has doubled in the last 10 years, and the total number of memberships doled out since the Association’s inception 20 years ago exceeds 20,000. But with only about 150 boats reporting completion of the route each year, Gold Loopers (those who have completed the route) remain an elite group. Would-be-Loopers have a lot of questions about successful completion of the Loop, including the ones here, which are the most frequent.

Q: Exactly What Is the Great Loop?

A: The Great Loop route totals about 6,000 miles, passes through more than 15 states and provinces and includes more than 100 locks. Loopers follow the route northward on the Atlantic Intracoastal Waterway (ICW), through Chesapeake Bay, around the tip of New Jersey, into New York Harbor, up the Hudson River, into the New York State canals, through the Great Lakes, south on the inland rivers to the Gulf of Mexico and around Florida. The trip includes passage through big cities like Chicago and New York and small towns, many of which were founded before roads existed, so Loopers travel in some of the most historic areas of our country, finding nostalgia and exploring long-forgotten slices of Americana.

While Loopers have traditionally completed the route in about a year by following warm weather around the Loop and spending summer on the Great Lakes and winter in Florida, more and more are undertaking the journey in segments, cruising for weeks or months at a time and then returning home to tend to other obligations.

A: Many Loopers are retirees traveling as a couple aboard their boat. However, technology, the availability of mobile service and WiFi around the route, and the rise in the number of people able to work remotely means that many other age groups are exploring the Loop. In addition, the increase in popularity of home schooling and the availability of on-line curriculum means more families are “boat-schooling,” giving their children opportunities to go beyond the curriculum and engage in experience-based education in the cities and towns they visit along the way.

A: The Great Loop has been completed in everything from a dinghy to a 100-foot yacht and including all types of vessels in between. Everyone’s ideal Great Loop boat is different, so the key to cruising the Loop successfully and enjoyably is choosing a boat that is right for you. While there are a wide-range of Loop-capable boats, there are a few requirements for your Looping vessel. First and foremost, it must be seaworthy. Although the Great Loop is primarily an inland route, there are some places where you’ll find yourself in “big water,” including the Gulf of Mexico, the Great Lakes and various sounds and inlets around the route where you are likely to experience some rough seas. Second, the boat you choose must have an air draft of less than 19.6 feet so it can clear the lowest fixed bridge on the Great Loop, which is located on the Illinois Waterway and cannot be bypassed by taking an alternate route.

There are also some places on the Great Loop where the water can be shallow, particularly during low tide, so you’ll have an easier time if your boat draws 5 feet or less. If you draw much more than that, you will have to pass up some options, like the Trent Severn Waterway, and getting into some marinas along the Loop will be challenging.

Most Loopers need not worry about the length or beam of their boat as there are really no restrictions on those dimensions that would prevent you from completing the Loop. The Trent Severn Waterway has a length restriction of 84 feet and a width restriction of 23 feet, but there are alternative routes if your boat exceeds those specifications.

Q: Do I Need Lots of Boating Experience?

A: While the Great Loop is not a technically challenging cruise (you’re not circumnavigating the globe, after all), it does require confident handling of your boat in unfamiliar waters. It also requires that you know the “rules of the road” and how to keep yourself and the people and property around you safe. If your Looping boat or boating in general is new to you, be sure to spend some time before the trip becoming acclimated. If you’re a complete novice, hire a training captain and practice until you’re capable and comfortable handling your boat. You can also take courses to learn boating skills or brush up on the skills you already have. Since every day on the Great Loop is a trip through unfamiliar waters, you’ll need to understand the rules of navigation, procedures for contacting lock and bridge tenders and how to contact other vessels in the area. Most Loopers will spend a year or more (sometimes much more) planning and preparing for departure.

Q: How Do I Get Started?

A: Get started by getting connected.

There are hundreds of details to consider before beginning your Loop. What do you do with your “dirt-based” home while you’re living on the water?  How do you get mail along the way?  What kind of electronics do you need aboard your boat?  What’s the best type of anchor?

The best way to learn all this is through your own research and connections with those who have come before you. There are many books and online resources that can help you, and you’ll find that cruisers in general, and Loopers in particular, are very willing to help. Plus, they love to share their experiences!  Don’t hesitate to get involved in online forums and Looper groups. Walk the docks and look for Looper burgees. Attend “dock-tails” and ask questions so you can learn from the experiences of others.

Almost without exception, when asked about their trip highlights, Gold Loopers mention the people they met along the way, so do get engaged, well before you drop the dock lines and head out.

Whether the Great Loop is a lifelong dream or a new item on your bucket list, the best advice is to do it in a way that is enjoyable for you . There is no right or wrong way to do the Great Loop as long as you maintain safety for yourself and those around you. Whether you choose a 25-foot tug or a 50-foot trawler, whether you spend 6 months or 6 years completing the route, whether you travel at an average of 6 knots or 15 knots, remember that it’s your journey. Make it your adventure of a lifetime.

Kimberly Russo has been the director of America’s Great Loop Cruisers’ Association (www.greatloop.org) for four years and has been working with AGLCA for ten.  She is a regular speaker about the Great Loop at events like the Miami Boat Show, Chicago Boat Show, TrawlerFest, and others. When not helping others with their Loop adventure, she enjoys cruising her home waters of Charleston, SC.

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• Trawler Forum
• General Discussion

Measuring Air Draft

• Thread starter CaptTom
• Start date Apr 19, 2017
• Apr 19, 2017

Is there a trick to measuring the air draft of a boat? The usual approach seems to be to read the manufacturer's documentation if available, or the PO's ad, estimate how much that might have changed with the addition or removal of other "stuff," then pass under successively low bridges until you get a sense of when you can make it, and when you can't. The problem with actually measuring is complicated by the fact that there's no straight line from the top of the anchor light to the waterline. Or from the deck. I was thinking I could put a long pole horizontally across the deck, then measure from that to the anchor light. Then I'd need to take two measurements from the pole to the water line, and average them, or else get both the pole and the boat perfectly level. I've never seen anyone do this, or for that matter, any other method of taking an actual measurement. I wonder if there's a better way. Like last month when I showed up at a newly-purchased boat to help a buddy take it home. I didn't have a 14' pole handy, and we had lots of bridges to pass under along the way.  

If your boat is the one in your avatar measure the tip of your antennae to the top of the fly bridge. Write down that number. Get your fishing pole out of its locker and lay it across the top of the fly bridge. Let out enough line to submerge a lead sinker about 2" below the surface while the boat sits for a minute or so. Lock down the reel and measure the amount of line and add this to the number you previously wrote down. That is your current air draft.  

"I was thinking I could put a long pole horizontally across the deck, then measure from that to the anchor light. Then I'd need to take two measurements from the pole to the water line, and average them, or else get both the pole and the boat perfectly level." That is more or less what we did but had to break it up in 3 segments and utilized a level to ensure the 'pole' was even across the boat. FWIW - I would not trust the manufacturers spec with the variables in play , remember that the number will change with added or subtracted weight as well as in salt of fresh water.  

Pythagoras solved this issue many years ago and provided it to Euclid. Measure with tape or string from your top most point straight out to the water preferably to abreast the beam, without touching anything else on the boat. Don't try measuring straight down but out and away from the boat. Then measure from the spot you are touching the water to the boats hull. Add 1/2 of the hulls width to the second measurement. You have established a right angle in which you now know the hypotenuse and one side. Do the math to solve for air draft.  

We measured similar to the way you are thinking also. Here's the sketch I made up originally. I have since added a few dimensions but you get the idea.  

Attachments

• Albin draft.pdf 15.4 KB · Views: 316

North Baltic sea

Ulysses is right, use Math. If you can't remember how, ask any reasonably intelligent 9th grader.  

Please note.... Width of the hull at the waterline is most often much less than the actual beam of the boat. Many of us have had boats where the 'tallest' fixed point is not on the centerline.  

Senior Member

All above advise is good. Make sure you measure when fuel, water and waste tanks are near empty.  

smitty477 said: Please note.... Width of the hull at the waterline is most often much less than the actual beam of the boat. Many of us have had boats where the 'tallest' fixed point is not on the centerline. Click to expand...

"distance to Center line." - How would you propose getting that distance?  

smitty477 said: "distance to Center line." - How would you propose getting that distance? Click to expand...

"Tape measure from where you are standing to the center line of your boat." Ahh - so it cannot be done while standing on the dock and you would need the boat level.  

smitty477 said: "Tape measure from where you are standing to the center line of your boat." Ahh - so it cannot be done while standing on the dock and you would need the boat level. Click to expand...

Here's how we've measured. Find a clearance that is marked well and accurately or that you can mark. This could be a dock or boathouse slip. In our case it's a covered boat slip. The entrance to the slip is a solid and straight beam and we've actually marked along the side the measured distances so at any time we can easily tell the clearance. It varies between 39 and 41'. Then we simply pull the boat under that entrance way and measure the distance from various points of the boat to the top. We might come up with something like tallest antenna 17', radar with other antennas down 21'. We'd then subtract from the current overall clearance, lets say 40' on this day. That would tell us that our air draft with the antenna up is 23' and with it down is 19'. If you found a well marked bridge you could even do it there. As noted below we've made sure to measure at lightest load and we've also measured at other loads. It's interesting to see the difference as your water draft also changes by the same amount. It was also interesting to compare to manufacturer's numbers. Of the manufacturer's boats we checked here's what we found. We measured two boats each from two builders and found them to be conservative. Even at the lightest load we could create we had more air draft than they indicated. Their numbers were clearly from a load that was impossible for us to be that light. Must have been all tanks completely empty and no supplies or extras on the boat. Similarly we had two divers measure water draft and even with all tanks full and everything possible plus 12 people on the boat we had slightly less water draft than they indicated. Note that one of these builders did supply a range based on load but even that range was conservative by a couple of inches. However, we checked one boat from a third builder. Their numbers were from the most optimistic view. Their quoted air draft was from a fully loaded boat in every way and several inches less than the draft we found in our worst case. Their water draft was less than we found in any load situation. They quoted 5'. Out numbers ranged from 5'1" to 5'3". I must say that on the day we did this, we got quite a few onlookers and those who were very convinced we were crazy, although one of them then asked if we'd check his boat. Now, once you have a firm grasp of your air draft, you still have one other problem. What does the number you get from the bridge records or tender indicate? Is the bridge accurately marked? A couple of times we've had discussions with bridge tenders that have been very interesting, but pretty much all over the place. We've found well marked bridges where the clearances were clearly based off the lowest area of the bridge. If you stayed centered under the bridge you had a few more inches. Nice, safe. The published numbers were also worse case on those bridges. Conservative. We liked. However, we found one bridge that had no markings and the quoted clearance was based on some really low water situation and the very center of an arched opening. The safe clearance was over two feet less than the number shown on charts and records. Clearly a dangerous situation as someone had found and posted on Active Captain when they lost a light going under. One other thing we keep in mind. Whatever air draft you come up with does not reflect waves or wakes caused by other boats.  

"No, I believe you are missing something. Can you not stand on your dock and get to your boat with a tape measure if someone is assisting you ? I have yet to find a tape measure with operational instructions, but I am sure that you can find someone that has some experience that can help you figure it out. Secondly the boat being level will help get an accurate air draft but the math will work whether it is level or not. If the boat is not level the tangent angle will still be to the highest point at that time no matter how the boat might presently be inclined." I did not have a dock nor did I have one when we were approaching the bridges on the canals. We were able to make sure that the distances were within about 1/4" by measuring using the simple methods above. It has been pointed out that you cannot just use the waterline distance as the hull is never plumb to the hulls full width - n or is the width even throughout the length of the boat. "I have yet to find a tape measure with operational instructions, but I am sure that you can find someone that has some experience that can help you figure it out." It is always a pleasure to exchange posts with folks that are both knowledgeable and sincere in their efforts to help.  

man n black

Veteran member.

Wouldn't it be easier to get a ball of twine...climb to the highest position on your boat and reel out the twine to water level. You could then measure everything above the highest point you climbed to with a measuring tape....combine and then bammo...you have your air draft...I'd add a little bit to that number just to be safe... Ch  

"Now, once you have a firm grasp of your air draft, you still have one other problem. What does the number you get from the bridge records or tender indicate? Is the bridge accurately marked?" absolutely +1 - we have seen this as well in the NE.  

Technical Guru

Go to a marina or dockside restaurant that has a balcony over the water. Bring a carpenters level and a tape measure. Get on the balcony and set level on something about the height of your boat. Level it and sight your boat mast down the length of the level. Measure from level down to the water surface. Get a helper on the boat to put a piece of blue tape on mast at sight level. Measure on boat from blue tape to top of whatever mast. Something like that, depending on boat and marina, etc. You can't rely on bridge markings. Can't say "well that one was marked 22', and we had 2' clearance, so we are 20'." Some bridges marked super conservative, some have arcs on lower structure, tides, etc.  

jleonard said: We measured similar to the way you are thinking also. Here's the sketch I made up originally. I have since added a few dimensions but you get the idea. Click to expand...

ulysses said: Pythagoras solved this issue many years ago and provided it to Euclid. Measure with tape or string from your top most point straight out to the water preferably to abreast the beam, without touching anything else on the boat. Don't try measuring straight down but out and away from the boat. Then measure from the spot you are touching the water to the boats hull. Add 1/2 of the hulls width to the second measurement. You have established a right angle in which you now know the hypotenuse and one side. Do the math to solve for air draft. Click to expand...

Ski in NC said: Go to a marina or dockside restaurant that has a balcony over the water... Click to expand...

Ski in NC said: You can't rely on bridge markings. Can't say "well that one was marked 22', and we had 2' clearance, so we are 20'." Some bridges marked super conservative, some have arcs on lower structure, tides, etc. Click to expand...

Ski in NC said: Go to a marina or dockside restaurant that has a balcony over the water. QUOTE] That would be nice, ,however..... If that was my plan I would still be looking as I have never found what you describe (in the last 11 years that is). Just sayin'. The boat that brought up this question was, coincidentally, an Albin 40. Click to expand...

Master and Commander

I did by myself years ago, like J Leonard showed in post #5, it took just a few minutes. I added 6" to the total and made stick on labels for the upper and lower helms. It is nice when bridges have tide boards and clearance marked. So far so good.  

My method in not proper but it works for me. I get my kid to stand on the hardtop and put his eye level with the highest point. I then take a tape and run it up from the side until he says it is level with the highest point. I measure that to a rail, I then measure from the rail to the water. Add those together and then add a couple of inches. Pray your correct when you go under that first close bridge. LOL We can do the measurement in a few minutes.  

Moderator Emeritus

Our boat was in a covered slip when we bought it. I took a 12' straight edge and stood on the hardtop. With a level on the straight edge and a Sharpie taped to the end of the straight edge I made the straight edge level and at the top of the radar dome. Them I made a mark on the piling supporting the roof over the slip. Next just measure from the waterline up to the Sharpie mark on the piling. Now that I had the air draft to the top of the radome all I had to do was measure the anchor light above the radome. By doing it this way, I could keep the boat from heeling if I stood on one side to measure to the waterline which would skew the measurement.  

Capt.Bill11

This thread cracks me up. I had no Earthly idea figuring out the air draft of a boat could be so complicated. ?  

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• Great Loop Information

Great Loop FAQs

The majority of the questions we receive are answered here. There are FAQs about the Great Loop route and about what the requirements are for a Great Loop-capable boat.

Questions about the Great Loop Route

What exactly is the great loop, what waterways comprise the great loop route.

Because there are several points on the route where there are choices that may send you to different waterways, we recommend you examine our Public Interactive Map.  However, the primary waterways on the basic route include:  

• The Atlantic Intracoastal Waterway
• The Chesapeake Bay
• The C&D Canal
• The Atlantic Ocean from Cape May to New York Harbor (or sometimes inland waterways through part of New Jersey)
• The Hudson River
• The Erie Canal (or a popular route option on the "Triangle Loop")
• The Oswego Canal (or continue on the Erie Canal to Lake Erie)
• Lake Ontario
• The Trent-Severn Canal
• Georgian Bay
• Lake Michigan
• The Illinois River
• The Mississippi River
• The Ohio River
• The Tennessee River
• The Tenn-Tom Waterway
• The Gulf Intracoastal Waterway
• The Okeechobee Waterway (or continue on the Gulf Intracoastal to the Keys)

How Many Miles Is the Great Loop?

How long does it take to do the great loop, how many states/provinces/countries are along the great loop.

The US. and Canada are usually part of the Great Loop, although one route option keeps you within the U.S. borders.  Some Loopers do a side trip to the Bahamas as well. Depending on route choices, you will go through at least 15 U.S. states and Canadian provinces, which may include:  

•     Florida
•     Georgia
•     South Carolina
•     North Carolina
•     Virginia
•     Maryland
•     Delaware
•     New Jersey
•     New York
•     Vermont
•     Quebec
•     Ontario
•     Michigan
•     Wisconsin
•     Illinois
•     Missouri
•     Kentucky
•     Tennessee
•     Mississippi
•     Alabama

Where on the Loop Is the Starting Point?

Why is the loop usually done counter-clockwise, why do aglca members fly burgees and what do the various colors mean.

The double swallow tail AGLCA burgee is the flag that binds America's Great Loop Cruisers' Association™ members. It's been called the welcome mat for Loopers and is proudly flown by our members whenever they are cruising. Members who fly an AGLCA Burgee receive instant recognition from the boating community and their fellow members.

The White Burgee is an indicator of AGLCA membership and can be flown by any of our members on any type of boat, even if it’s not your Loop boat. 

The Gold Burgee is the "Gold Standard" and is reserved for members who have completed the Great Loop Cruise.

The Platinum Burgee has been specially designed to identify our most experienced Loopers, those who have accomplished multiple Loop completions!

And, our veteran Loopers who display the Gold and Platinum Burgees as their credential of completion(s) are accorded the respect that goes with being someone who has done extensive cruising on America's Waterways.

In addition to members, AGLCA sponsors can also be seen flying burgees.

The Red Burgee represents the highest level of AGLCA sponsorship and is flown by our Admiral sponsors.

The Green Burgee represents the second highest level of AGLCA sponsorship and those sponsors are known as Commanders.

The Blue Burgee represents sponsors at the Lieutenant and Lieutenant Plus sponsorship levels.

Wherever you see one of these colors flying you can be assured that these sponsors will do whatever they can to assist you with your Great Loop journey.

Questions about Great Loop-Capable Boats

What's the best boat for the great loop, what air draft (height) restrictions are there on the great loop route.

The lowest unavoidable fixed bridge on the Great Loop is currently charted at 19.6’ and is located at mile 300.6 on the Illinois River.  The boat you intend to use for the Loop must be able to clear that bridge.  Some members with taller boats are able to get under 19.6’ by lowering antenna, radar arches, etc.  About 8% of our members have sailboats.  Most sailboats will need to unstep the mast to clear the bridges outside of Chicago and upstate New York.   Your choice of waterways through New York State and into Canada will also be dependent on your air draft.  If you can clear a 15' bridge, you have the option to take the Erie Canal to its western terminus into Lake Erie.  If you can clear a 17' bridge, you can do the "triangle loop" that takes you into Lake Champlain and through the St. Lawrence Seaway into Lake Ontario. (As an additional option on the triangle loop, if you can clear many eight foot bridges, you can take the historic, charming and free Lachine Canal through Montreal rather than the Seaway locks.) The final option is to take the Erie Canal to the Oswego canal to Lake Ontario. That route requires you to clear 21' bridges. Your air draft will also dictate which route you take off Lake Michigan.  To cruise the Chicago River through downtown, you must be able to clear 17' bridges.  If you can't clear that, you will take the Cal-Sag Canal which is south of Chicago to the Illinois River.

What Is the Maximum Water Draft (Depth) for a Boat Doing the Great Loop?

What is the maximum length for a boat to do the great loop, what is the maximum beam (width) for a great loop boat, what fuel range does my boat need to have, sign up for our free great loop planning guide.

Sign up for AGLCA’s “Great Loop Planning Guide” email series with tips, suggestions, and a timeline for planning your own Great Loop adventure.

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> > Please support our sponsors and let them know you heard about their products on Cruisers Forums. 21-06-2016, 07:54   for a bigger craft than the 28' we currently own, somewhere between a 38' to 42'. Since we plan to down from to next year. One potential we're looking at has a 5 and a half foot . Anyone ever navigated the with a this size? I understand the option to go out to open at some points along the way, though would rather stay inside. Thanks! 21-06-2016, 08:01   in question but you are at the upper limit of what I would suggest. 21-06-2016, 10:43   Boat: Gemini 105Mc 34' . Flooding due to rains and persistent east winds on the sounds have stymied boaters with 63’-64’ heights on occasion – sometimes for weeks. Don’t forget to include your wind-x, antennae, etc… in the calculation. I’ve not heard of serious issues for anyone with 6’-6.5’ draft except for the few spots just about everyone needs to time the tides (Exception: Dismal Swamp is a no-go for over 6’ – but an absolutely beautiful route). Good luck with the search. There are several sections easy to pop out and take the open ocean for the day or an overnight; however, it’s always nice to have options – nasty can last for weeks out there. 22-06-2016, 05:49   and Keys as well, so probably 5.5 is too much--less draft would be better. Just visited the blog about max draft for cruising S , and the idea of keeping it under 5' seems like a good one. Or even better, as suggested, we'll shop around for a center board. And yes, will also keep in mind air draft. The 385 we were considering, with the 5.5 draft, has a modified with 48'. Now we're looking at the 38' with center boards. We do want to keep to a well-made, solid for as well. Anyone had experience with those, opinions to share? Boat to sell??? 22-06-2016, 06:25   Boat: Tartan 40 , , and .) several on market. Definitely capable. Sent from my using Cruisers Sailing Forum 22-06-2016, 06:35   Boat: Pearson 422 . Sure someone with a shallower draft will fit in a few places you won't and they might be able to closer to the beach or bar than you but 5.5' would definitely not be severely restrictive. I've cruised the Bahamas with 6' with no problems. Whether your draft is 4' or 6' you just need to watch the , learn eyeball and plan accordingly. I can't really think of any major cruising area that 5' vs 5.5' will make that much difference. If you go as shallow as 4-4.5' that might open some shortcuts across the banks that wouldn't for the deeper draft but would probably come at the sacrifice of upwind performance. 22-06-2016, 08:16   Boat: none boat is 6'4" draft. I've taken my boat everywhere I took the first except aground! 22-06-2016, 09:07   Boat: Morgan 512 51' 512 more than 10 times. It is 5-1/2' deep and 64-1/2' tall with very, very few issues. That includes the Dismal swamp and all of . With extra high tides sometimes the bridge clearance is heart stopping, but if you look for the absolute highest spot and AVOID THE CENTER SPAN LIGHT you will be fine. That said, we did spend 4 days in Vero Beach waiting for the water to recede after 2 weeks of strong winds out of the east, but that was only once in over 10 years. Bottom line: 5-1/2' draft is fine below Cape May and you want to avoid big wakes when going under a bridge with 64-1/2' height . 22-06-2016, 09:08   have deemed the monies spent on dredging the ICW as wasteful (LOL) and therefore cut back on the process. Ironically the main intent of was to provide inside to commerce and that is still just as great (perhaps even greater) as it ever was. Also, if Florida and the Keys are on your agenda, you be wise to stay under 5'. The shoals and shallows will also present some ever changing challenges. If you are careful with and tides, and chart to avoid some areas, you will probably be fine with the draft you are considering. I would also suggest you look in to AGLCA (America Great Loop Cruising Association). The members there use the Atlantic ICW extensively and are openly helpful. Also consider Active as that also provides a plethora of good information that can be used. The $20 to join will be well spent. 22-06-2016, 09:26   Boat: Endeavour 42 CC Katash for a few weeks. Have sail up and down the icw for several years and never had a problem with a 61 foot mask and a 3-foot . Boat will be when we get back in about 4 weeks. is $119,000 comma no broker's involved. If you want to look at the boat go to endeavourowners.com . Go to the Section and look for 42 foot endeavors. Name of the boat is Katash. I have been to the Bahamas 4 times. 22-06-2016, 09:31   Boat: 1980 Tartan 33 c/b's are worthy coastal cruising candidates 22-06-2016, 09:34   have deemed the monies spent on dredging the ICW as wasteful (LOL) and therefore cut back on the process. Ironically the main intent of service was to provide inside to commerce and that is still just as great (perhaps even greater) as it ever was. 22-06-2016, 09:59   Boat: Boatless 40.5 Legend may be on the market. Happy to deliver her to Falmouth for you :-) Currently in Stuart Fl, sailed her down solo last year from Connecticut. 99k, new mast/standing which we had reduced from 63' to 62'. Fractional rig, easy to sail and fast, TONS of room :-) Plenty of pics and a story about her on the blog. Oh yea, shoal draft! 22-06-2016, 10:05   Boat: 1975 Gulfstar M53 22-06-2016, 10:33   , , , Thread Tools Rate This Thread : Posting Rules post new threads post replies post attachments edit your posts is are code is are are are Similar Threads Thread Thread Starter Forum Replies Last Post Nomad57 Dollars & Cents 6 02-07-2011 08:07 capt.cam Dollars & Cents 10 11-05-2011 21:30 labaxter Monohull Sailboats 21 18-08-2010 15:25 CaptainBW Monohull Sailboats 7 11-08-2010 15:06 ribbony General Sailing Forum 4 13-03-2006 19:11 - - - - - - - Privacy Guaranteed - your email is never shared with anyone, opt out any time. Great choice! Your favorites are temporarily saved for this session. Sign in to save them permanently, access them on any device, and receive relevant alerts. Sailboat Guide Tartan 34 C Tartan 34 C is a 34 ′ 4 ″ / 10.5 m monohull sailboat designed by Sparkman & Stephens and built by Tartan Yachts between 1968 and 1978. Rig and Sails Auxilary power, accomodations, calculations. The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more. Classic hull speed formula: Hull Speed = 1.34 x √LWL Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio .311 Hull Speed = Max Speed/Length ratio x √LWL Sail Area / Displacement Ratio A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more. SA/D = SA ÷ (D ÷ 64) 2/3 SA : Sail area in square feet, derived by adding the mainsail area to 100% of the foretriangle area (the lateral area above the deck between the mast and the forestay). D : Displacement in pounds. Ballast / Displacement Ratio A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize. Ballast / Displacement * 100 Displacement / Length Ratio A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more. D/L = (D ÷ 2240) ÷ (0.01 x LWL)³ D: Displacement of the boat in pounds. LWL: Waterline length in feet Comfort Ratio This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more. Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam 1.33 ) D: Displacement of the boat in pounds LOA: Length overall in feet Beam: Width of boat at the widest point in feet Capsize Screening Formula This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more. CSV = Beam ÷ ³√(D / 64) S&S Design No. 1904. The letter “C” has been adopted on the used boat market, “classic”, identifying it as the first 34 from Tartan. The second TARTAN 34, which is also a S&S design, is commonly referred to as the TARTAN 34-2. There was an option (rarely selected) to substitute a pilot berth for the cabinet storage to port, over and outboard of the dinette. The foot of the mainsail was shortened from the original design at least twice to improve balance and/or to lower it’s IOR rating. Hull 125 and later: E = 12.0’ Hull 200 and later: E = 10.5’ (displayed here) A yawl rig was advertised as an option. Embed this page on your own website by copying and pasting this code. Discover Related Sailboats Cruising World: 40 Best Sailboats About Sailboat Guide ©2024 Sea Time Tech, LLC This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. What Do Boat Measurements Mean? 11 Terms Explained! Boat measurements are crucial for maritime safety, efficiency, and compatibility. Navigating these measurements is vital for manufacturers and boating enthusiasts. Proper understanding ensures vessel selection, marina compliance, and safe navigation. 11 Main Boat Measurement Terms Length Overall (LOA) : The total length from the bow to the stern. It determines mooring space, marina fees, and navigation in confined waters. For example, a boat with a 30-foot LOA needs a slightly longer berth. Length on Deck (LOD) : Measures the hull’s horizontal length, excluding extensions like bow sprits. It provides a more accurate measurement of usable space. A boat might have a 35-foot LOA but a 30-foot LOD due to a 5-foot bow sprit. Beam : The width at the widest point, affecting stability and maneuverability. For instance, a boat with a 10-foot beam is more stable but less maneuverable than one with an 8-foot beam. Draft : The minimum depth required for the boat to float. A sailboat with a 6-foot draft cannot navigate waters less than 6 feet deep. Displacement : The weight of water displaced by the hull, reflecting the boat’s weight when loaded. A boat displacing 5 tons handles differently than one displacing 2 tons. Freeboard : The distance from the waterline to the upper deck, indicates how much of the boat is above water. A boat with 4 feet of freeboard handles choppy water better than one with 2 feet. Deadrise : The hull’s angle relative to a flat surface. A higher deadrise (sharp angle) cuts through waves better. A boat with a 20-degree deadrise performs better in rough water than one with a 10-degree deadrise. Air Draft : The height from the waterline to the highest fixed point. Important for bridge clearances. A sailboat with a 50-foot mast must consider bridge heights. Gross Tonnage : Volume measurement for large vessels, based on total internal space. For example, a cargo ship with 50,000 gross tonnage has a large capacity. Ballast : Weight added low in the boat for stability. A sailboat with 2,000 pounds of ballast is more stable than one with 1,000 pounds. Waterline Length (LWL) : Length at the waterline, affects speed and stability. A boat with a 25-foot LWL is generally faster than one with a 20-foot LWL. How to Measure a Boat Hull Length Overall (LOA) : Measure from the furthest point forward to the furthest point aft. Length on Deck (LOD) : Measure the deck length, excluding overhangs. Waterline Length (LWL) : Measure at the waterline. Beam : Measure the widest part of the hull. Draft : Measure from the waterline to the lowest part of the hull. Freeboard : Measure from the waterline to the upper edge of the hull. Deadrise : Measure the angle between the hull bottom and a horizontal plane. Hull Depth : Measure from the deepest point of the hull to the top of the deck. Coast Guard Boat Length Measurement The U.S. Coast Guard measures boat length using the Length Overall (LOA) method, from the bow’s tip to the stern’s end, including structural parts but excluding removable attachments. This measurement is crucial for regulatory and safety reasons, influencing boating laws and safety requirements. Recent Posts Responsibilities of a Fourth Engineer on Cargo Ships – September 10, 2024 The Role of Cargo Ships in Global Trade – August 22, 2024 Report: Yang Ming’s YM Mobility Explosion at Ningbo-Zhoushan Port – August 9, 2024 About the author I worked as an officer in the deck department on various types of vessels, including oil and chemical tankers, LPG carriers, and even reefer and TSHD in the early years. Currently employed as Marine Surveyor carrying cargo, draft, bunker, and warranty survey. Latest posts Is Maritime Security Necessary on Modern Ships? It’s vital for ships to stay vigilant. Isolation from land means having no backup or protection for miles, making them vulnerable to attacks and other threats. Equip modern ships using modern maritime security methods. Responsibilities of a Fourth Engineer on Cargo Ships A Fourth Engineer on cargo ships oversees engine room operations, machinery maintenance, and ensures compliance with regulations like MARPOL. The Quality Control Process in Marine Manufacturing Companies in the marine manufacturing space must have tight and effective quality control processes. What steps should an effective quality control process include? Need a boat to Pass Under a Bridge? When passing under a bridge with your vessel, there are various things that you will need to take into consideration, some of these being the air draft and bridge’s clearance.  Air Draft is a term found on the specification chart for most boats and is a measurement that could be very important when purchasing your boat. A vessel’s draft is the distance measured between the top of a vessel’s highest point to its waterline. Vertical clearance is the distance above the air draft that allows the vessel to pass safely under a bridge. Failing to consider air draft may result in being unable to calculate a vessel’s vertical clearance during a passage can be catastrophic.  A bridge’s clearance can be found displayed on charts as measured from the surface of the water to the underside of the bridge at Mean Highest High Water, which is the most restrictive clearance. The Mean Higher High Water (MHHW) is the average height of the highest tide recorded at a tide station each day during the designated recording period. It is used to measure the navigational clearance, or air draft, under bridges so that vessels can pass through safely. For our  MAKAI M37 Power Catamaran  the air draft, as measured from the waterline to the top of the roof is 3130mm which is 10ft 3in. The loaded waterline is the point on the hulls where the water reaches the boat loaded with fuel, water and other small items such as safety equipment.   If you have any other questions, we are always up for a chat and a challenge!  Contact us  today to find out more about our vessels and any other enquiries you may have. Follow us on  Facebook  and Instagram to stay up to date with all the latest news on Makai Yachts. Get Newsletter Privacy Policy https://calendly.com/makaiyachts/makai-m37-boat-tour?month=2024-08 What is a Ship’s Air Draft and How to Best Calculate It A ship’s air draft, sometimes called air draught, is an important measurement to consider when planning a voyage. It is one of the factors seafarers check if their vessel can safely navigate within harbors where suspended obstacles are present. While the regular draft and under keel clearance (UKC)... https://www.seamanmemories.com/ships-air-draft/ Leave a Comment Cancel reply Save my name, email, and website in this browser for the next time I comment. Subscribe To Our Newsletter Forums New posts Unanswered threads Register Top Posts Email What's new New posts New Posts (legacy) Latest activity New media Media New media New comments Boat Info Downloads Weekly Quiz Topic FAQ 10000boatnames.com Classifieds Sell Your Boat Used Gear for Sale Parts General Marine Parts Hunter Beneteau Catalina MacGregor Oday Help Terms of Use Monday Mail Subscribe Monday Mail Unsubscribe Air draft and ICW bridges Thread starter captron Start date Aug 29, 2017 Forums for All Owners Ask All Sailors In theory would this work (I don't think I would have the nerve to try it ) I have a Legend 40.5 if I see the tide boards reading 64 ft of clearance I will "ding" my vhf antenna on the bridge girders ,at 1800 rpm I'm cruising at 7 knots with a Flex-O-Fold 3 blade prop which at that speed and rpm will cause the stern to squat a good 6 inches at 2000 rpm maybe about 8 inches (can you say over propped) ??? my question in theory.......with the stern squatting 6 to 8 inches would that reduce the air draft???? look forward to your replies Capt. Ron   Captain Larry-DH Yes, in theory. It would increase your aft-leaning angle, and assuming your mast is stepped somewhere just forward of amidships, the deck level should not be raised by the bow wave. My question: Do you feel so confident in the accuracy of tide boards and tide tables that you'd risk your mast by making a 7-knot approach with little margin for error? I'd creep up on it if it was close.   Larry, That's what I do.............."sneak up on it"   Have not worked out the math but it seems to me that a squat of 6 inches at the stern would only translate perhaps as 2 inches at the mast at best. There are other factors like for how long can the boat hold the squat before its depth starts decreasing. The strength and direction of currents will also influence the depth of the squat. I think at best is a poor gamble; the tried and true methods are to plan arrival and approach at low tide or to heel the vessel.   We are always checking air draft. With speed we ride up on the bow wave being higher in the water. Yes we've bent antennas and anchor lights. Going slow we clear at our desired height. All U Get   All U Get said: We are always checking air draft. With speed we ride up on the bow wave being higher in the water. Yes we've bent antennas and anchor lights. Going slow we clear at our desired height. All U Get Click to expand Please notify us when and where you plan to try this method CR. I'll sail over to watch!   If I had to cheat on air draft, I'd be more likely to run my main halyard over to my tender that I had a fat boy run along side the boat & try to pull the sailboat over into a little bit of a heal with the weight of the tender. I would need a good reason to try even this trick. Waiting for proper tide would still be my first choice. If you are going to try that other trick, you might want to invest in some nylon bolts to mount your antenna with. Spare nylon bolts are cheaper than antennas.   SBO Weather and Forecasting Forum Jim & John Ggrizzard. If you go take pictures. This could be a viral YouTube video in the making. Maybe American Home Video entry. They have a 100,000 grand prize.   I'm on it!   I have 64.5 draft, went from NC to FL, made them all but scrap ant. several times and always went thru questionable ones on low tide, (had to wait 3 times, couple hours at most) even pulled up to the fenders and walked to boat thru. It seems to me if the stern is squatting, with the mast forward of the moment it might actually lift a little.   I went thru the dismal swamp with a reported 64 ft bridge (there is no tide in the canal and the Corp of Engineers keep the level to around 6 ft deep). I have a 63' 4" clearance to the top of the wind instrument, I also have a 3 ft vhf antenna and a 4 ft SSB/DSC antenna. Going under the 64 ft bridge was a nail bitter (remember not tide or wake to worry about - sort off). The metal antennas scrapped the bottom of the bridge. I lost the bird spike on the wind vane because it was hit by one of the antennas. One of the unknowns and my concern is when you are under the bridge and a wave/wake hits your boat you may bounce and hit the bottom of the bridge. I continued all the way to Miami with a couple of nail bitters/scraping the bottom of the bridges with antennas. I did go out from FLL to Government cut because there is a fix bridge in between FLL and Mia. The worse case was a bridge in Fl that had a 6 inch difference between hi and lo tide and no high board.   Velero49 said: I went thru the dismal swamp with a reported 64 ft bridge (there is no tide in the canal and the Corp of Engineers keep the level to around 6 ft deep). I have a 63' 4" clearance to the top of the wind instrument, I also have a 3 ft vhf antenna and a 4 ft SSB/DSC antenna. Going under the 64 ft bridge was a nail bitter (remember not tide or wake to worry about - sort off). The metal antennas scrapped the bottom of the bridge. I lost the bird spike on the wind vane because it was hit by one of the antennas. One of the unknowns and my concern is when you are under the bridge and a wave/wake hits your boat you may bounce and hit the bottom of the bridge. I continued all the way to Miami with a couple of nail bitters/scraping the bottom of the bridges with antennas. I did go out from FLL to Government cut because there is a fix bridge in between FLL and Mia. The worse case was a bridge in Fl that had a 6 inch difference between hi and lo tide and no high board. Click to expand jssailem said: Ggrizzard. If you go take pictures. This could be a viral YouTube video in the making. Maybe American Home Video entry. They have a 100,000 grand prize. Click to expand ggrizzard said: Please notify us when and where you plan to try this method CR. I'll sail over to watch! Click to expand Ok, I said in theory, I didn't say I was going to try it....... I know some of you will be disappointed to hear that. Regards Capt. Ron   For us, the boat IS the family pet.   This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register. By continuing to use this site, you are consenting to our use of cookies. Accept Learn more… Log in or Sign up You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser . Zud Senior Member Okay you gurus of Yachting, Easiest/accurate method of determining required air draft short of driving under the bridge and measuring the amount torn off of the mast/radar arch. Boat literature makes no sense...20'8" with TV dish removed but the light mast with radar is considerably higher on the boat and would be required/original equipment. How do I get a good measurement from top of radar arch to water level with all electronics removed?? Thanks Zud olderboater Senior Member Yes, the literature is useless. Others will have other ideas I'm sure, but here's how we did it. We measured a boathouse height from the water. Pulled the boat in, measured clearance. So our air draft was the height of the boathours opening less the amount we cleared it by. You can do the same under bridges that have accurate markings, note the word "accurate" as some don't, so I'd select more than one to check. We've double checked our boathouse numbers with bridges. Just as you need to know draft at different loads, make sure you take loads into account on air draft. This in addition to knowing it with all different equipment and height permutations. Capt J Senior Member Just lay a fishing rod across the hardtop where you can lay the rod verticle with a bobber on it and drop it down till it hits the water, then take it on land and measure it......if something sticks up above the hardtop measure that from the hardtop to the highest point and add to your measurement. I knew I could count on you guys !!! easiest and as accurate as need be. Will do ASAP Oscarvan Senior Member For RV's I use a laser level and large telescoping height pole. (Home Depot or Lowes) C4ENG Senior Member Could you use your docking plan or general arrangement drawings to calculate the air draft while using a pair of dividers and the measuring scale on the drawing for the vessel and then add it all up? Pascal Senior Member Home Depot sells measuring tapes.... J, Some of us don't fish and may not have fishing gear... You can still measure the boat, first from WL to deck, then the house, then the hard top or whatever. I thin measuring tapes are cheaper than a fishing rod and line, and lead most smart phones come with free calculator app so you can add up the various measurements Pascal said: ↑ Home Depot sells measuring tapes.... J, Some of us don't fish and may not have fishing gear... You can still measure the boat, first from WL to deck, then the house, then the hard top or whatever. I thin measuring tapes are cheaper than a fishing rod and line, and lead most smart phones come with free calculator app so you can add up the various measurements Click to expand... not a single fishing rod on this boat ... Hoping to keep it this way No, create an account now. Yes, my password is: Forgot your password? 172 COMMENTS Air draft Air draft (or air draught) is the distance from the surface of the water to the highest point on a vessel. This is similar to the deep draft of a vessel which is measured from the surface of the water to the deepest part of the hull below the surface. However, air draft is expressed as a height (positive upward), while deep draft is expressed ... PDF AIR DRAFT IS CRITICAL! Air draft (draught) is a term used to describe the distance from the top of a vessel's highest point to its waterline. Vertical clearance is the distance in excess of the air draft that allows a vessel to pass safely under a bridge or object. The consequences of failing to consider air draft and to properly calculate a vessel's vertical ... Measuring Air Draft on a sailboat Air draft is the total distance from water level to the top of the tallest equipment attached to the mast head. When going under bridges, it's important to ... Calculate Clearance Under Bridges & Cables The Final Calculation. To calculate clearance under bridges & cables then, all you need to do is add the charted height and the extra bit of space together. This will then give you the total space available for a given time on a given day. In order to see if you will fit under the bridge take the air draft of your vessel from the total space ... Drafting Boating: How to Measure the Draft and Why It's So ... A boat's draft refers to the vertical distance between the waterline and the deepest point of the vessel's hull. It represents how much of the boat is in the water. Measured in feet or meters, the draft is a critical specification for boat designers, manufacturers, and mariners alike. It is crucial in determining a boat's stability ... The Perfect Great Loop Boat The one absolute and immutable dimension for the Great Loop is an air draft of 19 feet, 6 inches, in order to clear the fixed Chicago railroad bridge. Of course, you can also complement your Loop experience with air drafts of 17 feet (downtown Chicago) or 15 feet, 6 inches (the Erie Canal). Air draft is arguably the most important dimension ... Ship measurements The lower the ratio the greater the boat's stability. Carlin - similar to a beam, except running in a fore and aft direction. ... Draft, Air - Air Draft/Draught is the distance from the water line to the highest point on a ship (including antennas) while it is loaded. Air draft is the minimum height a ship needs to pass under, while ... OCEANIS 40.1 (BENETEAU) Performance air draft: 18.78m / 61.58ft Performance rig: I - 15.65m / 51.33ft J - 4.78m / 15.67ft P - 15.40m / 50.5ft ... it will vary with the weights of fuel, water, stores and equipment. A boat's actual draft is usually somewhat more than the original designed or advertised draft. For boats with adjustable keels (centerboards, daggerboards ... Air Draft Air Draft refers to the vertical distance between the waterline and the highest point of a vessel, typically measured from the waterline to the top of the highest mast, antenna, or structure on board. It represents the maximum height that a vessel can safely navigate under bridges, power lines, or other overhead obstacles without risking ... Air draft explained Air draft explained. Air draft (or air draught) is the distance from the surface of the water to the highest point on a vessel.This is similar to the deep draft of a vessel which is measured from the surface of the water to the deepest part of the hull below the surface. However, air draft is expressed as a height (positive upward), while deep draft is expressed as a depth (positive downward). Thinking About a Great Loop Adventure? Here's What You Need to Know Second, the boat you choose must have an air draft of less than 19.6 feet so it can clear the lowest fixed bridge on the Great Loop, which is located on the Illinois Waterway and cannot be bypassed by taking an alternate route. ... She is a regular speaker about the Great Loop at events like the Miami Boat Show, Chicago Boat Show, TrawlerFest ... Oyster 495: Top 10 Best Best Nominee Draft/Shoal 7' 6" / 6' 0" Air Draft 74' 9 ... Sailing sailboats Top 10 Nominee boat review. By. Zuzana Prochazka. SAIL Charter Editor Zuzana Prochazka is a USCG 100-ton master who logs countless miles on all kinds of boats around the world and never misses an opportunity to raise a sail or crawl into the engine room of a new design ... Measuring Air Draft However, we checked one boat from a third builder. Their numbers were from the most optimistic view. Their quoted air draft was from a fully loaded boat in every way and several inches less than the draft we found in our worst case. Their water draft was less than we found in any load situation. They quoted 5'. Out numbers ranged from 5'1" to 5'3". Inside or Outside When Sailing the ICW Meri has an air draft of 63ft 4in and her keel draws 5ft 4in, so going all the way on the ICW was certainly an option. We'd also made two crossings to the Bahamas and back that winter, which meant we now had some offshore experience as well. Still, we were not yet comfortable with making a long passage, so on this trip we decided to restrict ourselves to offshore jumps of less than 250 miles. AGLCA Most sailboats will need to unstep the mast to clear the bridges outside of Chicago and upstate New York. Your choice of waterways through New York State and into Canada will also be dependent on your air draft. If you can clear a 15' bridge, you have the option to take the Erie Canal to its western terminus into Lake Erie. If you can clear a ... Maximum draft for cruising the Atlantic ICW Re: Maximum draft for cruising the Atlantic ICW. Going aground I feel is more about your level of risk taking than the draft of your boat. If 1 foot of extra draft is really going to be limiting ask yourself how often you would be willing to sail with 1 foot of water clearance. My first boat was 5'2" and my current boat is 6'4" draft. Tartan 34 C Air Draft 44 ′ 2 ″ / 13.5 m ... Sail area in square feet, derived by adding the mainsail area to 100% of the foretriangle area (the lateral area above the deck between the mast and the forestay). D: Displacement in pounds. 16.85 <16: under powered. Air Draft With weight variability boat to boat, I wouldn't buy a boat without measuring air draft if that's a critical factor for you. I like Raked's adding 10 feet to the measurement for real bridge clearance. All it takes is one wake while transiting to drop the rig if it's close. P . Last edited by a moderator: Oct 23, 2013. What Do Boat Measurements Mean? 11 Terms Explained! A higher deadrise (sharp angle) cuts through waves better. A boat with a 20-degree deadrise performs better in rough water than one with a 10-degree deadrise. Air Draft: The height from the waterline to the highest fixed point. Important for bridge clearances. A sailboat with a 50-foot mast must consider bridge heights. Need a boat to Pass Under a Bridge? You need to know the air draft It is used to measure the navigational clearance, or air draft, under bridges so that vessels can pass through safely. For our MAKAI M37 Power Catamaran the air draft, as measured from the waterline to the top of the roof is 3130mm which is 10ft 3in. The loaded waterline is the point on the hulls where the water reaches the boat loaded with ... Top 10 Best Boats 2025 Nominees Moody DS48, Nautor ClubSwan 46 The boat can be sailed entirely from the twin helms aft or from the optional interior steering position. The twin helms are two steps up from the regular cockpit floor. ... LOA 50'7" LWL 45'4" Beam 15'11" Draft 7'1" Air Draft 79' Displacement 46,650 lbs Ballast NA Sail Area 1,409sq ft (main and jib) Power Yanmar 110hp or 150hp ... What is a Ship's Air Draft and How to Best Calculate It 7 November 2023. A ship's air draft, sometimes called air draught, is an important measurement to consider when planning a voyage. It is one of the factors seafarers check if their vessel can safely navigate within harbors where suspended obstacles are present. While the regular draft and under keel clearance (UKC)... https://www ... Air draft and ICW bridges Jeanneau 45.2 Saugatuck, MI. Aug 30, 2017. #11. I have 64.5 draft, went from NC to FL, made them all but scrap ant. several times and always went thru questionable ones on low tide, (had to wait 3 times, couple hours at most) even pulled up to the fenders and walked to boat thru. Determining Air Draft (Boat height above water level) Pulled the boat in, measured clearance. So our air draft was the height of the boathours opening less the amount we cleared it by. You can do the same under bridges that have accurate markings, note the word "accurate" as some don't, so I'd select more than one to check. We've double checked our boathouse numbers with bridges. catamaran gulet motorboat powerboat riverboat sailboat trimaran yacht