MODIFIED LEVEL FLOTATION

Flotation regulations for manually propelled and less than 2 HP recreational boats.  33 CFR 183.301-335

Applies to:

Mono-hull Boats (not catamarans, trimarans, or pontoon boats): Mono-hull means that if you can draw a continuous line around the hull at the waterline when the boat is at rest it's a mono-hull. If it makes two or more footprints in the water it's a multi-hull.

Less than 2 Horsepower, gas or electric outboard motor, or:

Manually propelled. (Oars, sculls, paddles or pedals, etc.)

This category includes most dinghies and rowboats, and some small john boats.

Requirements:

The boat has to float when swamped, (that is; full of water), in an upright attitude. See the diagram in each test for the specific requirements.

So how do I know how much flotation to put in the boat?

The amount of flotation is based on three factors.

1. The boat weight: that is the weight of the hull, the deck, the seats, etc. Everything not in the next two categories.

2. The weight of the engines, batteries, full portable fuel tank, and controls. In this case, since this is for boats 2 HP or less it is either 25 lbs., or zero for manually propelled boats.

3. The weight of the persons. This comes from the persons weight on the capacity label.

Go to page on how to calculate amount of flotation .

What do I use for flotation?

Most people use polyurethane foam. Some use polystyrene foam. If you use polystyrene foam you must install it in a way that it cannot be attacked by gasoline, oils or bilge cleaners. See 33 CFR 183.112-114 on flotation materials.  Others use air chambers. Air chambers that are integral with the hull are allowed. Also, you don't have to pass the test with any of the air chambers punctured. Foam is a good solution, but some don't want foam in their classic wooden boats. In that case they can use balsa, or build air chambers into the boat. Sometimes wooden boats without engines will pass without any added flotation. DON"T TAKE MY WORD FOR IT! Test the boat. However if you add an engine, the bets are that it will fail unless there is some flotation to support the engine.

Excellent article in the USCG Boating Safety Circular #98 Spring 2022 concerning quality Control for floatation Foam

How do I know it works?

Test it!

The best way to find out if your boat passes is to test it. You can do the test yourself, or have a laboratory do it.  However, as of June 2014 the USCG Voluntary testing program has ended. The Coast Guard will no longer test your boat for free.  You will have to pay the laboratory to test the boat for you. Call the Coast Guard at or 202-372-1077 to find out about the test program.  The Coast Guard still purchases and test boats they suspect are not in compliance and cannot pass the flotation requirements. If this happens you will have to do a recall on all boats of that year and model, so it is better to test it before you start selling them. 

Here's how it's done.

You need to know the following:

The maximum weight capacity (the safe load ) your boat will carry.

How much weight in people it will carry

If you want to use 2 horsepower or less you need the engine weight : = 30 lb.

There are some things you also need to know before you do the test. What kind of weights will you use for the test? The test lab uses iron ingots. You can use anything that does not absorb water, which leaves out concrete or concrete blocks. You also need to weigh each of the weights with a calibrated industrial scale. These can be rented from companies that rent equipment for labratories.

You need to determine if the test weights will be submerged or dry. In the capacity tests the weights are dry, but in the flotation test they will most likely be submerged. Submerged they weigh less than they do dry. This is not difficult to calculate. The USCG, and ABYC publish tables of factors (determined from the specific gravity of the weight) for different materials. For iron the factor is 0.86. That is you need to add weight for iron, because under water it weighs less. For example if the amount of weight needed is 200 lb., you need to add 33 lbs to compensate for it's reduced weight underwater. (200/0.86 = 232.5 dry weight)

The table for the factors is at https://newboatbuilders.com/pages/factors.html

Then measure the following on your boat:(Click image for full size) Cockpit area. 40% reference area. Passenger area 70% reference areas. Two foot reference areas fore and aft. There are three tests to do.

TEST 1. The first is the level flotation test after an 18 hour soak.

Put your boat in the water. Put ½ the persons weight in the boat (assuming the maximum persons weight is less than 550 pounds. If over 550 pounds, add .125 times persons weight minus 550) in the 40% reference area. The Center of Gravity of all the weights needs to be in the 40% reference area. That doesn't mean all the weights have to be in the 40% area, just the Center of Gravity of all the weights. Pull the plug! Let the boat fill up with water. Leave it that way for 18 hours.

When you come back it should float like this: (Click image for full size) One end out of the water. The other end 6 inches or less under water (or out of the water too) measured at the 2 foot reference area. No more than a 10 degree heel angle. (You can buy a device at a hardware store that measures this).

Place ½ the weight for persons on one side of the boat. The center of gravity of these weights has to be in the 70% reference area on that side of the boat. You have a lot of lee way here. You can move the weights from front to back, or back to front to get the boat to pass as long as the Center of Gravity is in the 70% area, and 30% of the total passenger weight is in the 70% area.

Take the other ½ of the passenger weight out of the boat.

If this is a 2 HP or less boat, leave the 30 lbs where it is.

WARNING! Make sure you have some ropes or straps attached to the boat to keep it from rolling over. If you don't have enough flotation to keep it upright, that's what it will do. Then the weights will fall out and go to the bottom of the pool or lake.

When it settles down it should float like this. (Click image for full size) One end out of the water. The other end 12 inches or less under water (or out of the water too) measured at the 2 foot reference area. No more than a 30 degree heel angle. Experience has shown that if it goes 30 degrees it will probably roll all the way over.

REPEAT THIS TEST ON THE OTHER SIDE.

TEST 3. The final test is without the passenger weights.

Take all of the passenger weight out of the boat. Let the boat settle. It should float like this: (Click image for full size) One end out of the water. The other end 6 inches or less under water (or out of the water too) measured at the 2 foot reference area. No more than a 10 degree heel angle.

That's It! If you pass all these tests you have done everything the regulations require.

The most common reasons for failing the flotation Test;

Not enough flotation: (But you can also fail if you have too much flotation.)

Flotation in the wrong locations in the boat.

Incorrect foam density:  The calculations use 2lb density.  That is, one cubic foot of foam weighs 2 lb. If you use heavier (or lighter) you will fail unless you actually use a denser or lighter foam and used it's density in the calculations:

Improper kind of foam in the bilge: Flotation foam that is resistant to exposure to gas, oils, bilge cleaners, or anything that can dissolve or damage the foam, is usually polyurethane. But some manufacturers use polystyrene foams, the most common of which is Styrofoam (a trademarked name).  Stryofoam, and all polystyrene foams, will be dissolvedby gas, oils, bilge cleaners, etc. They must not be used in the bilge or anywhere they can be exposed to those solvents unless encapsulated so they can't be contacted.

Electric boats must follow the same requirements for foam as that for gas powered boats. 

Revised 10/28/2024 © newboatbuilders.com 2011 All rights reserved