LEVEL FLOTATION

Professional BoatBuilder On-line Course on Load Capacity and Flotation

Applies to:

Mono-hull outboard 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.

Greater than 2 Horsepower:

Less than 20 feet (measured on the center line, including rub rails):

This category includes most outboard motor boats.

Requirements:

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

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

Go to form to calculate flotation .

What do I use for flotation?

Most people use polyurethane foam. Some use polystyrene foam, that is, styrofoam. Others use air chambers. Air chambers that are integral with the hull are not allowed. They must be separate from the hull. Also, you have to pass the test with the two largest 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. There are other ways to provide flotation, however, some ideas are not that good . The two main reasons boats fail is not enough foam, and not enough foam to support the engines.

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, or the Coast Guard will do it for you. Call the Coast Guard at  1-202-267-0984.

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

The engine weight :.

Then measure the following reference areas on your boat:

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: (Link to diagram)

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).

TEST 2. The second test is the stability test. You need to do this one twice, once on each side of the boat.

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.

Leave the engine, batteries, fuel and control weights where they are.

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. (See diagram)

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: (Link to diagram)

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.