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.
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.
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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.
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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.
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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).
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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.
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.
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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.
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REPEAT
THIS TEST ON THE OTHER SIDE.
TEST 3. The final test is without the passenger weights.
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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.
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That's It! If you pass all these tests you have done
everything the regulations require.
Revised 03/06/2019 © newboatbuilders.com 2011 All rights reserved
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