urethane foam

[therigwelder]

i removed the rotten deck and water logged foam on my 16 ft tri-hull.I really don't want to go back with foam.what are the pros and cons with the marine polyurethane foam and is the foam really necessary?

[alan white]

Nah, go with returnable liter bottles. Guaranteed to float you as long as you own the boat. $20.00 worth will give you enough flotation.

[therigwelder]

okay your suggesting that i fill the boat hull full of empty 1 liter plastic bottles.then deck and fiberglass over them.ok i understand the floatation principal but its rather unusual lol.one liter bottles are definatley cheaper than a&b part foam.I am a redneck from mississippi and i have to thank you for the good laugh i just got.wonder how it would work with aluminum coors bottles rflmao

[Gian Milan]

Polyurethane absorbs water and petrol and should not be taken into account.
polythene would be ok, but it is in the panels so it is difficult to give the desired form.
It would not be possible to place the very strong polythene bags and then fill them with polyurethane?
and bottles ... should not we fill them with polyurethane?
placed under the deckhouse would have more resistance.

[therigwelder]

thanks alan i love the idea.my mind is working already ,i figure 50 -75 bottles ought to do it. just kidding

[therigwelder]

well 1 liter bottle has about the resistance of 3-5 lbs each. we use them for trot lines here in the south and ive caught many 3 lb catfish on them.the bottle theory is sound but the question is how many do you need for proper flotation for a 1500-2000 lb boat.hmm going green recycling?

[Gian Milan]

1 bottle, 1 liter, 1 kg of buoyancy.

76 bottles, 75 kg = 165.35 lbs


is safe enough?

scale metric includes:

Water
1 kg = 1 liter = 1 dm3

[therigwelder]

what would the required bouyancy be for a 2000 lb boat?iI figure the area under the deck to be 20 cubic feet

[Mr Efficiency]

20 cubic feet won't hold too many plastic bottles, you could count on at least a third remaining unfilled space I'd estimate. That being so, you have about 1000 lbs of bouyancy. You want bouyancy that won't destabilize the boat, which can happen if it is distributed toward the centreline of the boat, and not along the sides. And having it a little higher up along the sides helps that as well. This assumes the boat is swamped but upright, doesn't help if capsized, in fact may be easier to right if all bouyancy in the middle. Not that you are likely to be able to right it from an upturned position. Far better to be in swamped but still stable boat, than one upside down. You should err on the side of too much bouyancy rather than too little. You can factor in that fibreglass laminate has a specific gravity of about 1.6. Above all, don't join the people in heaven who elected to have no flotation.

[Gian Milan]

for 2000 lbs of buoyancy, are 907.18 kg of buoyancy.
So 907 one-liter bottles.
is a cubic foot = 28.317016 cubic dm.
If you have 20 cubic feet, each foot supports about 28 kg.

28 kg * 20 feet= 560 kg = 1230 lbs.

Sorry, if u need 2000 lbs, you will drown!

[Gian Milan]

However, I put odds to make the sides full of things floating.
If the boat had sunk for a few moments, it is proved that resurfaces not reversed.
the 20 cubic feet can be filled by half, for example

[tunnels]

Floatation down low is a little dangerous as it causes the hull to want to roll over in the event of being pooped so everything falls out and never seen again unless it floats , the motor is in the water and you are left clinging to a upside down hull !! nice one !!!. Up under the side decks and fore deck and in the back then the boat will sit relitively level and up the right way and you are able to stay inside the boat .
Foam is a waste of time and money , under floor space is best left free and able to breath and will stay dry so you boat will be light again !!. New wood needs to be sealled with resin and glassed in .
Get onto the US coast guard site and find floatation and bouyancy theres some infor worth thinking about !!all common sense mind you !!

[Herman]

Originally Posted by Gian Milan

for 2000 lbs of buoyancy, are 907.18 kg of buoyancy.
So 907 one-liter bottles.
is a cubic foot = 28.317016 cubic dm.
If you have 20 cubic feet, each foot supports about 28 kg.

28 kg * 20 feet= 560 kg = 1230 lbs.

Sorry, if u need 2000 lbs, you will drown!

Not completely true. You forget the buoyancy caused by the displaced water, or in other words, the volume of the structure (material of the boat).

Lets assume the boat is 100% polyester/glass, then a density of 1,6 of the material should be almost right.
907 kgs = 566 liter.

907-566 = 341 liter.

You need 341 liter of buoyancy to keep the thing afloat.

[michael pierzga]

Originally Posted by therigwelder

i removed the rotten deck and water logged foam on my 16 ft tri-hull.I really don't want to go back with foam.what are the pros and cons with the marine polyurethane foam and is the foam really necessary?

You can also use blue billet styrofoam for building floating docks .. Cheaper... http://www.buoyancyfoam.com/

[Gian Milan]

Originally Posted by Herman

Not completely true. You forget the buoyancy caused by the displaced water, or in other words, the volume of the structure (material of the boat).

Lets assume the boat is 100% polyester/glass, then a density of 1,6 of the material should be almost right.
907 kgs = 566 liter.

907-566 = 341 liter.

You need 341 liter of buoyancy to keep the thing afloat.

he asked in the post 2000lbs of buoyancy.
The calculations are for 2000 lbs.

Any case, someone will go on the boat ... something will be charged?

we can not know what he will do in boat.
He says 2000, I trust!