what is best way of adding floatation to a flatboat

[limitout]

I have a new flatboat and I will soon be having the floor and sides skinned over with aluminum sheeting so I need (want to) fill the void under the floor with some floatation foam.

my rule is if you are going to enclose something then fill it with floatation to because you can never have too much.

what is the best and most cost affective way to go about doing this?

I plan to go buy a bunch of that 1/2" closed cell dense foam board from the hardware box store and size and trim it to fit stacking it in layers or is there a better way?

the boat is a shallow vee so we are talking about filling the void between the rib braces that are 2 1/2" thick on the outer edge hull corner to around an average 4"-4 1/2" thick in the center keel area and the side areas are about 16" high going from only 1/2" thick at the top to around 3" wide at the bottom in the hull corner.

 

[robert graham]

Re: what is best way of adding floatation to a flatboat

I've heard of folks buying/cutting/installing many sections of those closed cell foam swim noodles...seems like it could work quite well....

 

[crabby captain john]

Re: what is best way of adding floatation to a flatboat

That sheeting will be slippery as ice. Any time you are going to add foam it must be 100% sealed so ZERO water gets in. Foam gets wet and waterlogged and all you have is excess weight.

 

[limitout]

Re: what is best way of adding floatation to a flatboat

I've heard of folks buying/cutting/installing many sections of those closed cell foam swim noodles...seems like it could work quite well....

never heard of that one before but any floatation is better then no floatation I guess

That sheeting will be slippery as ice. Any time you are going to add foam it must be 100% sealed so ZERO water gets in. Foam gets wet and waterlogged and all you have is excess weight.

umm, its impossible to walk on it since its under the floor so the foam will be completely encapsulated or enclosed between the hull and floor just like with fiberglass boats.

it will be layed on top of the boats bottom hull between the open exposed ribs / then layers of foam added to any areas that can be filled in / then 1/8" sheet of aluminum floor is welded over it onto the ribs and sides of the boat

I experimented with the white foam and it absorbs water over time much like spray foam, so even though its cheaper then the closed cell boards it isn't very good choice for floatation. I have used the closed cell boards from the box store in the past and even submerged for years it didn't absorb and water so I know its waterproof.

just wasn't sure if there was a better way to add floatation to it or if there was a cheap way to spray your own dense closed cell foam like those boards are made of?

I want to make her as reasonably unsinkable ads I can

 

[smokeonthewater]

Re: what is best way of adding floatation to a flatboat

I can't figure out what you are trying to say about your floor here but if the foam is "completely encapsulated" IE in a air tight container then the foam is useless added weight as the trapped air weighs less and has the same buoyancy.

If you are going to permanently trap foam behind welded in panels and NOT inside compartments then I would HIGHLY recommend using actual pourable 2 part closed cell flotation foam.... be a real shame to use that blueboard crap and have it break down over time....

btw it isn't gas or oil resistant

EDIT: imagine if your foam chunks caught fire during the welding process

EDIT again... "cheap" no there isn't a cheap way to do quality closed cell foam... if you want cheap then, as ghetto as it sounds, and definitely not my style, 2 liter and 20 oz soda bottles float and people have been known to build hundreds of them into a boat

 

[metriccrescentwrench]

Re: what is best way of adding floatation to a flatboat

If you're concerned about meeting USCG standards for floatation foam (it needs to be able to stand up to gasoline and oil as well as not absorb water for I believe it's a 30 day exposure) you'll use the 2 part pour foam in the 2 pound per cubic foot density. I get it from US Composites.

 

[limitout]

Re: what is best way of adding floatation to a flatboat

I can't figure out what you are trying to say about your floor here but if the foam is "completely encapsulated" IE in a air tight container then the foam is useless added weight as the trapped air weighs less and has the same buoyancy.

best way to describe it is its like the insulation in the walls of your house, the floor is the outside of your house, the ribs of the boat are your wall studs and the floor I am putting in goes on top of that like the sheetrock goes over the wall of your house to enclose it.

If you are going to permanently trap foam behind welded in panels and NOT inside compartments then I would HIGHLY recommend using actual pourable 2 part closed cell flotation foam.... be a real shame to use that blueboard crap and have it break down over time....

btw it isn't gas or oil resistant

yes I am planning to "permanently trap foam behind welded in panels" and looking for the best method to add floatation

EDIT: imagine if your foam chunks caught fire during the welding process

those closed cell foam wall boards are fire proof, it doesn't burn (even when thrown in a fire), it only shrinks and melts. that's why they let them build houses with it

the floor is going in as one uncut solid sheet so I don't know how I would be able to get the foam mixed and quickly centered near the keel for expansion in the 12"x4" x 2 1/2" high opening left on the ends of the floor section?

making big enough holes to pour the foam straight in isn't an option since he would have to melt away all the foam within 6-8" or more of the hole trying to weld those holes shut again and the foam would prevent the welds from sticking.

is there a system you can use to squirt it in by a hose or would I be best to spray it in before the floor goes in then sand away any excess that's higher then the ribs and in the way?

the floor will be spot welded to the ribs and my welder tells me any foam that might melt from the nearby heat is going to be minimal since he is welding to the ribs and not directly where the foam is

 

[smokeonthewater]

Re: what is best way of adding floatation to a flatboat

you pour the foam in after installing the floor

I would advise against putting any foam in small areas and instead only put it in large areas.... IE the bow and stern under casting decks and around live wells... bonus is insulated live wells.

Go to a dealership and study new aluminum bass boats....

Figure out how much flotation you actually need and do the math to get that amount instead of cramming every possible square inch full.

 

[limitout]

Re: what is best way of adding floatation to a flatboat

you pour the foam in after installing the floor

how? I cant even get my hand under the floor on the edge after its welded in and I still have 26" to go before I can get to the center keel where the expanding foam should be put to fill the void. I guess I could pour one section at a time and quickly cover it with a sheet of plywood and plastic visqueen sheeting so it doesn't stick to the wood.

do you know of a place that has the best prices to get the foam mix?

I would advise against putting any foam in small areas and instead only put it in large areas.... IE the bow and stern under casting decks and around live wells... bonus is insulated live wells.

yep, im not going to go crazy with it and I will try to not fill the ribs so air can get to it and it retains good drainage

Go to a dealership and study new aluminum bass boats....

as for seeing how the boats are built, that was great eye opener lol. the bow void had one bag of premixed foam in a bag stuck in it that was the size of a basketball and the rear seat when cut open had 3 of these bags so I had 4 basketballs of foam as the total floatation for the boat and motor. that was pathetic but those are the new and improved ways they build things today. those 4 bags might barely keep the empty boat from sinking to the bottom but it sure aint gonna float that 240lb motor the boat is rated for. that's one big advantage with fiberglass boats, they pour or spray in the foam so they don't skimp on floatation

Figure out how much flotation you actually need and do the math to get that amount instead of cramming every possible square inch full.

as for calculating of foam needed, I am opening the bow and rear seats for creating storage there so in order to make up for the floatation that "should" have been inside them, I have done the math and I need to fill every void under the flooring to cubic feet of floatation if they were full of foam.

 

[smokeonthewater]

Re: what is best way of adding floatation to a flatboat

There are many tricks but the foam is poured through access holes or injected with a hose and a funnel..... Do some research in the restoration section

When you do your math you need to understand that your boat and motor will weigh considerably less under water than on land.... "3 basket balls" may be pretty crappy but you may surprised that it takes less than you think... example... a group 31 battery is quite heavy but under water it can be lifted with one finger

I think you are overestimating the fire retardant properties

Foam and Foam Board Insulation | DoItYourself.com


"Fire Protection:

Foam insulation is relatively hard to ignite but when ignited, it burns readily and emits a dense, black, smoke containing many toxic gases. The combustion characteristics of foam insulation products vary with the combustion temperatures, chemical formulation, and available air.

Because of the dangers described above, foams used for construction require a covering as a fire barrier. One half-inch thick (1.27 cm) gypsum wallboard is one of the most common fire barriers. Some building codes, however, do not require an additional fire barrier for certain metal-faced laminated foam products. Check with your local building code/fire officials, and insurers for specific information on what is permitted in your area."

https://www.osha.gov/dts/hib/hib_data/hib19890510.html

 

[limitout]

Re: what is best way of adding floatation to a flatboat

what are the dangers/drawbacks of the risk of over expansion by putting too much foam in the void and how do you avoid not putting enough? I don't think it will pop any welds but it could deform the floor or bottom hull couldn't it?

the biggest grips I have come across with mixing foam has been uninsulated voids and cavities or over doing it

 

[smokeonthewater]

Re: what is best way of adding floatation to a flatboat

That's where the research in the resto section comes in... there are lots of threads there that cover the details....

actually it might be time to move this thread there.... Some of the guys that hang out there can help you work out the details.....

In short though you need to know the volume of the space you plan to fill and thus mix the correct amount of foam to fill without overfilling... also you can cut relief holes where excess foam will mushroom... after it sets up it is sliced off and a cover plate is put over the hole

 

[smokeonthewater]

Re: what is best way of adding floatation to a flatboat

You keep saying "uninsulated" a small void will have very little impact on flotation ..... I can't see any reason to worry about insulation in an open boat

 

[limitout]

Re: what is best way of adding floatation to a flatboat

You keep saying "uninsulated" a small void will have very little impact on flotation ..... I can't see any reason to worry about insulation in an open boat

I only said it once but uninsulated means unfilled void, that should have been obvious but "non floatation filled void" is a lot more letters to type.

I mentioned I wanted to maximize the floatation I can get in it so it would be best to do everything i can to avoid any practice that might increase the odds of vacant cavities being formed if I can.

I call the floatation foam "insulation" because I am from the home building industry so I used a familiar term to describe it. I am not trying to insulate anything.


i'll go look in the restoration section for recommendations on where to get foam the cheapest

 

[smokeonthewater]

Re: what is best way of adding floatation to a flatboat

I only said it once but uninsulated means unfilled void, that should have been obvious but "non floatation filled void" is a lot more letters to type.

I mentioned I wanted to maximize the floatation I can get in it so it would be best to do everything i can to avoid any practice that might increase the odds of vacant cavities being formed if I can.

I call the floatation foam "insulation" because I am from the home building industry so I used a familiar term to describe it. I am not trying to insulate anything.


i'll go look in the restoration section for recommendations on where to get foam the cheapest

US COMPOSITES is where to get it

"should be obvious" is a worthless phrase.... If we assume that a poster MEANT something different than they SAID we get problems... say what you mean and use as many words as needed..... BTW "leave unfilled void" doesn't take any more typing than "leave uninsulated void"

Just wanted to make sure we were on the same page..... kinda like your signature line......

The poured in foam will leave much less void space than cut chunks because it will perfectly conform to the space.... Even if you don't manage to fill the top inch of the thin side area.....


for drainage, just lay in PVC pipe along the keel

 

[limitout]

Re: what is best way of adding floatation to a flatboat

EDIT again... "cheap" no there isn't a cheap way to do quality closed cell foam... if you want cheap then, as ghetto as it sounds, and definitely not my style, 2 liter and 20 oz soda bottles float and people have been known to build hundreds of them into a boat

cheap in this case means keeping costs at a reasonable amount compared to buying the foam board sheets, not rednecking it with soda bottles and packing peanuts like some backwoods shade tree mechanic.

I only do things "the right way", but I also have to live on a budget but at the most reasonable way to keep expenses down so shopping around for the best prices on the right materials I need.

a 4x8x1/2 sheet of foam board at the box store costs around $12 so that means that method costs me $12 for 1.3 cubic feet of foam floatation but there is always some waste so i'll round that off to an average cost of $12 per cubic foot.

If you're concerned about meeting USCG standards for floatation foam (it needs to be able to stand up to gasoline and oil as well as not absorb water for I believe it's a 30 day exposure) you'll use the 2 part pour foam in the 2 pound per cubic foot density. I get it from US Composites.

thanks, im not building the boat, im just modifying it, so there is no USCG inspection required so im not required to meet any USCG standards or anything like that so im doing this just for my own peace of mind and safety

 

[smokeonthewater]

Re: what is best way of adding floatation to a flatboat

don't take things as personal hits on your character

the point I was making was that the good foam used exclusively in boat building is not cheap... it is pricey

I didn't imply that you were a "redneck" just that there is no cheap alternative other than the really cheap option of boards..... personally I don't consider the bottles a bad thing but just not fitting for my or your needs..... they are at least as viable an option as lumber yard sheets

likewise M C didn't say you HAVE to comply with USCG standards... he said "if you care about...."

 

[roscoe]

Re: what is best way of adding floatation to a flatboat

you may surprised that it takes less than you think... example... a group 31 battery is quite heavy but under water it can be lifted with one finger

This, I find interesting. Will have to try it.

I will likely find that you have stronger fingers than I do, because I know I couldn't lift 2 18# river anchors with one finger.


FWIW, 5 cu ft of foam will give you about 300# of buoyancy.

In "sheet" form, that would be a 4' x 8' x 2" sheet of foam.

When swamped, the amount of buoyancy in the boat will determine if the boat is just at the surface, or if part of it is held up out of the water.

 

[limitout]

Re: what is best way of adding floatation to a flatboat

FWIW, 5 cu ft of foam will give you about 300# of buoyancy.

In "sheet" form, that would be a 4' x 8' x 2" sheet of foam.

When swamped, the amount of buoyancy in the boat will determine if the boat is just at the surface, or if part of it is held up out of the water.

the way I had it figured out.

the boat is 350 lbs and the 240 lb motor so that's 600 lbs of floatation needed not counting gear and extras so based on the room I have under the floor, I can get 4'x8'x2" of foam plus an unknown amount in the center keel area where its deeper so that's maybe 1-2 cubic feet extra so im still short of where I need to be for the dry weight on land. I don't know how you would calculate the underwater weight for the required floatation.

there is something to what smoke is talking about where things weight less under water but it sounds like he is over exaggerating by how much lighter things are.

I think if I ever swamp it, it wont float above water but im hoping I have enough to stop the motor from sinking to the bottom. even with modest floatation im sure the bow will stay sticking out of the water a little bit.

 

[jbcurt00]

Re: what is best way of adding floatation to a flatboat

Have you considered riveting the aluminum deck down rather then welding it? I read your description of the pending deck work, and your planning to weld the new deck to the ribs & hull sides, correct?

Unless the welder is extremely familiar w/ welding the particular aluminum your boat's made of, welding can work harden the hull.

What's the plan to keep the new aluminum deck from being slippery..........