8ft foam boat?

conan

Member
I'm thinking of trying to build a foam boat and I've gotten several ideas and plans.
Most call for 2 sheets of foam to be fused together to make a 12ft by 4ft boat.
Could this be cut down to 8ft and have just one sheet (double thick 4inches) and still float.
It needs to hold about 275 lbs but will only be used in 1 ft of water or less.
I'm not up on my hydro physics for floatation. Please somebody do the math for me.
Thanks
 
yes it will float.. but those boats are worthless. too much trouble.. you spend just as much money as buying a fatboy, and it weighs just as much.

Jeff
 
Really do they weigh that much? I was trying to add up 4 sheets of foam plus 1.5 gallons
of epoxy and glass. Also about 20 ft of 1x6 wood for a cockpit. 1 sheet of 1/4 inch plywood
for the floor and alittle hardware.
 
well my vote is to build out of aluminum :)


Wood/glass boat can be built pretty darn lite and would cost you about the same amount of cash plus it will last
 
CTB, based on your materials listed your boat will be about 80 lbs. Mine was 83 lbs when finished, but it was 12 feet, this extra length only added a few pounds to it.

In all foamers are fun boats to build, but they are really messy since the dust is lighter than wood and floats all over the shop when you are trying to clean it up. Two years later and I am still dealing with blue dust hiding behind stuff.

The other thing that is "wrong" with foamers is the air trapped in the foam. No matter when you build it, at some time the boat will be in conditions warmer than when it was sealed in epoxy. Then the air expands and delaminates the epoxy from the foam substrate. It won't matter if you use an epoxy seal coat before glassing or not. Physics will always win.

Fiberglass wrapped boats are only as strong as what is being wrapped by the fiberglass. House insulating foam is not that strong. If you were to pony up for some Diviny Cell structural foam then you could get a strong boat. That is what they use in top end foam core surfboards.
 
yep, what he said. i don't care how much glass you put on that spongy foam.. hit a stump and it will push it in enough to dimple it.. then it's got a crack or a hole. not that it will sink or take on water. but a PITA anyway. save your money and buy one.. or build a kara or devlin etc.

Jeff
 
WHoa, my post was gone, and I even previewed it????
Well it was long, here's one pic of my boat that might fit your needs
laying.jpg

 
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Ray your statement about the strength of the boat being limited by the strength of the foam is incorrect. I'm not an engineer, but I've done some reading on this and the foam/glass sandwich (with glass on either side of the foam) is far stronger than just the foam. The foam adds little to the strength of the composite. The reason is to bend that sandwich, you've got to compress one side of the glass and stretch the other side. The farther apart the two skins are (i.e., the thicker the foam), the stronger the composite. Lots of lightweight and strong structures are built this way, including kayaks, surfboards, and hovercraft. I'm surprised to hear that closed cell foam will release gas with an increase in ambient temperature. I did not encounter that problem with a hovercraft I built, in part a foam and glass sandwich (the foam being the white styrofoam), that sat in the heat of the sun in South Louisiana for 2 years.

All in all though, I'd build a Kara if I wanted to build a small boat for duck hunting, and try to make it as light as possible. Can you buy something that will do about the same for about the same amount of money? Maybe so. You will also avoid getting addicted to boat building. Might be the way to go.

Ed.
 
Hate to reply to my own post, but after looking at it again, I agree with Ray if he's referring to impact resistance. I would guess that to make the boat as impact resistant as a wooden boat, you'd have to use so much glass and epoxy it would be heavier than the same boat made from wood.

Ed.
 
Ed ,
one ther thing is I think you both are talking about two different foams. orgianlly I beleive he was speaking about a regular lumber yard type am and the comparsion was to something like "[font=Verdana,Arial,Helvetica]Diviny Cell structural foam" or a simular type such as the honey comb panels or another high denisty foam used in the marine or aircraft industry

It's my opinon that the foam is a poor choice useless he intends to spend the money to buy the high desity material . I also don't see a true weight savings in the foam for this size vessal to justify the cost
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I agree. I think the foam boat idea was worth a try, but from what I've heard from the various builders, for the most part didn't work out. I thought about attempting one myself before they were all the rage on the internet, from my experience with the hovercraft, but was warned off of the idea by something I had read that was written by very prolific boat designer/naval architect: foam core was impractical for boats less than 22' LOA. I think you're better off building a wooden boat. I've seen glass over divinycell used in some bulkheads in a fibreglass mudboat that's built by a small scale builder in South Louisiana, that seemed to hold up pretty good. I can't imagine what building a whole boat out of that stuff would cost, though.

Ed.
 
I think some may want to recondsider their thinking on foam/fiberglass composites. Not all foam is the same, this is for sure. Not all structural foam is the same either.

The most expensive and best built yachts are all foam/fiberglass composites. The foam is only there to make the sandwich lightweight compared to the same thickness of just fiberglass and resin. Sort of like an I-beam construction in a larger plane.

The next generation Navy Destroyer class (DGX) is going to use composite (foam/fiberglass) in some of its structures. I think they have considered the strength of the composite sandwich.

If it was me, I would use some of the lighter weight structural foams from P{enske COmposites of some of the other manufacturers of such products. This gets you lightweight, strong composites.

Mark W
 
CTbarbarian:

Hey- i just wanted to add to the discussion, as i went the foamer route myself. after a dewquestions on this forum -all very helpfull- i went scrounging around construction sites for foam and scrapwood, found all i needed and set to work on laminating and shaping. my hope was for an 8 footer as well. same basic needs as you set out.

my findings:
a) the "dust" sucks. It's still everywhere and it can be a real treat to clean out of your tools/shop/wife's car/ and it has a great habit of hitching inside the house and drifting up to it's true habitat: the 10 ft, recessed skylights
b) stiffening w/ stringers is required. the cockpit + cockpit decking had to be fairly beefy. more weight.
c) seaworthy it wasn't. very wet w/ dog/dekes/bag o' dohnuts aboard. The afternoon winds are a real consideration in my area (CO) and getting caught out in any open water was not fun.
d) it wasn't as durable as I had hoped. it did not fair well at all w/ submerged beaverchews.

in all, it's gone after one season. i'll be going w/ wood+glass for my next one.

hope this helped,
geoff
 
Ed and Robert, yes I was talking about the difference between the blue board and the jet fighter/yacht foam. The blue board is not as closed cell as one would hope, and it has little compression strength when compared to diviny cell. Ed, I've read that same research and I would have no problem with using the foam used in the research except that I don't want a second mortgage on my house to build a dingy- there are much cheaper ways as you know.

I think the hot air delamination is caused by the multiple layers of 2 inch foam board creating large air pockets between them. On the 'fuge, I think two other foam builders mentioned this last summer as problems with their boats. In all a small population of builders, and only 3 mention this as an issue. I know that on my boat I had gaps between the wide faces of the sheets that I couldn't fill with expanding foam once things were cured.

As hard as hunters use their gear it is important that they have something that they can bash up a bit and not worry about it. A foam boat will have a hard time in this environment, unless it is loved and coddled.

However, it is really hard for the home builder to make a boat with curved chines if they can't mill cedar strips. With foam you can make a well rounded hull with some rocker all by using sand paper and a day in the driveway. But you will have to care for the boat more than any other piece of gear.

Last winter I played with some 1" blue board and a frame to hold the foam in compression so that it would have the cross section of a KARA. I placed a layer of 4oz glass on each side using RAKA. This test piece of foam hull turned out shockingly strong in its arched shape. It gave me hope for my next foam boat, but I could not get the build method to work out since the 1" blue board would only bend so far, and could not bend in a compound curve at that thickness without breaking. If it was thinner it would have worked, but we don't get 1/2" blue board here. We can get 1/2" diviny cell though and it won't take that much of it, so maybe one day.

Right now I am thinking of cedar strip mini sneakboxes just because the materials are dirt cheap and the smell when milling it just too nice.
 
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