What is the most buoyant foam?

In search of buoyant foam to add to a sinkable dingy so it doesn't sink.
I suppose it must be PVC, core cell, divinicell, etc. ? Know a source for these foams?
What about that 'blue stuff'? used in docks, that seems cheap and plentiful but is it 'floaty' enough?
Holds up a fricken heavy dock..so..
The plan is to take a sailing dingy, a Dyer Dhow to be exact, which when fulled rigged and capsized, will sink..( ask me how I know !) and make it self rescuing....reverse engineering.
Just about the stupidest thing is to have a sailing dingy which is NOT self-rescuing.
I did locate a factory in NJ that is said to build the most buoyant foam ever, mostly sells to military contractors: ie. General Dynamics ( they make submarines) and the cost is incredibly high. I don't have Pentagon budget. Maybe the damn subs would be cheaper if they could get cheaper foam which worked well. That is the foam I am looking for.
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Overlord of Anarchy
San Diego
Things 'float' by displacing water. If the object weighs less than the water it displaces, it 'floats'. So the only way to make foam 'float' better is to make it lighter.
However - you do not state how you're going to keep this foam attached to the dinghy, or if you will try to waterproof the foam (yes, some foams absorb water)
Simplest way to achieve the desired result (self rescue of dinghy) is to use styrofoam. cut into shapes that fit snug into whatever spots you can find (preferably up high) to fill in. Styro is waterproof, reasonable strong, cheap, easy to cut to shape. It will need some UV shield for long term usage

The Q

Super Anarchist
I use polyethylene foam, very buoyant, very light, used for packaging so very cheap..

Extremely cheap for me as I got just under 1ft square by 1 or 2 or 3 inch thick punch outs from packing for free.

I put a piece in a bucket of water under a brick for a weekend. Took brick out and it floated to the top, a three inch thick piece had less than 1/8 inch below waterline. The same as when I put it in..


Super Anarchist
You want your basic "helium foam". It's made by blowing helium into the foam as it forms. Way better than the older style "hydrogen foam" which had a few issues around people that smoke.

Christ I can't keep going...

Serious answer:

The blue or pink extruded polystyrene (insulation board) doesn't absorb water.

The white polystyrene made of little beads (bead board) does absorb water.

The pink/blue foam has a density of 28 kg/m3. Sea water is 1025 kg/m3. Therefore a cubic meter of foam will support 1025 - 28 kg/m3 = 997 kg.

Polyester resin is made with styrene so it will dissolve this foam. Use epoxy to glue it in place.

Polyethylene foam is OK (the white crinkly stuff you'll sometimes see packing TVs or computers) but will absorb a bit of water. Glue in place with contact cement.

Corecell/PVC foams like divinycell start around 45 kg/m3 but commonly 60 or 80 kg/m3. They support less weight because they are heavier. And they are lots more money.
Thanks the information (esp. Zonker ~ good stuff ! )
"The blue or pink extruded polystyrene (insulation board) doesn't absorb water."
I have one sheet of this, its a light-bluish-silver-grey.
Yes, so the plan is to sculpt and form it to fit two spots: bow and thwart seat. The rear foam part will be covered by Sunbrella-like cloth and used as a seat when hiking out.
Both will be tied/secured in place. When these things capsize, nothing likes to stay put.
They are ROW boats were never really designed to sail or capsize or race.. It's like racing a Toyota Prius for crissakes ....but since it's winter, it's more like ice-racing a Prius.
My goal is to get it secure enough for summer-time self-rescuing-sailing when it's too windy to be out and no one is around. That will be fun and warmer.



Super Anarchist
How about this?



Super Anarchist
Pour in place works if you have somewhere to pour it into...

You can fiberglass cover the foam for mechanical protection. 2 thin layers of 6 oz/200 gm cloth will do. If you get gasoline from say a dinghy outboard motor it will dissolve plain unprotected foam. Once more - you must use epoxy not polyester resin.


How long do the PVC bags last in the sun if left installed permanently?
We used to apply sunscreen to our opti bouyancy bags. The thought was to help protect from the sun — I’ve heard of people doing this on ribs as well. I would guess my set had a few thousand hours of UV exposure and were still going strong when the largest size bags came into vogue and were replaced.


WLIS (ish)
Seems like the opti bags last years and years, but to @Will1073 's point, an annual UV protectant will make a huge difference. We recently got a used PVC dinghy. While I would have much preferred Hypalon, finding a good used Al hull RIB is really hard. We started applying this after doing some research:


Super Anarchist
Nope. Except helium is lighter than air so the weight of the air in the bag versus helium is better. But way better to use a slightly bigger bag if you need more buoyancy

Kenny Dumas

Super Anarchist
Lots of options, so constraints are essential:
Don’t create any traps that water can and will get into. It gets in way faster than it gets back out
Don’t use styrofoam, the blue or pink big box foam is the right material for a job that doesn’t require big loads
Cut with a sharp filet knife with one or two metal straight edges. Rough cut and trim the edge to fit
If it’s a super cheap job, a thick coat of latex house paint is enough for kick protection under a seat
Spray adhesive works great but the cheap stuff dissolves foam fast
I’d use a single layer of 4 oz, epoxy and rattle can the exposed surfaces. UV will break down the epoxy in a year