Floatation of wet foam

[fritz3000g]

Hi all,
I didn't get a response on another forum and wondered if you smart folks know.
Is there anywhere that I can find an estimate for the water displacement / flotation capacity of waterlogged closed and open cell foam?
I'm wondering how much additional flotation (read new space) I could get by converting from open to closed. I could make a conservative estimate, but would prefer to do the actual math. If nobody knows I might try a test with a couple cubes of each.
Thanks!

 

[Hayden Watson]

Open cell foam is my definition Open so it will become saturated and no provide any meaningful floatation.

 

[DrJudyB]

A cubic foot of fresh water weighs about 62 pounds.
A cubic foot of salt water weighs about 64 pounds.
When you displace a cubic foot of water with air, you get 62-64 pounds of flotation.
The closed cell foam adds a few pounds, maybe 2-4 pounds per cubic foot, depending on the density of the foam.
So each cubic foot of foam will provide between 58 and 60 pounds of flotation.

Get coast guard approved, marine-grade foam. It absorbs very little water, just a few percent of its flotation. Non-marine grade closed cell foam can and does absorb a significant weight of water.

Saturated foam doesn't provide any significant flotation.

 

[fritz3000g]

Thanks DrJudy.
How do you know this about foam (not providing any floatation when saturated)? For this to happen, the water would have to expel air from any air pockets somehow. I can see how it could saturate the material through capillary action (I've picked up saturated foam and it's definitely heavier) but I don't understand how it would expel the air from closed cell foam.
Any ideas how long it takes to saturate when submerged?
Do you know what makes marine foam different?

 

[DrJudyB]

How do you know this about foam (not providing any floatation when saturated)? For this to happen, the water would have to expel air from any air pockets somehow.

HI Fritz,
Sorry, I did not mean to claim that closed cell foam can be 100% saturated. Open cell foam can get saturated.

Good marine foam meets Coast Guard standards for flotation. It will not loose more than 5% of its bouyancy power even when exposed to gasoline or oil or bilge cleaner, etc, for 30 day. It will last a very, very long time in water without losing more than 5% of its bouyancy.

Coast Guard Standards for flotation.
https://www.google.com/search?q=U.S.+Coast+Guard+Regulation+#+33+CFR+183.114&oq=U.S.+Coast+Guard+Regulation+# 33+CFR 183.114&aqs=chrome..69i57&sourceid=chrome&ie=UTF-8

2 part polyurethane foams don't melt if you get gelcoat, epoxy or polyester resin on them. Here's one example:
http://www.uscomposites.com/foam.html

Judy

 

[JimInPB]

I have shopped for a lot of used boats in my day, both for myself & for other people. I have seen plenty of boats with waterlogged foam. Some of them sat very low in the water.

Even boats that I believe had zero change of having anything other than factory foam inside them, have soaked up water when given enough time. This includes the glassed in stringers in Aquasports, the foam sandwich in Boston Whalers, Etc. Once the outer shell is cracked, if they sit in the water long enough, they will gain weight.

Anytime I am wanting to buy a used boat, a sea trial is always part of the equation. Without that, you are just crossing your fingers & hoping for the best.

If you have waterlogged foam & you want to estimate how much water it has soaked up, drop the boat in the water, then measure how far too low it sits, then calculate the cubic feet of extra water that is being displaced, then use Dr. Judy's numbers to calculate the weight. Adding new foam in another part of the boat will not remove weight. If you want the boat to float correctly again, you have 2 choices. 1) cut into the foam & let is dry out (think in terms of years) or 2) dig out the old foam & put in new. I have done both.

 

[fritz3000g]

Great info thanks! That's really useful and not a bad price.
So here's a question: If I have a bunch of open cell dry foam blocks, and I surround them on all sides with pourable marine foam, will they remain dry for 30 days as well? In other words, does marine foam resist the capillary movement of water, or does it just resist absorbing it?

 

[fritz3000g]

Wanted to bump this. Does anyone know if marine foam surrounding normal foam will absorb water? In other words, will the water seep through the marine foam and be absorbed by the non-marine foam?
I could test this if there was a place I could get a hold of a small quantity of marine foam.
Thanks!

 

[topcat0399]

I am in process of off loading the old factory foam and not replacing it.
If you have a boat that is way heavier than stock empty (as mine very much is)
I think the foam is false security. I'd rather have the room.
If I did replace it it would simply be with pink foam board from Home Depot or some such.

Just sayin'

 

[walt]

Your boat is at least 30 years old so I would think you have a pretty good idea of how the factory foam will behave over at least the next ten years. Is it all water logged now? You could probably do a simple test and weigh a chunk, find the volume and determine a weight per volume and compare that to some new foam. Ie, what is the problem you are trying to solve?

Nothing at all wrong with the 28 year old foam in my old Mac but my boat has always lived in dry climates.

 

[Gunni]

You can buy sheet closed-cell polyurethane foam suitable for marine floatation that is in the 2-3 lb/cu.ft. Use Judy’s water density values to figure how to make that work for you. I can say that the good stuff is expensive.

 

[JimInPB]

If you describe what you are actually trying to do, it might help people here to help you. I am not understanding why you would want to encapsulate open cell foam in closed cell foam rather than go with all closed cell foam.

DrJudyB already posted a source of marine foam, where you can buy quantities as small as 2 cubic feet for less than $25. Are you looking for a quantity smaller than that in order to conduct you test?

 

[Jackdaw]

Here's a general question: Do people find positive buoyancy in a keelboat to be a valuable feature? If so, from what fate? I'm just curious.

 

[JimInPB]

Here's a general question: Do people find positive buoyancy in a keelboat to be a valuable feature? If so, from what fate? I'm just curious.

Anytime I am further from shore than I can swim, I consider positive buoyancy to be a valuable feature.

 

[Jackdaw]

Anytime I am further from shore than I can swim, I consider positive buoyancy to be a valuable feature.

I'd agree in a 170 and 212, they (in particular the 170) can go over easily. But in a keelboat?

 

[JimInPB]

I'd agree in a 170 and 212, they (in particular the 170) can go over easily. But in a keelboat?

Yes, in a keelboat, including the several Beneteaus that I have had offshore.

 

[Sumner]

Anytime I am further from shore than I can swim, I consider positive buoyancy to be a valuable feature.

http://1fatgmc.com/boat/mac-1/2015 Bahamas/2-Bahamas-3/Bahamas-Page-24.html

Having the above behind the boat gives me a little reassurance that we stand a chance if the boat was to go down. I have no idea if our Mac would still float or not. Haven't removed any foam but have added a lot of weight, but also a lot of sealed storage containers and water containers that become empty with use so maybe that has offset the weight some.

The Endeavour for sure won't float and when we got the boat the bilge pump wasn't effective. Now have 3 with two of them being high volume and they empty the water out of the bilge in record time now...

http://purplesagetradingpost.com/sumner/endeavour-plumbing/page-16.html

...... Still hope to never hear them come on,

Sumner
================================================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...
Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas

 

[Jackdaw]

Yes, in a keelboat, including the several Beneteaus that I have had offshore.

Interesting. What Beneteaus? I'n not personally aware of any with positive flotation. My real question is what is the rational for wanting it? Sinkings are so rare, and even then the boat awash to its decks is not any better (worse actually in most conditions) than a liferaft.

 

[Meriachee]

The 26c had a surprisingly small amount of foam in it, and the video showed it down to the rub rails. I think Jackdaw is referring to the added incentive of a few thousand pounds of lead wanting to drag it down. The math homework ( which I neglected to do) probably suggests that there isn’t enough foam to prevent the keel from winning the struggle.

 

[fritz3000g]

Per JimLmPb's comment, I'm trying to improve the flotation in my Mac25. I have a bunch of open cell foam that's pretty dry, but as Judy says it water logs quickly when submerged so I don't want to trust it with my family.
I'd like to fill in the gaps between it with marine foam rather than fill the whole cavity for cost reasons, but I want to know if that will prevent if from getting waterlogged or whether the water will enter the old (but encapsulated) foam anyhow.
The other advantage to this is that if I can fill all the gaps between the foam blocks I'll have more flotation and so can open up some of that space for water storage.