View Full Version : flotation foam
10-29-2001, 01:28 PM
I need to add significant flotation to an old fibreglass 14' ob hull. I am looking for a source of block/sheet closed cell foam. Do any of the construction insulation panels qualify? The foam would be probable encased in plywood. I am aware of the mix stuff.
You would want to make sure that whatever you use is a close celled foam to help reduce water absorption. I had check here locally with a company that supplied foam for building floating docks. It was fairly inexpensive. You might want to look in that direction.
Here is a link to some foam used for docks. I can't say one way or the other if it is closed cell. You might want to call and ask them.
Check out the thread on this forum "flotation", Which was posted in April of this year.
There are several things to consider about flotation. All foams float but have differing properties so you should consider what is most important to you. If cost is the only factor the foam boards from orange hell will probably work as well as anything. In areas where it would be hard to inspect the foam could be deteriated and you would not know, especially if fuel makes contact.
Sprayed Urethane foam is like hardened glue when it sets-up. The overspray is a mess to clean, but most importantly urethane foam makes deadly gas when it is burned.
A product called ethafoam, closed cell polyethlene is fuel resistant, comes in sheets 4'x8'x1.25"->3.00", is non-toxic when burned, can be cut/shaped with a knife, glues well, is shock resistant, durable, flexible, and generally user friendly. The only negative is that it costs more.
If total safety is considered the ethafoam wins hands down. Packaging companies use this stuff for high-end electronic items, probably your last computer was packed in ethafoam. Usually the stuff is off- white/creamy color, although I have seen light blue and pink shades. It is fairly easy to recognize by its waxy smooth feel and its toughness. I think this is either the same or similar material found in PFD throwing seatcoushions,formally, typeIII life preservers.
Here in Port.,OR at least two companies carried the ethafoam brand and one other similar product. You might be able to buy, at a reduced price, cut-out pieces from a packaging company in your area, who can't use pieces under a certain size.
I cut and fitted a 23'boat sides with ethafoam in a few hours, no glue necessary just a squeeze fit between frames.
10-29-2001, 09:08 PM
When the subject of floatation comes up, most think of foams to provide it. Truth is, the best floatation this side of a vacuum or helium is just plain air. If you are going to seal the foam in a watertight chamber, why do you need foam at all? Could be that a couple of sealed chambers are all you need.
If you do need foam, the easiest good floatation is the common styrofoam that is found at you local building supply. It is usually blue but may also be pink. Can be had in 3/4 and 2 inch thickness and width to fit between wall studs spaced 16 and 24 inches apart. Styrofoam is closed cell and not affected by waer but gasoline and other solvents are death to it.
I use styrofoam (usually coated with epoxy to protect it) when it is to be put in an unsealed space for floatation. Mostly I use sealed plywood chambers which work fine.
10-30-2001, 07:42 AM
Tom, the pink stuff is polyisocyanurate and the blue stuff is similar. Polystyrene foam shows the individual beads that were expanded and is white.
I agree with you that air chambers are best, though they are not CG-approved, but whose sailing your boay-you or the CG.
Any foam can get wet, waterlogged, and extremely heavy. Many production fiberglas boats exhibit this problem after they get a few years old and water gets into the foamed-in-place flotation which is generrally low in the boat where it passes the CG level flotation test, but makes the boat's most stable position upside down.
This is why so many swamped boat incidents end with the survivors atop an upside down boat. In our summertime NC waters they usually survive overnight.
10-30-2001, 01:57 PM
Perhaps I've been misinformed. I've been using the blue stuff instead of fiberglass for years in house insulation that can get flooded in a hurricane. My shop had 12 inches over the floor in Dennis in 1999 and I was glad that I took this precaution.
I have polyisocyanurate sheets that are yellow - go figure.
I know from experience that the beaded stuff used in most dock floats and cheap coolers will soak up lots of water. The blue stuff is not beaded and I was informed it was polystyrene and closed cell. In any case I coat it with epoxy although I know that you will say that does no good. Not being a chemist, I'm in the dark, but I've never noticed it taking up any water. I will make some weight gain tests and see.
10-30-2001, 02:35 PM
Gawd...all this dialect.....IT'S PING PONG BALLS fellows......solves all problems....
10-30-2001, 11:00 PM
I have given some thought to ping pong balls also, I too think they would be an excellent flotation material but wouldn't the cost be a abit prohibative?
10-31-2001, 07:14 AM
well, you buy them in bulk. That's what they use in all the wooden flat speedboat with outboards type thingies.
10-31-2001, 08:57 AM
If you hole the hull full of ping-pong balls, don't they just float away? Bleeding ping-pong balls? http://media5.hypernet.com/~dick/ubb/biggrin.gif
10-31-2001, 09:54 PM
Where do I buy bulk quanities of ping pong balls?
11-02-2001, 01:05 AM
You can use empty plastic 2 liter coke bottles, Evian water bottles, etc., with the lids screwed back on. Or those 3" rigid balls they put under indoor playstructures at McDonalds & Discovery Zone. Or maybe any other sealed balls they sell for peanuts at toys r us. If the ping pong balls are stowed someplace where they'll try to migrate, stuff them into fishnet stockings, creating a nautical look. :D
11-02-2001, 08:22 AM
All this bottles and balls stuff sounds distinctly unseamanlike. Definitely non-salty.
Small boat as recycle bin http://media5.hypernet.com/~dick/ubb/rolleyes.gif
A plastic daysailer I had in a former life had styrofoam beads sealed into polyethelene bags glassed into (under) the seats. At least you didn't have to look at it and it filled the space better than a junkyard full of bottles and balls and other assorted trash that would float. http://media5.hypernet.com/~dick/ubb/biggrin.gif
11-02-2001, 08:54 AM
I'm not sure if the idea of using ping pong balls or plastic bottles is serious or something of a joke. But if anyone is actually thinking about doing that, don't forget that it is not possible to pack these items into a solid mass. A significant amount of the volume taken is wasted, i.e., the space between the balls or bottles provides no flotation.
Even though foam is slightly heavier than bottles I think foam would give more flotation while using less total space.
11-02-2001, 09:11 AM
I was thinking of the "plastic jar method". Pretty -no, unsalty-Yes! but it`s light, dosen`t absorb water. Lots of different shapes and sizes so thay could be packed pretty tight. They would be also easy to remove for periodic inspection of the hull etc..
I believe the pink and blue products are extruded polystyrene and the white bead board is compresses polystyrene. Go with the extruded.
11-02-2001, 10:45 AM
I am considering using styrofoam packing chips stuffed into the kind of heavy duty clear plastic bags that you make up with the plastic bag tubing and a heat sealer (we have one at work for shipping). The air in the bag is sealed in, and the chips just keep its shape. With the heat sealer the bag ends can be sealed on angles to make different shapes to fit- more or less triangular if you wish.
11-02-2001, 12:06 PM
How do I calculate how much foam I need. I will know the weight of the boat, motor etc.?
11-03-2001, 04:23 PM
This may sound absurd to many, but . . .I scrapped a small sofa about a year ago and was looking real hard at the removable seat & back cushions; so took off the covers and stacked the foam to see what we had. My calcs came up with about 350+/-# floatation. My thought being to encase 'em in trash bags and squish 'em into nooks & crannies; after all they would be conformable to unusual surface/volume configs.
11-03-2001, 11:22 PM
If there's a flat sheet of foam laying against wood (or the flat surface of a plastic bag full of whatever) aren't you asking for rot? Designers don't seem to worry about this when they tell you to fill up the space with foam. But inevitably, some water will get into the space (whether it's sealed or not) and then you've got damp wood with no ventilation.
If you have round shapes like jars, bottles, or balls, the air space between them gives you no bouyancy But that space isn't wasted, since it provides ventilation as long as the floatation chamber is either open to the air or is vented at the dock by removing an inspection port or watertight hatch.
If foam goes into a chamber that can't be guaranteed to stay bone dry, shouldn't there be dowels or spacers to let air circulate between the foam and the wood? Does anyone do that?
11-04-2001, 07:22 AM
A reader sent me the Coast Guard Safety Standards for Backyard Boat Builders. COMDTPUB P16761.3B. It is very helpful in flotation calculations. For those who care, "flotation" is the correct spelling with "floatation" a variation according to my Webster's.
11-04-2001, 01:44 PM
In my extreme youth I did a lot of things .......errrrr.......conducted many scientific experiments......for which I never got caught. It was in one of these that I discovered that ping-pong balls burn very nicely. Enthusiastically, even.
There is no question that they make excellent flotation. One must address two issues: One is the fact that there is a fire hazard, but of a different nature that the urethane/isocyanurate foams. The former is not self-extinguishing while the latter may be, but under prolonged flame exposure the smoke from the latter is quite toxic. The second issue is that a block of foam tends to be held captive, whereas a large volume poured full of free-flowing spheres can, if physically damaged, release said spheres. Your floatation then may go floating downstream, leaving you with a hollow space full of water. Someting that held the ping-pong balls captive, such as a few judicious squirts of spray-foam, or even foaming spray contact adhesive [3M makes something called 77 spray adhesive...if the solvents did not attack the ping-pong balls it would be a viable candidate] should do the trick.
11-04-2001, 01:59 PM
I think the plastic jars idea is a good one......now hmmmmm should I use jiff or skippy jars. http://media5.hypernet.com/~dick/ubb/biggrin.gif
11-05-2001, 04:23 PM
I visited with the guy that built the old gaffer I grew up with last time I was back home and brought up this very question. His attitude was that I didn't need to worry about it. His arguement was, "OK, suppose you manage to swamp her, it's wood right? If you tied that hunk of lead down there to a bundle of wood the same size as all the wood in your boat, you think it would float?" I can kind of see his point, but there has to be more to it than that... Doesn't there?
11-05-2001, 09:55 PM
Don't forget that engines and batteries and steering gear and people(to some extent) don't float very well. In addition you want some extra flotation so that the boat can float a little bit out of the water. If it is placed right there is a better chance of righting the boat and pumping it out.
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