Positive bouyancy foam

[Sayla]

Anyone have suggestions on fire/heat/flame retardent foam for positive bouyancy application ? I'm considering doubling it as insulation (underdeck and internal topsides) also.

Thanks Sayla

[Ian McColgin]

I've happily used Hi-Bond but I don't think it's flame retardent. You'll need to roam the manufactorers to see if there is one.

The reaction is quite exothermic so too big a pour will get really hot. Also, depending on the shape you could have problems getting a proper expansion as curing foam binds up and prevents full expansion in narrow spaces.

I don't do it enough to count as an expert but so long as you leave expansion room it'll be fine.

One of my first spaces I did a careful volume calculation and figured I could make one mix, pour away and slap the deck on before it fully expanded. Well, I calculated the space wrong and the foam expanded so hard as I was tacking the glued around the edges deck piece in it pushed it up, so I sat on it and got mild searing, not even second degree burns, on my legs as the expanding foam lifted me up. Cleanup was a real bitch. So leave a hole that extra foam can bubble out of and be filled later.

Talk to a pro if you don't like the existential approach to learning.

Fun with boats.

G'luck

[Sayla]

Thanks Ian

I was actually considering prepared sheets, to be glued in place, or even encapsulated during the process to increase fire resistance. I thought there may be certain brands that the marine world approves of. I've noticed there's a product called polyphen (? NZ product) that claims fire retardance, but I know there's likely a lot more to it than reading certain specifications.

Sayla

[ssor]

There is a foil faced urethane building insulation in the US. The canned urethane foam makes very good adhesive but fire resistance is unknown to me.

[ricktidd]

McMaster Carr sells a wide variety of sheet foam. I'm sure you can find what you need there. I have used a closed cell PVC foam in the past for oceanographic instrumentation. It cuts and shapes easily, and if you epoxy coat it, it will have a nice durable surface.

[McManusBoatWorks]

A few more details on where you plan on installing would help. Are we talking in an engine space, behind ceiling, etc.

Would the area be prone to condensation. You sure would not want to trap moisture behind the insulation and rot out all your hard work. Think vapor barrier is this is the case. Also think closed cell foam.

I have seem some fire retardant sprays that building contractors use to fire proof steel structures. They talk about the insulating properties. You might look into those products.

I have seen a number of different foams used as flotation and insulation on boats.

I have had a number of boats that had styrofoam block cut to fit the space and used as floatation.

I had a 25 foot cruiser that had styrofoam board insulation sandwiched in the ceiling space as insulation. The same boat had block styrofoam under the floor serving primarily as sound absorbtion. It is hard to tell if it was origninal but the foam suffered no ill effects from the bildge water. Just dont get any fuel on it because the fuel will disolve the foam.

I once used the standard insulating foam board from Home Depot placed between the aluminum hull and plywood decking to create some sound deading and add to the floatation on my 14 foot skiff. It has been in service for over a decade without illeffects to the foam. It is closed cell of course.

My Boston Whaler hull is filled with expandable urethane foam. They swear by it. The stuff is expensive but it does a job no other material can do.

On a small job one time I bought an expandable foam in cans from Home Depot. I cut styrofoam blocks to fill the space and then sprayed the foam into the surrounding voids to fill the rest of the area. It was a messy job and looked it but it was covered over so only I know how ugly it turned out. You might try it though to help you seal around a board insulation.

I talked to at aluminum boat manufacturer the other day and they spray closed cell urethane foam on the entire ceiling, walls, and hull down to the water line prior to installing the ceiling. They spray it on so they get a good coverage and a vapor barrier to prevent condensation on the hull. They hire a subcontractor to come in and spray it. You might see if you can find a contractor in your area that will do it for you.

You can buy kits that come with all you need to spray it but again it is expensive. Experience is very benefical on such a job. It is very hard to judge the expansion rate since it varies so much with temp and application configuration. I can picture myself spraying it and then the blob overtake me, the boat, and the shop.

What ever you do, dont get the urethane on you. Once it drys it wont come off your skin for weeks.

[Sayla]

Thanks for that,

I'm looking to put it wherever I can hide it to help achieve positive bouyancy, yet not be too obvious - not broadly against the wet hull. I don't want to conceal the hull from inspection, although I've considered utilising some in the bow sides below waterline where an impact may occur from a log or some other object of the deep, and removable pieces elsewhere to fill corners below waterline - perhaps a differently encapsulated type around the engine compartment for isolation and sound deadening.

Above a ceiling, the back of cupboards against internal hull topsides, the head, corners in the stern, lazarette etc. It will take a fair bit to achieve positive bouyancy overall, but I believe it possible without being too obvious. Fire safety in the material is primely important though.

Sayla