aluminum boat floatation

[monsterfishin]

I have seen my share of aluminum gas tanks foamed into glass boats that corrode from trapped water in the foam. I was wondering about how to prep a aluminum boat that was to be foamed to insulate/sound deaden/add floatation so as to not create the same problems the gas tanks in sea rays had? This is on a used boat that has bin in salt water, not new aluminum.

[CTMD]

Don't use spray foam. If you can find it use Polyethylene.

If you go here then follow the link to the advice on fitting foam. There is some good advice.

The only thing I disagree with is they suggest spray foam as a viable option. Which no-one should ever put in a boat for any reason.

[pjay9]

At the end of the summer there are tons of places unloading pool noodles which do not absorb water and compress slightly and cut with a sharp knife. Since they stack like cord wood the water that may enter the cavity has a way out due to all the tiny longitudinal opens between the logs/noodles. Also since you can make them tight against each other they have a better tendency to absorb the sounds made by aluminum and stay in place. Unlike the cut and stack expanded white foam which chafes and breaks did gives up tiny little pills of white foam...eventually I'll be pulling the deck and replacing the white CRAP flotation with noodles...also at your local foam supply company you can usually get the stuff cut in big sheets any thickness and cut it to fit your spaces. IMHO, Capt PJ

PS do not use expanding pour in foam, it get waterlogged eventually!

[trouty]

The first alloy boat that I built - i put thru commercial passenger survey.

It had to have flotation foam fitted.

The naval architect who designed it used his program to calculate the volume under floor for foam fitting and compared that to the special calculation for buoyancy to work out how much foam was required under the floor.

I don't remember the calculation formula but it takes into account the amount of fuel and how much less weight than water the fuel displaces - it takes into account your passengers body mass and so on and so forth.

Anyway - you then have to put this much foam into the hull.

The survey authority specified what foam I MUST use (and for good reason).

I was told that it had to be:-

Fire retardant, high density, closed cell, Poly urethane.

Fire Retardant - so it doesn't speed the rate of fire on the vessel and kill people or give off deadly fumes etc.
High Density - If the vessels dumped by a wave and pushed underwater - low density foams can compress under the pressure - thus not displacing sufficient water to float and continue to sink.
Closed cell - so it does NOT absorb water and add to the displacement weight of the vessel beyond the actual weight of the foam.
Poly Urethane because it is fuel stable.

So imagine you filled it with styrene pool noodles as someone suggested?
Spill even half a cup of fuel into the bilge and instead of flotation foam you have a sticky black goo that will run out your bung holes!

Now back to the RIGHT displacement foam.
By nature it crumbles.

If it crumbles, with say the pounding over waves - and water should get under the floor into the bilge, then as the water runs down to the bilge pump, it will take the foam crumbles with it & block the bilge pump screen, run it dry, and burn it out, just when you need it!.

For this reason, when you place foam under floor for buoyancy, it should be scribe cut into blocks that fit between frames and stringers, with a spacer beneath to keep it elevated OFF the bottom sheets so that water CAN run to the bilge pump and bungs, and to prevent it corroding the bottom and sides sheets.

This can be done by encapsulating the foam blocks with f i b e r g l a s s - or heavy duty plastic and 100mph tape.
That's the RIGHT way to do it.

Others will attempt to justify their own method - that's human nature after all - just makes sure it satisfy all the above safety requirements.

Cheers

Cheers

[monsterfishin]

Wow ! I did not expect such rapid response and good thoughts! I am new to this site and spent most of yesterday reading up before posting. This question came up in my mind as I dreamed of my next boat, and have had people suggest that the problems of noise and chill could be fixed by spray foam or bed liner. Usually these suggestions are from people who do not have a aluminum boat, so they have nothing to loose! As I am getting ready for next fishing season and fixing the core issues in my glass boat (I go over them every 3-4 years) I always start the new (to me) boat dream, and think about how to make Modifications that dont come back to haunt me after a few years. Thanks again.

[pjay9]

"So imagine you filled it with styrene pool noodles as someone suggested?
Spill even half a cup of fuel into the bilge and instead of flotation foam you have a sticky black goo that will run out your bung holes!"

Since I am the one who made the suggestion, I'll give you some more info regarding the foam. What I did in my TC (Truck Camper) for better moisture proof and tough abrasion resistant insulation and in a boat to replace water logged pour in expandable foam I( used the sheet material I mentioned above. That sheet material is POLYETHYLENE. http://www.polyethylenefoam.net/

I also used in some places the foam used to make standing pads around tools for machinists. I wrapped my TC pipes with pipe wrap from Lowes.

The following pictures are for your observational pleasure.

Show four types of corrrect me if I am wrong ployethelene foam which I tried to burn...it melted, Top left and going clockwise blue polyeth sheet material I got from local supplier, campers bed pad from sporting store, pipe wrap and foot pad.



Same four samples sitting in gasoline. No recation!



White expanded bead foam sitting in gasoline....go to bottom picture NOW!!!


Expanded white foam, I think it is called polystyrene...correct me if wrong... melts when burned couldn't get any samples to burn on own all need a sustained flame.



It took that long for it to MELT!!!! in gasoline. About a second! That is what is used in my boat under the floor.



If enuf of the stuff got gas soaked it may be a gooey mess...who knows! But is coming out!

So my conclusion is that i will use polyetelene sheets and noodles to redo my flotation and to provde for a quiter AAB.

At least they didn't use the pour in expanding S@&T!

Capt PJ