Polyurethane Spray Foam in Aluminum Hull

Hi All,

New to the forum as of today.

Here is my situation. I have a 40' house cruiser with an aluminum hull and fibreglsss superstructure. I have gutted the interior right down to the bare aluminum and glass. This boat is 40 years old and the hull is in incredible shape. it was built to commercial specs using 1/4" alum plate and huge inverted U shaped longtitudanal stringers. There is some old styrofoam insulation still glued to the lum that I have yet to scrape off.

I am completely refitting this boat as a year round liveaboard. Being in Toronto, we get some pretty cold winter nights so thermal insulation is important, but more importantly, I need to create an air and moisture barrier between the inside, and the outside. As a former contractor, I am well aware of the problems of condensation in poorly sealed residential construction.

I would like to spray foam the hull with closed cell polyurethane from the cabin sole up to the the superstructure and then spray in a fire retardant barrier. I have priced this out at about $1,200.00 which isn't cheap, but it is a lot easier than trying to fit panels of any kind.

I have read a lot about spray foam in boats and there seems to be so many contradictory opinions. The concerns I have noted are:

1. Fire hazzard
2. Trying to work on / make changes to the hull after it has been foamed
3. Blowing up the boat or setting it on fire by welding after the foam is applied (not good)
4. Corrosion of the aluminum
5. Trapping water

All of my plumbing and electrical and cabling will be run through chases within the interior of the boat. There will be no foam below the water line (the cabin sole sits just above the water line). All the through hulls in the hull sides (above the water line for AC/shower sump etc...) will be in place before foaming. I am actually putting in 2 extra through hulls in case I ever need them. All welding work ( the little that there is) will be done prior to foaming and the aluminum hull is water tight. There will be no deck fills, pump outs, ports or any other possible places for water intrusion in any of the areas that will be foamed...again the only break in the foam bariier will be the hull side through hulls.

Given all this, the only concern that I feel I can't adequately address is corrosion of the aluminum. This one kinda boggles my mind as the foam adheres to the aluminum and creates a vapour barrier so the warm moits cabin air can't get to the aluminum.

If you have stuck with this long winded post this far, thank you Any feedback would be greatly appreciated. I have posted some pics. Note, the ports shown in the forwad v berth pics will be removed and welded over.

Re: Polyurethane Spray Foam in Aluminum Hull

Re: Polyurethane Spray Foam in Aluminum Hull

mike2003mdm said:

Hi All,
1. Fire hazard
2. Trying to work on / make changes to the hull after it has been foamed
3. Blowing up the boat or setting it on fire by welding after the foam is applied (not good)
4. Corrosion of the aluminum
5. Trapping water
.

Click to expand...

#1... They make a fire retardant foam.

#2... Just dig out the foam that is in the way and then replace it.

#3... See #1

#4... It only corrodes the aluminum if water stays trapped between the foam and aluminum for an extended period of time, wood and aluminum will do this too.

#5... It would only trap water if you have a leak in your structure, wood does this too.

Urethane foam on traps/absorbs water if it is submerged for an extended amount of time, from the USComposites foam supplier site:


Common Applications: Our 2LB density marine foam is recommended for void filling in nonstructural applications. This product can be poured underneath decks and inside cavities where a lightweight flotation foam is needed to provide buoyancy. This foam has been tested in accordance with U.S. Coast Guard Regulation # 33 CFR 183.114 . This foam is approximately 95-98% closed cell which resists absorbing water, however continuous water submersion can eventually lead to loss of buoyancy over a period of years. We recommend this product strictly for flotation applications. If looking for a liquid foam for sculpting or casting we recommend using at minimum our 3LB or 4LB density.

Keep your houseboat well maintained/dried in and you shouldn't have any problems

Re: Polyurethane Spray Foam in Aluminum Hull

thanks jigngrub,

My requirement is for a spray foam for thermal and vapour barrier. Flotation is not a consideration with this requirement and pour foam is not suitable for my application.

Re: Polyurethane Spray Foam in Aluminum Hull

Welcome to iboats.

Based on the size and your requirements......... yes there are fire retardant foams that are installed inside homes. Check with an installer and go for it.

You could leave drain channels under the foam and as stated above....... if it leaks it will absorb water.

Re: Polyurethane Spray Foam in Aluminum Hull

It's all pretty much the same stuff, just applied in different ways. The floatation foam in my boat was sprayed in at the factory.

They use the same stuff on some of my job sites when we build insulated warehouses.

The iboats store here sells spray foam kits, same stuff for a different application.

Re: Polyurethane Spray Foam in Aluminum Hull

Mike, I would be concerned about condensation finding it's way into the foam and eventually finding it's way to the hull...but a barrier coating before putting the foam in should eliminate that issue.

There's a naval architect (retired in Alva, Florida) named Tom Colvin who specializes in alum and steel boats. At one time he was the head of the marine division for Alcoa Aluminum...he knows his stuff. You may be able to google some of his writings for info. He was very responsive and friendly to my (and to others I sent his way yrs back) email questions 10+ yrs ago so you may try that...but he is probably 90+ yr old now.

bp

Re: Polyurethane Spray Foam in Aluminum Hull

Bag your foam then ..

Keep it independent of your structure with bagging material.

You only have to dam off the foam were needed I would think.

YD.

Re: Polyurethane Spray Foam in Aluminum Hull

BillP said:

...but a barrier coating before putting the foam in should eliminate that issue.
bp

Click to expand...

Yup, it's called paint.

Yacht Dr. said:

Bag your foam then ..

Keep it independent of your structure with bagging material.

You only have to dam off the foam were needed I would think.

YD.

Click to expand...

Instead of going through all of that trouble I'd use the EPS sheet foam with a dead air space between the inside and outside walls which also happens to be a good insulator too.

The EPS sheets may be the OPs best bet against corrosion, for peace of mind, and easy removal for future modifications.

Re: Polyurethane Spray Foam in Aluminum Hull

Thanks everyone.
BillP, I checked out Tom Colvin's site....lots of good info, thanks for the pointer.
The more I think about it, the more I am leaning toward XPS sheet with a vapour and firer barrier on the cabin side. I have to "frame" the boat anyway to finish the interior so I can attach the foam sheet to that and apply my vapour/fire barrier over top. I will still foam the fibreglass sections and still apply the same fire barrier.

In attaching the wood framing to any alumnum, I was going to use aluminum bolts will aluminum washers to keep the wood off the aluminum and then resin coat the wood as added protection. If I go this route, there is going to be a fairly large void between the foam sheat and the hull running the full length of the hull on both sides. Should I vent this void to the outside? I am concerned that if any moisture does get in there and I have sealed the void air tight, it will just build up over time.
Also, any recommendations on the wood to use for interior structural framing ? I was going to use regular spruce construction lumber (2x2, 2x3, etc...) resin coat it, insert my foam sheet between the frames and then attach my 1/4 " marine ply to the frames.

Thanks