Your thoughts on sprayed foam insulation for aluminium yacht hull

A client keen to build an aluminium 75ft sloop, wants to spray coat the hull with a poly foam insulation layer but final choice is mine.
While I agree there are physical advantages (reduced grounding damage) as well as the dampening affect I'm not entirely in favour.
My reasoning being if any work is required in later years stripping the foam out for access or welding is a huge problem plus the fire hazard. I prefer glued pins fix of a 50mm thick foam board or thermal matt/tapped joints. Although not having the same sound dampening/deadening effect it does offer better temperature insolation.

I'm interested in hearing other ideas or experiences before I make a final decission.

Cheers

 

Many of these "wonder" foams tend to be very hygroscopic, thus creating a perfect environment for poultice corrosion. You need to check, apart from that which you have mentioned, how you're going to seal the foam from moisture, permanently! Generally not a good idea to spray/foam onto aluminium.

 

Without foam in the tropics would be a basting dish. I would suggest hardly suitable for human accomodation.

Alluminium hulls are noisy things --wont foam hlep.

You can hold battons in the foam to pic up fittings for furniture.

 

Agreed. But you missed the obvious bit:

 

I dont understand --if he wants to spray the outside or the inside with anything he wants why should he not foam the inside after.

 

Normal practise is to apply mats, foam or what ever thermo/accoustic material to the hull inner skin before beginning interior fit out first fix panels or liners.

No other way is possible unless building a 1000tonne plus vessel that allows for floating bulkheads with secondary inner partician wall liner system.

 

My steel boat was foamed and was cool here in the tropics . In the foam was battons and were fastened well by the foam . It was an easy matter for the fit out to start the interior on that. Ceilings were flat and its was an easy matter to fit out without drilling into steel.

Under the foam was perfect epoxy paint after 9 years. The foam was to the water line only. I had a massive discount off the fit out becaue of the ease of work becaue of the battons placed in the foam. The boat had been built professionaly.

There is only one desirable feature of alluminium and we all know what that is after that it is a pain. But that desirable feature makes the undesirables almot tolerable.

 

Ive never seen a boat spray foamed or insulated below the waterline so any " grounding damage " is not a consideration. Besides the flotation value of insulation is nill.

You MUST insulate a metal boat. Spray foam or sheets ? is the question. Spray foam is effective , cheap and I have never seen any corrosion problems. The foam is applied on top of a sandblasted, epoxy coated metal surface. The problem with spray foam is all the unproductive man hours the fitters need to carve the foam out when fitting the hull out. Many man hours. Im presently struggling to run 2 hydraulic hoses , making a huge mess, on a yacht with a spray foam deck .

In future, when works must be performed ,spray foam removal is troublesome. But also consider that removal of sheet foam for works is not easy...you cant reuse the foam sheets and adhesive removal is tedious.

Overhead leaks in a spray foam deck are very difficult to isolate. Foam sheet has a natural drain way path along its edging and is easier to troubleshoot.

I would suggest spray foam on the hull sides, waterline to sheer then closed cell foam sheet on the bottom of the deck .

Stern peaks, forepeaks, engine room, and certain other sections are insulation free or specialized insulation is used...not spray foam. Specialized foam insulation is used aft , below the waterline and on top of the propellers to minimize prop noise.

Im not updated on insulation specs. fire resistance is important when choosing a product. Consult a specialist for insulation choices and make sure that all cable, plumbing runs, equipment fitting points are well specified by the shipyards engineer before insulation begins.

Simple fittings like overhead incandesent lighting, DC DC power supplies..... will overheat when insulation is applied to close. Your shipyard engineer should be aware of the airspace requirement for equipment.

 

I generally agree with Michael's assessment. Foaming steel and aluminum hulls from the waterline to the sheer is quite common here in the US. Sound and thermal insulation are the reasons it works. It is very rare that the hull will have to be repaired by replacing plate, particularly above the waterline. Minor damages and dents can be filled with exterior fairing putty. But even if plate does have to be replaced, the foam can be removed from the repair area--it's messy, but it can be done. I am designing a 66' aluminum sailboat now and the owner/builder will foam the accommodation areas from the waterline to the sheer.

Eric

 

And remember, Sound insulation is a separate discipline. If the owner of the yacht is concerned about "sound " you should consult a specialist. I'm presently sailing a boat that was specialist consulted and it is so quite that you can clearly .....hear the noise. Sound deadening is a very challenging endevour.

 

Having lived in several buildings where the sound deadening was sort of done right and needing to do some research in the subject - it takes a very small error to undo a massive amount of good sound deadening work - I would expect a boat to be much more difficult to keep quiet - a very experienced expert would be a very prudent addition to your design team.

 

You can absolutely float decks and bulkheads on a 75 ft boat. You are going to build secondary panels over whatever insulation you install anyway. In which case I prefer the pins and thermal product route. Steve.

 

That's correct. Foam can help but is not enough. Where soundproofing is a problem (engine rooms, for example), multi-layered insulating materials should be used, usually made of one or two layers of a soft, sound-absorbing material (foam or mat) and a layer of a heavy, sound-reflecting metal or gum between. Vibration propagation path has to be considered too, which is a science on its own when done properly.

If this is just about thermal insulation, I'd rather go with sheets of closed-cell polymer foam - like Armaflex (or similar and cheaper brands), glued to the hull (one side is usually adhesive). It gives a uniform thickness and a neat look when applied, plus is much easier to remove (didn't say "easy" - just "easier") then a foam. You can also feel more confident it won't absorb water. And (important characteristics) Armaflex is non-flammable. The negative side is, as usual, a higher cost.

Cheers

 

Yes Armaflex is good.

I don't like the applied foam either. It also apparently gasses off considerably for a long time.

Alloy either needs a good surface sealing paint or oxygen. I've seen problems in an alloy sailboat that had bilge water often up around the lower foam insualtion, the foam soaked up the water and the hull had locally corroded through within 5 years of being built.

Cut foam closed cell panels can be used with bare alloy and still allow drainage and oxygen to get to the alloy surface.

However I have seen a lot of steel boats where blown in foam seems to have worked very well.

 

I had a look at MIGRANT (2nd Gazelle built by Tom Colvin). It lasted 30+ years in the hands of the original owner without foamed insulation. Rusted through in less than 5 after the 2nd or 3rd owner sprayed insulation and caused a water trap. When I saw the boat there was an external plate doubler over the rusted area.

I'm planning on the sheet insulation approach myself, over epoxy coated steel. Seen enough problems with the foam in place approach to not want to try it myself.

PDW