To Foam or Not To Foam

[OldRover]

I know the general topic has been covered a few times before, but I decided to post to see if there is any up-to-date info I may have missed and also to help think through things. I have two portions of my major rebuild project – fuel tank installation and a freezer/refrigerator installation. Like many other boats in the early 80s, just about everything was foamed into place. My rebuild is due to the cabin being flooded with rain water prior to my purchase. So needless to say I am an extreme example foam holding moisture – basically I removed soggy sponges…
My fuel tanks are 53 Gal aluminum and where foamed in place. Other boats that I have worked on went the route of foam removal and creation of ‘glass over wood cored bunks to slightly elevate the tank and then strapping secure. No problem with fairly rectangular tanks. I saw one guy who used neoprene ‘hockey pucks’ adhered to the tank bottom and sides with strapping to secure. Unfortunately I do not know where to obtain these spacers (which really did look almost the size of a hockey puck, just slightly softer). My tank shape complicates things since they are 68 inches fore to aft and the inner side facing the bilge is 11 inches tapering to 1 inch on the outer side with the bottom conforming rather closely (but not exactly) to the hull curve. Amazingly both tanks seem in good order (starboard side pressurized OK, port has a pinhole on top probably from a stray screw). I’d like to keep these old tanks (unless a complete cleaning and final survey reveals something). Creating a bed or bunk system for these seems daunting since the bottom is curved and not consistent. Plus, setting up hold-downs is looking to be a challenge as well. Foaming is quick and easy (hence the original use). If moisture infiltration can be prevented it is a good option. The original install used ‘glass over the edges so no foam was directly exposed. But it is evident that this was not a perfect solution and is pretty scary with one side of each tank facing the bilge.
The fridge box was also totally foamed into place – all sides and below. When this got wet the galley cabinet rotted from the inside out. Thankfully the bulkhead head a thick veneer added that continued completely down behind the fridge. The veneer was a total loss, but the bulkhead survived with only a tiny two inch diameter soft spot which was easily addressed. The foam does a great job of holding things in place and provides some insulating value. But I think there are better insulations that would increase efficiency. Plus I am gun-shy about having the bulkhead and the new cabinet in contact with foam which may lead to rot. So here I need to insulate as well as secure.
Any thoughts on alternatives to foam, or use of foam while keeping it dry would be greatly appreciated.

[belizesailor]

Foamed in aluminum tanks would worry me. If you get moisture in constant contact with the tank it can set-up corrosion. The usual recommendation is to install them with some room to breath (and dry) -- like the "hockey puck" installation you mentioned.

[Mike Banks]

In a wooden boat foam is sooner or later going to have to be removed. Much better if it were not used in the first place--but when one buys a second hand wooden boat with a bit of vintage to it--there is likely to be serious rot between the ply or strakes and the foam.

I had a heck of a lot of trouble removing it from the main beams of a trimaran--and because it had been there--rebuilding them. It would have been far better to have empty space which could have been force-ventillated as part of the engine blower system. Instead of all this foam--an inflatable bladder with a gas bottle to inflate it would be far better and take up little room.

I reserve foam for insulation purposes only. This has some value as reserve bgouyancy--but not much. For emergency flotation I use air mattresses (separated from the sole by slatted risers. These are cheap to buy as emergency flotation, and can be inflated from a compressed air source such as a scuba bottle very quickly for use elsewhere in t5he hull if one is taking on water.

For what it is worth--I would get rid of all foam except for the chill box or refrigerator cabinet insulation. I would NEVER have it in contact with anything of structural importance or the hull itself. This is my experience--others may have not suffered the damage I have had in my vessel from its presence.

I find that engine mounts and shock absorber mounts of polyurethane make reasonable buffers for tie down strapping. These need to be epoxied to the hull timbers so that they can not allow any chafing for admittance of moisture.

The last comment I have is to pile in the salt. I use swimming pool salt and throw it all over the bilges and recesses of the hull interior. It does produce some moisture by dragging it from the air--but nothing that eats timbers lives in brine.

Fair winds and calm seas to you all--

[Ike]

I agree with everything said so far. I have been telling boat builders and boat owners since the 70's, do not foam metal tanks in place. It almost always results in corrosion and is the lazy way to mount a tank. When the USCG created the regulations for recreational boat manufacturers, they did not outlaw foaming tanks, but they created requirements that made it very difficult to comply with. One of those requirements is that the adhesive strength of the foam to the tank has to be greater than the sheer strength of the foam. This means that under stress the foam has to break before the bond breaks. In practice this is almost impossible to achieve. So what happens is over time the foam shrinks and separates from the tank, and if moisture gets in there it never leaves.

Also if you use two part pour foam, or spray foam, they are notorious for absorbing water. The last thing you need next to an aluminum tank is moisture.

As was said, the only place you should be using foam is insulation. For that you would be better off using sheet foam. Sheets of insulating foams can be purchased in any home improvement store, and it's inexpensive.

[senormechanico]

Aerogel.
Live it, Love it.
PITA to work with, but at least it's not itchy.
I'm getting ready to redo the hot water tank insulation so I can use excess solar electricity to keep it hot.


Really.

See Aerogel refrigerator insulation threads on CF

[OldRover]

Thanks for the responses.
I have never worked with Aerogel, but another person also suggested it. Said the only negative was that it’s pretty messy, even worse than Styrofoam since it was dustier when cutting. My thought was that I could use it to wrap the fridge and probably end with better efficiency and space away from direct contact with the wood. I'll just have to devise a way to secure it.
Given my flooded cabin, I am shocked the fuel tanks did not suffer more, I have dealt with others much worse. So looks like the aversion to foam still holds. Devising proper hold-downs is still challenging, but I should come up with something. I guess the final major hurdle for me is dealing with the irregular gap between the hull and tank bottoms. I have been searching for the ‘hockey puck’ spacers. The other thought I had would be to use foam in dots or bars, drop the tank to set, pull the tank, and ‘glass over with enough layers to support.

[belizesailor]

Originally Posted by OldRover

...I have been searching for the ‘hockey puck’ spacers. The other thought I had would be to use foam in dots or bars, drop the tank to set, pull the tank, and ‘glass over with enough layers to support.

What about just cutting them from heavy rubber sheet material? This type of material is usually readily available in most places and you can cut to whatever irregular shape you need.

[mikereed100]

I agree with what's been said about foaming in tanks, especially aluminum, but I think foam is getting a bad rap here. When used in the right context it can be very useful, for example, as emergency flotation in dry areas. This excerpt is from the US Composites site under FAQ's about polyurethane foam:

14. Is this foam water resistant?

Yes, but with the following caveat. The foams that we sell are considered closed-cell, which means that each cell that makes up the foam structure is completely closed off from surrounding cells which prevents it from acting like a sponge. It is completely safe for this foam to be in contact with water for hours/days/weeks and even months with no adverse effects. However, it should never be submerged in contact with water permanently. Over a period of years the water contact can begin to soften the foam and cause it to lose its closed-cell status. This foam is designed primarily to be used as an insurance policy in case of damage/holes that could cause a vessel to lose buoyancy. Pinhole sized openings would essentially have no effect on the foam since the amount of exposure is so minimal but you should always make repairs as soon as possible to keep the foam effectiveness as good as possible. This will be the case with all after market closed-cell polyurethane foams and even manufacturer installed foams.

Oldrover,
Building beds for the tanks need not be too difficult;

Scribe a line where you want the beds.
Take the curve of the hull at the lines with a jogglestick.
Transfer the curve onto your wood.
Cut at a 90 degree angle.
At regular stations along the length of the beds, take the angle of the hull with a bevel guage.
Measure the distance of each angle from 90 degrees at the width of your wood and mark on your wood.
Connect the dots and plane the bevel into the wood.
glue it to the hull with lots of thickened epoxy and glass over.

Should take less than half a day including making the jogglestick.
Might be a good idea while you have the tanks out to weld "feet" of angle aluminum for fastening to the beds.

[OldRover]

I have made bed rails before, but at least the tank was straight. So it was just dealing only with the hull curve. I have not done anything like this one - both surfaces are complex curves with nothing to use as a reference. The foam I took out ranged from 1.5 to almost 4 inches and was fairly wavy. I'm not sure how the tanks wound up that way. My guess is they tried to follow the hull curve as best as possible, but unfortunately it more closely resembles a potato chip. That is what is really throwing me.
Also, the foam debate is why I posted and I really appreciate the input. The definition of dry space seems to play a big role. In my case, I am pretty sure my foam was below the level of water held below deck and probably for a long duration. Even after a few years of no water, the foam was completely saturated. In normal service this situation should never occur again even in rough conditions. The only thing that bugs me about the foam is that my boat is not the only one I pulled soggy foam from. Although, given the prolonged contact with the rain water and diesel, the foam and surrounding surfaces did survive better than many ‘in service’ boats I’ve seen. So the contradiction for me seems to be the foams are rated at 95% or higher closed cell, but seem to hold water readily. I think that the flotation and insulation properties due not exclude moisture retention.
In some respects the original design was pretty good. But I think the use of foam was more time and money saver for the manufacturer than a purely engineering decision. I think that I can do some fiberglassing to ensure no foam to wood contact. Foam to aluminum is another thought. But from a design perspective there is one more issue. The tanks run over 5 feet along the bilge. The upright water tanks are located along the hull topsides in alignment with the fuel tanks. Any moisture from this area would need to pass over the fuel tanks to reach the bilge. No foam does provide a much better path.
Oh, and a side note. Another reason I am leery about foam is diesel spills. Only a small amount made it to the foam, but the smell was intolerable. The thought of ripping it all out again if there is even a tiny spill is not too thrilling.

[Mike Banks]

Any tiny spaces between foam and timber if exposed to the atmosphere will eventually get wet--even if above the water-line.

Plastic Aerial cables become wet inside after a while because they "pump" in water as the day and seasonal temperatures fluctuate. On a hot day the air expands--as evening or a cold day arrives the air contracts--drawing in moisture which never gets completely expelled during the next cycle. A space does not have to be wet to rot--just moist. Circulating air and salt is the answer--and tanks need to be supported on several lateral mounts between which air can pass. Fibreglass faced with nitryl or neoprene rubber sound good to me. Mine are tanks built to span the hull floors--and they sit on rubber mounts tied down with polyester toggle-ropes and timber toggles. Nothing corrosive prone there--and easy to undo--no threads to corrode.

Use non-electric level indicators if you use metal tanks. Nothing like battery potential to create corrosion--as if differential aeration was not enough--

[OldRover]

I think the best way for me to go is to pick up some sheet stock and cut spacer blocks. I envision six or more per tank. Hopefully I can find stock that is three eights of inch or slightly thicker. Start off with two layers for each pad. Drop the tank in place and check for those that are shy. Add layers as needed. Maybe a tad tedious, but doesn't sound bad. I'll epoxy hold-downs to the inner hull and use synthetic straps. I did see a mess where a guy used stainless straps. He did have rubber strips in between, but something shifted and the two metals wound up in contact. Plus, I think I can cinch fabric straps nice and tight with less effort.
If I do foam in the fridge box, I will ensure no direct contact with the surrounding wood. Although I think there are better insulators like Aerogel that would be best once I devise a good way to fix the bowl in place.
On a side note, I am taking a little extra care in screw locations and component shapes to enable a cleaner disassembly if ever needed. Doubtful I will ever need to gut the main cabin. The mrs. says I am jinxing things.

[OldRover]

A quick update. Sometimes the most obvious is the answer. I decided to try using hockey pucks. While online searching for somewhat softer pucks like for street hockey, I found a bucket of foam practice hockey pucks. These are about 2.5 inches in diameter and .75 thick and are made from a fairly dense closed cell EDPM which allows for some compression. They work great as tank spacers. Go figure, hockey pucks... Now I have better drainage into the bilge than original and great air circulation.

[Ike]

I guess I can add that to my list of innovative solutions. Never seen that done before.

[colemj]

Good thing you did not use a standard hockey puck. Those are made from vulcanized rubber and have a large carbon content. Carbon and aluminum do not go well together - with aluminum paying the price. EDPM will be fine. Even better if you glue them to the tank with a polyurethane adhesive to prevent any moisture from sitting between them and the aluminum.

Mark

[Danosimp3]

aside from a poor bonding agent, foam is a water displacement tool. It can keep your boat from sinking if there is enough foam. A cubic foot of foam can displace about 65 pounds of seawater. so a 6,500 lb vessel would need 100 cubic feet to keep her afloat near the design waterline. you could get away with 30% of that just to keep her form sinking. that would be about 30 cubic feet. But, that takes up allot of would be storage space on the chance the boat could sink. In my refit, I opted for storage opposed to reserve displacement.