Foaming my Hull

[jdschwass]

Hi all- I am new here, but I have been doing a lot of reading recently on this forum, and it has been great.
I just picked up a project boat. It is a 1970's (I think) Starcraft Jet Star V. Aluminum,15 foot. I have the boat stripper down to the bare hull, and plan to turn it into a bass style boat.
I am planning to install a subfloor in place of where the original floor was, and then build the top deck up higher. I am dead set on getting lots of foam in this boat, but I dont want to compromise drainage or risk having wet foam. This is my plan, just looking to see what other's think

The boat ribs run left to right, across the hull, with a small drainage groove through the middle that runs to the bilge. My idea was to run pink high density foam insulation lengthwise along the hull across the top of the ribs. So there would be a one inch gap underneath. Then I would lay a large sheet of thick vapor barrier over the whole inside of the hull, and then install the new floor, which I am planning to use 1/8 inch aluminum. Once the aluminum is down, then I will drill holes and use pour foam to fill the remainder of the void.
My thinking is that the pour foam will give me the reinforcement and damping I want, while still leaving some air gaps under the floor for potential water to flow out. Also, since there is a layer of plastic between the bilge and the pour foam, and the floor is sealed on top, there is a very low chance that water will ever get near the pour foam. It also reduces the risk of pour foam being in contact with the aluminum hull, which I have read about being a potential issue. If I ever had to remove the foam in the future, it should also be much easier to remove.

I'd appreciate any thoughts... maybe i'm out to lunch.

Thanks!

 

[Bob Sander]

I dunno... I don't like the idea of foam in the bottom of a boat. At least not foam that you can't easily remove if or when it waterlogs.

I would be more inclined to do some form of removable floor board system so you can easily open it up for cleaning every so often. I have an 18 foot open aluminum and with the leaves, dust, dirt, rainwater... etc, it gets pretty disgusting and starts smelling after a while.

 

[Lectro88]

I second Bob Sander thoughts.
Also another thing that you should consider with an aluminum hull…. All Those Rivets, they a lot of times develop leaks.
Or you may develop a leak somewhere under the foam, be it on bottom or sides of hull.
So all things considered I think you have an ok plan, but I would have the foam sections or panels somewhat easily removable. But
Fastened in place securely as you deem fit.
I have an old 60’s model Starcraft that’s way down on the list of restoration.
It also has right/left, side to side supports.
So I get what you are saying.
Mine has old foam in the bottom already, not sure if that’s original or modified by previous owners.
Having things removable and yet secure throws a little twist in the design but it’s certainly doable I think.
Get creative or someone may chime in with more ideas.

Just my thoughts.
Keep us posted on progress.

 

[jdschwass]

Thanks for the comments. Leaky rivets at some point in time is definitely my concern, otherwise I would just seal the hull entirely. By using hard foam across the ribs, it still allows water to drain if it does leak. Then having vapor barrier between pour foam and hard pink foam allows the foam to never see water. I have 1/16th aluminum sheet for my subfloor. So once filled, nothing is getting in. If I ever had to remove the foam, I could remove aluminum floor, and the pour foam would lift out with the vapor barrier... no contact with aluminum.
I will keep you posted with my progress.

Cheers.

 

[jdschwass]

This is where I have gotten so far...I put down 2 coats of liquid rubber. It is brushed on thick, and seals up any minor leaks, though there were none I could find; just piece of mind. Then I have laid down 1 inch high density insulation across the ribs, which allows water to still flow to the center of the hull, and back to the bilge. I have just temporarily fit the aluminum subfloor. Next step will be to lay the 6 mil vapor barrier plastic over the pink foam, then install the aluminum overtop. Then I will rivet the floor down solid, silicone all joints and seams, and then lastly pour the foam through the aluminum floor.
I am just hoping that the pour foam will still give me the hull rigidity I want given that there is a bit of an air gap under the pink foam.

I just keep questioning whether I am better off laying the plastic in the hull without the pink foam. The water could still make its way to the bilge I think, but the pour foam would be better molded to the hull. With the plastic, removal wouldnt be all that bad if it ever came to it.

 

[Reserector_]

Have you tested some pour foam on the foam board to make sure one won't eat the other? They are different types of foam.

Oh, and one tip on the pour foam; heat is your friend. If you have the liquid at room temperature, and preheat the hull with a blow dryer or two, it will expand really well, giving you maximum yield, and lightest weight.
I did my ski boat one side at a time, because that's how ski boats are. Not a big area at once, is what I'm getting at.
With the holes in the floor (sole) I stuck a blow drier in the end that I wanted to start on and let it exhaust out of the far end. Let it run until the outside of the (fiberglass) hull was 95°F. I used a temp gun to measure it.
when I poured, it expanded like crazy, which is what you want. The heat from each batch reacting in the hull was enough to keep it hot while I mixed the next batch. And so it went.
I was worried I would need to buy more to finish the job, but had some left over when done.

From the looks of it, one 2-gallon kit would be way more than enough for your boat if you go at it that way. Buying it in quarts is probably not all that economical. IDK.

 

[jdschwass]

Have you tested some pour foam on the foam board to make sure one won't eat the other? They are different types of foam.

Oh, and one tip on the pour foam; heat is your friend. If you have the liquid at room temperature, and preheat the hull with a blow dryer or two, it will expand really well, giving you maximum yield, and lightest weight.
I did my ski boat one side at a time, because that's how ski boats are. Not a big area at once, is what I'm getting at.
With the holes in the floor (sole) I stuck a blow drier in the end that I wanted to start on and let it exhaust out of the far end. Let it run until the outside of the (fiberglass) hull was 95°F. I used a temp gun to measure it.
when I poured, it expanded like crazy, which is what you want. The heat from each batch reacting in the hull was enough to keep it hot while I mixed the next batch. And so it went.
I was worried I would need to buy more to finish the job, but had some left over when done.

From the looks of it, one 2-gallon kit would be way more than enough for your boat if you go at it that way. Buying it in quarts is probably not all that economical. IDK.

I have not tested it, but the solid foam is separated from the pour foam by a layer of 6 mil vapor barrier. I did buy the 2 gallon kit, and I did my first test pour last night, so far so good. I am going to increase the heat though. Up here in Canada it's below freezing, so all I need to do is crank the shop furnace and wait for a bit. Any foam I have left over at the end I will use above the subfloor once I start getting things framed in.

Also, before I poured the foam, I poured a gallon of water into the bow. As I had hoped, it ran under the pink foam and back to the bilge. So if I ever have a leak, the hull can still drain. And any water that comes from above wont get through the subfloor, and still goes to the bilge.

I'll keep you posted on my successes, or failures perhaps.

Thanks.