Boat Insulation - Sheet and Pour Foam Advice Needed

[mossberg]

Hi everyone—

I'm redoing a late '80s Bass Tracker, stripping it down to the aluminum hull, adding cut-up closed foam sheets to floor/compartment walls, framing in some new hatches, replacing the transom, fixing leaks in hull, etc. I'd also like to re-add poured foam in places that make sense, but want to make sure the pour foam is isolated and not able to expand to fill in drainage channels. I pulled a lot of heavy, water-logged pour foam from the boat because most of the boat's drainage channels were completely blocked throughout the front and back of the boat by the pour foam and water had no place to go. I've fixed this.

I'd like to get your thoughts on my foam insulation plan.

1. Add measured, cut-up sheet foam (2" and 1" purple closed cell foam sheets from Home Depot) between boat ribs in floor (this keeps the drainage channels open)
2. There is no drainage channel in the center of the boat (just two on the port and starboard sides). I'm planning to drill a 3/4 hole in the floor robs in the center of the boat to allow any trapped water to move.
3. Put the aluminum subfloor (.060) and decking (.090) over the sheet foam between ribs.
4. Fill in any gaps between compartment walls with sheet foam.
5. After the boat is framed out and compartments created, and where it makes sense in the front and the back of the boat, add in pour foam, e.g., between PVC for rod locker, empty areas between side of hull, compartments, etc. This pour foam would be added to areas above the aluminum subfloor that are completely isolated in the front and back of the boat, adding back in places where it was previously.
6. Just to state the obvious I will have added conduit and wired the boat before doing any pour foam anywhere.

Any concerns with adding pour foam on top of the aluminum subfloor in isolated areas?

Lastly, I've read concerns about sheet foam being used close to the transom and bilge, given that fuel that comes in contact with sheet foam will destroy it (I run a 60HP Johnson 2-stroke). So I was not going to install foam board in the last two ribs. I've also thought about taping the closed foam board closer to the back with aluminum HVAC tape as an additional layer of protection. Is that a bad idea?

Any thoughts, concerns or advice with the above plan? Thanks!

 

[LDUBS]

#2 - Drilling a 3/4 hole through the ribs. How much structure does that leave? I'm not familiar with how these boats are built. Is the seam between the ribs and floor water tight? Ini other words would there be drainage if not blocked?

About the concern with fuel melting the sheet foam. If the form is covered by a floor of some sort, I personally would not worry so much about it. A catastrophic fuel leak might be an issue with the foam, but minor spillage from time to time should be OK.

 

[Azdesert]

Adding the pour foam on top of the subfloor is IMO the best way to do it. Using closed cell sheets under the subfloor and you should have a nice set-up that should last years and provide non water logged service. In the transom area you can wrap the sheets to prevent fuel from getting on them and breaking them down. If you put foam of any kind in the transom area consider making that part of the floor removable so you can inspect and remove and replace that foam as needed. Pretty easy to do that really, just use screws instead of rivets. Sounds to me like you have a solid plan in place. Good luck with the bulid.

 

[LDUBS]

Adding the pour foam on top of the subfloor is IMO the best way to do it. Using closed cell sheets under the subfloor and you should have a nice set-up that should last years and provide non water logged service. In the transom area you can wrap the sheets to prevent fuel from getting on them and breaking them down. If you put foam of any kind in the transom area consider making that part of the floor removable so you can inspect and remove and replace that foam as needed. Pretty easy to do that really, just use screws instead of rivets. Sounds to me like you have a solid plan in place. Good luck with the bulid.

Good stuff, but am not following the first sentence about pour foam on top of the subfloor???

The ply floor in my boat is screwed down. I can't think of a downside and it seems for ease of removal that would be preferred over rivets.

 

[Still Afloat]

Why do you need a subfloor and a deck? It would be stiffer and easier if you just use .125” plate for the deck and forget the subfloor.

 

[Azdesert]

Good stuff, but am not following the first sentence about pour foam on top of the subfloor???

The ply floor in my boat is screwed down. I can't think of a downside and it seems for ease of removal that would be preferred over rivets.

Pouring the foam on top of the sub floor and under the main floor keeps it from being in direct contact with the hull. That stuff gets water logged over the years and can end up causing some corrosion. Doing it that way helps it from getting water logged. The pour foam can add lots of weight to the boat over time. North Country Jet Boats stopped using it about 5 years ago because of these problems. If the design of the boat has a subfloor, IMO it is the best way to add pour foam, a floor slightly above the hull doesn't give you this option.

I really wanted to add pour foam on my current project because it does help with stiffing the hull, as well as floatation. But because I am only putting a floor in I elected to pass on using pour foam because I don't any of the known problems in the out years.

 

[Still Afloat]

Pouring the foam on top of the sub floor and under the main floor keeps it from being in direct contact with the hull. That stuff gets water logged over the years and can end up causing some corrosion. Doing it that way helps it from getting water logged. The pour foam can add lots of weight to the boat over time. North Country Jet Boats stopped using it about 5 years ago because of these problems. If the design of the boat has a subfloor, IMO it is the best way to add pour foam, a floor slightly above the hull doesn't give you this option.

I really wanted to add pour foam on my current project because it does help with stiffing the hull, as well as floatation. But because I am only putting a floor in I elected to pass on using pour foam because I don't any of the known problems in the out years.

I can see a few problems with this concept:
1. Will the working time of the pour foam allow adequate time to set the deck?
2. The weight of the two aluminum sheets combined is excessive. One sheet of less total thickness would be strong enough.
3. How will you remove the deck in the event that the hull needs service?

If you are really trying to get the best fit from the foam sheets, you may want to consider building or buying a hot wire foam cutter. The foam could be cut in a rib fashion and laminated. This would provide a tight fit for maximum floatation and deck support.

 

[Azdesert]

I can see a few problems with this concept:
1. Will the working time of the pour foam allow adequate time to set the deck?
2. The weight of the two aluminum sheets combined is excessive. One sheet of less total thickness would be strong enough.
3. How will you remove the deck in the event that the hull needs service?

If you are really trying to get the best fit from the foam sheets, you may want to consider building or buying a hot wire foam cutter. The foam could be cut in a rib fashion and laminated. This would provide a tight fit for maximum floatation and deck support.

With that method getting to the hull would be a issue. Typical subfloor is only .030 so not much weight, the two floors and framing is still less then a 3/4" plywood floor, certainly more costly too. In the OP's case he is going to use .060 on the subfloor, so a little heavier. Normally the foam is poured and then cut to fit after it cures.

I just put in a couple of .090 pieces today on a side panel and the framing still needs to be close to a foot apart to keep it from getting beat up.

Those hot wire cutters are a great tool to have if you do much of that work, or even for one project it could be worthwhile.

 

[EricMN]

Hi everyone—

I'm redoing a late '80s Bass Tracker, stripping it down to the aluminum hull, adding cut-up closed foam sheets to floor/compartment walls, framing in some new hatches, replacing the transom, fixing leaks in hull, etc. I'd also like to re-add poured foam in places that make sense, but want to make sure the pour foam is isolated and not able to expand to fill in drainage channels. I pulled a lot of heavy, water-logged pour foam from the boat because most of the boat's drainage channels were completely blocked throughout the front and back of the boat by the pour foam and water had no place to go. I've fixed this.

I'd like to get your thoughts on my foam insulation plan.

1. Add measured, cut-up sheet foam (2" and 1" purple closed cell foam sheets from Home Depot) between boat ribs in floor (this keeps the drainage channels open)
2. There is no drainage channel in the center of the boat (just two on the port and starboard sides). I'm planning to drill a 3/4 hole in the floor robs in the center of the boat to allow any trapped water to move.
3. Put the aluminum subfloor (.060) and decking (.090) over the sheet foam between ribs.
4. Fill in any gaps between compartment walls with sheet foam.
5. After the boat is framed out and compartments created, and where it makes sense in the front and the back of the boat, add in pour foam, e.g., between PVC for rod locker, empty areas between side of hull, compartments, etc. This pour foam would be added to areas above the aluminum subfloor that are completely isolated in the front and back of the boat, adding back in places where it was previously.
6. Just to state the obvious I will have added conduit and wired the boat before doing any pour foam anywhere.

Any concerns with adding pour foam on top of the aluminum subfloor in isolated areas?

Lastly, I've read concerns about sheet foam being used close to the transom and bilge, given that fuel that comes in contact with sheet foam will destroy it (I run a 60HP Johnson 2-stroke). So I was not going to install foam board in the last two ribs. I've also thought about taping the closed foam board closer to the back with aluminum HVAC tape as an additional layer of protection. Is that a bad idea?

Any thoughts, concerns or advice with the above plan? Thanks!

I thought about doing something similar on my rebuild. In the end, I used pink foam sheet above the ribs and pour foam on top of that…. I have pictures on my rebuild post

https://www.tinboats.net/threads/northwood-1675-dlx-fisherman-rebuild.50296/

Works well for my build as it allows for good drainage towards the center of the boat.

 

[LDUBS]

I guess I'm still scratching my head. If waterlogged pour-in foam is a concern, why not just use styrofoam boards under the floor. It can sit right on the hull bottom and can be easily replaced if ever needed.

 

[thill]

For what it's worth, I will share a method of mine.

On one boat, I laid 1" sheet foam under the floor framing. This allowed complete drainage underneath, since the sheet sat off the hull on top of the ribs. Then I used fill foam from a can to secure/seal it for the pour foam that went on top of that. It worked VERY well.

I didn't want the foam actually glued to the bottom of the plywood, so I poured less than I thought it needed until I learned the expansion rate.

I always want to fill the area without having to trim the top, which would expose the cell structure of the foam. So, it is best to mix in small batches, and then mix more if it doesn't expand quite as much as you want. Even a little drizzle of that stuff can do wonders to seal up an area.

This may be a method that can give you the results you are looking for. I wanted good rigidity and floatation without the risk of saturated foam or trapped water underneath. This is my go-to in similar situations. I did other things, to prevent water coming in from the top, but using sheet and pour foam was successful in the lower layers.

 

[Azdesert]

I guess I'm still scratching my head. If waterlogged pour-in foam is a concern, why not just use styrofoam boards under the floor. It can sit right on the hull bottom and can be easily replaced if ever needed.

That is what I'm currently doing, but I would have liked to use some pour foam because it provides some added stiffness to everything. I thought about pouring some on top of the sheets just as mentioned above, but I need to have those deeper sides because my balance and walking issues only seem to get worse with the passing of time. Plus as you said, remove and replace as needed.