Outrageous idea? Lightweight floor and decking FOAM

I have been wanting to reconfigure my boat. My first attempt at a build was fall of 2015. I used wood and carpet and what I thought were innovative ideas to save weight with this material. I recently shared my 1442 NCS project on here https://www.forum.tinboats.net/viewtopic.php?f=21&t=42208

The raised floor gave me a good fishing platforme when not on the front or rear deck, but now I realize that I don't necessarily like the raised floor idea and would prefer more deck space and less floor space as a trade-off. While fishing I also pull my rods out of the in-floor locker and leave them all sit out as I change up what I'm using every few minutes unless I'm just killing them on a single certain lure. Well, pulling rods out of the floor isn't always easy - especially if there's a dog in the boat or even if carrying some extra camping gear as it needs to be moved to open the hatches.

That being said, my brainstorming lead to addressing using as little material as possible in any location that has a good solid base already - think 3/8 plywood instead of 1/2. I'd fill the cavities below the floor with the pink foam and then lay a sheet of carpeted plywood over the top. Now, I work for a lumber company and when I end up dealing with something out in the warehouse or a delivery truck there have been many times when I ended up walking around on top of or at least stepping over a sheet of the pink foam while it was laying flat on the ground. It is actually a pretty solid surface while obviously very light. I was going to save weight over my current build by reducing my plywood thickness from 1/2" to 3/8" thick (would save 11 lbs per sheet actually and my plan uses almost 2 full sheets). But the purpose of the sheet on the floor for me is just to have something to wrap the carpet around and lay it down. With the full support of the foam sheets between the ribs, why use plywood at all? A sheet of 3/4" or 1" foam makes just as flat of a floor as plywood and weighs only a fraction of what even 3/8" plywood weighs. What affect would carpet glue have on the foam sheet? How would the carpet-wrapped foam sheet hold up to weather? I could use the same thing for the front and rear decking where the sheet simply lays over the existing aluminum base. Assuming the use of 1" foam, I could extend any platform using a lightweight framing but planning for it to be 1/2" higher and using 1/2" plywood on that while making it flush with the top finished height of the 1" foam.

Am I onto something or is there a reason this won't work?

Now if you've stayed with me so far, I'm gonna go ahead and get really crazy. Being in the building industry, I see things like this (deck framing with rigid insulation - link here https://www.forum.tinboats.net/viewtopic.php?f=3&t=42868 ) and it prompts more creative notions out of me. I'm reminded of SIPS (structural insulated panels) for home building. Simply sandwiching foam insulation between two relatively thin sheets of plywood can be used to engineer house walls and support the entire weight of windows, headers, and a whole roof. While building up any platform for your boat, whether it be a storage hatch or the framing surrounding a raised deck, 1"-2" foam sandwiched between 3/16 luan to create a "mini" SIP sounds to me like a good possible application.

All wood would be properly sealed of course. Adding foam, and eliminating wood, all in one, would make it light - probably even lighter than aluminum framing and aluminum sheets?

OK. Maybe I'm totally in la-la land.

One step ahead of you - check my build

onthewater102 said:

One step ahead of you - check my build

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I see that is a pourable foam. Did you create a mold to make panels out of it?

I am mainly inquiring about closed cell insulating foam sheets such as the pink Owens Corning and carpeting directly over that. You used FRP but a sheet of that is pretty heavy.

I have an older 1648 flatbottom that has only a rear bench seat and an extended front deck, so the middle of my boat is all open floor. I used 2" pink rigid foam between the ribs (yes my ribs are 2" tall) and 3/8" plywood then carpet. Main reason I stayed with the plywood is because I use foldable lawn chairs for seating and having a person's weight on only 4 small seat feet requires something a bit stronger for a floor. If you are using fixed seating it might be a different story.

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Comparing weights of materials - the FRP would be good application for my SIPS inspired decking and compartment wall idea. Maintenance-free and lighter compared to a thin plywood.

With more research into the foamular150 insulation, I have no qualms about its weatherability. I will look at various flooring adhesives and be sure there won't be a issue with applying them to foam.

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I went with poured expanding urethane foam because it will not dissolve if accidentally exposed to gasoline. Any spill in the boat could slosh around and get at the underside of the foam.

I did not make molds, you simply frame out a cavity you're going to fill and have the covering ready for it and pour the foam in. Only in one spot did I have to drill through the FRP to allow me to fill an air pocket that formed - and that was easily patched with fiberglass prior to painting. The issue you encounter is drainage. I set vinyl hoses under the FRP but they were only 3/8" ID and were not big enough. I pulled the hoses out from under the foam which freed up larger passages for water to drain. In addition I cut holes through the deck and the foam to the floor channels underneath and installed grates on the main floor basin so now rain water quickly drains to the back of the boat where the bilge can pump it out. I keep it covered just the same.

My 1436 decked out is still light enough that with the contents of the boat emptied, the outboard and trolling motor removed (my trolling motor is attached with a minn kota quick release plate) two people can still carry the boat to launch it. Only other way I could think you could accomplish that with wood would be to have the flooring panels sitting atop an aluminum skeleton and have them removable.

It sounds like we are all on the same track here. My "new" deck on my 1652 G3 is made up of a sandwich of

Blue foam panels laid LOOOSLY in between the aluminum supports. They are laid in there loosely so that, if and when water gets in, the loose fitting panels allow drainage around themselves. The boat has three large drainage slots front to back.

On top of the Blue foam, I have a very thin aluminum sheet. I now think that it wasn't necessary at all, but it was left over from my scrapped Lowe 1648. My original plan was to glue the topping onto the aluminum sheet.

1/4 Exterior plywood with vinyl sheeting tucked under the edges and screwed down.

I made up the decking in two sections. That way, I can easily remove one or the other if I have to get to the wiring underneath.

richg99

richg99 said:

It sounds like we are all on the same track here. My "new" deck on my 1652 G3 is made up of a sandwich of

Blue foam panels laid LOOOSLY in between the aluminum supports. They are laid in there loosely so that, if and when water gets in, the loose fitting panels allow drainage around themselves. The boat has three large drainage slots front to back.

On top of the Blue foam, I have a very thin aluminum sheet. I now think that it wasn't necessary at all, but it was left over from my scrapped Lowe 1648. My original plan was to glue the topping onto the aluminum sheet.

1/4 Exterior plywood with vinyl sheeting tucked under the edges and screwed down.

I made up the decking in two sections. That way, I can easily remove one or the other if I have to get to the wiring underneath.

richg99

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Certainly laying a sheet of any substrate being it wood or metal or FRP over the top of a sheet of foam would not raise issue and is a very common practice. I am specifically trying to figure out usefulness of the foam itself as the overlying material to be wrapped in carpet as the finished layer.

Just guessing here, but.. I believe that most laminated sheets get a lot of their strength from a solid glued top and bottom. Those tops & bottoms are mostly smooth non-porous materials. It is my bet that carpet wouldn't provide that stiffness. Any glue would quickly tear the foam and separate. Strength would be lost.

Anyhow, IMHO.
Richg99

richg99 said:

Just guessing here, but.. I believe that most laminated sheets get a lot of their strength from a solid glued top and bottom. Those tops & bottoms are mostly smooth non-porous materials. It is my bet that carpet wouldn't provide that stiffness. Any glue would quickly tear the foam and separate. Strength would be lost.

Anyhow, IMHO.
Richg99

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Picture this: wrapping and gluing carpet to a foam sheet, then laying it flat on an aluminum floor and walking on it. Then suppose it gets rained on a few times and you continue to walk on it. Any issues with the foam board?

Big as I am, I'd think that I'd have dents, knee marks and loosened carpet areas in a week.

Heck, if you like the idea, get a sample piece of carpet and glue it to a piece of foam. Walk around, knéel, etc. for a week. Experiment. richg99

You're not talking about major money in your test subject. Carefully cut your carpet and if it fails you can always re-use the carpet. You'll be out the price of a foam board...hardly a budget buster in the world of boating.

I stripped my boat and began fabricating my new layout.

Front will be extended with 1x2s and have a 1x2 "stud wall" with 1.5" foam sheets in the spaces. I can then wrap that wall directly with carpet for my exposed vertical structure. Top support surface will be 3/8" plywood (1x2 structure underneath will be 12" spacing). Once the front deck is flush between the new structure and the factory aluminum, I have cut 1.5" foam sheets to cover the surface. I sealed and glued 1x2 "blocking" onto the foam's edge where hinges can be attached for my hatches. I've cut one of the front hatches already - I build up around the hatch opening with 1x2s and then use 3/8" plywood for the hatch door but cut 2" wide strips out of the 3/8" plywood that I laminate with wood glue to the underside around the edges and one in the middle to make it structurally sound. It is as strong and as thick around the edges as 3/4" plywood but at about 2/3s the weight. The 3/4" thickness of the hatch door plus the 3/4" thickness of the 1/2s around the opening bring it flush with the 1.5" foam finished floor.

I was going to only use 1" foam not 1.5", and I will in all other areas. But I wanted to recess my trolling motor foot pedal into the front deck floor without having to cut a hole and then furthermore add structure and weight to support it. So I just cut out the foam around the foot pedal so the pedal can be 1.5" lower. I could have used 2" foam I suppose to make this recessed area even deeper, but I consider the material I would need to use in other areas such as hatch openings and additional height in the structure that extends the deck to build that stuff all up an additional 1/2" and that is a significant amount of weight. Too thick of material would also make the deck higher than I would like it to be.

I get on a roll when working and just go without thinking about taking pictures along the way. I'll post what I can later. I hope I'm done with this in 2 weeks.

Good plan.

However, my wife laughs when I say things like....

"I hope I'm done with this in 2 weeks."

Save more weight ... especially when wet! Ditch the carpet and use marine vinyl ... less wet when dry, significantly less weight when wet ... and last 2-3X longer, if not more.

I have been thinking about pink or blue foam between ribs, covered by foam puzzle mats. The puzzle mats could be screwed into the ribs to hold them in place -- just use big washers. You can buy 24 sq. ft of grey puzzle mats with a faux diamond plate texture for about $25.

https://www.amazon.com/CAP-Barbell-Puzzle-Mat-piece/dp/B0041FQZMW/ref=sr_1_3_sspa?s=toys-and-games&ie=UTF8&qid=1505830355&sr=1-3-spons&keywords=puzzle+mat&psc=1