Aluminum angle w/ 4lb foam backing

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Jul 14, 2023
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Hello tinboats forum! New here and trying to understand what is needed aluminum wise in the case of using 4 lb foam for boat floor.

Here is the layout of the boat:
  1. 14' long
  2. Approx. 48" wide floor
  3. Ribs are 15" on center w/ drain holes in center
Here is my plan:
  1. Create a 6" center channel opening to access the underside of the ribs and or for cleaning
  2. Use angle aluminum 21" long to form support the width of floor
  3. Add bracing to center aluminum angle and inner most part where the drainage channel is
  4. Add 60" angle tie together each floor support and to give support for removable center floor piece
Here is a diagram of what I am trying to do, hopefully this help.


I've seen posts saying to use 1"x1" 1/8 T6 aluminum angle where you could just add bracing in the center point, but I want to be able to access the underside for cleaning etc if needed.

Also, I'm not clear on what span I can achieve with T5 aluminum since I believe w/ the 4 lb foam and only spanning about 10" in sections for the most part I could get away with something like 3/4" x 3/4" x 1/16" T5. However the piece to tie them together from front to back would need to be more like 1.5"x1.5" T5. Yes, I know that T6 would be stronger, but I can get the T5 for free. Also, T6 is not available in 1/16" thickness so I would be adding additional 1/8" height to the center when I want that to be lower in reality to help drain to center. I really just want the foam to be doing most of the work and use the aluminum to help hold everything in place while I pour.

Is there a reference to aluminum angle span tables? I assume I am not going to find anything in the area of a 10-12" span for reference since this is not much of a span...

Obviously I know a lot of people are against pour in foam and I have removed soggy foam myself in the past and understand the risks which is why I am planning to build the floor with drainage channels etc to help the foam stay dry and allow it to have the opportunity to drain out if it does become wet because we know if will happen at some point.

Hopefully someone can help, this seems like it might if anything be overkill with 4 lb foam once the plywood is on top.

I've not worked with pour in foam since the early 80's, so really am not familiar at all with today's products. If there are options, I would opt of the one that would add the least amount of extra weight to the boat

I would consider have some of those top chords go all the way across (see red lines in the pic below). It just seems like it would tie everything together. You would still have good access to the center channel. That would also give you support if you wanted two separate hatches over the center channel.

It seems like allot of extra work for that 6" channel. If you go forward with it, agree with LDUBS, have those continuous cross-pieces for the extra side to side support.
Thanks for the replies. I agree, it would be extra work. I wanted the opening for another reason actually, the 1.5" angle that spans from rib to rib would actually need to support more of the load vs the foam (I don't think I'll be able to get the foam full under the inside angle) in that spot and if I had to cut notches into the angle to fit over the cross-pieces that would weaken that?

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