# Coosa BW 26 vs Marine ply



## Fishtex (May 10, 2014)

You can’t replace marine ply with foam core 1:1, foam core requires a different lamination schedule, typically. That particular version of Coosa has fibers in it so it is stronger, but you would still likely use thicker version of Coosa than you would use if going with ply, and then additional glass. Obviously the application is a factor, ie, hull panels, stringers, transom and bulkheads vs a console or baitwell or cooler. 

In every foam core build Ive seen, the foam core is 2-3 times as thick as the ply version. I’m talking about real marine ply like Okume, not junk acx.

When in doubt I would pose the question to the designer and see if there is a foam core layup schedule available. I wouldn’t guess on something like this, it’s structural. The ol “that seems pretty strong” doesn’t cut it. Hull pressure at speed is pretty incredible. If the build is too light it typical wouldn’t fail right away, it would fail over time. At the same time you don’t want to use too much glass and defeat one of the main reasons for using foam core. 

If the boat plan is stitch and glue, converting from ply to foam is possible but the core thickness comes into play and can create problems when trying to get everything to line up correctly. For example, side panel to hull bottom at the chine. If the design is old school ply on frame, I wouldn’t attempt it. 

Coosa is heavy when compared to other foam cores. Once you adjust the layup schedule you don’t save much weight and you usually increase the cost substantially. You’ll also have use more molds so you don’t get sag between the stations. 

It’s easy to work with, cuts nice, easy to machine. I believe it will also hold fasteners. It seems to work with polyester and epoxy but the layup would be different. My preference is for epoxy with foam. 

It’s not a bad idea, the devil is in the details.


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## blkmnstr (Jun 7, 2019)

Thank you Fishtex. Yes it will be a stitch and glue build. I was mainly wanting it for weight and for having a wood-free hull. I guess it'll be pissing against the wind for weight purposes.


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## JC Designs (Apr 5, 2020)

What design? I wouldn’t build nor would I recommend using Coosa for an entier build. Their are better and lighter options for hull coring. Divynicell, aircell, klegecell, carbon core, core cell are a few that come to mind. From strictly a weight stand point, foam won’t save much over a properly built wood core. However, you will have the no rot advantage. I am personally a foam only guy but do really LOVE the way a wood boat rides, feels, and sounds on the water!!! As mentioned, if you go with wood... use epoxy and a good grade marine ply. Or better yet IMO, cedar or cypress strip plank it! Pot all fastener locations, make sure all joints and ends are sealed and she’ll out live us!


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## JC Designs (Apr 5, 2020)

Also, I can help with the wood to core conversion with a little more info. I am a builder, repair tech, and consultant, James


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## blkmnstr (Jun 7, 2019)

Thank you for the responses. I think I will be building it out of divinycell H80. It's the Phantom 22' designed by Jaq from boatbuilder central. It's not so much a weight thing as a no wood. I have built a few wood core with my father and know first hand they will stand the test of time when done correctly. We have always used okoume 1088 with epoxy. Jc, have you ever used "Pultruded fiberglass" for securing things such as tower brackets or reinforcing the transom. Young boats quoted me a price for hatch insets and covers so I will most likely be getting those from them but will need a way to secure them in place. Again thanks for any information.


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## blkmnstr (Jun 7, 2019)

JC Designs said:


> Also, I can help with the wood to core conversion with a little more info. I am a builder, repair tech, and consultant, James


I can try to send you the digital plans via message on here if you like?


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## JC Designs (Apr 5, 2020)

No need, I’ll give BBC a call in the next few days and work on a lam schedule for you.


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## DuckNut (Apr 3, 2009)

Go back to BBC and get the plans for a composite build. Do not even attempt to build without it.


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## blkmnstr (Jun 7, 2019)

DuckNut said:


> Go back to BBC and get the plans for a composite build. Do not even attempt to build without it.



Thanks. I was able to get a lamination schedule from them today. It was actually less than what I was planning on doing. 

Bottom panel, from outside:
Graphite-epoxy
1 layer 12 oz. biaxial 45/45 with 8 oz. mat (1208)
1 layer 12 oz. biaxial 0-90 no mat
foam Divinycell H-80 12 mm (1/2”)
1 layer 12 oz. biaxial 0-90 no mat
1 layer 12 oz. biaxial 45/45 with 8 oz. mat (1208)

Topsides (side panel) and false transom, from outside:
1 layer 12 oz. biaxial 45/45 with 8 oz. mat (1208)
1 layer 12 oz. biaxial 0-90 no mat
foam Divinycell H-80 12 mm (1/2”)
1 layer 12 oz. biaxial 45/45 no mat
1 layer 9 oz. woven

Deck:
Same as topsides
Bulkheads:
Same as topsides
Sole:
Same as topsides
Stringers and floor frames:
1 layer 12 oz. biaxial 45/45 with 8 oz. mat (1208)
1 layer 12 oz. biaxial 0-90 no mat
foam Divinycell H-80, 12 layers 12 mm (1/2”) epoxy glued
1 layer 12 oz. biaxial 45/45 with 8 oz. mat (1208)
1 layer 12 oz. biaxial 0-90 no mat
Cap stringers with unidirectional carbon fiber tape 1” wide

Keel:
Extend in and outside skins from bottom panels over keel and overlap 6”.
Tab keel with 2 layers biaxial tape 12 oz. 45/45 each side
Offset all edges at least 1”


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