Coosaboard for transom

[ProfzrX]

I was considering using Coosa board for my stringers and transom. I'm building a PH22 and will be powering it with a Pro XS 250 hp. Has anyone on here used coosa for their transom with a higher HP like I am planning? If so how has it held up? I plan to use 1 1/2" coosa for both. Thanks for any advice.

[fallguy1000]

Use the bluewater 26# minimum.

Check with Mertens for glass schedule.

It is the only product I'd use for a high hp boat.

[ProfzrX]

Thanks fallguy. I planned on using bluewater #26. A local boatbuilder (Mirage Custom Boats) advised me to sandwich (2) 1" pieces with 1708 biaxial, then use two layers 1708 biaxial inside and out. Also, build transom knees into the stringers.

[fallguy1000]

Thanks fallguy. I planned on using bluewater #26. A local boatbuilder (Mirage Custom Boats) advised me to sandwich (2) 1" pieces with 1708 biaxial, then use two layers 1708 biaxial inside and out. Also, build transom knees into the stringers.

1708 leaves very close to a perfect 1mm glue joint. There is another way to attain it, but the 1708 is a good idea. Pay attention to the wetout of the core. You must roll epoxy on both cores.

If you are able; 9-10" of Hg under vacuum is ideal. For a single part; you might get away with a really good shop vac.

The designer is the one to specify the layup.

[cvincent]

I used a different product the aquaplas III foam core and Jacques advised to use 120oz on each side for a 115hp. No problems so far with about 100hrs of run time and trailering.

Check with Jacques, but I would go no less than 5 layers of 1708 on each side with the hp you are considering.

[fallguy1000]

I used a different product the aquaplas III foam core and Jacques advised to use 120oz on each side for a 115hp. No problems so far with about 100hrs of run time and trailering.

Check with Jacques, but I would go no less than 5 layers of 1708 on each side with the hp you are considering.

Yes. I, too, believe he is light. A lot depends on other structures; knees, motorwell, etc. But I would think more in the neighborhood of 85-150 ounces of glass appropriate for the 250hp.

[ProfzrX]

Thank you for the advice. I sent Jac a message asking for his recommendation and ask if he would respond via this thread. Thanks again.

[fallguy1000]

...per side 85-150 ounces is 5 lauers of 1700 or up to 6 layers of 1708..

[jacquesmm]

I would never specify one layer 12 oz. or even 1208 for the transom of a 25 footer. There must be a misunderstanding there.
Is this the CS or CX25?
Please read the foam notes. I see a total of 9 layers there specified there, with various fiber orientations.
Do you have the file titled foam notes? All the foam specs are in there.

Please check that you did you use those specs for all other parts and use a high performance resin like Silver Tip.

[jacquesmm]

It looks like there are 2 questions in thread: foam specs for the CX25 and foam specs for the PH22.
The specs are different.
Let's separate the two discussions.
Do not build a foam sandwich hull with the plywood glass specs, it will fail.