Pat that just made me depressed. 9 layers of 1700 to reach 1/4". I don't see that happening for me.

Thick is not necessarily strong and vice versa.

You are using 1700 which has no mat so it wont be as thick and you are using epoxy (I have been very happy w Raka) which is the right answer for biaxial without mat. I used alternating layers of 1708-1808-1708-1808-1708-1808 on the inside of my 1.5" thick Coosa core and it was almost too thick and caused fit problems. Plus it was heavier than I needed and expensive. I wish I had used glass without mat (1700 or 1800) as it would have been lighter, cheaper (much less resin), thinner and almost as strong (mat is not strong but it provides a good adhesion layer and separates the biax layers; kinda like core).

You should do a small test layup - maybe a foot or two square on something like cheap 1/4-3/8" plywood if you want to understand how strong the glass is. Rotate alternating 1700 layers by 45 degrees for a more uniform directional strength. Jump up and down on it and watch the plywood separate if/when you finally get it close to failure - that's one reason you are using Coosa. 6 layers of 1700 is ~0.180(vac layup) - ~0.20(hand layup) and scary strong. A 1.5" core separating the inner and outer layers is like an I beam with strength in all directions.

Thanks Pat. I know it is strong, I only worry about the thickness for the motor mount bolts. The DF300 is 610 lbs, I thought I needed thickness to resist the bolts trying to pull through.

Just got back to my room from the Arlington Cemetery visit and what do I see?? A 300 hp Zuke free for the taking??? :)

Add 3-4 layers where the motor mounts - not the whole transom. :D

And put a Honda box over that motor so Don thinks it weighs about 900 lbs

Transom is in. I went with 4 layers of 1700. When I build the splashwell/transom knees I'll run another layer or two of quadraxial in the center 1/3 of the transom to provide thickness for the motor mounting bolts. Attachment 14979

I`m putting Ficht stickers on the skinny girl`s OP`s.
Those scumbags from Miami will drive right by.

Or paint 'em gray and put HPDI on 'em. It's like a "Force Field".

Maybe a Wish You Were Here album print on the back???
Fire ... dut dut dut.

You have not lived until you have seen a Ficht bomb lose their injectors and launch
a cowling a hundred feet in the air...

Soros is such a POS. His engineers told him not to launch them...
Many generations of hard working shops lost everything to that
asshole.

Your using two 3/4 cossa boards and then 4 layers of 1700 and your worried about bolts pulling threw? I don't think you need to worry.
I have seen too many heavy outboards out there bolted up with four bolts with small washers on two 3/4 layers of pine bc grade exterior ply that only had a few layers of matt only on the back side. Some how they seem to not fall off into the drink.
Yours seems to be well done and if you use large fender washers or large square washers like use in the electrical field on power poles and strut hangers to spread the load out some you will not have an issue.
On my 20's bracket transom ear I used 4"x1/4" anodized aluminum flat bar to help spread the load of the outboard bolts which is over kill.
You can even take the 4" flat bar and cut 4x4 squares out and use them to back the bolts as washers to spread the load out but that coosa is tough stuff and you shouldn't have much compression issues with it.