OEM Mercruiser for bravo transom assembly installation --- transom thickness a min of 2 in max 2.25 in.

2.75 thick transom - stock bravo transom assembly and stock inner plate installed --- one could not install the nyloc nuts properly on the studs.

Composite transoms always seemed that way to me to, like they shudder when you go into gear.

The transom on my Pantera is 2.75 thick. From Pantera

Now I feel bad about having the transom filled with coosa. But I am hoping that the experiences you have had are with another type of coosa meaning not a solid 2 inch thick piece maybe 3 layers of 1/2 inch coosa board?I have 2 in solid with 4 layers of glass behind the coosa to stick it a.But if this is a mistake it is better for me to pay more to have the work re done.This is sad because I listened to someone say this was the way to go , someone who supposedly knows and more Fiberglas on the front side.

everyone on this forum thinks coosa is good for transoms
https://www.thehulltruth.com/boating...osities-2.html

Also I heard that formula and Outerlimits uses coosa in the transoms from the factory

you will be fine, it really is a great product and in most cases you'll never have an issue. My cases were race boats and run very hard, i personally still prefer a quality marine ply for transoms and stringers. I run my stuff very hard at times and just dont care for the way composites flex, especially the solid sheets thats why i laminate in layers of half. In your case with your cat my only concern would be what resin they used and that it was properly installed. With composite panels you really have to use an advanvced system, vinylester or epoxy. Poly does not bond well and elongation is far to low for it to bond to the foam proper. This is actually one of those topics where there are many sides, most guys will argue the benifits and i agree with nearly all of them. My only reservation is with high load high performance applications, we can experiance some issues over time, high performance boats can be a bit of a special case. I really would not worry to much about your boat, get 'er done and enjoy

most factories do use it now and its the only way to go in this day and age in new boats. For my application and for how we run these things (or how i do anyways lol) i still prefer three layers of half. The other thing a lot of guys dont realize when doing stringers in composite is you can no longer just through bolt engine mounts. You have to "shoulder" the mount somehow to take the shear load off the bolts. They will oval and shift quickly in the rough water offshore environment.

for Mercruiser ? and using a STOCK bravo OEM transom assembly with stock mounting stud lengths ? Basically anything 2.5 and up for transom thickness, the stock installed studs would be too short - one would have to install longer ones in a stock Bravo / Alpha transom assembly. And with any thicker transom, if the stock exhaust Y pipe was used, that would throw all that out of placement as well.

Info from OEM Mercruiser engine installation guide for Bravo and its the same for alpha's. I had to search for this info as how I could post it up here on oso. Its fairly current info below in the link..

Just saying - Back in the day we would have to install in new boat lines engine(s) & drive packages. New hulls without the transom even cut as the dealers picked what engine packages were going in from Mercruiser - OMC - VOLVO - Yamaha - sterndrives.

https://forums.iboats.com/filedata/fetch?id=7077691

Well that sounds better if it the boat can still be usable.But I appreciate your help and comments because there are not many sources with good information and less about performance boats.
I want to make sure with you,The boat is with 4 layers of glass starting at the back where the ground down fiberglass skin is and there is a 2 inch board of coosa and then there will be another 4 layers of glas hopefully will be about 2.5 thick.The drives are #6 dry sump

Looks like they need to grind it alittle cleaner , and more for some wider tabing.

like i said you will be fine, its a great product. My biggest concern would still be with resin, fabric choice and that its being installed properly. the four layers on each side are gonna help stabilize the surfaces and help prevent compression issues.

I'm going to add this for composite vs wood. Long ago, or so it seems, I was a manufactures rep in the ski/snowboard industry. At the time I worked for Atomic Snowboards. We used a wood core in all of our boards. At the time Rossignol started using the THC core. This was a foam core with Kevlar and carbon in it, very similar to Coosa board. For the average person this core would work just fine. I myself hated it, it felt dead and un-responsive, but it was a little lighter. Put this same core under an olympic athlete, and good luck. When Bode Miller went from Fisher to Rossignol he was snapping ski's. I don't think he was able to finish a run with out the skis breaking, I believe in the end, they ended up getting him wood cored skis. That was the last year he used Rossignol, the next year he was back to wood core skis and Atomic.

As Dave has said, composite has its place, but high performance, high load is not one. Wood is made to flex and hold its strength, it is a tree after all. Foam cannot take constant flexing and hold up, and least none that I've seen.