Inside transom Skin thickness

[LegacyT]

Soo my project Baretta is coming together. Got the old plywood transom, bed stringers and Balsa coring out. Used bluwater 26, Coosa's stongest stuff. Reglued it in with west epoxy. Now the question is how thick should the inside transom skin should be. The orginal was ~1/8" csm. Not very tough and the edge around the transom plate cutout wasnt even glassed in. I plan to use 18 oz biax with epoxy, one layer with resin builds 1/32". I also sleeved the mounting holes aswell. The total thickness is 1/2 outer original skin, 1.5" Coosa, and inside skin? As is I gotta admit this seems way tougher than what was in there before!

 

[Bondo]

Re: Inside transom Skin thickness

Soo my project Baretta is coming together. Got the old plywood transom, bed stringers and Balsa coring out. Used bluwater 26, Coosa's stongest stuff. Reglued it in with west epoxy. Now the question is how thick should the inside transom skin should be. The orginal was ~1/8" csm. Not very tough and the edge around the transom plate cutout wasnt even glassed in. I plan to use 18 oz biax with epoxy, one layer with resin builds 1/32". I also sleeved the mounting holes aswell. The total thickness is 1/2 outer original skin, 1.5" Coosa, and inside skin? As is I gotta admit this seems way tougher than what was in there before!

View attachment 227581

Ayuh,.... I donno what the Volvo spec's are, but Merc wants 2", to 2, 1/4" total thickness,...
True, level, flat, 'n even all 'round, where the plates set,...

I imagine Volvo would be the same,....

Total thickness determines the drive's spline engagement depth,...

 

[zool]

Re: Inside transom Skin thickness

The older VP's don't use an inner transom plate/gimble so the tolerances aren't as specific as with the newer VP and Mercs...The shield bolts will allow for 2 1/2"+ thickness and the parallelism doesn't need to be as exact. I see you have the bevels already cut for the steering fork area and trim cylinders on the lower sides..which is important for future service.

Heres the manual for torque specs, if you don't already have it.

http://www.marinemechanic.com/volvo/Volvo Penta Workshop Manual.pdf

 

[LegacyT]

Re: Inside transom Skin thickness

Everything should be identical dimesion wise as the transom plate is mounted to the outside which hasnt changed at all. Mounting holes are drilled in the same spots. Only difference might be a in total transom thickness which only affects the studs from the transom plate, which are plenty long enough. I'm just wondering about skin thickness from a structural standpoint... Original was 1/16-1/8 inch uneven csm. So Is it safe to assume that 2 layers of 18 oz biax with epoxy totalling an even 1/16" is plenty strong?

Thanks,

 

[greenbush future]

Re: Inside transom Skin thickness

Wouldn't that part of the strength be gained through tabbing beyond the I/O plate? That's how it's accomplished in traditional transom replacements I think, tabbing to the sides of the boat as well as tieing into the stringers and sole. How was it set up originally? What does Coosa recommend?

 

[ondarvr]

Re: Inside transom Skin thickness

Transoms are rarely done correctly when it comes to the skin thickness on either side. The rule in composite cores is to try and keep both skins equal in thickness and type of glass, this helps ensure the laminate won't warp and that one side doesn't fail be fore the other (one side being significantly thinner reduces the strength dramatically).

But...since the original was just a very thin skin of CSM with polyester resin and it survived all those years, it's not going to make a difference what glass you use with epoxy, it will be stronger, hold up better and last longer.