Transom Thickness Question

cmezzino

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I was reading a this and another thread regarding I/O transom thickness. I see all the data in the thread that says min 2” and max 2 1/4”. My question is where is that data actually? I searched and searched and cannot find anything. I have the factory Volvo-Penta service manual for my boat and can’t even find it in there.

I understand that if the transom is too thin, the input shaft could bottom out in the coupler. What if it’s too thick? Will the shaft not go in far enough?

I’m replacing the transom in my 97 Glastron GS 205, Volvo Penta 5.7 GS PLKD and right now I’m at 1 3/4”. I’m trying to decide whether to build up with glass or add another 1/4” doubler with glass in the center.

Thank you you for any help that can be offered.
 

GA_Boater

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cmezzino Moved this post out of an ancient, inactive thread so you get some answers.

It's in the V-P section because the thickness is specified by V-P. I don't know the exact range for V-P, but the 2" to 2 1/4" numbers are what Mercruiser recommends.
 

Scott Danforth

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1/4"-5/16" of outer hull, 1-1/2" of wood, 1/8" - 3/16" inner transom skin

that gives you 2 to 2-1/4" transom thickness.

specified in the rigging manual.
 

Bondo

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What if it’s too thick? Will the shaft not go in far enough?

Ayuh,..... Welcome Aboard,..... Now ain't this soooo much better than a pm,..??......

The less shaft in the coupler, means less spline is engaged, so torque limits are lower,......
If 1 inch is engaged, yer at 1/2 the designed strength,.....
 

cmezzino

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Thank you all for the replies and thank you for moving this thread. I was afraid the old thread was, well...old.

So, if this 1 3/4" is too shallow, will the shaft bottoming out in the coupler be obvious when I go to put it back together during a test fit? Or...if it fits together with no obvious bottoming out and all seems normal, would you think it's okay at this thickness?

Rather than use two 3/4" pieces for a total of 1.5", there are three layers of 1/2" glassed in between for a little more than 1.5". So that, plus the thickness of the hull as manufactured is where I'm at.
 

Bondo

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So, if this 1 3/4" is too shallow, will the shaft bottoming out in the coupler be obvious when I go to put it back together during a test fit? Or...if it fits together with no obvious bottoming out and all seems normal, would you think it's okay at this thickness?

Ayuh,.... It's days of work if you put it together, test fit, 'n it binds, back to the bare hull to add a shim,......

I'd do the shim Now, myself,.......
I hate buildin' backwards,.....
 

Scott Danforth

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I agree, your over thinking it

2 layers of 3/4" ply glued together with tite-bond III

PB the edges, make a fillet

Tab in place with a layer of CSM and two layers of 1708

then skin the inside with a layer of CSM and two to three layers of 1708

you will find that your final thickness is between 2 and 2-1/4"
 

cmezzino

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Update... I ended up needing 3/8" so I glassed in another doubler and achieved an overall thickness of right about 2 1/16" all the way around. Parallelism checked out from top to bottom and side to side all within spec.
 
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