Question on transom repair

[Fishermark]

Just bought a project boat - 1985 Wellcraft 192 American. It has a Mercruiser I/O. The transom was rotted out, so I tore it down and removed the old top layer of fiberglass and rotten wood.

I have read the various posts and watched many of the videos... thanks to those who posted them, they are helpful!

I have run into a bit of a problem, and not sure how to handle it. When I removed the old wood, I noticed that there was a big ridge on the back of the fiberglass. It looked liked they had glassed in the wood at two separate times. There is about a six inch wide section across the top of the transom that is thicker than the rest. In fact, if I take a straight edge and run it up from the bottom to the top, the top six inches is flat against the straight edge. The thickness around the keyhole also goes from thinner at the top to thicker at the bottom.

What's the best way to deal with this issue? Any thoughts? Here's a couple of pics and a drawing to show what I mean.

 

[jbcurt00]

Re: Question on transom repair

Since the taper all appears to be above the keyhole, I'd guess that the dimension thru the keyhole necessitates plywood of a certain thickness to make the total dimension thru the keyhole 2-2.25". The area above the taper did not require plywood that thick. To allow a smooth transition from thick to thin, the plywood was tapered. This allowed the fiberglass to layout smooth & transition and look 'right'......

Maybe ^^^??

 

[Fishermark]

Re: Question on transom repair

I don't know why they did it that way... and since this is my first attempt at restoring a transom I don't have enough experience to say whether or not it is unusual. My problem is if I simply put a doubled up section of 3/4" plywood up to the ridge, then it will vary in thickness at the keyhole - by nearly 1/4" from top of keyhole to the bottom. If I put one large piece of doubled up plywood - big enough to cover the entire transom, then I will have to deal with the gap.

I've seen the "peanut butter" fiberglass... is that a viable solution? It seems like it would take a lot of fiberglass resin to fill the entire gap.

 

[ondarvr]

Re: Question on transom repair

The only thing you need to be concerned with is the mounting surface for the outdrive, get it right and you're fine. Any other unevenness is of no concern unless it bothers you.

You don't need to fill it to glass over it, just eliminate any sharp radius so the glass can easily follow the contour and not leave air bubbles.

 

[Bondo]

Re: Question on transom repair

The only thing you need to be concerned with is the mounting surface for the outdrive, get it right and your fine. Any other unevenness is of no concern unless it bothers you.

You don't need to fill it to glass over it, just eliminate any sharp radius so the glass can easily follow the contour and not leave air bubbles.

Ayuh,...... Ditto,.... Yer plywood transom piece should follow the flat plane of the keyhole,...

If the Entire transom of the hull ain't covered, So What,....

If ya put a separate piece across, above the flat plane of the keyhole, So what,...

The flat plane of the keyhole is critical, anything else can be shimmed, peanut-buttered, whatever,...

That's the Beauty of wood fiberglass composites,...

 

[Fishermark]

Re: Question on transom repair

Again, the problem is that if I simply put a sheet across the flat plane of the keyhole, then the two surfaces will not be parallel. They will be flat, but not parallel. It will be thinner at the top of the keyhole than the bottom. I can measure more carefully, but it appears that it will be between 1/8" to a 1/4" thinner at the top. I don't know the allowable variance for that. If that is within parameters, then yes, I am good to go.

 

[ondarvr]

Re: Question on transom repair

You were given The dimensions in jbcurt00,s post above. There are many options in how you get there, fill, sand, shim, etc, every situation will be slightly different. The inside and outside surfaces need to be parallel.

Just make it a uniform and solid clamping surface and you're fine.

 

[Bondo]

Re: Question on transom repair

Again, the problem is that if I simply put a sheet across the flat plane of the keyhole, then the two surfaces will not be parallel. They will be flat, but not parallel. It will be thinner at the top of the keyhole than the bottom. I can measure more carefully, but it appears that it will be between 1/8" to a 1/4" thinner at the top. I don't know the allowable variance for that. If that is within parameters, then yes, I am good to go.

Ayuh,.... I guess I misunderstood,...

Yes, it's Most Important that the area where the transom assembly attaches is flat, 'n true, over the whole area,...
Equal, All around at 'tween 2", 'n 2, 1/4",....

I generally shoot for an even, flat true 2",....
I even made a "Go-No go" gage out of a piece of scrap aluminum,...
Basically a l_l, with fingers long enough to reach, 'n check All of the area the transom assembly touches,...

 

[jbcurt00]

Re: Question on transom repair

The dimension thru the keyhole necessitates plywood of a certain thickness to make the total dimension thru the keyhole 2-2.25". It can fall anywhere in that range, but it does need to be parallel to the exterior transom.

{edited to be more relevant**

The interior face also needs to remain flat and perpendicular to the centerline of the boat:

Parallelism

If you ignore the changing thickness thru the taper, and run the plywood across the 'void' will the interior face remain parallel to the exterior transom skin? If so, if thru the keyhole, the dimension falls in the 2-2.5" range, you can fill the void w/ PB when you are applying PB to bed the transom. There will just be more PB in the void then elsewhere. Don't over tighten your clamping system, you don't want to deflect the transom skin or the newly made transom plywood into the PB filled void.

Make it hairy PB w/ the addition of 1/4" chopped strands. You can make your own by cutting up scraps & leftover pieces of CSM & 1708.

 

[JASinIL2006]

Re: Question on transom repair

{edited to be more relevant**

The interior face also needs to remain flat and perpendicular to the centerline of the boat:

Parallelism

If you ignore the changing thickness thru the taper, and run the plywood across the 'void' will the interior face remain parallel to the exterior transom skin? If so, if thru the keyhole, the dimension falls in the 2-2.5" range, you can fill the void w/ PB when you are applying PB to bed the transom. There will just be more PB in the void then elsewhere. Don't over tighten your clamping system, you don't want to deflect the transom skin or the newly made transom plywood into the PB filled void.

Make it hairy PB w/ the addition of 1/4" chopped strands. You can make your own by cutting up scraps & leftover pieces of CSM & 1708.

This is exactly what I did with mine. I applied a thick layer of hairy PB to bed the transom, and then I clamped until I hit the desired thickness. (The extra PB that oozed out just became fillets.) I was worried about the fiberglass hull around the keyhole deflecting as I clamped down on it, so I make a shield out of plywood to so I wouldn't have to deal with any unevenness caused by one clamp or another being a little too tight. If you look at posts #53-55 in my resto thread (see link in my signature below), you can get an idea how I did it.

I had the good fortune to get help from some of the same folks who are commenting above. I am glad I listened to them...

Good luck,
Jim