Transom rot: repair or replace

"Clamping board" is the term I was looking for (I wrote "Engine support"). Yes, I will look into glassing around/over the edges , the hull sides are wooden planks but at the rear of the boat they have become very thin.

 

In order to glass around the edges; you will need a radius of 1/4" minimum. You may find glass taping the edge easier and then using peelply. If you wet the peelply well; you can see air voids. Tape works if needed as well. It also helps to hotcoat the edges before laying the tape. Then after tapes cure; you would lay a single piece over the transom and neat coat over it to blend the tape hump. It will only be visible to a trained eye.

 

Also, use heavier glass on the inside margin. Take a closeup pic. I will tell you what I would do then.

 

The problem is that you have a double planked boat. We don't know if the planks were glued to each other or if there is a layer of cloth between them. Where the "ends are getting thin" the wood has rotted away, there is no amount of epoxy repairing that regardless of how the boat is planked. Sure you can put the transom in, run a fillet of epoxy and put fiberglass tape over, but it's just a bandaid. If the planking is not sound wood the rot will just spread.
I also don't see any scarphing on the replaced section of the ribs, just butts, that is wrong and will not hold.

 

Rumars has a valid point. We need to know what you did here. You cannot leave any rot and removing all the rot may result in too little surface to bond the transom to properly.

 

These butts are not right. You can repair your repairs...

I will finger sketch the way I would try to, but it may be a little unconventional...

 

I think you can undercut the patches you installed with an oscillating tool and overcut the old frame.

Assuming the old frame is 12mm thick; your scarf would be 8x12 or say 9cm. And the undercut of the new piece same. Then you can piece in. This picture is not to scale. The overall length of the repair piece on each butt you did wrong would be 18 cm or so....might be easier to remove the repair you did wrong...or...

An alternative would be to glass over the butts on the top of the joins something like two pieces of 1708 on each join one 4" long and other 3" long in that order. Sort of unconventional, see what Rumars says..

 

If you glass over them; make sure to prewet the wood and allow the epoxy to go to gel time or the old wood will drysuck your tapes and they will bond poorly

 

I see three ways to do this boat:
1. Quick and dirty. Cut the last few centimeters of the boat, fix the transom to good wood.
2. Normal repair: scarf in new plank ends.
3. Restauration: remove planking, clean, glue the two layers together with epoxy. Sounds complicated but it's not, only time consuming.

 

3M 5200 has no place in this repair. Much of the strength of this boat comes from attaching the transom to the relatively flexible skin. The skin gets it's stiffness from being rigidly attached to the stiff transom. 5200 is a FLEXIBLE adhesive. if you attach the transom with it, it will allow flexibility between the skins and the transom. What you have from a stiffness standpoint is only the screws because the 5200 allows flex and the screws will work in the skins and wallow out because that's the only thing holding this together. Basically from a stiffness standpoint you have to assume that the 5200 is not there because it flexes and the screws don't. If you try to fiberglass over it, the glass will tend to crack unless the glass is really thick. If you've glued the transom in with 5200 you'll need to essentially make some kind of doubler to stiffen that joint or it's going to crack and eventually let water in and you'll have a rot problem later.

 

oof dah

I missed that he did that.

He is gonna need to cut that out now.