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How would you patch this?

Oct 22, 2014
14,950
CAL 35 Cruiser moored EVERETT WA
the transom being plenty strong, even with a big hole cut out of it.
Transom on your sailboat is designed to hold the hull out at the designed shape. It also stops water from entering the boat when the following wave crests and breaks on the transom. Waves have surprising force that a proper transom must hold back or in the case of an open transom designed boat the wave enters and then drains back out.

With the hole you have created a place of entry and no exit. If you just repair with a "thin skin" of glass and resin you put the boat at risk of inundation by an ill timed wave. Of course if you never take the boat out of the bay or only sail in gentle breezes, you need not worry.
 
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Likes: ggrizzard
May 17, 2004
3,208
Beneteau Oceanis 37 LE Havre de Grace
Since I retired from the boat repair business
Not to :deadhorse:, but the math for a boat repair business might be different than for a first time DIY repair project. The size of this repair is what, about a quart of resin? The difference in price between a quart of polyester and epoxy is a whopping $25. It’s not like a business doing repairs with gallons upon gallons. A first time DIY-er might spend, say, 16 hours on the repair, fairing, and painting? In that case I think it would be worth the extra $25 to worry less about how to make sure to get a perfect secondary bond. If the polyester doesn’t work out for any reason redoing it is going to hurt a lot more than the extra $25.

Also, the shelf life of epoxy is lots longer, so any that goes unused for this project can be used for whatever the next one is in a couple years. Polyester might be expired by the next time a repair need comes up. In a repair business with a constant material turnover that’s less of a concern.
 
Jan 1, 2006
5,701
Slickcraft 26 Greenport, NY
@souzag818. Maybe your response was a bit bellicose for this forum. You've got a lot of experience which would benefit members of this group. Please hang around. Disagreements are the currency of this realm. It's not a bad thing.
From your view, based on your experience in the business, time is money. So the faster to a solution the better. Other people here are DYI and looking for a solution without regard to time. It's another mindset. Try to embrace it. Have you ever done a repair and wished you didn't have a customer breathing down your neck about cost? How would that change how you would approach a repair? It's worth discussion.
I sail on a modified Seafarer 23 on which the owner cut the skeg and rudder off, hung a rudder off the transom and cut a slot on the transom to allow for the tiller travel. That was thirty years ago. He has collected a lot of trophies since. There was a saying, "If you can see him, he is beating you!"
Just saying, there's room for different opinions.
 
Oct 22, 2014
14,950
CAL 35 Cruiser moored EVERETT WA
There is a reason when doing a layup on a large hole you use a backing plate. The plate provides a smooth surface to layer against.

You need to be careful to get the fiberglass cloth fully saturated with resin.

If the back plate is not there to provide support after the fiberglass lay up then you need to spray the plate with release agents. That way you will be able to pull the plate away from the cured glass.
 
Jul 18, 2020
36
Tylercraft, O'Day T-26, 25 Lake Michigan
There is a reason when doing a layup on a large hole you use a backing plate. The plate provides a smooth surface to layer against.

You need to be careful to get the fiberglass cloth fully saturated with resin.

If the back plate is not there to provide support after the fiberglass lay up then you need to spray the plate with release agents. That way you will be able to pull the plate away from the cured glass.
What you see here is a layer of tape as a backing plate and then behind (inside the boat) is a board I had pushed against the tape. Yes, it's not perfect but it isn't without any backing - had that been the case I think the dimples would have been way worse.

It's true, I do need to saturate the cloth more. Hopefully it's not too late to wet up some of those areas/add more layers
 
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Oct 22, 2014
14,950
CAL 35 Cruiser moored EVERETT WA
a board I had pushed against the tape.
Ideas... My thinking is that the backing board would be as stiff (no flex) as the area being repaired. I would bolt or screw the backing board to the transom. Sure there would be bolt holes, but they can be easily filled after the job is complete. I would also place pressure against the backing board in the middle so that I can saturate and also press against the glass cloth to smooth the resin throughout the 1st patch layer and all additional layers. You are going to have a lot of layers.

I recently watched Andy from Boatworks Today discuss the approach to laying the glass over a hole. He chooses to lay the smallest to largest patch layers over the hole. Theory is that each of the patch layers is in contact with the hull (as the patches grow each successive layer over laps the last and is attached to the edges of the hull which you ground back). This provides the strongest bond to the hull and all of the patches are attached to the hull. If you do the opposite the only layer attached to the hull would be the first one.