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How would you patch this?

Jul 18, 2020
41
Tylercraft, O'Day T-26, 25 Lake Michigan
There's a hole where the previous owner had placed an outboard. I want to close it back up. Would you lay glass over the whole area or use a hybrid of wood and glass? The fiberglass in the area only seems to be about a half inch thick so the wood almost seems like a waste of time. Thanks!
 

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May 27, 2004
1,676
Hunter 30_74-83 Ponce Inlet FL
There is a product called "G 10" that might be perfect for that repair. It's factory made fiberglass
sandwich board/sheet.
If you look up "Boatworks Today" on Youtube, you will see a boat re-builder who has other methods, with details, including how he is currently rebuilding a Bertram transom with foam board and fiberglass.
 
Jan 11, 2014
7,498
Sabre 362 113 Fair Haven, NY
A few months ago, Andy Miller from BoatWorks Today demonstrated how to patch something similar. You can find his channel on YouTube and Patreon.

Go to the West System Website and download their manual, its a free download, the manual will also give you good advice on how to patch the hole.

The Readers' Digest version: Grind out a 12:1 bevel on the outside or a 6:1 bevel on both sides and layup glass on both sides to fill the hole. Then sand, fair, and paint or gelcoat. Not hard, but a bit time consuming.
 
Jan 1, 2006
5,835
Slickcraft 26 Greenport, NY
It doesn't look like there is a wood core in that transom so I wouldn't be inclined to add one. I agree with dlochner about the repair. Conceptually not complicated but pretty hard to achieve excellent results particularly in getting it flat.
 
Oct 19, 2017
6,818
O'Day 19 Littleton, NH
Conceptually not complicated but pretty hard to achieve excellent results particularly in getting it flat.
A wood core would only be necessary as a form to help get the shape you want.

It looks like you could lay a piece of 1/4" plywood against the inside and glass over to repair the hole, then remove the wood. Of course, if you have a piece of prefabricated sheeting, go with that, or will save you work.

-Will (Dragonfly)
 
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Aug 2, 2009
450
Catalina 28MKII Muskegon
How about a big sticker?

Actually, I'd agree about backing it with wood. Then, building up the layers as needed. And, definitely bevel the edges so the whole layup has something to hang onto. I don't envy you getting the end result to look completely seamless. That's going to be some fussy work.
 
Jan 11, 2014
7,498
Sabre 362 113 Fair Haven, NY
Any wood used is only needed for a temporary backing plate.

If I was to do this job, I think I would work from the outside with a 12:1 bevel and make a backing plate out of 3 or 4 layers of 1708 cloth and then attach that to the inside with some thickened epoxy after it cured. This will give you something firm to work against.

Then following the instructions on West System website, I would lay up multiple layers of glass, again using 1708 glass. The outermost layer would be the mat side of the 1708 and it would be a little proud of the transom. Once everything is cured and solid, the real fun begins with sanding, oh glorious sanding. Bring the glass down even with the gel coat. and then begin to feather the existing gel coat. You'll end up with a big dimple with both the patch and the original glass exposed. Then fair, and fair and fair. Eventually, it will be smooth enough.

When it is smooth enough, time to put on the gel coat and sand and buff it out.

A common assumption of first time glass repairers is that only one coat of fairing compound is needed and if it needs more, then you screwed up. This is not a good assumption. It will take several coats of fairing compound and the creation of a lot of dust before the hull is ready for gelcoat. Also, West System and microballoons can be used for fairing, however, this often leaves pinholes. A compound like Total Boat Total Fair or Interlux Watertite fairing compound will leave a smoother final finish.

Get a good sander and lots of sandpaper. :beer:
 
Jul 18, 2020
41
Tylercraft, O'Day T-26, 25 Lake Michigan
How about a big sticker?

Actually, I'd agree about backing it with wood. Then, building up the layers as needed. And, definitely bevel the edges so the whole layup has something to hang onto. I don't envy you getting the end result to look completely seamless. That's going to be some fussy work.
Maybe I haven't made a name for myself around here yet, but nobody envies anything I'm doing @Siamese
 
Jul 18, 2015
42
South P10 Pugetopolis
Well, working from outside means no itching powder inside the boat.

When I added a plotter to my boat I removed the old depth finder from the cabin wall. Since I already had the interior stripped for a rebuild, I filled the hole from the inside; mounted a piece of ply with generous release agent so my patch matched the curve of my house. Saved some time.

In your case, working from the outside makes sense. If your planning to add a stern ladder over the hole it might make sense to obtain some 1/4"" coosa board for your backing, and leave it in place to provide a backing plate for the new ladder.

West system website is a great resource.

Be sure to take some pics as you progress, it will help the next person.
 
Nov 17, 2018
10
Wauquiez Pretorien Washington
No need to use epoxy. Polyester resin would be plenty strong and cheaper. Definitely 12/1 bevel, bi-axial glass, and something for a temporary backing, like a piece of Formica, or plywood with wax paper. And all the usual precautions- dust masks, gloves, glasses...







p
 
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Jan 11, 2014
7,498
Sabre 362 113 Fair Haven, NY
No need to use epoxy. Polyester resin would be plenty strong and cheaper.
When the esters, poly or vinyl can chemically bond to the substrate they are strong. However, when it comes to mechanical bonding, epoxy beats the esters hands down.

For a small patch or a non-critical area, polyester might be an acceptable choice. For the transom, a stronger bond would be better.

Cheaper is seldom better.
 
May 27, 2004
1,676
Hunter 30_74-83 Ponce Inlet FL
I'm perplexed as to why one would advocate the use of plywood in the OP's transom rebuild
when more durable materials are available? Did any of you have a bad experience with G 10 or the foam board that Andy on Boatworks Today is currently using?
 
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Nov 17, 2018
10
Wauquiez Pretorien Washington
When the esters, poly or vinyl can chemically bond to the substrate they are strong. However, when it comes to mechanical bonding, epoxy beats the esters hands down.

For a small patch or a non-critical area, polyester might be an acceptable choice. For the transom, a stronger bond would be better.

Cheaper is seldom better.
The transom is obviously strong enough, especially with a big hole cut out of it...Any additional strength would be moot. At this point you're just patching a big hole. And more so if you plan to gel coat over it.
 
May 17, 2004
3,278
Beneteau Oceanis 37 LE Havre de Grace
The transom is obviously strong enough, especially with a big hole cut out of it...Any additional strength would be moot. At this point you're just patching a big hole. And more so if you plan to gel coat over it.
The problem isn’t strength, it’s getting the patch to adhere properly and durably to the existing fiberglass. Epoxy will make that bond better than polyester over an already cured polyester surface.
 
Jan 11, 2014
7,498
Sabre 362 113 Fair Haven, NY
The transom is obviously strong enough, especially with a big hole cut out of it...Any additional strength would be moot. At this point you're just patching a big hole. And more so if you plan to gel coat over it.
Strength is an issue if the an outboard is going to be mounted there.
 
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Nov 17, 2018
10
Wauquiez Pretorien Washington
Strength is an issue if the an outboard is going to be mounted there.
"if"...being the key word. The original transom, which would have been polyester resin, and more likely roving and chopped strand, not biaxial cloth, would have been strong enough to mount an outboard, with an appropriate backing plate. With poly and biaxial, at the least, the original strength would be there, it can be gel coated or painted, and the repair could be finished quicker.
 
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Jan 11, 2014
7,498
Sabre 362 113 Fair Haven, NY
"if"...being the key word. The original transom, which would have been polyester resin, and more likely roving and chopped strand, not biavial cloth, would have been strong enough to mount an outboard, with an appropriate backing plate. With poly and biaxial, at the least, the original strength would be there, it can be gel coated or painted, and the repair could be finished quicker.
The strength of fiberglass is a combination of the resin and the cloth. Since this is a case of secondary bonding, i.e., bonding to an already cured hull, the strength of the secondary bond is vitally important. Polyester resin or Vinylester resin do not have the secondary bonding strength that epoxy has. Mounting an outboard will add a lot of stress to that part of the hull. The builder knew that, that section of the transom is about twice as thick as a similar area on my boat which is 10 feet longer and more than twice the weight. The stresses come from the weight of the outboard levered out over the transom, the kinetic energy that develops from the motor bouncing on the mount, and the torque from the outboard when it is running.

Polyester resin is strong enough in this application if the bonding is primary, i.e., chemical where the polymers link together. This is what happens when the hull is laid up. This repair is not about primary bonding, it is about achieving a strong secondary, mechanical, bond between the new glass and the old cured glass in a high stress area.

A backing plate simply spreads the load out from the bolts and reduces point loading, it does not add to the strength of the transom.

There are places where polyester resin could be used, in places where there is little stress and in a smaller repair, someplace like the interior furniture. But not on a large hole on a transom.
 
Nov 17, 2018
10
Wauquiez Pretorien Washington
SMH...I never said a backing plate added strength. Everyone knows it's only to spread out the load. I stand by my original statement about the transom being plenty strong, even with a big hole cut out of it. There are places where epoxy is the logical, structural way to go, but this isn't necessarily one of them. It's just over kill, and unnecessary expense and time. Boats were being repaired with poly resin for decades, and are still going strong. I've personally extensively modified two of the three sailboats I've owned with polyester resin and biaxial, including changing the transom and modifying the cabin top, and have no signs of problems with secondary bonding on the one I still own. And those modifications were done in 89... You have your opinion, I have mine. Since I retired from the boat repair business, after 35+ years, I don't have to watch a YouTube video to be told how to do a repair in fiberglass, and become an authority, but what do I know...Peace out
 
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