# Transom wood replacement for Grumman



## Fishfndr (Aug 24, 2014)

I'm trying to figure out how to get at the wood board on this 1977 Grumman 3.8 12 ft. aluminum boat. Do I really have to remove the two triangular brackets on the left and right ends, along with all 36 rivets? The problem I foresee is trying to replace those rivets with stainless steel thru bolts, because there is this blue foam insulation running down both sides of the boat, so I can't get behind it to put a nut and washer on there. 

Anybody done this before? Ideas?


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## Ail (Aug 24, 2014)

It looks to me like you will have to remove:

The bolts from the braces
The motor scuff plate
The gunwale end caps

and then you may still not be able to get it because there looks like there is a lip running along the top of the transom you might have to cut off, or bend up.

On my boat the lip was only centered along the middle of the transom so after removing the brace bolts, the gunwale end caps and the scuff board, I could bend the lip up to get the transom wood in or out. I riveted my gunwale caps back on with blind rivets.


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## surfman (Aug 25, 2014)

Is it possible to remove the lower lip or angle and go down with the board instead of up? You will have to remove the braces I can see that but that would be easier and better. Although you could cut off the top cap and then rivet a new one on.


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## Southern Appal (Aug 26, 2014)

I had to remove the rivets for the stern-facing end caps. I left the rivets on the port and starboard side end caps. Removed all the rivets and/or bolts and nuts from the transom lip and bent the lip out enough to tilt transom board and slide it out. Reinforced lip and transom cap with some aluminum angle.


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## Fishfndr (Aug 26, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=364377#p364377 said:


> surfman » 25 Aug 2014, 07:40[/url]"]Is it possible to remove the lower lip or angle and go down with the board instead of up? You will have to remove the braces I can see that but that would be easier and better. Although you could cut off the top cap and then rivet a new one on.



I was hopeful this idea would work, but the bottom lip is riveted in there too, all the way across, and then I'd have to remove all of the rivets for those braces in the middle, which include rivets on the _bottom_ of the boat that I really don't want to deal with. Assuming I have to remove those corner brackets on the left and right corners of the stern, how do I get them back on there with that blue foam in the way? Would pop rivets work? Or have I got to figure out how to take off the foam as well?

What a nightmare. I just can't believe they make this piece of wood so darn hard to replace, since it's of course going to fail at some point.


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## surfman (Aug 27, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=364344#p364344 said:


> Ail » 24 Aug 2014, 18:04[/url]"]It looks to me like you will have to remove:
> 
> The bolts from the braces
> The motor scuff plate
> ...



This looks like the best option, let’s face it if you are going to repair it, it is going to take some work, nothing is easy. But, it really doesn't look that hard. For all the above waterline rivets you can use pop rivets and they do make blind pop rivets too but, the solid rivets are better and not that hard to put in either, unless you can't reach them then you need a buddy to hold the anvil.


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## Fishfndr (Sep 7, 2014)

I just finished this project and I thought I'd share my process and things I learned for the next person who has to do this on a similar boat. I mostly used the instructable at https://www.instructables.com/id/Transom-replament/?ALLSTEPS as a guide.

The first step was to remove the two corner brackets and all 36 rivets. The biggest challenge here was starting a straight hole in the center of the domed rivet head, but good center punching made it not so bad. 


As Southern Appal predicted, I had to bend the lip up to get the transom board out. I spent a long time figuring out how to do this. I tried getting a piece of steel under there and bending the whole thing, but what eventually worked was these special vice grips (thanks to my neighbor). 


I ended up having to bend up the first angle (the tab of metal pointing down when I began) and then bending up the resulting 90 degree angle section by section until the sheet metal was all one plane. I worried a good bit about bending the whole transom out of shape, as it started to bow considerably (with the center protruding like in a convex shape). I ended up C-clamping a 2x4 and piece of angle iron across the back. Not sure if that was necessary, as the whole piece of sheet metal actually became concave after I took out the board. 




The board came out without too much trouble, just started prying with screwdrivers, and then it came out. 


And here's the obligatory, gratuitous shot of the completely rotted out transom board, which was ready to fall apart and had a thriving colony of small insects living in it. 


My board needed to be about 1 7/16 in. I ended up getting nominally 1/2 in. oak plywood and sandwiching three layers together with gorilla clue, per the instructable. For some reason he used pressure-treated plywood, which, as everyone on here says, is a no-no (or perhaps it doesn't matter due to the fiberglassing coming up next, in which case pressure-treated is unnecessary anyway). So I just used high-quality, non-treated oak plywood, I think seven layers per sheet.
By the way, the Gorilla Glue cleanup is much easier if you just chisel off the extra bubbly bits after it dries. Don't bother trying to clean it with a wet towel when wet as the bottle says, the stuff sticks to your fingers and is a pain to get off.

The issue I next worried about was totally not addressed in the instructable, which is the added thickness of coating the board with fiberglass jelly. I was also replacing a piece of masonite that was the motor scuff plate, which I made out of 1/4 in. oak plywood which I was going to fiberglass. Since the thickness of that piece was not crucial, I fiberglassed it first and found out that the fiberglass jelly added about .100 in. 
Since the plywood layers I had glued fitted exactly into the channel at the bottom, I planed the board .100 to accommodate the added thickness from the fiberglass jelly.

I found out that the jelly was much easier to apply smoothly if you put in less hardener than the can recommended (the instructable talked about a pea-sized amount instead of a 3-in. strip). But that does change the curing time from under an hour to several hours. The first layer went on pretty rough, then I did a second layer just to fill in the low spots. An orbital sander pretty quickly took care of the high spots and rough edges. You really need a respirator for both applying the jelly and sanding it. That stuff will make you woozy in short order. 


Miraculously, the board fit in quite well. I had a helper stand to the side to check squareness while I drilled the holes through the transom. Everything lined up well enough.


The next challenge was getting that darn lip back down. This turned out to be a four-step process, using the vice grips, then C clamps anchored onto the bottom channel, 
then hammering with a rubber dead-blow hammer, then C clamps again, applied horizontally this time, to bring the upside-down U back into shape.

Next I replaced the two corner brackets, using pop rivets. I had to drill some clearance behind the ones that were directly above the new board.


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## Fishfndr (Sep 7, 2014)

And here's the finished product. The whole thing took a couple of weekends, with lots of interruptions and some fiberglassing and curing time in between. Should be rock solid for a long, long time.


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## lckstckn2smknbrls (Sep 7, 2014)

What type of fiberglass resin did you use, Polyester or Epoxy? Did you use fiberglass cloth?


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## Fishfndr (Sep 7, 2014)

[url=https://forum.tinboats.net/viewtopic.php?p=365705#p365705 said:


> lckstckn2smknbrls » 07 Sep 2014, 21:17[/url]"]What type of fiberglass resin did you use, Polyester or Epoxy? Did you use fiberglass cloth?


 I used fiberglass resin jelly. https://www.autozone.com/autozone/accessories/3M-1-qt-Bondo-fiberglass-resin-jelly/_/N-260o?itemIdentifier=265315_0_0_

No cloth. Just smeared it on there with a bondo applicator. Took a surprising amount, about two cans ($40) for a 4 ft by 7 in board.


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## lckstckn2smknbrls (Sep 7, 2014)

[url=https://forum.tinboats.net/viewtopic.php?p=365711#p365711 said:


> Fishfndr » Sun Sep 07, 2014 9:09 pm[/url]"]
> 
> 
> [url=https://forum.tinboats.net/viewtopic.php?p=365705#p365705 said:
> ...


It appears to be a polyester resin, without the fiberglass cloth it won't last.


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## Fishfndr (Jun 30, 2018)

[url=https://forum.tinboats.net/viewtopic.php?p=365705#p365705 said:


> lckstckn2smknbrls » 07 Sep 2014, 21:17[/url]"]
> It appears to be a polyester resin, without the fiberglass cloth it won't last.



You were completely right. It has rotted. Glad I at least recorded everything I had to do to replace it because I have to do it again. 

Thinking about using a Coosa board this time.


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## thedude (Jun 30, 2018)

Even if the resin failed how is there that much moisture in the boat? Does it take on much water? My transom board is cut just shy of the floor so it doesn't wick the water should it get in.


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## lckstckn2smknbrls (Jul 1, 2018)

You want to use ACX, BCX, CDX plywood. It's made with water proof glue. Then seal the transom with the old timers formula.


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## Eric3501 (Jul 7, 2018)

Hey everyone, first post after much searching. Possibly in the wrong places as usual...any way, my question is, "what exactly is sealing the Old Timers Way?". I have never heard of this. Please explain. Thank you.


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## CedarRiverScooter (Jul 7, 2018)

Search for 'old timer's formula'

Spar varnish & boiled linseed oil + something else, I believe


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## lckstckn2smknbrls (Jul 7, 2018)

CedarRiverScooter said:


> Search for 'old timer's formula'
> 
> Spar varnish & boiled linseed oil + something else, I believe


The last ingredient is Mineral spirts.


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## Fishfndr (Apr 1, 2019)

In the middle of this re-repair now. The replacement board "sealed" with fiberglass resin jelly was totally rotted, with an even more thriving colony of bugs and grubs living within. Going with the Coosa board this time. My only quandary is what to use for the outboard scuff plate mounting board on the stern side of the transom. I think it was some kind of masonite originally and I tried to seal masonite with the same useless fiberglass jelly stuff last time. Want to find a 1/4 in plastic that will stand up to salt and water and UV (though I can paint it to protect from the sun) to replace. That board will not be so difficult to get at, though.


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## surfman (Apr 3, 2019)

If you are using polyester resin or some similar fiberglass resin instead of epoxy, it won't last. Fiberglass resin is great with glass in it but, sucks without it, it will just flake off. For the outside piece, if you feel you need that just epoxy coat a piece of 1/2 ply or get a piece of 1/8 aluminum.


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## CedarRiverScooter (Apr 3, 2019)

For the water-side board, consider using a cutting board. They are HDPE. You can't glue it but the motor bolts should hold it on. You can get them at HD or wallys.


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