Gregor 12 - Transom Repair/Replacement

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AlexB

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What's up, guys?

I'm getting ready to replace the transom wood in my 12 foot Gregor (1977), and I figured I'd start this thread to document the process and hopefully get some good advice along the way.

As you may know, Gregor boats have two triangle-shaped transom braces that are welded to the floor and bolted through the transom. The transom wood is sandwiched between the braces and the aluminum hull itself, and there's an aluminum "cap" that wraps over the top of the transom wood. There is no way to replace the wood without either cutting the transom braces or severely bending the aluminum "cap".

After speaking with some folks at the Gregor factory, I came up with a plan. I'll slice each transom brace off with a horizontal cut ~3 inches above the floor. After sliding the new wood into place, I'll repair the two braces by "sandwiching" them with plates of 0.125" 6061 T6 aluminum and secure with SS hardware.

That brings up my first question...

What do you suppose is the best tool to get a nice clean cut through the thin aluminum transom braces and 0.125" thick aluminum sheet? I have at my disposal (1) jig saw, (2) angle grinder, (3) circular saw, (3) hack saw, and (4) oscillating multi tool. Whichever tool I decide to use, I'll need to buy a new blade for it, so I welcome your suggestions there, too.

Thanks in advance, and stay tuned for some pictures.

Cheers,

~Alex
 
I would either bend the top cap up (which is what I did on my boat) or cut off the top cap and fabricate a new one.
Can you post some pictures?
 
Most likely that aluminum hull is 5052 alloy, so that's what I'd use.

I bought a sheet 5052 H3 full sheet and have some left over, so depending on the size needed I could cut some and send you shapes needed - just pay fair price plus shipping.

A sawz-all with fine blade cuts through aluminum like butter, but can be tough for an accurate cut. I cut my 5052 with a new fine blade in a jigsaw and it was super.

I will add, for detail cuts, even through fiberglass, where I really needed to be "on the line" to make accurate cuts, say like on a helm dash or such, I always would buy a new (never would use a used blade ...) 'laminate' blade that cuts on the down-stroke. This gives the tool more control and leaves a extremely clean cut on the visible surface.

Oh, and insulate the SS hardware from the aluminum, even if only heatshrink on the bolts and nylon washers under the bolt hears and nylok washers/nuts.
 
Huh. How did you finagle the new wood around the two welded in corner gussets? My transom wood is the same width as the transom, so I don't see how I could lift it past the corner gussets.
 
DaleH said:
Most likely that aluminum hull is 5052 alloy, so that's what I'd use.

I bought a sheet 5052 H3 full sheet and have some left over, so depending on the size needed I could cut some and send you shapes needed - just pay fair price plus shipping.

A sawz-all with fine blade cuts through aluminum like butter, but can be tough for an accurate cut. I cut my 5052 with a new fine blade in a jigsaw and it was super.

I will add, for detail cuts, even through fiberglass, where I really needed to be "on the line" to make accurate cuts, say like on a helm dash or such, I always would buy a new (never would use a used blade ...) 'laminate' blade that cuts on the down-stroke. This gives the tool more control and leaves a extremely clean cut on the visible surface.

Oh, and insulate the SS hardware from the aluminum, even if only heatshrink on the bolts and nylon washers under the bolt hears and nylok washers/nuts.

Thanks for the advice. Are 6061 T6 and 5052 alloys dissimilar enough to cause a problem? Or was there another reason for your suggestion? I have already bought the 6061 T6, but if the 5052 is truly a better choice I'm sure I can find a use for the stuff I ordered.

I'm still hesitant to try bending or cutting the cap. I'm confident I can make a clean repair using straight cuts and bolts, but I'm not sure I'd be happy with the results of going at my boat with a rubber mallet.

Lock Stock - You mentioned the option of fabricating a new cap. How might I do this? I just have basic hand tools and I don't have much experience working with aluminum.
 
Hull makers use 5052 sheet over 6061 as it bends easier and is a work-hardened material, where the other is thermally hardened. In metals, their is toughness (ductile) and strength. Too strong and it's brittle. Looking at the formed features on most tin boats and you can easily see why a tough but bendable aluminum is used.

Sounds like you're just using reinforcing plates to mate the cut areas ... so I'd just use what you have.

Have fun! Please let us know how you make out ...
 
Thanks, Dale.

You're right. The aluminum shouldn't see any bending stress in the situation, and frankly I think it will be be way overbuilt with two 1/8" sheets to repair the thin (1/16"?) piece I'll be cutting. To make the repair even more burly, I also ordered some 1/8" thick 1.5x2" aluminum angle that will wrap around around the 90* bend of the transom brace (the bend that gives a flat surface for bolting to the transom). The angle will be secured with more SS bolts and should restore all of the original rigidity/stiffness of the brace.
 
AlexB said:
Huh. How did you finagle the new wood around the two welded in corner gussets? My transom wood is the same width as the transom, so I don't see how I could lift it past the corner gussets.
I cut through the welds with a grinder, then had them welded back on.
 
I will be making a new transom cap for the StarCraft Falcon I'm working on. I plan on using two pieces of 3/4" aluminum angle 1/16" thick and one piece of flat stock aluminum 1-1/2" wide 1/16" thick.
The transom is 1-1/2" thick so the 2 pieces of angle will cover it. I will anneal the aluminum so it is bendable. When I have the angle shaped I will rivet the flat stock over the top of the angle.
 
lckstckn2smknbrls said:
AlexB said:
Huh. How did you finagle the new wood around the two welded in corner gussets? My transom wood is the same width as the transom, so I don't see how I could lift it past the corner gussets.
I cut through the welds with a grinder, then had them welded back on.

Ah. I see. I'm really trying to avoid the need for welding. I still don't have a trailer (or a motor...) for the boat, so it would be tough to transport it to a welding shop. With the cut+bolt method, I should be able to get the transom fixed up quickly so I'm ready to hit the lake as soon as I score a trailer and motor. And, if the transom wood ever needs to be swapped out again (boat stores outside), I can just unbolt it.
 
lckstckn2smknbrls said:
I will be making a new transom cap for the StarCraft Falcon I'm working on. I plan on using two pieces of 3/4" aluminum angle 1/16" thick and one piece of flat stock aluminum 1-1/2" wide 1/16" thick.
The transom is 1-1/2" thick so the 2 pieces of angle will cover it. I will anneal the aluminum so it is bendable. When I have the angle shaped I will rivet the flat stock over the top of the angle.

Thanks for the reply. That sounds like it'll come out real nice, but also sounds quite time consuming. Fun, too, but With my limited free time I prefer to spend it fishing. :)
 
AlexB said:
lckstckn2smknbrls said:
I will be making a new transom cap for the StarCraft Falcon I'm working on. I plan on using two pieces of 3/4" aluminum angle 1/16" thick and one piece of flat stock aluminum 1-1/2" wide 1/16" thick.
The transom is 1-1/2" thick so the 2 pieces of angle will cover it. I will anneal the aluminum so it is bendable. When I have the angle shaped I will rivet the flat stock over the top of the angle.

Thanks for the reply. That sounds like it'll come out real nice, but also sounds quite time consuming. Fun, too, but With my limited free time I prefer to spend it fishing. :)
There is another Gregor build in the conversion and mod forum that has some pictures. It shows the transom as being flat across the top, if your boat is the same there would be no need to anneal and bend the aluminum angle. Being flat would make fabricating a new transom cap very easy.
 
The transom is flat across the back, but I'd still have to grind off and re-weld the corner gussets, which I would very much like to avoid (I hate paying other people to work on my things).

Here's my plan for transom wood... Gregor told me the original transom was constructed of three *actual* 1/2" sheets of plywood glued together to create an *actual* 1-1/2" transom. Today's 1/2" plywood is 15/32", or 1/32" shy of 1/2". If I sandwich three of today's 1/2" sheets together, I'll be about 3/32" shy of 1-1/2". If I sandwich two 3/4" sheets together I'll be 2/32" shy. But, if I sandwich two 1/2" and one 5/8", I come out 1/32" OVER the desired 1-1/2" thickness, which should work great with a little light sanding.

Here's my plan for the wood:

1)Trace the old transom board, and cut out the three new pieces using circular saw and jig saw as needed.

2)Wipe them clean and glue together with Tight Bond III (other suggestions?). I figure I'll place them on my basement floor and pile a few bags of cement on top to keep them flat and situated while the glue dries.

3)Touch up the edges with a sanding block, Surform, or whatever works.

4)Slide the wood into place, clamp it securely, and drill each hole.

5)Remove the wood and "overdrill" each hole with a ~1/2" bit.

6)Cover/seal each hole with tape on one side, fill each hole with Marine Tex epoxy, and allow to set.

7)remove the tape and clean up a little with a sanding block.

8 ) After a quick swipe with some fine sandpaper, thoroughly seal the transom wood with the "old timer" blend of boiled linseed oil, spar urethane, and mineral spirits until no more will soak into the wood. For applying the old timer blend, do you just keep applying it heavily in one sitting until it puddles then let it dry and call it good, or do you apply it in coats like you would with paint?

9)Possibly paint with some oil based paint? Is it necessary (or recommended) after applying the old timer blend?

10)Slide the wood back in place, clamp securely, re-drill holes through the cured epoxy, and reinstall new SS hardware. I'm still looking at different options for an insulating layer/substance between the SS and the aluminum. Duralac seems to be a decent choice, but I don't know about it's waterproofing capabilities. Any recommendations for a good bolt hole sealer/insulator that won't form a permanent bond in case transom ever needs work again?

I welcome any tips or suggestions.

Thanks in advance,

~Alex
 
Here's a picture of the transom. Should I plan to replace the little piece of sheet metal that's screwed to the wood? I could see it protecting the wood, but it also adds four screw holes that water could possibly enter.

Do you guys bolt your outboards straight in contact with the transom wood, or add a little sheet metal? I'll be storing the boat in the yard with the motor removed, if that makes any difference.

7f7e93e7241668e35d4d2c77ba19a662.jpg



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This is (approximately) where I plan to cut the transom braces.
d65465e1319fa3ccd6426cd4869ecc3a.jpg


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A few suggestions from my experience replacing the transom in my 1648:

1. Rough cut your wood, glue and THEN cut to size. Much easier to cut the final piece to size than trying to cut 2 seperate pieces exactly the same size. This also allows you to screw around the perimeter to "clamp" the wood while drying without putting holes in your final piece. It doesn't have to be perfect (mine certainly wasn't) but you want to try and get it as close to the original as possible.

2. I'd suggest sealing the wood, once you have it glued and ready to go (titebond III is what i used), with some epoxy resin. I replaced my transom almost 4 years ago and it's as good as new. It does stay covered outside, but gets put through the ringer year round hunting and fishing. I'd imagine my transom will outlast me.

3. Do not drill your new transom holes from the old wood, use the actually transom as a template. What I did was had my wife hold the new wood up to the transom while I drilled the top 2 mounting holes. I then bolted them into place and then, using the existing holes in the hull itself, I drilled out the remainder of the holes. Everything then lined up really well. I did this after my second coat of epoxy. This allowed for the last coat of epoxy and the coats of urethane to seal up the holes a bit.

4. If you go the epoxy resin route, get some good spar urethane that is UV resistant to protect your transom from the sun.

5. Take a few pictures of the original transom and bracing before you remove it. I couldn't remember how a few pieces lined up but luckly I had taken pictures of the boat when I first brought her home. Was nice having that reference.


I didn't have to cut any bracing out to replace my transom. My knee braces were secured to the hull with solid rivets. But I did do a LOT of aluminum work putting in a floor, deck and hatches. I used an angle grinder with these blades from Home Depot for all of my aluminum cuts. The wheels are thinner than standard grinder wheels and cut quicker through aluminum, but they do wear out faster than standard blades. Worked great for me. https://www.homedepot.com/p/Diablo-4-1-2-in-x-0-040-in-x-7-8-in-Thin-Kerf-Metal-Cut-Off-Disc-DBD045040101F/202830995

Here is the start of the transom work in my build thread. Hope it helps.......https://forum.tinboats.net/viewtopic.php?f=83&t=26774&start=30
 
Great advice! Thank you!

I like the idea of gluing THEN cutting. Sounds like it'll work great.

I definitely plan to use the aluminum transom itself as a guide for drilling holes, pretty much exactly how you described. I also plan to use a drill bit guide to ensure all my holes are drilled at the proper 90* angle.

Regarding the epoxy resin seal... Are you suggesting the epoxy go on over the "old timer" seal, or instead of it? And how does the UV resistant spar varnish come into play if I'm dealing with epoxy?

Thanks again. I'll be sure to check out your thread.


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Good point about taking photos along the way. It's always nice to have a reference to look back on

For cutting and repairing the transom braces, I plan to clamp the new aluminum sheet and aluminum angle in place and drill holes through the whole "sandwich" BEFORE I actually cut the braces. Then I'll remove the new materials and make the cuts. That way I won't have to worry about factoring in the blade kerf when I put it all back together.


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AlexB said:
Great advice! Thank you!

I like the idea of gluing THEN cutting. Sounds like it'll work great.

I definitely plan to use the aluminum transom itself as a guide for drilling holes, pretty much exactly how you described. I also plan to use a drill bit guide to ensure all my holes are drilled at the proper 90* angle.

Regarding the epoxy resin seal... Are you suggesting the epoxy go on over the "old timer" seal, or instead of it? And how does the UV resistant spar varnish come into play if I'm dealing with epoxy?

Thanks again. I'll be sure to check out your thread.


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Not a problem.

Yeah, the gluing and then cutting is the way to go.

I have no idea how well that seal mixture you're planning on using will last or how protective it will be on a wood transom. I do know that exopy resin is great at sealing and protecting the wood. Unless someone else has experience with that "old timer" seal with good results, I'd go with the epoxy resin. Should last a VERY long time if done properly. The spar will go over top of the epoxy once it is cured. I think I used 2 coats of spar. It is only for UV protection since the epoxy resin does not provide any on its own.
 
I glued the layers of plywood together before I cut the transom to it's final shape.
I applied the old timers all at once on one side and the edges once it would not soak up any more. I then flipped it over and applied it that side. I then stood the transom on 2 pieces of scrap 1"x2" and left to dry.
3m 4200 is a good choice if you think the bolts might have to be removed in the future.
Wood sealed with old times will last for decades.
 

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