Where to Start...

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Where to Start...

Postby gts » Fri Aug 17, 2018 4:10 pm

So I finally figured out why I could never find the serial number on the transom of my '67 offshore from Peshtigo - the transom had been replaced thirty or so years ago. It's bowing out now because this replacement transom was not sufficiently thick for the engine it was carrying. And some of the stuff that was glued along the bottom edge of the transom to provide for additional fasting area for the hull - that stuff is rotting.

The bottom of the boat has been patched multiple times, sometimes by just cutting out the rib(s) and gluing a piece of plywood down to buttress the bottom repair. In other cases, the plywood patches inside the hull ended up as water traps keeping whatever water did get into the bilge from draining properly and worsening the problem of rot around the sister keelson on the starboard side where most of the bottom repairs were made.

The keelson - a former wooden boat specialist thought encasing it in epoxy would be a lasting professional repair. All that did was trap in the moisture and make the problem worse in the long run.

So I've got serious problems - transom, keelson, and ribs / bottom.

So where to start? Can't do the bottom without doing something about the ribs. But the bottom and ribs are both fastened to the keelson. So keelson first? Then sister all the ribs that are cracked, missing, or rotting? Then start unfastening the bottom and scarfing in new sections, fastening as you go along to the new ribs and keelson? And then finally address the transom last?

I've got some serious hog in the bottom from the missing or broken ribs. Is there any way to confirm the hull shape is fair during the rib installation process? Are there any lines drawings for the proper hull shapes?

George
gts
 
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Location: NJ

Re: Where to Start...

Postby LancerBoy » Mon Aug 27, 2018 5:25 am

Sounds like some very serious issues with this boat. Which to tackle first is tough to say. I think you will have to build a temporary support structure for the hull to maintain the shape as you remove components to make the repairs and replacements.

There are NO line drawings or plans for any of the Thompson boats.

If you are on facebook you will get more responses than here. No one hardly ever looks at this forum these days. There are two Thompson facebook groups: Thompson Boat Owner's Group and Thompson Antique & Classic Boat Rally.

Andreas
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Re: Where to Start...

Postby gts » Wed Aug 29, 2018 1:00 pm

Thank you, Andreas. Good to see you're still here. It's been a few years since I posted...

I've been scrupulously trying to avoid Facebook. That's where all the Thompson restoration discussion is these days?

Is there an archived thread in Restoration that covers ribs and bottom and keelson in one place? I notice an excellent sequence with pictures by 62cruiserinc on "Plywood garboard removal" that step by step removes the entire bottom off the boat leaving all the ribs exposed. But the thread stops there. And at that point, how could you shape a new rib? The originals were bent over a strongback during construction, correct? So without duplicating all the jigs used for original construction (or at least constructing one jig for every rib that needs attention) I'm thinking it would be best to leave the bottom on and replace the ribs first. That way you have something to "form" the rib against. As long as the "hog" in the bottom is not in the keel / keelson itself, the hull should pop back out to fair with a new steamed rib (and no external pressure on the hull like a trailer roller or jack pad).

Since I plan to replace the previously repaired bottom planks with fresh plywood I can just cut through / grind down those rectangular plywood patches that were applied on the inside of the hull as backing for those earlier "Dutchman-style" hull repairs. That's why they cut out ribs to begin with, to make room for the flat patches. The short rib segments meant those sections of the hull were more susceptible deforming as the boat sat on its trailer. And of course, those cut rib ends rotted with trapped water since there was no limber hole for drainage.

What about a jig in the fashion of the sister keelson but much closer / parallel to the keelson itself as a way to anchor the "keel" end of those new ribs? Then the sequence would be to do the rib replacement first, fastening the ends to that sister keelson jig. Then replace the keel / keelson with fresh wood. And then finally, start removing hull plank sections and scarf in new wood.

I understand this is a big undertaking. And I still have the transom issue to address. But I was asking myself why build a 12 1/2 as a project if I can practice on the Thompson first?

George
gts
 
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Joined: Wed Sep 19, 2007 4:13 pm
Location: NJ


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