1986 19' Atlantic rebuild

Questions about boat repairs with our resins and fiberglass: hull patches, transoms and stringers, foam, rot etc.
goingbogueoutdoors
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Re: 1986 19' Atlantic rebuild

Post by goingbogueoutdoors »

Inside and outside stringers done with glass. Cutting three bulkheads tomorrow, hopefully will tab and glass by the end of the week
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fallguy1000
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Re: 1986 19' Atlantic rebuild

Post by fallguy1000 »

I was wondering about that gap... so, from a design perspective, the load on the transom really needs to be pushing on the stringers.

I apologize for not seeing this sooner, but load transfer is supposed to be done in a line. And this also explains my earlier confusion and commentary about the gap. You can't tab the stringer properly at the transom box.

Obviously, you are way past any major design changes, but you really ought to consider significant tabbing of the transom box to the stringer. This will help keep the loads transferring into the stringer more versus loads creating lateral strain on the bond.

I don't think anyone would design the stringers and box this way anymore if this was original. The way it would be done is for the box to end and the stringers to begin.

You can either use tabbing, or you can put a short stringer say 2-3' long in front of the box. Yes, you have a ton of epoxy in the seam, but the issue is load transfers are not in a line.

A lot depends on horsepower plan. If this boat were getting 300hp; I'd say you must add sisters. For 115hp; just fillet and tab as I've drawn. This is a top view. This will prevent the epoxy and filler bond from cracking. Epoxy and cabosil is not as strong as epoxy and tapes!
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fallguy1000
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Re: 1986 19' Atlantic rebuild

Post by fallguy1000 »

You also ought to tape the top of the gap to avoid the chance for any ingress. Water that finds its way down in the gap is never leaving and if it finds it way to wood; it will rot. A piece of 1708 on an epoxy puddle is cheap insurance
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fallguy1000
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Re: 1986 19' Atlantic rebuild

Post by fallguy1000 »

A lot of people may guffaw at my comment, but what happens at the transom is the key. The force on the transom from the engine is forward and it creates deflection in the transom. If the forces are pushing onto the stringers; they are transferred to the hull and deflection is less.

This is why we oftentimes see knees on a transom. It is to transfer loads into the hull and to reduce strain on the transom.

In the case of this transom; it is certainly not wide and this helps, but all of the loads are not being transferred into the hull in direct paths and this creates strain on the transom and the bonds of it to the stringers.

Another option for you would be to add a small stringer up the middle of the transom to the next bulkhead instead of two sisters. That stringer would directly transfer loads from the center of the transom into the hull and not allow transom deflection.
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TomW1
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Re: 1986 19' Atlantic rebuild

Post by TomW1 »

fallguy, the stringer should also be stabbed to the transom even more importantly than the box. I would also tape the top of the stringer to the box for water egress with 4oz. tape. This further helps transfer the forward power to the stringer and the bottom of the boat. On Jacques plans stringers are taped to the transom on both sides. Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

fallguy1000
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Re: 1986 19' Atlantic rebuild

Post by fallguy1000 »

The transom is the front of the box.

The stern panel or transom, call it what you like is getting some loads, but not like the box.

4 oz woven is not considered waterproof Tom
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TomW1
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Re: 1986 19' Atlantic rebuild

Post by TomW1 »

The epoxy makes 4oz waterproof, then fairing, primer, and layers of topcoat. Sorry about my mistake on the transom had to go back and look at the very beginning of the thread to see where the motor went :? Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

goingbogueoutdoors
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Re: 1986 19' Atlantic rebuild

Post by goingbogueoutdoors »

Been busy. Yes going to tab more on the transom, as well as put a layer of 12oz. In that void
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fallguy1000
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Re: 1986 19' Atlantic rebuild

Post by fallguy1000 »

What's the other boat?
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goingbogueoutdoors
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Re: 1986 19' Atlantic rebuild

Post by goingbogueoutdoors »

fallguy1000 wrote: Thu Jan 26, 2023 9:17 pm What's the other boat?
22’ Twin Vee catamaran. Just glued the sold down this week. Done the transom and bulkheads already

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