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Improving Upper Shroud Chainplates

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wanderer13
1st Mate

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USA
76 Posts

Initially Posted - 03/13/2016 : 14:12:58

I have never liked the fact that Catalina attached the upper shroud chainplates to a plywood bulkhead in the Catalina 25. I was already rebuilding my bulkheads this winter because they were badly delaminating due to a leaky chainplate at some point in its lifetime. I took this opportunity to devise a stronger mounting solution for the chainplate. I eliminated the idea of a knee due to the limited headroom on the 25. So, I came up with the idea of a backing board on the opposite side of the bulkhead from the chainplate that tied into the molded bulkhead tab. I salvaged a length of 5 x 3/4-inch mahogany board from another boat project. I routed the sides and one end of each board with a decorative ogee and varnished them. The flat butt end of the board fits just underneath the lip of the molded tab which I believe will provide more strength. I epoxied the mahogany board to the bulkhead and attached it to the chainplate, through the bulkhead with stainless steel 1/2-inch bolts.

I also added two more anchor bolts just below the chainplate (you can see them in the photo), in addition to the three bolts on the lower part of the bulkhead. The original bulkhead was screwed into the molded tab with self-tapping screws every 6 inches. I increased this to one screw every three inches.

Your thoughts and critical review are appreciated!

1981 Catalina 25 FK/TR

DavidBuoy
Admiral

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USA
707 Posts

Response Posted - 03/14/2016 : 04:58:50

Nice, should add some strength. I haven't really heard of a particular problem with these chain plates ripping out due to the original design, but I may be wrong. I do have to say though, those bulkheads looks clean enough to eat off of! Are they laminated or painted? Actually, is your cabin top painted as well? The coloring suggests it compared to the pop-top.

Captain Rob & Admiral Alyson
"David Buoy"-1985 C25 SK/SR #5053

wanderer13
1st Mate

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USA
76 Posts

Response Posted - 03/15/2016 : 19:45:46

quote:
Originally posted by DavidBuoy

Nice, should add some strength. I haven't really heard of a particular problem with these chain plates ripping out due to the original design, but I may be wrong. I do have to say though, those bulkheads looks clean enough to eat off of! Are they laminated or painted? Actually, is your cabin top painted as well? The coloring suggests it compared to the pop-top.

Thanks, DavidBuoy. I do know of quite a few instances where the mounting holes have elongated due to water saturation of the original plywood bulkheads. That suggests possible failure. Like you, I don't know of any total failures of the chainplates - I guess I tend to over-engineer things.

My replacement bulkhead is 1/2 inch marine grade plywood. Two coats of Epoxy, and two coats of Interlux one-part Brightsides. Not sure about the cabin top overhead - the PO might have painted it, although it looks mighty smooth for a paint job. I do like the white, though. It opens up the interior quite a bit.

1981 Catalina 25 FK/TR

dasreboot
Admiral

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804 Posts

Response Posted - 03/17/2016 : 12:31:31

so bright it hurts my eyes!

Todd Lewis
Eowyn 87 TR/WK C25 #5656
ARWEN 84 TR/SK C25 #4031
www.mainsailsailingschool.com

Voyager
Master Marine Consultant

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USA
5358 Posts

Response Posted - 03/20/2016 : 09:23:48

That's a beautiful improvement in design, I like the idea of a cleat reinforcing this very critical component.
That said, maybe you should hang a picture or add a tapestry...

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

wanderer13
1st Mate

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USA
76 Posts

Response Posted - 03/20/2016 : 15:56:26

quote:
Originally posted by Voyager

That's a beautiful improvement in design, I like the idea of a cleat reinforcing this very critical component.
That said, maybe you should hang a picture or add a tapestry...

Ahh. Yes, the new table is missing! Not to worry, that expanse of white bulkhead should be filled when the job is done.

Thanks for the comment, Bruce!

1981 Catalina 25 FK/TR

Bladeswell
Captain

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USA
490 Posts

Response Posted - 03/25/2016 : 10:24:21

Hi Wanderer,

While your work looks great I'm not so sure I would have gone that way. While it will serve to spread the load some, I can't agree that you have done very much to add strength. You see, Woods are not very difficult to split along the direction of the grain. Which happens to be how the chain plate bolts are aranged in your application. I can understand your apprehension about the chain plates being only attached to (plywood) however plywood is made by laminating several layers with the grain of each layer going the opposite direction. How many layers will depend on the quality of the plywood in question. Higher quality usually means more layers. And then the laminating process and glues come into the quality question. And then for marine grade plywood, there can not be any voids in the materials.
If I were concerned about strengthening the chain plates, I would have bought or had made some 5/16-3/8 stainless steel. I would have them cut to the same size basically as the chain plates except shorter of coarse. And then you would have an ugly but very strong reinforcement . True Blue water sail boats have their chain plates attached directly to the hull, not a bulkhead. I hope this was useful.

bladeswell

C25 TR FK Hull #973 1979 L-Dinette. So.Cal.

wanderer13
1st Mate

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USA
76 Posts

Response Posted - 03/27/2016 : 16:24:09

Very good point, Bladeswell. I didn't think about the wood grain direction. Since the chainplate is still on the bulkhead side and the bolts go through both the plywood bulkhead and the mahogany backing boards, I think it'll be ok. At the very least, I spread the load a bit. Thanks for the feedback.

1981 Catalina 25 FK/TR

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