New Chainplates

Clark November 30th, 2016

I had to remove a few chainplates for an unrelated project and one of them broke upon removal. I guess I can count myself lucky it happened this way, rather than in full combat mode. Only 49 years old, and it just fell apart in my hand! I plan to write a strongly-worded letter to these Alpha England people about the quality of their product:

I blame the dreaded crevice corrosion:

Years ago I read something about replacing stainless chainplates with titanium, which is stronger, doesn’t corrode, doesn’t crack, and yada yada. I looked into it, and Holy Halyard Slaps! For the price of two simple (meaning flat), small, titanium chainplates I could buy enough 316 stainless bar stock in AND A BRAND NEW DRILL PRESS, which was long overdue:

Upon further reflection, I might have made them out of silicon bronze, but if my 316 stainless chainplates last half as long as the old ones I’ll come out winning. Brion Toss has a good riff on the subject here.

After getting my bar stock from and my new benchtop drill press from good old Sears, I set to work. Cutting was straightforward with an angle grinder with a stainless cutting disc, followed by a grinding wheel.

Drilling holes was also straightforward, using the slowest speed on the drill press, and lots of cutting oil. The old chainplates were countersunk for flat head screws. This would not only be a lot of work, but it seems to me it reduces strength by removing material, and provides a lot of hidey holes for crevice corrosion. My new chainplates will have non-countersunk holes and round head screws, with heads standing proud.

Then comes the hard part: They say the way to prevent corrosion is to polish the chainplates to a mirror finish. I was more or less successful at this, but I started my sanding with a 50-grit disc on an angle grinder, which left some irregular gouges. In the real metal polishing world they have all kinds of wheel sanders for the heavy stuff. I moved up into my higher grits with an orbital sander, then stainless polishing compound on a polishing wheel. All went well, but in the final result I could still see the gouges from my angle grinding. I’d say it’s good enough, and still qualifies as a “mirror finish,” but a mirror finish on some ridges and valleys left by my aggressive angle grinding. I think a belt sander would do a better job, but my belt sander broke.

While I was at it I replaced the backing blocks on the interior with G10. The old backing blocks were teak:

I’m on a kick lately of using butyl rubber, instead of polysulfide, for bedding deck hardware. Which is better? Ask me in twenty years. With butyl rubber it’s a long process of gradually tightening the fasteners over days or a week, as it is stiffer stuff, and takes a long time to squeeze out and find its place:

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Comment by Mike
2017-03-28 13:03:26

Looks like some really good work.

A comment on butyl… I had to remove some stanchions on a 38 year old Hunter. The 38 year old butyl was still just as soft and pliable as the brand new butyl I had intended to use when I replaced the stanchions.

I’m definitely a believer when it comes to butyl tape.


Comment by Clark
2017-03-28 17:10:01

Hi Mike, Fellow boat repair blogger. I’ve been using butyl for everything for a few months now. It’s way nicer to work with, too…no gloves needed, just a little solvent to get off the most tenacious bits. I’ve NEVER seen it in a chandlery, strangely enough, but I think glaziers use it almost exclusively. I’m sold.

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