Chainplate drilling

[benz]

I've just purchased a sheet of silicon bronze to make chainplates of for my Cape George 31. I've seen some boats with the bolt holes drilled exactly on center, and others where each bolt drifts toward the opposide edge of the chainplate than the last. Is there any advantage (or dis- )to staggering them thus? I like the look of it, and my seeming inability to measure anything straight might be masked by this tactic.
Thanks in advance.
Ben

[Renoir]

The purpose of staggering holes is to better distribute the load and hence strain on the grain of wood hulls. Other materials like fiberglass do not benefit from staggering because of the greater uniformity of the material in two-dimensional tensile strength.

[Douglas]

Hi Ben, I too replaced my chainplates and had to drill the staggered holes in the wider double shroud plate.

My asumption for the staggered holes was to "Spread The Load", over a wider area, as that single plate was used for 2 shrouds.

My pre-bent plates were cast by Pete of P T Foundry, but they were supplied holeless.

I ended up drilling only the top bolt hole first, then squareing up the hole with my Bosch Jig saw, because I was using carriage bolts with the square shoulder, under the head.

I then dry-bolted the new chainplate in place, and marked the hole pattern from inside the boat.

Bruce Bingham wrote a book titled Ferro Cement Boat Construction, or something like that,,,, He describes how to determine the shoulder width needed around the chainplate toggle pin hole, so before you drill the pin holes, you might look at that book.

On my boat a BCC, with mast supplied by Forespar, I found the tang linkplates at the mast to shroud attachment through bolts, to NOT have enough shoulder to hole setback,,,,, something like a 7/16" shoulder, when Bingham's book recommends a 5/8" shoulder .

I also found that the cone-type step drill bits were excellent in drilling a very nice "round" pin hole in the new plates, after first drilling a 1/8" pilot hole.

Would you be able to disclose the price that you paid for that Silicon Bronze plate ?

Out here in SE Asea, I recently had my Silicon Brnz plate supply stolen, so I am trying to establish the value of the loss, drats !

[benz]

Thanks, Renoir...good nutshell reply.
Douglas, I got my pintles and gudgeons from P T foundry, and the price of that convinced me to buy stock and make the rest of the fittings myself. I don't have to worry about matching holes, since the boat is new and has no holes at all yet. I just have to worry about getting the chainplates in the right spot...
I paid $9.50 per pound for the Silicon Bronze plate from Atlas Metals. The 22x48x3/8 plate weighs 125 lbs, so it was quite steep. I ordered some other stock from them at the same time, (1/4" plate and 3/4" rod) to save on shipping, I just hope I bought enough so I don't have to ever again.
Mind if I ask the width of your chainplates, and how many bolts each?
Best,
Ben

[Douglas]

Hi Ben, T Y , for your reply as to the current price of Silicon Brnz per pound, from Atlas.

Congrats on your Cape George ownership, I always liked their boats, and hoped that they would acquire the recently available BCC and FC molds.

I will check the width of the brnz C-plates this upcoming weekend and send you the measurements,,, here on the forum.

I too used silicon bronze plate (1/4") for my boomkin and whisker stay chainplates,,, they seem to be holding up fine for the last 8 years.

I was happy to have Pete do castings for me, because he was a sailor first before being a foundry. He knows that our lives depend on his work, unlike general purpose foundrys.

In future I would have specified Aluminum-nickle bronze instead of Manganeese . I don't think Aluminum-nickle brnz comes in sheet or plate, just ingots .

[Douglas]

Ahoy Ben, my dbl shroud chainplate is 2 3/4" wide and 24 1/2" from the bottom edge to the toggle hole at the top and then has the needed shoulder width. We used 3/8" carriage head bolts.

I did photograph it so that you could see the staggered hole pattern, but I don't know how to post it as an attachment yet ,,,,,,,,, oh , later I see we can't post attachments here, drats !

Another thing comes to mind, which I heard somewhere, and put to good use, is after form bending the brnz to fit the curve of your hull , then give the lower tip of the plate a little extra bend in, before mounting it. This is suposed to keep the chainplate tip tight against the hull during hull flex and loading.

Douglas