Chain plate bolts

Hi all,
I am getting ready to install new chain plates. My rectangular aluminum bronze bar should be here tomorrow.

My conundrum is how long are the bolts I will need? I have the BCC construction manual and it lists a bunch of carriage bolts, ie 6 3/8 x6" etc. So I pretty sure I need those 6. And it lists 24 3/8 x 2 1/2, so I figure those are for the main chains since it requires 24 for them. But I may be wrong.

But I can’t figure out what else I need. I am doing the main chains, the whisker and boomkin chains.


I have a bolt leaking, wondering what best to use to seal at this stage. May have to withdraw and reseat.

Ahoy Gary , The longer 6" + bolts are the ones that go thru the rubrail and channel blocks .

The 2 1/2" bolts are about right for the rest . I usually error on the longer bolt side, and cut them off as needed.

Are you going to use silicon bronze bolts ? Oh , and remember to champhor the bolt holes in the gelcoat , which traps the bedding compound and forms a sort of “O” ring around the bolt .

Thanks Doug, yep silicone bronze. The bolts cost as much as the bronze stock…yikes!

There was another thing that came to mind , since you will be fabricating each C/P . That is the orientation of the square hole you will have to cut-shape for the carriage bolts. What do you think Mike A. would reccommend ? I also wonder what the “Brion Toss” rigging forum would reccommend ?

I am wondering if anyone knows how to choose a proper orientation or is just “hap hazzard” Ok ?

In my Port Townsend Foundry C/P’s I drilled one lowest hole first, then used a H/H jig saw to cut the round hole square for the carriage bolt .

Then bolted it in , Then clamped the top of the C/P in place , marked the holes from inside the boat , then drilled and cut square the holes as needed. Of course these PT Fndry C/P’s were pre-formed to the hull curvature , unlike your flat stock .

Seacap, I’ve read that aluminum bronze bar stock is not appropriate for chainplate use, as there’s galvanic corrosion issues when it’s immersed in seawater. I’m going to be using C655 silicon bronze for mine for that reason.

And a note for people looking at C655… it’s a bronze that can be heat-treated to a temper, and the different tempers have very different strengths. The “Annealed” (or non-heat treated) version is LOWER than 316 stainless, so you’d want to upsize to get the same strength. I’m going to get mine treated to H02 (half hard), which is comfortably stronger than stainless.

A couple of publications that should answer the question about aluminum
bronze (nickel aluminum bronze) applications in seawater. The short answer
is aluminum bronze is suitable for marine applications.

The two aluminum bronze bumpkin tangs we installed on our Flicka African
Moon, were mostly immersed in saltwater and we saw no deterioration in the
metal or on the surface.

By-the-by, most if not all U.S. made bronze seacocks are made from lead red
brass. Naval brass and gunmetal, C85555 (Davey & Co, Ltd) are suitable
for marine applications. Further, there is no legal definition for bronze.
Oh, gunmetal is 85% Cu, 5% Sn, 5% Pb and 5% Zn - good “stuff” for marine

Sorry, I am just wired this way.


On Fri, Mar 8, 2013 at 12:46 PM, BCC Forums wrote:

Ahoy Rod , I , for one , are quite happy with the way you are wired and the same for Bil of BCC Zygote .

I haven’t read the Larry Pardey Wooden Boat construction book yet , but somewhere I read that they used aluminum - nickle bronze casted chainplates on Seraffyn (sp-)?

I saw those very same C/P’s on her when the new owners purchased her from Roger . They were a more silver color than a green bronze color , and yes they were longer and continued down the hull below the waterline. Not mentioned , but I expect Larry wanted a static or passive ground plane for lightning protection , because he was using a wooden mast .

Sam told me that Shaula’s gudgeons and pintles are made of naval bronze. I needed to know because I was replacing the worn pins in the pintles. I guess naval brass and naval bronze refer to the same alloy? So as of hull 59, 1981 at least, many or most of us have some zinc in our underwater bronze fittings. So far, I haven’t had any problem with our gudgeons or pintles. Has anyone?
Dan Shaula

Thanks for all the input guys. Thanks for being Rod Rod!

So I will be using silicon bronze bolts on my aluminum bronze flat stock chain plates. I have the design drawings that were sent out for the manufacture of the original SS CP’s. So far the measurements check out with the drawings. And the square holes are aligned horizontally.

None of my chain plates sit in the water. The boomkin plates are close, but no cigar.

I have read so far about bending the aluminum bronze (a non ferrous metal). You heat it then quench to prepare it for bending. As opposed to a ferrous metal that you heat/bend/quench.

That’s it for now. I am awaiting my Bolts and working in a friends shop on the fabrication. Hope to have them on by the end of the month.

Somewhere I read, nickel aluminum bronze is not a good casting material but
this does not seem to be the case: .
Still, I would confirm this notion.

Traditional bronze hardware is available from Davey and Company, LTD in
England and also from R. W. Rope in the U.S.: . We purchased our
three-strand English Braid rope from them as well as several pieces of
bronze hardware. Davey and Company offers gunmetal tradition chainplates.
Once I purchase several feet of hemp three-strand rope from Gordon at R.W.
Rope. The intended use is hand sewn canvas buckets but alas, the smell of
traditional cordage takes you back to when Falmouth Cutters, Falmouth Quay
Punts and Pilot Cutters sailed the western approaches. The men who sailed
these unforgiving waters were known as “Westermen”. Sorry, I am a hopeless
romantic lost in another time and place. Hum, I need to purchase more of
that hemp cordage.


On Fri, Mar 8, 2013 at 7:35 PM, BCC Forums wrote:

On the square hole clocking… we recently replaced Mandy?s C/P’s and aligned the square holes horizontally. Our reasoning was that a square is about 40% larger diagonally than across the flats so having it at an angle would reduce the cross sectional material of the C/P? weakening the area around the bolts. The worst case would be clocking it to 45 degrees, that would create a natural bend line across the C/P and point the ?V? of the square (the most likely place for a crack to start) right at the parts edge. Also, to reduce the tendency for cracks to form at the inside corners of the square, it?s helpful to have a small radius in there if you can.

BCC#32 Mandy