Converting to and Fabricating Bronze Chainplates/Tangs

[blahman]

Brion and others,

I know of (but do not own) Norman Skene's book, but do not know of what you're speaking when refering to "L&A's" specs. Could you be a bit more specific?

Thank you for your time!
Aaron N.

[Jack]

Blahman

Here are a few links to most recent stuff. (as in just this past week)

http://www.madmariner.com/node/37560/print

http://www.duckworksmagazine.com/09/...opes/index.htm

Give me a few minutes and I will have photos of the Westsail on my photobucket URL below.....along with a few candid shots of Brion maybe....:-)

[Jim Fulton]

In the Rigger's Apprentice and on this forum we are repeatedly cautioned to size (wire) rigging to the loads that the boat will exert on the rig. However, much of the publicity on Dynex Dux emphasizes how much stronger it is than wire in addition to being lighter. People seem to be using Dynex Dux that is much stronger than the wire it replaces. In some applications this might be a good thing. But, according to what I have read, Dynex Dux rigging should be tensioned to something in the neighborhood of 15% of breaking strength. This being the case, a fully-tensioned Dynex rig might exert excessive loads on the hull or deck. Shouldn't the Dynex be sized for strength in the same way that wire is?

Jim Fulton

[Jack]

There is a number of things to consider. Dynex does not need to be tensioned to 15%. In fact you do not size Dynex Dux that way. You size it to eliminate creep and stretch. It is so strong you do not use the same set up.....sorta

Here is an example: Westsail 32 Formerly had 1/4" and 5/16" SS wire. Brion says to never load a shroud more than 10% of it's breaking strength and a headstay/backstay more than 15%. If I recall 20% is the ultimate maximum on any wire.

1/4" wire is 6,900 lbs
5/16" wire is 10,600 Lbs.

The maximum tension on your stays should never exceed 1590 lbs. (15% of 10,600)

This would be the same tension you put on a Dynex Dux rig....those numbers.

This is the number we use to determine what size Dux rope to replace the wire. Our rule is keep the static load or tension under 15% of the breaking load of the rope, and you will eliminate creep and stretch. In fact it stretches less than wire, when sized properly.

We used 9mm Dux on the Westsail. Breaking strength 26,500 lbs. If the Westsail is tensioned to 1k or so (in reality) We have a huge margin before we ever reach the 15% point.

15% of 9mm Dynex Dux is 3,975!

By replacing the rig with rope that is more than two times as strong, we have gained a huge leap in overall strength, and have no stretch or creep. The rig uses the same tension numbers as with wire.

You are right, if we were to tension it to the 15% of the ropes strength, we would pull the mast right trough the bottom, or some other nasty thing.

I uploaded a bunch of photos of the boat on the URL below. Enjoy!

[blahman]

All,

I spoke with Pete out at PTF today and he assisted me in understanding the alloys. Basically, the cast alloys with high corrosion resistance are fine choices for chainplates, so aluminum bronze, aluminum nickle bronze; things in the C95XXX range. The trouble with these bronzes is that they are very hard, inelastic, strong metals, so working with them is trouble. Fabricating using silicon or manganese (wrought) bronze is much easier for its elasticity and bendability; it can be cold worked.


Most of PTFs castings are C955 or C954, aluminum nickle bronze or aluminum bronze. If they are going to be working a piece, they cast it of silicon bronze to enable easier working.


So the 3/8" aluminum bronze stock will work great, the trouble will be bending it. It can't just be put in a hydraulic press as it'll crack or shear; it has to be heated. I didn't ask him about the procedure for heating and working with the metal as that's his trade! I'm going to dig on the internet to see what I can learn and then decide whether or not I'll by the stock and make the chainplates.


Chainplates from PTF would be $180/ea, plus $100 for bending, plus $150 or drilling. Boomkin and bowsprit whisker tangs would be $90/ea. So I'm going to check into working the metal myself and doing it for $300 total as my pockets just can't support that now and I don't want to keep sailing on cracked chainplates!

Anyone have knowledge of working with the cast alloys?

Thank you all for your time!
Aaron N.

[Andy Schell]

Hi all,

I'm specifically interested in bronze chainplates as well. I have a '66 Allied Seabreeze yawl with inboard chainplates mounted on the bulkheads, which I plan on replacing with bronze, on the outside of the hull. Incidentally, I'm already in the process of re-rigging with Dynex Dux as well, having installed twin backstays to replace the original split stay. The stuff is awesome, incredibly easy to splice, and the deadeyes / lashings look rather dandy on my old yawl, as they did on the Westsail in Annapolis. I actually spliced both backstays in the cockpit while we motored down the ICW just last week, installing the stays dockside.

Anyway, I found another source for DIY bronze. Atlas Metals, based in CO, supplies all sorts of metals, including silicon bronze, that comes in convenient 2" wide x 1/4" thick strapping, sold by the 6' length. Saw their ad in Wooden Boat magazine, and talked with them on the phone, just out of curiosity. Not sure yet what my solution will be, but they seem like a good lead. Google them. Also, anyone considering the Dynex Dux with questions can feel free to contact me for personal details of how the re-rig is going on 'Arcturus.'

Cheers,
Andy
www.fathersonsailing.com

[Jack]

Andy, I have to smile at how stoked you are. I swear, I feel like street corner preacher sometimes.....I mean it is hard to get your arms around how cool/fun/great/amazing...well you get the idea...:-)

Glad to hear you have become a user and believer in Dynex Dux. It will certainly mess with your head