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post #1 of 9 Old 07-29-2013 Thread Starter
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Minimum reasonable breaking load for forestay of 31' ketch?

Last year I replaced all the rigging on my '79 Westerly Berwick ketch, including a roller furler system that works with hank-on sails. It basically is a pair of barrel swivels with a drum which is attached as part of the forestay, so that the entire forestay rotates when furling the sail.



The main mast rigging, which is an exact copy of the original rigging, aside from the furler, has a breaking load of 3500kg but the furler has a breaking load of only 2700kg. The manufacturer assures me that it is more than strong enough for the boat, but I can't stop worrying anytime the wind picks up whether I'm going to lose my forestay.

Am I worrying needlessly? What is a minimum reasonable breaking load for a forestay for this size of ketch?

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post #2 of 9 Old 07-29-2013
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Re: Minimum reasonable breaking load for forestay of 31' ketch?

You can pretty easily look up the breaking load of the original forestay -

Wire Rope (Trawl Rope) - Galvanized, Bright, Stainless, IWRC, Fillerwire & Rotation Resistant | WorldWide Enterprises, Inc.

Stainless Steel Marine Rigging Wire Ropes - Loos & Co., Inc.

My guess, the original was 7/16 inch.

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post #3 of 9 Old 07-29-2013
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Re: Minimum reasonable breaking load for forestay of 31' ketch?

7/16" on a 32' boat? no. 1/4" would be used on most boat that size. 2700kg is a bit should be ok. if you have 5/16" then it would be a bit light. I have a 33" racer and the forestay is 3600 kg breaking strength. and a lot more sail area on the main mast then a Berwick

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Re: Minimum reasonable breaking load for forestay of 31' ketch?

Previous and current wire for main mast is 1/4 inch wire with 3/8 inch clevis pins.

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Re: Minimum reasonable breaking load for forestay of 31' ketch?

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Originally Posted by overbored View Post
7/16" on a 32' boat? no. 1/4" would be used on most boat that size. 2700kg is a bit should be ok. if you have 5/16" then it would be a bit light
The clevis pins used in the roller furler are 5/16" (8mm). I don't know if there would be any benefit (or even drawback) to drilling those holes out to accommodate 3/8" (9.5mm) clevis pins.

All the other rigging components and connections, such as the turnbuckle and including the holes at the top of the furler drum, accomodate 3/8" clevis pins...

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Re: Minimum reasonable breaking load for forestay of 31' ketch?

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Originally Posted by chucklesR View Post
You can pretty easily look up the breaking load of the original forestay -

...

Stainless Steel Marine Rigging Wire Ropes - Loos & Co., Inc.

...
Well, according to the Loos site, 1/4" 1x19 316 stainless (which is what I have) has a breaking strength of 6900lbs which is 3130kg, so that's not too far off from 2700kg. Not sure how much that 430kg difference makes in practice...

Wouldn't the crimped terminals have a lower breaking strength than the wire itself? I.e. the actual crimping?

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Re: Minimum reasonable breaking load for forestay of 31' ketch?

both swaged and nicro press ends are rated at 100 % of the wire

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Re: Minimum reasonable breaking load for forestay of 31' ketch?

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both swaged and nicro press ends are rated at 100 % of the wire
OK, so the question then remains whether that 430kg difference in breaking strength has any practical significance such that I should be worried in heavy weather....

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post #9 of 9 Old 08-02-2013
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Re: Minimum reasonable breaking load for forestay of 31' ketch?

Man there are a lot of potential failure points on that thing...

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