Thursday, February 4, 2010

Project: New Inner Forestay Padeye

Project from 2004 (before the bowsprit replacement of 2009)

Crevice corrosion is nasty stuff.

When we first took possession of Eolian, the inner forestay padeye looked a little weird - like it was mounted incorrectly. The front edge was higher than the back edge. Over time, that "weirdness" became more pronounced, until it looked like this (once application after application of various types of caulking - mostly silicone - were removed). Obviously, something was going wrong here, and attention was required.

After the caulking removal, I found that the pad had two pieces of 1/2" stainless allthread welded to its underside. These penetrated thru the entire bowsprit and deck, and were provided with nuts against the underside of the deck. So, on the initial assumption that the forward nut had never been made up completely because of the extreme difficulty of reaching it, I spent perhaps 8 hours wedged into the chain locker, up in the very pointy end of the boat, mightily struggling with the nut (no, I do not suffer from claustrophobia). During the course of this time, I managed to turn it perhaps 2 full turns, which should have substantially reduced the gap on the exterior. In fact, there was NO CHANGE.

Unfortunate conclusion:
The reason the forward edge was lifted was that the forward rod was broken somewhere inside. Using a sawzall, I cut the rod off the bottom of the pad. Then in the now more easily accessible gap, I worked on cutting the rod at the rear of the pad.

I was unable to complete the aft cut tho, because the blade began digging into the wood of the bowsprit. So I decided to break the remaining portion of the aft rod. It was far easier than I had
anticipated... and in fact, it did not break at the cut I had made, but instead below it. After the pad was removed, it was easy to pick the end of the forward rod out of the hole.

The forward rod, due to the design (the tension of the forestay is directed substantially aft), handles almost the entire load. Sometime in the 23 years previous to our purchase, the forward rod parted due to crevice corrosion. This left the entire load, in an extremely unfavorable position, on the aft rod. It was cracking, and had cracked nearly 2/3 of the way thru when I took the hammer to it.

This was caught in time... just. It would have failed sometime when we had only the mizzen and the staysail flying, probably in 25+ knot winds. Then the staysail boom would have been flailing all over the bow, doing substantial damage and creating a very dangerous condition.

Further efforts in the chain locker revealed that the remaining portions of the allthread were NOT going to move. So, they were abandoned in place.

I designed a replacement pad, larger than the original. After fabrication, this was installed over the ends of the abandoned rods, bedded in a generous layer of polysulphide. It is held to the bowsprit with 4, 3/8" stainless hanger bolts (think: "lag studs"... that is, lag bolts, with the hex head cut off, and the shank threaded with machine threads), capped with acorn nuts. The 4, 3/8" bolts provide a greater bolt cross section than the original 2, 1/2" rods, and spread the load over a greater surface area and greater number of fasteners. The new pad is twice as wide as the old, providing a significantly better ability to resist the side loading that the sail puts on it.

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