Systems of measurement on a sailboat: imperial versus metric.

The last couple of times sailing Skiron I noted that the self-tacking jib wouldn’t fully cross over following a tack. I found that releasing the sheet a little would fill the sail with wind and the sail would ultimately cross over. One afternoon, for some reason or other, I decided to look at the hardware of the system because it seemed the car on the self tacking jib was getting stuck as it was crossing the rail. I noted that the forward screw bolting the mechanism to the center of the deck was raised and was actually blocking the easy passage of the car. This was indeed the problem preventing the jib crossing over after a tack. It had nothing to do with the sheet.

This image shows the forward screw on the plate holding the rail in place. You can see that the screw is raised. I had actually screwed it down slightly before taking this picture. Note there is a teak plate of sorts to which this unit is attached.

I attempted to seat the screw with a screwdriver. It seemed to have worked. A few hours later the screw had risen to its elevated location.

I wrote Annika and Bjorn to ask their opinion regarding the screw that was backing out of the plate. They sent the following photographs.

They noted that the teak plate had been added. It was not original. They also noted the bolt was not original. It had clearly been replaced. One can see the different shape of the head of the bolt when comparing to the one I first one I have posted.
The right-most nut is attached to the bolt that anchors the rail for the self-tacking jib.

I suspected that the nut had come off the bolt or that the nut and washer had pulled through the fiberglass of the deck. The ceiling of the cabin was going to have to be removed to permit inspection. That task was simple enough.

Inspection revealed that the nut that was supposed to be on the bolt and two washers had worked themselves completely off the bolt and were laying on the topside of the ceiling. This should be an easy fix!

I placed only one of the washers on the bolt then started the nut onto the bolt with a partial turn. Then, I used my socket wrench to attempt to tighten the nut. Curiously, the not would not go on more than a turn and a half. Something was amiss. I thought that either the nut or the screw was stripped.

The bolt in question as it was found on inspection. The washer and nut are missing.

I proceeded to the local rigger to speak with Tom, the owner, who recalled Skiron was constructed in Sweden. He suspected the nut would need to be metric. Indeed, it was. He checked the nut on a similar bolt and it worked fine. He suggested that the bolt may not be metric. The nut was 8 mil. The closest imperial measure was 5/16. Tom provided me with a 5/16 nut and suggested I try it on the bolt. This seemed quite reasonable and, especially, since Annika and Bjorn has noted that the bolt has been changed. Perhaps one of the prior owners had employed a new bolt.

Tom was right. The new nut fit the bolt perfectly. Problem solved! The bolt had indeed been changed from a metric one to one with an imperial standard of measure. Unfortunately, however, whomever did the repairs did not utilize the proper nut.

Tightening the new nut over the bolt against the washer.
The new nut and washer are securely in place.

It seems critical to ensure that pieces parts that match are used to repair a sailing vessel. The consequences of not doing so could be rather serious. Imagine if the unit failed offshore on a long passage without an opportunity to ask a rigger for advice and finding oneself without a spare. At any rate, I’m glad to have remedied the problem at hand. I’m delighted that I wasn’t required to do so in a more precarious situation than with the boat secured at the dock.

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