RE: Cotter Rings
Thu, 13 May 1999 13:57:39 EDT

- - - - - - - - - - - - - - - - - - - - - - - - - - -
West Wight Potter Website at URL
- - - - - - - - - - - - - - - - - - - - - - - - - - -
n a message dated 5/13/99 10:07:49 AM Pacific Daylight Time, writes:

> I've seen postings on both the Potter and the Montgomery lists about cotter
> rings coming out of clevis pins and turnbuckles. I've never had that
> experience, and don't quite see how it could happen. For those of you have
> had or are familiar with them coming loose, could you post what you know of
> the incidents. In particular, is there any difference between the plain
> cotter rings and the ones which have the end slightly bent inward for ease
> of installation and removal. Is there any apparent relationship between
> size of the clevis pin or turnbuckle, the through-hole, and the cotter

Hi Dennis et al,

According to Bruce, the boss of the Rigging shop at Svenson's Boatyard, a
flapping line/lazy sheet catches on the ring or cotter pin and pulls it out,
especially at the side mast shrouds. Or a shoe lace. Or loose clothing. Or
a struck jib flapping on the foredeck. Or a fender line slung over the
chainplate. It's just Murphy's Law in operation.

The two places Bruce cautioned me to be especially carefull about were the
top and bottom of the forestay. If you lose either of those fittings, your
mast is coming down sooner, not later. Most people neglect the top of the
forestay, but on a trailer-sailer that can get bent or pulled out while
trailering. A slapping haylard can catch on it and pull it out to create the
conditions leading to disaster.

When the ring or cotter pin is lost, you don't necessarily notice right away.
Tension on the fitting would keep the clevis pin in place until vibration
worked it loose or you reduced the tension on the fitting by jibing to the
other tack or running downwind.

I've gone away from using the cotter rings with the end slightly bent inward
on really critical locations, since they can catch on something more easily
than the unbent ones. I use the heaviest guage ring/pin which will fit
through the hole, even though they're harder on the fingernails than the
lightweight ones. ( My thinking here is that well matched diameters reduce
point loading and the potential for failure through shear or fatique. And
heavier guage rings are less easily bent.) Then I tape over them. It's
overkill, but the thought of rig failure scares the living day lights out of

Bruce told me he sees at least ten rigs fail every season because of a lost
clevis pin. Thousands of dollars in damage (and occasional loss of life or
injury), all because a cotter pin or ring wasn't taped down. Scary stuff,
but forewarned is forearmed

Judy B.