some thoughts on tendons

From: Jay Runge (
Date: Tue Apr 14 1998 - 11:13:48 PDT

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From: Jay Runge <>
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Subject: some thoughts on tendons
Date: Tue, 14 Apr 1998 11:13:48 -0700 (PDT)
In-Reply-To: <> from "Ed Scott" at Apr 13, 98 10:52:26 pm
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Since there has been so much safety discussion after the Carlos
paddle, and much of it aimed at the separation of board and rig, I
was inspired to type these observations. Sorry it is so long, but
it is a big subject.

Remember! The first rules of sailing safety are:
1) Nobody is coming to get you
2) (therefore) Be prepared to get yourself back.

These tendon universals are great! You can easily replace the parts
that tend to break for a few dollars and keep using it with confidence.
But I have noticed a couple of things to watch.

1) When the tendon gets old, it begins to crack horizontally around the
small bolts that are holding it in the cups. The problem is that unless
you take the universal apart you CANNOT SEE THE CRACK by inspection.
The crack is hidden in the cup. I saw one that was cracked 2/3 of
the way through, but still looked new from the outside, and had been
used by the owner that day. It was due to fall apart in: a) one day
b) one month c) who knows? It was replaced that minute, so we never
found out how many more bends it had.

Once every 30 days or so, you should take apart the tendon part of
the universal to clean and inspect. If you have never taken it apart
you will have some trouble due to the corrosion caused by the different
metals in the bolt and the cup. I had one old bolt break on me, but I
was able to get the broken pieces out and replace the bolt. I have had
to use vicegrips and fire to get one apart. But if you take it apart
and clean it often, cracking and corrosion will not be a problem.

While you have the tendon out, you can easily replace the bolt that
secures the universal to the board. It is a special bolt, you will
have to get a new one at a windsurf shop. You remove the base with
2 screws and the new bolt just drops in. Once a season, maybe?
Your universal may not have this bolt if it is a quick release type.

2) There has been some talk that the little piece of safety rope that
is supposed to keep the board and rig together is not strong enough.
I looked it up, and it turns out that it is pretty strong. From the
Marlow catalog, Marlow 8-plait pre-stretched polyester 4mm (that is
the white line with the orange and black markers) has an average
breaking load of 840 pounds (380 kgs). The 5mm is 1325 pounds (600 kg).
>From the Samson catalog, the LST Yacht braid (various colors) 3/16
(5mm) breaking strength is 1200 pounds. The Samson Trophy braid 3/16
is 1150 pounds. 'Average breaking strength' is a bit vague, and they
always test a new unworn piece of line, but it looks like the line
is strong enough.

I think the problem is in the knots. They never are under a load so
they never get tight, unlike the knot at the end of a downhaul or
outhaul. When the tendon breaks, the wet knot tied in slippery
polyester just slips right out. I have used 2 vicegrips on a wet line
on my universal and pulled the knots as tight as I could, and I bet
I could walk out there now and just untie them with my fingers.

I don't have a solution to this problem. Maybe a different knot.
Seizeing the line would work (and be old-time nautical). Maybe using
a vinyl covered SS wire and Nicropress fittings. A splice in lines
this size is difficult, not too practical. Maybe lots of wire ties?

If you do the first thing, the second thing may never be an issue.


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