Re: Forestay failure -Reply

Clair&Edgar (N1122@mail.aai.arco.com)
Wed, 23 Sep 1998 08:19:47 -0900

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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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With our Genoa on a roller furling, I have witness a tremendous amount of
tension on the forestay. In addition to that, the forestay also provides
the "third leg" to the tri-pod arrangement that holds the mast up. Ted's
observation that the mast pad eye for the forestay may be an intentional
"weak point" is a valid one. These design considerations are often
intentional. Although I would prefer that the weak point was something more
easily replaceable. Like a weak link in the rigging between the forestay
and the pad eye. Also keep in mind that many of us are "pushing the
envelope" in the use of our potters in terms of willing to put her through
the paces in heavier weather. Keep in mind the stock factory built P19 is a
good basic fair weather day sailor/week-ender. But the P19 is also designed
and built in such a way that it can be easily modified, upgraded and
reinforced to take on more aggressive conditions. Adding backing plates,
replacing pop rivets for screws with nuts and washers, adding bulkheads,
extra layers of fiberglass, additional structural and flotation foam,
larger engines, etc. can be accomplished fairly easily for those of us who
dare venture into the back yard marine engineer world of pottering.

Regards,

John & Terrie
P19 Sassea, # 950
Lake Chelan, WA

Ted Dyer <TD7876@mail.gates.com> on 09/23/98 06:32:28 AM

To: wwpotter@tscnet.com, phrrld@ttuhsc.edu
cc: (bcc: Clair&Edgar/AAI/ARCO)
Subject: Forestay failure -Reply

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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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Just to start things off on forestay failure: (I hope to learn
something here): 1) The aircraft industry uses a rivet called a
Cherry Max that is a very high tensile item, just barely pullable
with a standard rivet gun. It is often backed with a washer. I'd be
willing to bet that these are the strongest pop rivets in existence.
Expect to use a numbered drill to create the hole. 2) Is stronger
always better? Many structures contain planned failure points.
Perhaps it is better to pull a rivet out than deform the mast or pull
a chainplate on the deck. Considering that your failure mode was
wear and not catastrophe, I think this is worth thinking about. 3)
Am I wrong in thinking that the forestay does not experience a lot of
tension under sail, but rather supports the jib and jib halyard as
they provide the bulk of the tension? That would mean the wire cable
construction is used, not for ultimate strength, but to simply
counter the fraying/stretching/size difficulties encountered where
line is used. Let the feeding begin.

Ted Dyer
P19 #1044
Penelope