[Public-List] Chainplate spacers ... rig tension
dfjtessier at hotmail.com
Tue Mar 24 09:06:34 PDT 2009
Glad you weighed in. And if I understand what you have shared with me off line, you have had not inconsiderable
success racing against the highly tensioned coastal fleet using moderate tension on your standing rig!
Based on my study to date of our mast support beam and the bolts from one chainplate,
it appears that our #319 has not experienced the very tight tuning and hard sailing
that other vessels have. As a cruiser I am inclined towards a somewhat (<-emphasis
on somewhat) less taught rig. And at least in principle, I want to have the discipline
to flatten sail or reef when our rail goes down and we approach hull speed. Not sure whether
this discipline is different from that needed to come out of a few days becalmed with one's sanity
more or less intact (and the engine unused) -- this distinction needs some further meditation
becalmed in a fog out in Lake Superior..
> Message: 8
> Date: Tue, 24 Mar 2009 10:02:48 -0500
> From: Don Campbell <dk.campbell at sympatico.ca>
> Subject: Re: [Public-List] Chain plate spacers - role of friction
> To: Alberg 30 Public List -- open to all
> <public-list at lists.alberg30.org>
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> While a number of people have discussed friction and the need for
> things to be rigid for friction to work as designed on paper, no-one
> has mentioned that there will be some compression due to the core of the
> truss being wood. IF that center part of the truss is wet, and I have
> the feeling that many are or have been, then the structure of the truss
> is not as contemplated in the paper design!
> I replaced the forward lower knees this last year on #528 and found
> plywood core, very dark from water and total delamination on one side
> between the polyester resin and the plywood. This resulted in a total
> failure of the design of the truss and the only thing holding was the
> glass tape, which was in extra tension because of excess torque from the
> hull wall to the holes. Wet wood or wood that has been wet maintains
> very few properties of the original material. The worst part is that you
> don't know how bad the system is and assume it to be as it was when
> built. This is not necessarily so.
> The net result is that as long as the knee is stronger than the wire
> or the joinery from wire to the fittings on the ends of the wire,
> something else will break first. That is a good thing because one does
> not want the hull to crack if it is the knee that does go first. If
> backing plates make things so strong that the knee cannot give even the
> 3/4" through the bulkhead, then be ready to damage the hull if that part
> ever tries to let go (as in a collision where rigging is snagged with a
> shock load from external mass) There are times when failure is a good
> thing, and planned failure even better. .
> When it comes to rigging tension, I think some of you who use high
> tensions on your rigs will notice that you can deform the curve of the
> hull at the chainplates with the loads possible on the wire. To me,
> this is excessive, as it just forces the mast down through the deck
> beam. There is always excessive stress on knees and chainplate bolts in
> this rig tension too (and little wonder the original bolts deform).
> Don #528
Chat with the whole group, and bring everyone together.
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