On Sat, 09 Feb 2008 16:32:23 +0100, Daniele Fua
wrote:
Drew Dalgleish ha scritto:
On Fri, 08 Feb 2008 19:18:53 +0100, Daniele Fua
wrote:
Thank you very much. I have also found few Loos retailers on this side
of the Ocean. Unfortunately I will need both rod and wire gauges and for
a couple of ranges which makes the total purchase rather expensive. The
idea is quite simple so I wonder if it would be very difficult to
construct a device myself; calibration would be an almost impossible
issue but, at least, once the tension of the rig is nearly set at a
correct value by an experienced rigger, a selfmade device could be
helpful in equalling the tensions at both side of the mast and
maintaining it in time.
The mechanical device is for sure the easiest way but... any idea why a
"twang hearing device" would not work? Maybe a piezo pick-up and an
oscilloscope? In any string instrument the change of the pitch is
strictly correlated to the tension (beside the mass/length, the
stiffness coeff., etc etc of course), isn't it?
Daniel
Isn't the tension at both sides of the mast always equal with the mast
leaning to one sise or the other if the stays are tightened unevenly?
This is a good question that made me think. Yes, probably yes! The mast
itself is not able to give any resistance and for an obvious physical
law, in static condittions both shrouds will have equal tension.
Responding to some of you: I am referring to a classic cruiser-racer
sail boat designed by S&S in the 80' with a quite tall rig, LOA 41'. Two
orders of spreaders and only one rod vertical shroud running from the
deck to the outer part of the first spreader. Assuming that the rigger
did the right thing, from the deck I can only operate on two opposite
vertical shrouds and two opposite diagonal. I have read several things
on how to adjust the mast and have a pretty good idea; my original post
was based on the belief that a tension gauge may improve the adjustment
but you make me think that maybe this is not true.
I enjoy very much your comments and advices and thank you all.
Daniel
The problem would be to establish what is the proper tension.
The designer would have used the hull's resistance to being heeled to
calculate the load on the rig, and thus the strength of the stays and
shrouds, but how tight? As another poster has said, you don't want the
rig too loose as the mast flopping back and forth puts undue stress on
things. On the other hand excessive tension may deform the hull to the
extent that you get stress cracks in the gel coat (actually saw this
on two catamarans rigged in Thailand.
Most authorities on tuning rigs say that (1) the mast should be
vertical; (2) the mast should be straight; and (3) the lee shrouds
should not be unduly loose. (note: I am avoiding mast fore and aft
bend).
Googling +sailboat +"rig tuning" gets some 4,000 sites on this
subject.
http://bbs.trailersailor.com/forums/...frames/read/92
for example.
I would offer one caveat though. Not all posts on the Internet are
actually authoritative. Many are made by individuals who are really
just describing "how they did it" and "how they did it" may actually
be incorrect. My suggestion is unless the procedure is described by a
known authority (Brian Toss, for example) take it with a grain of salt
and do more research to determine whether the poster actually knows
what he is talking about.
Bruce-in-Bangkok
(Note:remove underscores
from address for reply)