On Fri, 08 Feb 2008 19:18:53 +0100, Daniele Fua
wrote:

ha scritto:
On Fri, 08 Feb 2008 00:41:04 -0500, Wayne.B
wrote:

On Wed, 06 Feb 2008 16:57:58 -0500, wrote:

Loos makes the best known gauges for both wire and rod rigging. Available
online, or at many chandeleries.
http://www.google.com/search?hl=en&q...ge&btnG=Search

I was going to post some links, but realized that the OP is not in the U.S. and
would get more useful links by doing his own search where he is located. This
link will at least let him see what it is he's looking for! Thanks for the
addition.

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

Just a comment:

Are you talking about a racing boat or a cruising boat? If a class
racer then there should be some information about rig tension in some
of the class groups. If a cruiser then generally speaking the rig is
tuned by adjusting tension while under sail to make the mast stand
straight, or have the required bend.

Unfortunately, the latter description is only valid with older boats -
my own for instance has two lower and one upper shroud (each side) and
all can be adjusted at deck level. A more modern rig with upper
shrouds terminated somewhere up the mast would obviously be much more
difficult to tension properly at sea.

One point to consider is that all rig tension is ultimately fed into
the hull which is not a rigid structure, thus you actually want the
lowest tension that will keep the mast straight with no slack wires on
the leeward side. It is very possible to actually flex a hull by
tightening the shrouds too much. You quite frequently see boats with a
"hold down" strut tieing the deck to the keel to control this flexing.

I would suggest that given that a boat is not a rigid structure and
mast loading is a constantly changing number depending on sails
carried, wind, waves, ballast, etc., it is more important to adjust
the rig so that tensions on both sides are equal, rather then be
adjusted to some specific tension. In my experience (cruising only)
this can be done by simply "shaking" the shrouds to feel how tight
they are and by looking up the mast.

(Turned into quite a long comment :-)







Bruce-in-Bangkok
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