[Rhodes22-list] shroud tension
Roger Pihlaja
rhodes22-list@rhodes22.org
Tue, 20 Aug 2002 07:56:38 -0400
Jack,
Here's a copy of the rig tuning procedure I use:
The 1st thing you want to do is measure the length of the forestay on center
from pin-to-pin. On my 1976, standard mainsail, Rhodes 22, this measurement
is 333.625 inches. Write this number down because it is very important.
If your forestay length is more than a couple of inches different than this,
you might want to reset it 333.625 inches as a reasonable starting point.
Now step the mast. Take the excess slack out of the forestay & backstays
with the backstay adjuster. You don't want things real tight at this point.
All upper & lower sidestays should be slack. Go to the base of the mast,
pull a halyard taut along the mast & sight up the mast from the rear & from
the side. Any deviation from a straight mast will show up as a gap between
the mast & the halyard. There should be no observable bend or bowing in the
mast. If there is, the mast may have been dropped & bent at some point or
may have some other problem. You should call Stan at GBI & he will be able
to help you work out your problem.
I like to use a Loo's tension gage. The model 91 is the appropriate range
for the Rhodes 22. Remember to always measure the tension at the same
relative position on each shroud every time. On Dynamic Equilibrium, I
have marked these measurement points with little spots of paint on the
wire right at my eye level.
The upper sidestays are adjusted next. Raise a tape measure up the mast on
a halyard. Measure to the same point on each side of the boat. I like to
use the edge of the toerail right next to the sidestay. Tighten the
turnbuckles a little at a time on each side to adjust the upper sidestays
until both sides are the same length +/- 1/4" & tensioned to approximately
300 lbs +/- 5%. This procedure assures the top of the mast is centered in
the boat & the upper sidestays are tensioned equally port & starboard.
What you do next depends upon whether your boat has the IMF mainsail or a
conventional mainsail.
On an IMF mainsail boat, I would adjust the 4 lower sidestays so they were
all approximately the same tension. I would start with approximately 200
lbs +/- 5% on all 4 lowers. This is not a lot of shroud tension. Check for
mast straightness with the halyard again. You want the mast to be straight
in order for the IMF furling mechanism inside of it to be able to turn
without binding &/or excessive wear on the bearings. Minor bending or
bowing can be taken out with the lower sidestays. However, I would call
Stan at GBI if I couldn't get the mast to straighten out with a difference
of about +/- 15% on lower sidestay tension.
My Rhodes 22 has a conventional mainsail. I have a very roachy fully
battened mainsail which has been cut to respond to mast bend. I have my
backstay adjuster set-up to adjust quickly from the cockpit with calibration
marks on the line.
Tighten the turnbuckles equally & a little a time on each side to keep
things reasonably centered. I adjust the forward lower sidestays to 400 lbs
+/- 5% of tension, and the aft lower sidestays to 200 lbs +/- 5% of tension.
Then, check for mast straightness with the halyard. Believe it or not, the
standard mast on the Rhodes 22 is such a stiff telephone pole that, at 200
lbs differential tension on the lowers, there will be a barely detectable
fore/aft bend in the mast with no sails set & the backstay adjuster slack.
At 400 lbs of tension on the lower forward sidestays, when the backstay
adjuster is tensioned, primarily only the upper half of the mast is pulled
towards the stern. The forestay is tightened & the mast is bent at the same
time. Both actions are exactly what you want to obtain proper sail shape in
a high wind situation.
Now go out sailing. On a close hauled course, put up enough sail to heel
the boat over about 15-20 deg. Make certain the rudder blade & centerboard
are all the way down. On my Rhodes 22, the above tension settings cause the
mast to remain straight & more or less centered in the boat. The primary
thing to check is the upper sidestays. On my Rhodes 22 with the above
unloaded tension settings, at 15-20 deg of heel, the windward upper sidestay
should have about 450 lbs tension & the leeward upper sidestay should have
about 150 lbs of tension. I have my upper sidestays set-up such that the
leeward upper sidestay tension drops to 0 lbs at about 30 degrees of heel.
At this point, the windward upper sidestay will be under about 600 lbs
tension. Note, normally the stays are set-up to give proper shroud tension
& the correct amount of weather helm with full sail set. This tends to
limit the weather window in which you can do this sort of tuning.
When all sails are properly trimmed & the boat is "in the groove", there
should only a slight amount of weather helm. If there is a huge weather
helm, or neutral, or lee helm; then, you need to adjust the rake angle of
the mast. If you have neutral or lee helm; then increase the forestay
length. To get rid of excessive weather helm, shorten the forestay. The
balance of the boat is very sensitive to this mast rake angle, so change it
in increments of about 1/2" at a time. Note, a slight amount of weather
helm
is desirable because it provides feedback to the helmsman, thus allowing
him to steer a better course. Excessive weather helm tends to tire the
helmsman out.
Once I'm happy, I lock the adjustment in place by taping the lock nuts on
the turnbuckles. I find I only need to do this adjustment once. The
Rhodes 22 is such a strongly built little boat that nothing ever seems to
stretch or bend. I do check the side-to-side upper sidestay length at the
beginning of every season; but, it's never changed in the 13+ seasons I've
been measuring it. Trailering set-up only involves adjusting the lower
sidestays since the rest are not disturbed.
As far as rig tension settings on the trailer vs. off the trailer, I've
found the
only rig tension adjustment that significantly changes is the backstay
tension.
You can set the tension on the rest of the standing rigging according to the
above procedure on the trailer. It will be very close to optimum when you
get the boat in the water, certainly good enough to do the on-the-water
fine tuning described above.
FYI, I slack off on the backstay tension when Dynamic Equilibrium is not
being sailed. As I mentioned above, the backstay adjuster has sufficient
power to affect the shape of the hull. Greatly exaggerated, imagine the
ends
of the hull being pulled upward like a 22 foot long banana when the backstay
adjuster is tight! There is no sense leaving the hull & rig under that kind
of
stress when the boat is not being sailed.
Jack, I hope this description of rig tuning helps you. Good luck!
Roger Pihlaja
S/V Dynamic Equilibrium
----- Original Message -----
From: "Jack Goldberg" <j_goldberg@hotmail.com>
To: <Rhodes22-list@rhodes22.org>
Sent: Monday, August 19, 2002 7:47 PM
Subject: [Rhodes22-list] shroud tension
> This list has been helpful in the past, so I'll come to the trough of
> knowledge to feed again.
> I noted with interest the thread about the mast plate bolts coming loose
and
> the response with regard to the tension of the shrouds. My 84' has a
> standard main. When I bought the boat this spring, the shrouds were very
> loose (obout 3 inches of play from side to side at about 3 feet from the
> deck. The guy I bought the boat from said that was OK, but now I'm
worried.
> Is there a spec' on how tight (or loose) the shrouds should be under no
> load?
>
> Jack Goldberg,
>
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