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Shroud Tension
WARNING: While discussing and testing
shroud tension at the C&C Regatta we discovered that the Loos gauges can
vary by at least 3 or 4 units or several hundred pounds tension. Please use the
numbers below as a guide and not as absolute values.
I have been asked to post something
on shroud tension. Firstly I would like to reiterate what "Crown
Royal" said in his "Words of Wisdom" because I think they are
very true.
Rigging Tension.
1996
Contrary to popular thought, a slack rig
is more punishing on a hull than a properly adjusted tight rig. Insufficient
tension will not reduce the loads transmitted to the hull. Slack rigging
will punish the spar and rigging needlessly by allowing excessive movement,
chafe and shock loading.
A properly adjusted, tight rig should
not damage fiberglass hulls. On the other hand overly tight rigging will
cause hull or spar damage. In order to extend the life of your boat and
equipment, I would recommend that you purchase one of the gauges on the
market. It is a small investment for the safety and extended life of your
boat.
I thought I could gauge the tension in a wire by
"feel", until one year a borrowed a gauge and measured my shroud
tension after I had set it up by hand. I was surprised to find significant
differences from side to side and of course I had no idea how it was set the
previous year. I immediately put a gauge on my Birthday list.
I guess it's like most things, if you ask five
people you get five different answers. However, I will risk declaring the four
basic rules I use.
-
The leeward shrouds should never be
slack even when beating in a good wind
-
The shrouds should not be too tight
(less than 25% of breaking strain)
-
The mast should be straight and
vertical in a port/starboard sense
-
The mast should have a modest
pre-bend and rake in a fore/aft sense
I have recorded the rig tensions I
used over the last five years and include the average values below. You should
recheck the tensions after a couple of weeks and tweak them if necessary. I
don't place much importance to the forestay as I have an adjustable backstay.
|
Shroud Tensions (5 Yr Average)
|
| |
Forestay |
Fwd Lower |
Upper |
Aft Lower |
| Diameter |
3/16" |
5/32" |
3/16" |
5/32" |
| |
|
|
|
|
| Average
Loos Gauge # |
12 |
25 |
28 |
24 |
| Minimum |
8 |
23 |
27 |
22 |
| Maximum |
13 |
26 |
30 |
25 |
| |
|
|
|
|
| Avg. LBS. |
270 |
660 |
750 |
610 |
| |
|
|
|
|
| Breaking
LBS. |
4700 |
3300 |
4700 |
3300 |
| |
|
|
|
|
| % of
Breaking |
5.6 |
20.1 |
16.1 |
18.5 |
|
|
|
|
|
NOTE FROM DAVE
While browsing I checked the comments on shroud tension and Andrew's numbers
that he uses on the Loos Gauge. To my surprise your numbers are
almost the same, my uppers are one number higher. I have been tweaking my rig
for 8 or 9 years and seems to work well. While on the subject I find the
following is the way to tune your rig. With all rigging loose, tighten the
uppers and get your mast plum. This is the time to put in the rake. I use the
main halyard and measure from side to side until it is plum now hand tight all
the rigging. I then bring the uppers close to the tension I require. Then do the
lowers to the tension you want. Finish with the uppers to the tension required.
Now check to see if your mast is in column. If not adjust your lowers again. I
find the best thing is to fasten the main halyard at the base of the mast (with
no boom) I then take up a bit of tension. Then compare your mast to the straight
line of your halyard. The whole job takes about 45 minutes. After a sail in
winds of about 15 knots check again and adjust. BUT you have to have a gauge.
There is no way without.
Dave Smith
