Tuning shrouds is an art. There are two stages -- rough tune at the dock or
on the trailer, and fine tune while sailing.
(BTW, I know just the basics about tuning shrouds, and right now I'm on a
project to learn more. My rigger tuned my shrouds for me once and taught me
how, but I'm defintely no expert. So I may have some small mistakes in this.
Maybe sometime later this year, when I've learned more, I'll write up a full
tuning guide to the Potter 19)
1. On land: First, get the mast straight from side-to-side. You can take
the main halyard and pull it to the chainplate on one side, note the length,
and then take it over to the other chainplate. If the mast is straight from
side to side, the halyard should be the same length from side to side. If
not, tighten the appropriate turnbuckle to pull it over.
Shroud Tension -- This is the way my rigger showed me. The upper shrouds
should be tighter than the lower ones. for the uppers, if you take two
fingers and pull the shroud gently, sideways, at about 4 feet off the deck,
the shroud should move about 1.5 inches (two or three fingers width) before
you feel a marked increase in resistance. You've got to pull gently or else
you miss the point where the resistance increases markedly.
The lower shrouds should be *much* looser than the upper ones. The purpose of
the lower shrouds on a fractional rig is to limit forward bending of the mast
at the middle when you vang (or tighten your backstay if you have an
adjustable one). They aren't necessary for lateral stabilization of the
mast; the uppers are suffiecient for lateral stabilization. If the lowers
are too tight, they prevent the middle of the mast from bending forward,
which "sucks" the draft out of your sail, flattening it and reducing power in
heavy winds.
My lower shrouds are almost floppy when the vang and/or backstay are loose.
They are set to get real tight when there is about 2" of forward bend in the
mast. This keeps me from bending the mast too much. that 2" of forward bend
takes about 6" of draft out of the mainsail when I need to flatten it in high
winds.
~~~~~~~~~~~~~~~
For front to back straightness (called mast rake), you can start by
eyeballing the boat from 30 feet back. Or you can use a level to get the
cockpit seats level (adjust the trailer) and then put the level on the mast
and adjust until the mast is perfectly upright. That's a starting point for
your tuning after sailing it.
Forestay and backstay tension -- don't succumb to the temptation to make your
forestay loose, just so that you can attach it easier. The luff of your jib
(leading edge on the jib) will sag when you sail and you won't be able to
point high and the boat will have a tendency to turn downwind (called "lee
helm") and heel too much . It needs to be pretty tight. Get that forestay
tight !
~~~~~~~~~~~~~~~~~~
2. As for tuning on the water, there are two things you want to check for.
The first isn't too hard -- when you're sailing, look at the leeward shrouds,
They shouldn't be really, really flopping around. if they are, you've got
them too loose. A little slack is okay (unless you subscribe to the
shock-loading school)I don't know how much is too much, wish I could give you
some better guidance, but.... I'll just do the best I can.
When you're out sailing, the leeward (downwind) shrouds shouldn't be sagging
a great deal, but they will certainly be less tight than on land. There are
two schools of thought on this. some folks say a little loose is okay. some
say they should still have a little tension, or else it shock loads the
rigging when you change tacks. I don't know which school is correct. Mine
are defintely loose on the leeward (downwind) side, but they don't sag with a
curve (unless I've got WAY too much sail up , in which case I'm also heeling
too much and wrestling the tiller).
The second part of tuning on the water is more complex. It has to do with
weatherhelm. Weatherhelm is builit into a boat. It means that the boat
should turn it's nose into the wind if you let go of the tiller. That's a
good safe thing for a boat to do, right?
So while you're sailing, you should have to lightly (and I do mean lightly)
pull on the tiller to keep the boat from rounding up into the wind. The
basic idea here is that if the mast is raked aft too much, you'll have too
much weather helm. you'll have to pull too hard on the tiller to go straight
and the rudder will be acting like a brake. To reduce weatherhelm, you
loosen the backstay and tighten the forestay. If the mast is raked too far
foward, you might have a "leehelm" --which is dangerous because if you let go
of the tiller, the boat will run away downwind!
There are other things that can increase weatherhelm too -- too much sail
area, too much heeling, too much mainsail compared to jib, too much weight in
the front of the boat (not likely on a P19, with two people in the cockpit).
Rousmaniere's book "Annapolis Book of Seamanship" has a couple of nice pages
on tuning for weatherhelm on pages 85-87. He also gives a method of
measuring weatherhelm to know if you've got the right amount. (Your tiller
should be at about 2-3 degrees off center when you've got the right amount of
weatherhelm, assuming you hae your boat loaded correctly and you are heeling
appropriately, which for a Potter is 12-15 degrees or so)
~~~~~~~~~~~~~~~~~~~~~
As for fastening the turnbuckles -- do you have closed body turnbuckles with
two nuts on the top or do you have open body turnbuckles (where you can see
the threaded part of the toggles)? Somebody else will have to advise you on
the specifices of the closed-body ones, cuz I have open body turnbuckles.
If you have a CDI on your jib, you have at least one open body turnbuckle,
inside the furling drum. don't forget to put a cotter pin in that, because,
for sure, it will unsrew itself loose when you furl and unfurl the jib! That
will bring your mast down.
The general idea is that once you have the length set and tuned, you need to
fix them at that length. On my open-body turnbuckles, I put cotter pins
through tiny holes in the threaded part. A cotter pin is like a bobby pin of
stainless steel. you put the pronged end through the hole and then separate
them about 30 degrees. I cut off one prong and bend the very tip of the end
60 degrees, leaving just enough length to catch on the side of the turnbuckle
body. I cut the other prong a little shorter and leave it straight. Then
wrap about 3 or 4 layers of self-sticking riggers tape around the turnbuckle
body and cotter pin. Don't bend the cotter pin prongs way out, you won't be
able to pull them out in an emergency. (My rigger taught me that)
On the closed body turnbuckes, I guess you just put tape around the locking
nuts, but i really don't know what I'm talking about here... :^) Somebody
else chime in here, please???
You also need to put riggers tape around the circular clips that hold the
turnbuckles to the chainplates and shrouds. You don't want to have a jib
sheet (line that you use to trim the jib) or your pantleg pull out that clip
by mistake!
~~~~~~~~~~~~~~~
Hope that helps. When in doubt, spend a few bucks and get your local rigger
to show you how. Read Rousemaniere's chapter 1,2, 3 (on sail trim) and 15
(on heavy weather sailing) so you understand what you're doing to your boat.
That's better than all the words I could possibly write.
Best,
Judy B
In a message dated 9/26/99 8:53:44 PM Pacific Daylight Time,
gpotter@calinet.com writes:
>
> The only thing that happened that I have to figure out is the turn buckles
> on the shrouds kept coming loose. I have to "tune" the rigging this week.
> Back out to the parking lot I guess. But now I know how to raise the mast
> the mast raising system so I know I could get the mast up by myself and
> tune the rigging. I think I'm supposed to tape them or something once
> everything's tuned. Any ideas?
>
> I remember reading on this board how to tune the shrouds but now I can't
> find it. Can someone point me to it again. Sorry.
>
> gretchen
> <><
> P19 #1121 "Sparrow"
>