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West Wight Potter Mailing List maintainer
dfarrell@ridgecrest.ca.us
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Potter-ers,
Chris and I thought you might like to read the rest of the story about the
lee-helm Sunday on his boat, so we decided to forward it to you.
Judy
> -----Original Message-----
> From: chris.beatty [mailto:chris.beatty@bankofamerica.com]
> Sent: Monday, March 27, 2000 3:36 PM
> To: DrJudyB
> Subject: RE: Balancing the helm when reefing - Mast attitude
>
>
> Judy,
>
> You have just touched on what I was trying to ask yesterday on
> the boat: What
> if we had just tensioned the backstay? See, we slacked the
> backstay to hoist
> the mast and secure the CDI foot. When I did this for my trip to
> Monterey last
> weekend, I counted the turns on the turnbuckle (an even dozen).
> But, I'm not
> even certain it was tuned up after I had re-tuned the slack
> shrouds. When I
> put the mast up this weekend, I was talking to my friends and
> forgot about the
> backstay. I didn't realize it until we hoisted the main sail and
> confused the
> backstay for the topping lift!
>
> I guess what I would like to know is, how much tension is
> appropriate for a
> backstay? Is there a tension to start at? With the upper and
> lower shrouds
> tuned to the 14% and 10% range respectively (as is suggested in
> the fractional
> rig tuning guides I have read--and per your suggestions), I had a
> devil of a
> time getting the CDI foot off to lower the mast. It was much
> easier once I
> loosened the backstay. Is this what others have found? Or was
> loosening the
> backstay the wrong thing todo?
>
> The upper and lower shrouds are set aft the mast (in a fractional rig),
> therefore when I tuned my slack shrouds, I also placed additional
> tension on my
> forestay/CDI. How does one judge the proper tension on a
> "forestay" when ones
> forestay is really a "CDI?"
>
> I realize that re-tightening the backstay is something that I
> should do before
> hoisting the main sail ;-) but how much? I have had similar
> "forgets" when I
> get to talking to interested parties on the dock about the Deep
> Blue,... Oh the
> trials and tribs of being a POOP!
>
> Chris Beatty
> P19 #1176 Deep Blue
> Alameda, CA
-----Original Message-----
From: Judith Franklin Blumhorst, DC [mailto:DrJudyB@pacbell.net]
Sent: Tuesday, March 28, 2000 10:21 AM
To: chris.beatty
Subject: RE: Balancing the helm when reefing - Mast attitude
Ohhhh, my goodness - you loosened the backstay 12 turns?!? I must have
missed that VERY important detail. I remembered that you told me you had
retuned the side shrouds, but I didn't hear you say that you loosened the
backstay to raise the mast and didn't re-tension it!!!
Yes, we should have re-tensioned the backstay! That would certainly explain
why the boat handled so differently on Sunday than it did the last time I
sailed it! That really was a nasty lee helm.
On Redwing, we have an adjustable backstay which we loosen completely to
raise the mast. When we're sailing, I adjust it to get the desired helm
under a broad range of conditions. For my boat, the mast is correctly raked
when the mast flexes about 1 inch - that gives me just a little weather
helm. If I sailed with no tension on the backstay, it would probably have
weather helm. I do loosen the backstay entirely when sailing almost dead
downwind to improve sail shape, but otherwise it has significant tension on
it at all times.
Your boat is a little different, but not that much, because you have an
essentially fixed length backstay. The tension we set the first time we
tuned it gave you about 2-4 degrees of aft rake. We also set the forestay
pretty tight to prevent sagging when you point. That much tension would make
it hard to attach the front forestay pin. You probably do need to loosen
the backstay to put up the mast, and if you do, you need to tighten it
afterwards!!!
One alternative would be to get a lever-release that opens and closes,
giving you a temporary way to de-tension the backstay while mast raising.
Johnson makes a very nice lever release for around $60, and I'm sure others
rigging manufacturers do too. The other alternative would be to put some
blocks in there to make the backstay adjustable, but that puts some
additional responsibility on the skipper not to be too heavy handed (and I
have some concerns about how the well the DM5 masthead is attached to the
mast if the skipper is much too heavy handed)
In general, my impression is that the forestay should be about as tight as
the uppershrouds. On a fractional rig, My impression is that the backstay
should be a little looser than the forestay. Those are just starting points
for tuning. In reality, the degree of mast rake required to produce
weatherhelm while your sailing is what determines the relative tensions of
the two stays. I just started with about 2-3 degrees of measured rake on
your boat for the docktune and then tested it on the water. It worked pretty
well under sail and the helm felt very good, and the boat was responsive and
fast. I wasn't too concerned about really fine tuning it, because I knew
the wire rope would stretch after a few hours of sailing, so we'd just have
to re-tune it again soon.
The reason I start with tensioning the forestay about as tight as the uppers
is that that's a good starting point to keep forestay sag to a minimum.
(and a some other complex reasons that have to with how the mast responds
dynamically to increasing wind that I won't go into here) A sagging forestay
causes the jib to belly out alot and really hurts your boat's ability to
point. Unfortunately, that much tension makes it impossible to attach the
forestay on a trailerable without some mechanical advantage. On my boat, I
use the winch to get enough mechanical advantage, and that's even with
loosening the backstay.
How the hull floats, fore to aft, affects weatherhelm too. (It seems like
more than one person has moved the battery up under the vberth to good
effect (like I did) and put alot of other weight up front like extra
anchors, etc) How you trim the sails affects weather helm, as you saw
demonstrated when I used the sails to steer the boat Sunday. BTW, like most
other skippers who are new to the Potter, you had a tendency to oversheet
the main on points of sail below a close haul. That increases heel and
makes her "feel" faster, but in reality you're probably going slower and
needlessly increasing weatherhelm. If you trim so there's 12 degrees of
heel, she has really good manners when the gusts hit and she's fast to boot!
How much sail area you have fore and aft affects weatherhelm, but not
usually to the degree that happened last Sunday. I thought it was very weird
how she sailed Sunday, and I was totally freaked out when I couldn't make
her point. I just wanted to get home! I had visions of us sailing downwind
until we ran out of Bay ;^) Once that worry was eliminated, I was content
to enjoy a leisurely sail on someone else's boat, with somebody else doing
all the work. That was a treat.
I wasn't about to mess with the tuning on the water. I remembered you said
you had tightened the side shrouds, but I completely missed the fact that
you had loosened the backstay 12 turns. I thought it was still about how I
left it last time. I figured the rig tuning issue could wait until Monday
morning, which is when I started this thread.
Chris, maybe you ought to post this to the full list, because it clarifies
what was going on with your boat last Sunday. You wrote me via private
email, but I think it's a good one for the list.
Fair winds,
Judy
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