Would you mind listing some of the sailing books you use to learn about sail
trim and so forth?
Thanks
gretchen
<><
----- Original Message -----
From: <JBlumhorst@aol.com>
To: <wwpotter@tscnet.com>
Sent: Thursday, September 16, 1999 8:40 PM
Subject: Sail Trim Primer [Was: P19 Outhaul -- Was Re: P-19 Sail Flutter ]
> - - - - - - - - - - - - - - - - - - - - - - - - - - -
> West Wight Potter Website at URL
> http://www.lesbois.com/wwpotter/
> - - - - - - - - - - - - - - - - - - - - - - - - - - -
> In a message dated 9/16/99 1:55:21 PM Pacific Daylight Time,
> 72602.3066@compuserve.com writes:
>
> > - - - - - - - - - - - - - - - - - - - - - - - - - - -
> > West Wight Potter Website at URL
> > http://www.lesbois.com/wwpotter/
> > - - - - - - - - - - - - - - - - - - - - - - - - - - -
> > OK....I guess it's time to fess up and add my dumb question, since I've
> > been quiet for awhile and just enjoying all the posts. Even though I've
> > been sailing for a number of years, it's been all on small daysailors
with
> > a minimum of equipment. Along with being self-taught, here's my
question:
> >
> > What is an outhaul and what is it's purpose and how is it used?
> >
> > Same question for the downhaul.
> >
> > Opps! That's 2 questions! And I sometimes wonder how I manage to get
> > anywhere on my boat, knowing as little as I seem to know.
> >
> > At any rate, thanks in advance for your answers and putting up with
what
> > may qualify as a Top Ten Dumb Question for 1999.
> >
> > Bruce
> > P-19 #969
> >
> Hi Bruce,
>
> Here's something I wrote back in May of this year. I call it my "Sail
Trim
> Primer". It's got the basics of how and why you use all those danged
ropes
> hanging off your sails. From the feedback I got last time, I kept it
simple
> enough so people were able to actually understand and use the information.
> Give it a read!
>
> PS -- After you get a chance to ponder how the controls work, there's an
> addition or perhaps correction I need to make about the vang and twist at
the
> top of the sail. But the info in it is generally correct and I haven't
the
> time to write the addition.....
>
> Best,
> Judy B
> 1985/1999 WWP-19 #266 "Redwing"
> SF Bay, CA
>
> Forwarded Message:
> Subj: Re: Shrouds & Bendy Rigs
> Date: 5/20/99 9:50:54 PM Pacific Daylight Time
> From: JBlumhorst@aol.com
> To: wwpotter@tscnet.com
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - -
> West Wight Potter Website at URL
> http://www.lesbois.com/wwpotter/
> - - - - - - - - - - - - - - - - - - - - - - - - - - -
> In a message dated 5/20/99 6:07:08 PM Pacific Daylight Time,
ttursine@gnt.net
> writes:
>
> > OK, Judy, now that my opinions are out, it's time to learn something.
> > I've never had the opportunity to experiment with a "bendy" rig, so
> > I'm curious about the nature and magnitude of the effect. Your talk of
> > 1"-2" changes implies a powerful cause/effect relationship.
> >
> > In the absence of an adjustable backstay, changes in sail flatness and
> > draft position (to accommodate wind ferocity) are made by adjusting
> > halyard, outhaul, and sheet tension -- and maybe the vang if one sails
> > sans traveler. My question is: does creating a concavity in the luff
> > by bending the masthead sternward offer an additional capability or is
> > it just an alternate, easier way to adapt to increasing winds? More
> > simply: are the results _significantly_ different/better or just more
> > easily achieved?
> >
> > Regards,
> >
> > Bill Combs
> > WWP 19 #439 (Aug 1987)
> > "Ursa Minor"
> > Fort Walton Beach FL
> > ttursine@gnt.net
>
> Hi Bill et al,
>
> I'll take a shot at answering your question in more detail.
>
> I'll try not to go into toooooo much detail. and bore you to tears.
>
> Here's an advance tip before you wade into my sometimes dense writing.
Pay
> close attention to what part of the sail is being depowered by the
trimming
> technique. Different trimming techniques affect different parts of the
sail,
> but they all do the same thing, power up or power down one particular
section
> of the sail. The key is what part of the sail are you trimming.
>
> Regards,
> Judy
>
> PS. I tend to be completely blind to my typos and errors right after I
> write something, so please forgive my obvious errors and confusing parts.
> Cut and paste sometimes screw things up royally. It's the best I can do
on
> short notice.
>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Introduction and executive summary :)
>
> Backstay.
> Initially flattens *middle* third of sail and depowers the draft. Further
> tightening loosens and depowers the *upper leach*.
>
> Outhaul.
> Flattens and depowers the *foot* of the sail
>
> Vang,
> Flattens the *middle* third of sail and depowers the draft. *Powers up
the
> upper third* at the leach by reducing twist off in gust, too much vang
makes
> boat very twitchy, causes increased heeling especially in gust.
>
> Cunninghma (halyard, boom downhaul). Tightens luff of sail and moves
draft
> forward. Offsets tendency of draft to move aft in strong wind. Keeps COE
> forward and *reduces weather helm*. Plays a very minor role in flattening
> the draft
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Explanation:
>
> This is geared towards the P19 mostly.
>
> If your shrouds are properly tuned, tightening the backstay doesn't bend
the
> tip of your mast aft half -- it primarily bends the middle of the mast
> forward. Tightening it doesn't create a concavity along the leach of the
> sail-- it primarily pulls the middle of the sail (where the draft is
deepest)
> forward and flattens the draft.
>
> The outhaul flattens only the bottom 20-30% of the sail. The foot of the
> sail doesn't give you more than a small fraction of your power. You can
> significantly depower the sail by tightening your outhaul, but not alot
> compared to flattening the draft. The draft is where the sail generates
most
> of its power.
>
> In order to flatten the middle third of the sail where the draft is, you
have
> to bend the mast in the middle forward somehow. It's quite startling how
> much flatter the draft gets when you bend the middle of the mast forward
an
> inch or two. It reduces the depth of the draft on my P19 sail by almost
50%
> and depowers it significantly. By bending the mast, you depower the most
> powerful part of your sail, right at the draft.
>
> When you first start to tighten the backstay, you primarily flatten the
draft
> by moving the middle of the mast forward. If your shrouds are properly
> tuned, the lower shroud limits any more forward bending of the middle of
the
> mast after about two inches.
> If you continue to tighten the backstay just a little more, then the mast
> tip gets pulled down and back a little. Just an inch inch of backward
> movement of the tip loosens the tension on the very top part of the leach,
> and it gets a little floppy. When a gust hits, it twists off and spills
> wind. Your boat is more stable in the gusts. You have enormously
increased
> the comfortable and safe wind range of your sail, because now you've
> depowered the very top of it, the part that makes you heel so much.
>
> In the absence of a back stay, the only way to bend the middle of the mast
> forward while our sailing and thereby flatten the draft is by using the
vang.
> Tightening the vang pulls down on the leach, and the tight leech bends
the
> mast. It pushes the middle of the mast forward, flattening the draft in
the
> mainsail. The vang's good for flattening the draft and depowering the
middle
> third of the sail, but there's a trade off. You've actually made the sail
> less forgiving in the gusts by tightening the leach.
>
> With a vang, the top of the leach is even tighter than before, and it
can't
> twist off and spill wind in a gust. The center of effort in the main is
> effectively higher than before. The wind powers up the tip of the sail
with
> every gust, and that's a long lever arm with which push the boat into a
hard
> heel. Your boat is a lot twitchier in the gusts, and less forgiving of
> helmsmen's error. Heeling over like that digs the chines in and increases
> the weather helm, especially on a hard chined boat like a Potter or a
Force 5
> (my dinghy). Now you're fighting to keep her nose from rounding up into
the
> wind with every strong gust.
>
> On a lot of boats with a vang and no backstay (like many catamarans, the
> Laser and the Force 5, and windsurfing sails too) the top section of the
mast
> is tapered and much more flexible than the rest of the mast. That's to
> restore the ability of the top of the sail to twist off laterally and
spill
> wind when a gust hits it. Even still, there's definitely a point of
> diminishing returns with a vang unless you can hike way out.
>
> Tightening the main halyard, as you suggest, moves the draft forward. So
> does moving the boom down with the downhaul. That's a good thing thing to
do
> when the wind velocity increases. There's a tendency for the draft in
the
> sail to move aft as the wind builds, which gives you increased weather
helm.
> When it's really windy, you want to be sure your halyard is nice and tight
so
> your draft doesn't move aft.
>
> But it's hard to adjust the halyard (or downhaul) once you're already
rigged
> and the wind starts to build. That's why most boats with a fixed
gooseneck
> have a cunnigham. The cunningham is a line that goes through a cringle in
> the sail a few inches above the gooseneck. When you tighten the
cunningham,
> it has the same effect as tightening the halyard or the downhaul for the
> boom. When it's really blowing, you want to tighten your cunningham.
> Incidentally,
> it does flatten the draft just a tiny bit when you tighten the boom, main
> halyard or cunningham.
>
> The sheets don't do much to the sailshape. Mostly they just change the
angle
> of attack. The one exception is when you lock the traveller car in place
on
> the track (if there is a track) and two-block the main sheet (tighten it
> maximally so the blocks on the boom are kissing the blocks on the boat).
> Then you're pulling down on the boom, much like a vang does. This bends
the
> mast forward in the middle, depowering the draft, but tightening up the
top
> of the sail so it can't twist off in the gusts. Sometimes it's
advantageous
> to do that, but usually it's better to use a backstay or a vang if you
have
> it.
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Everything I wrote above applies equally to apparent wind, not just
absolute
> wind. After all, we all sail on apparent wind not absolute wind. High
wind
> trimming works well for pointing in moderate winds, low wind trimming
works
> well for downwind reaches in moderate winds.
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Whew! That's a lot to try to explain. I hope I did a decent job. You can
> read a better, more detailed explanation in any good sailing text. I was
> mainly trying to sort out the different used for most common sail trim
> techniques, what they do and why you might use them.
>
>