Re: Genoa tracks

Kent Crispin (kent@songbird.com)
Wed, 3 Mar 1999 17:07:13 -0800


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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On Wed, Mar 03, 1999 at 01:27:33PM -0800, Eric Johnson wrote:
>
> On that last point, i'm not 100% convinced that the ability to sheet the
> headsail in so far is of major benefit on a potter. Remember that proper
> headsail trim is generally when you sheet in just enough so the headsail
> isn't luffing. I certainly don't use as tight an angle as I could even with
> my arrangement, yet I go upwind just fine. I could point higher, but I'd be
> pinching and stalling the keel in that situation, so i wouldn't actually get
> anywhere any quicker. I've done a lot of research on racing and whatnot, and
> its so important to have boat speed that you should often trade it off for
> pointing anyways (e.g. better to be going 3 knots at 50 degrees relative to
> true wind than 2.5 knots at 45). I'd REALLY like to race Jerry or Judy
> sometime to test some of these theories of mine.

I'm not much of a sailor, but I am mathematically inclined...

Here's a little table of what a difference in 5 degrees pointing
makes in your actual upwind speed:

10-5 degrees: 1%
15-10 degrees: 2%
20-15 degrees: 3%
25-20 degrees: 4%
30-25 degrees: 5%
35-30 degrees: 6%
40-35 degrees: 7%
45-40 degrees: 8%
50-45 degrees: 10%
55-50 degrees: 12%
60-55 degrees: 15%
65-60 degrees: 18%
70-65 degrees: 24%
75-70 degrees: 32%
80-75 degrees: 49%
85-80 degrees: 99%
90-85 degrees: infinity

That is, if you can point at 30 degrees off the wind instead of 35
degrees off the wind while maintaining the same boat speed, your true
upwind speed will increase by 6%. Alternatively, it means that if
you point 5 degrees higher than 55 degrees off the wind, and you
pinch and slow down boat speed by 12% or more, you have gained
nothing in terms of true upwind speed.

At 90 degrees you make no forward progress at all, of course. The
extreme numbers at the top are meaningless for sailboats, though I
understand that ice boats can point *very* high, and can get up
incredible speeds (they are going so fast that the apparent wind is
shifted a great deal from the true wind).

These are purely theoretical numbers, of course.

-- 
Kent Crispin                               "Do good, and you'll be
kent@songbird.com                           lonesome." -- Mark Twain