For what its worth, Forespar gives whisker pole sizing info for C&C:
http://www.forespar.com/products/sail-spinnaker-pole-size-guide.shtml
In PHRF Long Island Sound, the max whisker pole length is equal to your
LP measurement. If you use your J-length spinnaker pole instead, PHRF
LIS gives you a +6 credit for LP above 135%, and +3 for LP from 120% to
135%.
Neil Gallagher
Weatherly, 35-1
Glen Cove, NY
On 8/24/2016 10:49 AM, Michael Brown via CnC-List wrote:
Hi Rick,
I am not familiar with the rule of thumb for optimum whisker pole
length, though it looks like
the geometry is setting the pole at right angles to the boat, and the
jib holds a 60 degree angle
at the tack.
For light air dead run I set the jib at 90 degrees to the centerline
to maximize projected sail area
and ignore flow around the sail. As you say a barn door.
About 3/4 the way down there is a chart in the section "Drag
Predominate ( separated flow )":
https://en.wikipedia.org/wiki/Forces_on_sails
The driving force ( Fr ) in the right hand side diagram is at
maximum with the sail at 90 degrees.
Also the drag force is directly in line with the boat, presumably
where the mark is, where as if the
sail was at a 60 degree angle to the wind the lift would also be at 60
degrees.
I am in an area where PHRF allows long whisker poles and no
adjustment for length. In light air
and flat water the barn door trim seems to be the fastest.
Michael Brown
Windburn
C&C 30-1
From: "Rick Brass" <rickbr...@earthlink.net>
If your J is 13?6?, the LP of your 155 is 20?11?. By the rule of
thumb, the optimum whisker pole length is about 16?9?.
With the 13?4?pole at the mast and perpendicular to the centerline
of the boat, the line from the tack fitting to the end of the pole
is 19?1?. Perpendicular to the center line would project the sail
out as far as possible (which is what the whisker pole is supposed
to do). There should have been some curvature to the sail, which
you want so you get the maximum pressure on the sail (a cupped
shape generates more pressure than a flat barn door shape). I find
I usually run the pole about 15 to 20 degrees forward of the mast
to promote that cupped shape.
The LP of your 135 would be about 18?3?, so the spin pole would
stretch the sail flat and still be a bit forward of perpendicular.
(Optimum whisker pole would be 14?7?) You might need to run the
spin pole at a forward angle to get the proper sail shape, though
that doesn?t get you the maximum projection of the sail.
And the essence of a whisker pole is that the length is
adjustable, so you and match the length to the size of the
headsail you are flying.
Mike Hoyt?s comment that a pole longer than J costs you seconds in
most PHRF areas is true. But not in all areas. And some of us are
cruisers who want to get the most out of the boat, even though too
short handed to fly the spin except on a log run.
Plus I have always thought the use of J for max pole length in
non-spin racing to be arbitrary and slightly inequitable in those
regions that give a separate rating for spin and JAM racing. Seems
like if you race JAM, you ought to be able to optimize the boat
for JAM racing.
Rick Brass
Washington, NC
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what we do, please help us pay for our costs by donating. All Contributions are
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