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A
pic you might be interested in. It is a 1=20 scale model of
a 90 foot sled scheduled to begin construction in Jan 2003.
It will have a canting keel as well as water ballast, and
if all goes well, should be rocket fast. This picture was
taken last week in the Wolfson wind tunnel of the University
of Southampton, where the Spitfire fighter was tested. It
is taken at 17 degrees apparent wind angle, with 15 K apparent
wind speed. As you might surmise, apparent and true are the
same here. We test for the best ratio of Driving force (DF)
vs. roll moment (RM). There are sensors at the bow and on
the bar thru the hull which measure these forces, which can
be seen in the photo. The little D size battery unit just
to leeward of the cockpit is a remote video camera with the
same view as a sail trimmer! The test goes something like
this.
The
sail trimmer (via remote control) sets the sail trim as he
feels best, and a sample is taken via computer. Then he is
free to play with trim, aiming for better numbers. When the
best numbers are achieved and more samples taken, the sails
are trimmed tighter and tighter, until the efficiency is on
a deep curve downward.
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Then
the sails are eased back to peak, thru the best numbers, and
begin the curve downward, again samples being taken thru the
process. This process is repeated for several apparent wind
angles, relevant to the sail, and repeated for all the sails
being tested. In this three day test, we ran thru 3 jibs,
4 a-sails, and two mains. All in all, we ran something like
250 runs over the 3 days. The goal is to establish VPP's showing
the advantages of a Genoa over 100% jib, crossovers from genoa
to code "0", "0" to reaching assy. ect.
In
the end, this will go a long way towards developing the polars
for this boat, and will have a definite influence in the finished
design of the boat. It is accurate to a point where the large
roach main shown held the same slight DF advantage thru the
range of angles.
Kind
of a cool shot that I thought your readers might like.
Keith
Lorence
06/03/2002
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