[quote=erice]been thinking about how the theory, fastest - 90degrees, has differed from my experience, top speeds - 100-120degrees.......maybe time for some definitions
90degrees to the wind should offer the best efficiency or fastest speeds at low wind strengths for day to day sailing
most of the polars you see tend to show 10mph winds
on my 5.2, once the wind picks up enough to lift my hull, even with my 75kg/170lbs fully trapped out, the boat is reaching it's max hull speed? on a true reach of 25kph/16mph/15knots and it will do this in about 12knots of wind which is most windy days where i sail
at those speeds the windward hull is just out of the water and the wind on the rig is forcing the leeward hull as deep (draggy) as it can safely go. this deep bow sends back a bow wave big enough to hit the outer edge of the forward beam as it is tilted into the waterflow.
this acts as a big brake with almost a fire hose of water spraying up
on that point of sail - (90 degrees), on that boat - (1975 designed 17foot beachcat without spin), with only my righting moment - (75kg/180lbs), the boat seems to be hitting a wall
any more wind at 90degrees just lifts the hull higher and over into a capsize, or buries the leeward bow deeper into a pitchpole
to avoid either i have to either dump sheet so the rig dumps power, or i have to steer upwind
on the rare occasions that the winds are reliably blowing the waves into white caps, 15-20knots?, it is will also moan through the rigging and send everything humming
that's the sign that it would be suicide to try and sail a reach with only my 180lbs to hold down 19m2/220sqft of sail (that when i usually remove the jib before going out and blow the traveller in tacks to prevent being weather-vaned into irons every tack)
those are the conditions where i recorded my absolute top speed of 30kph/18mph/16knots and that was hiked out as far aft as possible on a deep reach. seems you gotta have both bows working for you on a 17foot beach cat in the white caps
that was once 3 years ago when i first bought the boat
perhaps if those winds come again and i get some foot straps aft i could trap out well aft and tighten that reach up a little to get a bit faster and still have both bows buoyancy to balance the huge tipping moment on the rig
another way to go faster for me might be to fit a spin so i could make more use of the wind while sailing deeper
<!-- editby --><em>edited by: erice, Aug 08, 2009 - 07:11 PM</em><!-- end editby --> [/quote]
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