Lately I have been working on working with my tell tales to better trim my sail or adjust my course. I also am trying to get my head around "apparent wind" . There has been some great information about apparent wind on this thread:
http://www.hobiecat.com/community/viewtopic.php?f=13&t=14327I also been have dying to find out how fast I am going when the going is good. I bought a used Gamin hiking GPS. I found I can tuck it into the tramp pocket to keep it from moving and giving false readings. Also I can take a glance at it when I am on starboard tack. As I fine tune the sails or course to try and improve the flow of my tell tales, I try to feel the change in speed. I found that the GPS was supporting my analysis of the change.
The day I did this I paid attention to the sound & feel of the boat and watched the gps, so I can better estimate my speed without it. My gps did show a max speed of 18.6. Does that seem reasonable?
On apparent wind, Chris Berman in his book
Catamaran Sailing from Start to Finish writes:
Quote:
DOWNWIND SAIL TRIM
With an understanding of how tell-tales work, you can keep your sails working at their optimum, especially when you’re tacking downwind. The course that gives the most speed for the least extra distance is about 135 degrees from the wind, or about 90 degrees from the apparent wind (figure 6).
When your shroud yarns are streaming directly across your cat, you’ve got a 90-degree apparent wind. If you sail higher than 90 degrees (to 70 or 80 degrees) the shroud yarns will angle forward of the beam. And if you sail too low (100 to 110 degrees off the wind) the shroud yarns will angle behind the beam. So, to keep the wind at 90 degrees, watching the shroud yarns is critical. You want to sail as low on the wind as you can without cutting off the flow of air across the backside of your sail(s). A good way to get at this trim is to start the run with your sail(s), traveler(s) and/or barber hauler all the way out. From this point, slowly trim the sail(s) in and head up .until the leeward tell-tale begins to lift and flow aft. If the shroud yarns don’t indicate a 90-degree apparent wind, you have to either alter your course or sail trim until they do. Remember, you can’t get a 90-degree apparent wind if your sails are not receiving air flow across their Leeward sides.
Reaching downwind in a series of tacks is something most catamarans do with no problem. However, una-rigged cats with Less than 130 square feet of sail area cannot sail effectively by tacking downqwind with the wind at 90 degrees. Small unarigs just can’t generate enough speed with the wind at 90 degrees to justify the extra distance sailed.
I found I could rarely get the 90 degree angle he is taking about. Any suggestions on how to do this?
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