Re: Raising Centerboard

Gordon (hlg@pacbell.net)
Sat, 17 Apr 1999 08:02:34 -0700


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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Great post, Dave. Thanks for doing the math. It does appear that 10 or 15
degrees aft could be effective in reducing weather helm without affecting
stability significantly.

Harry

>Soooo, heres a little table which should help us understand why "raising" the
>board slightly can change the way the boat handles without imposing
>significant danger:
>
>Angle Cosine Sine
>0 deg 1.0 0.0
>5 deg .996 .087
>10 deg .985 .174
>15 deg. .966 .259
>20 deg .939 .342
>30 deg .866 .500
>45 deg .707 .707
>60 deg. .500 .866
>75 deg. .259 .966
>90 deg. 0.0 1.0
>
>We can multiply each of these entries by 100 to get a percent change in
>height with angle - So "raising" the board by 15 degrees, as I suggested
>before, actually leaves the board at 96% of it's original depth while moving
>it back 26%. 10 degrees would maintain 98.5% depth while moving the board
>back by 17%. Going back 30 degrees leaves 86% of the board down while moving
>it back by 50% of it's length.
>
>At 45 degrees things become even (71% depth, 71%aft), the change in depth the
>same as the change in fore/aft position and after that the relationship
>reverses and we are then quickly lifting the board out of the water.
>
>I hope it's obvious here that while raising the board a little is okay (in my
>opinion, anyway), raising it more than, say, 30 degrees will have diminishing
>returns in balancing the helm and will start to seriously compromise the
>ability of the boat to "self-right". Coming from a background of sailing
>dinghies with unballasted boards which are frequently raised all or part way
>may make me more cavalier with this than is prudent, so it is probably better
>that I suggest that readers of this not interpret it as advice or
>recommendation. If there is any question in your mind, leave the board all
>the way down.
>
>Best regards to all,
>
>Dave Kautz
>P-15 #1632
>Palo Alto, CA