Autopilot Suggestions for F28 CK

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Re: Autopilot Suggestions for F28 CK

Postby hxschiller » Wed Feb 10, 2010 10:46 pm

If someone wants to retain the look of the F-28/33 cat ketch rudder, but improve the steering, one should look at the cute compromise that (our Hero) Garry Hoyt devised for the Alerion Express Cat 19. The thing loooks like a barn-door rudder, but contains a high-aspect ratio fin within it (like a mini-centerboard). I believe that some of the "weather helm" that's ascribed to these boats is simply lousy leverage. Some of it can be ascribed to sail trim, and lastly to the chubby shape of these boats, which when heeled over present a highly asymmetric shape underwater.
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Re: Autopilot Suggestions for F28 CK

Postby Michel » Thu Feb 11, 2010 6:32 am

I sailed both the F33 and the F44 catketches. The F44 has no weather helm at all.
I doubt it's the rig causing the weather helm; my F33 with original wraparounds had a 66% to 33% division of the sail area across the main and the mizzen. The F44 has a 55% to 45% division; the mizzen is much larger comparatively, so you would expect the CoE to be much further aft. The F44 has an unbalanced rudder, but on a full skeg, and a fin keel and as I said, hardly or no weather helm; only a bit when heeled too much. I think the design parameters used for the F33 and F28 (max draught and necessary volume in the forward part of the hull) caused the CLR to be too far forward in relation to the CoE.

What helps a bit is to trim your masts as far forward as possible, to reduce rake as much as you can. I found a noticeable difference when I did this on my F33. You might even consider moving the mast base collars aft an inch or so to remove all rake.

The Pardey's solution to put lead in the rudder helps a bit with floating rudders, but it's fighting the symptom, a heavy helm, not the cause, the wrong positioning of CoE and CLR in relation to each other. And Freedom rudders don't float.

Also, balancing the rudder is not really solving the problem, just hiding it by making the helm lighter.
Michel Capel, Freedom 44 #4 1981 'Alabama Queen', NED8188, cat ketch with wishbones, home port Enkhuizen, the Netherlands, 52*42.238'N 005*18.154'E.
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