Effectiveness of tabs on trailing edge of rudder

[Bowdrie]

Not used on the rudder, but the first iterations of the S&S Swan/PJ 43, ('65>~'70/'71,) used a trim tab at the rear of the keel fin.
It was used to balance the helm and reduce drag, and it was effective enough in helping to lift the boat to weather that the IOR banned its use.
Those who wished to use it in IOR could accept a penalty, or alternately secure the tab to prevent its use.

[TrentePieds]

Hello again Andrzej :-)

Your comment "I tried to reduce the amount of rudder angle I would apply in high winds” suggests to me that you're “over-pressing” the boat. I may be mistaken, but that sounds to me like you are needing a lot of weather helm to prevent her from “rounding up” when sailing with the apparent wind forward of the beam. You haven't mentioned your sailing experience so forgive me if I am making untenable assumptions :-)!

So here is my take on sailing a ketch: To keep her tracking when “on the wind” you balance the sails. You don't use the rudder to prevent her from rounding up. In consequence you can't be inducing unwanted drag. The rudder, when you let go the tiller, should be trailing behind the boat like an obedient little puppy. When you have achieved that happy state, bringing the boat about is an evolution INITIATED by application of rudder, but COMPLETED by trimming the sails. We can talk more about that if you like.

The Seawind will handle more like a miniature ship than like the toys and floating condos that have become fashionable during the last half century. You have already touched on her being a little difficult to handle when making sternway. I grant you that she'll feel “odd” and unresponsive when compared to modern boats, but learning to make “prop walk” work FOR you is something we old geezers all went through. There again, we can talk more if you like.

Next time you take her out, try to use this for a guideline, just as an experiment, and see if that will not relieve the weather helm: On a "twelve knot day" trim her out on a beam reach wearing a #1 jib (area about 80% of fore-triangle), full main and full mizzen so that she is footing along at the maximum speed you can make her go. Trim your jib and mizzen sheets so she has just a touch of weather helm. Then trim you mainsheet so the luff of the main just “lifts” (i.e. shows a hollow where it's back-winded by the luff), then harden the sheet till the hollow JUST disappears. 6½ knots is “hull speed”, so expect something like 5½ when sailing like this. Watch your clinometer. If she heels more than 15º (average as she rolls), it's time to take a reef in the main. Leave the jib and mizzen as they are. She should now average a 10º heel, and track without attention to the tiller for a minute or two at a time. When you let go the tiller it should be “wagging” back and forth through maybe 3 inches. That is the indication that the rudder is NOT generating “form drag”. I also means that the rudder is not affecting the effective position of the Centre of Lateral Plane. But let's not get too “scientific” :-)!

If she begins to heel consistently more than 15º after the wind has come up and after you a have taken the second reef in the main, it'll be time to come down to a #2 jib. This may require being accompanied by the first reef in the mizzen. The whole secret is to keep her heeling between 10º and 15º while adjusting the amount of canvas and the trim of the sheets so she has just that tiny touch of weather helm.

As for creativity above the water line: Why not make a “tiller comb”? A tiller comb is a WONDEFUL device for them wot singlehand a ketch of this nature :-) And maybe reefing combs for your booms?

All the best

TrentePieds

[CarinaPDX]

I use a removable trim tab as part of my wind vane system. Instead of using a pendulum to amplify the wind force with the water force the tab does the same and directly drives the rudder. The wind part of the system is a modified Hydrovane that the original manufacturer used to offer (the conversion from horizontal axis to vertical axis is reversed as the tab is steered in the opposite direction to the tiller). It is a very powerful system. I also use part of the vane system to drive the trim tab with a tiller pilot, which saves a lot of energy and is more powerful. The tab does increase steering effort and is a nuisance when maneuvering so I remove it when entering harbor (it is hung on traditional pintles and gudgeons).

If not used as part of a wind vane and/or autopilot I don't think there is a lot of value to a trim tab on a sailboat. While it could be used to offset the prop wash under power to give a neutral helm it would have to be moved back to center for sailing, so just one more thing to do. Of course it could be used to steer the boat by hand but then you would have to retrain your muscle memory as it works in the opposite direction. Under sail there should be very little force required on the helm, and if that is a problem then adjust the sail trim. I'm not seeing a win here...

Greg

[Oceanride007]

Becker rudder is something I have thought about a lot, it can be more efficient, but to do it properly the balance point should be moved to 50% from leading edge, and the mechanism to tilt it, is design problematic. Big ships use them because it obviates need for stern thruster.

I have skeg hung rudder which makes getting leading edge fwd is also issue, can be done, but will look ugly.

[andrzej0nl1ne]

TrentePieds, thanks so much for the sailing pointers, they're invaluable. You are correct in assuming my novice skills. Your advice on 10 - 15 degrees of heel and less head sail set off a light bulb. Unfortunately it is winter in NY and she's on the hard this year, so I'll have to wait until May to practice your pointers.

Unfortunately all my expert sailing friends are not experienced with a ketch rig so don't know what to do with that extra sail. I, by the way, find it wonderful especially at above 25 knots of wind where jib and jigger is a wonderful state. I would also love to understand better the relationship between mizzen and main with respect to sheeting angles. But this of course is getting to the real issue but off topic. Perhaps we can start a new thread specific to techniques sailing a ketch. I've scanned the web and located many words but of little use. If you're willing, you will find me a ravenous pupil.

Thanks again for the advice.

Ak

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