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sail/rudder control


QB2
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Is it the efficiency of your rudders or the centre of effort in the sail or a combination of both that determines the amount of weather or lee helm you can have?

Off Humpybong yesterday my AO was spearing downwind in the gusts when on a beam reach. I had the tiller pressure go from weather to lee helm from moment to moment even tho the rudder-tiller system is tight and has no slack.

Could it be sideways rudder movement on the centre bolt or something else? Would having different rudders (1 AO/1 mari)make a significant difference

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  • 2 weeks later...

QB2,

Probably all of the above, also check the "toe-in/toe-out" situation along the centre-line... Another culprit could be that you have the rudders "over-balanced"... That is, they could be tucked in under the hulls too much.

Set up on the trailer with the rudders down, sight one down the centre-line of one hull and use some gaffer tape to hold in position... Then check toe-in/out by measuring the leading edge and trailing edge distances between the rudders (at the same height) just above or below the hull bottom to transom join. This will tell you whether you have either (toe-in/out) malady...

Then hold a straight edge/batten down the transom (this should line up with the rudder pintles/gudgeons) you should have NO MORE than 17 percent (so they tell me... who is they?, just the voices) of the rudder blade in front of this pivot line... move the rudder rake accordingly....

Hope this helps.

Regards,

Leroy smile.gif

Edited fro spilleng mshtaces

[This message has been edited by Leapin Leroy (edited 11 October 2007).]

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  • 1 year later...

If your stay wires are a bit loose, the rig will move forwards and back a bit on a broad reach, moving the sail centre of effort.

Centreboard height also affects the helm, with boards up increasing weather helm.

Bring the rudders under the transom reduces steering effort and weather helm, but increases forces, which can result in blades breaking and the transom pintles ripping out (recent experience).

I'd suggest getting the rudder blade angle right first; so that there is a manageable amount of pull on the tiller extension when going flat out on a reach. You might experiment with wedges or blocks between teh pintle and the hull.

Then set the mast rake so that the boat just tends to round up when sailing close-hauled upwind. Achieve this with a bit of trial and error with stay lengths.

Most people advocate as much mast rake as you can get away with, as it is claimed to increase pointing ability and reduce nose diving. Too much rake though will just cause drag from weather helm correction on the rudders, and make tacking difficult, as the boat wants to stay pointing into the wind.

Another factor is the pintle axis. If the axis on which the rudders pivot is vertical relative to the waterline, then all the rudders do is make the boat turn. If the axis is raked, with the top pintle forwards of the bottom one, then the boat tends to dip the nose when you pull the rudder, and raise the nose when you push the rudder.

Good luck!

Tony Hastings

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