understanding weather helm

[jbshu24]

Okay, in trying to rebuild my rudders, I'm trying to understand what amplifies weather helm. I see how mast rake, rudder rake and rudder shape would create weather helm, but I'm trying to understand why my left arm get tired so much faster from having to tug on the tiller in good wind, while my right barely has to pull at all. I've faired my rudders with fiberglass a little and that has helped, but not a lot. Since my left arm is tiring, it seems that I have to add more shape to the outside of the port rudder so that it has more lift and doesn't pull as much.

In reading one post on loose rudders, I'm not sure how a loose rudder would give more pull than a stiff one. Even if the rudder turns a little, wouldn't you be able to pull the tiller a little more and get it back to the position of a stiff rudder?

Does the downwind rudder create all the helm, or does the upwind rudder do anything? (I like to sail with the upwind rudder out of the water ) I know some people like to toe their rudders in or out, but it seems like that wouldn't matter one bit if the upwind rudder is barely in the water.

any ideas?
thanks in advance,
Jon

[Eric2101]

Experiment.... Swap your rudders to see if the problem persists. I suspect rudder rake as the 1st issue , butt, you never know.

[Matt Haberman]

Jon,

Looking at your photograph of the damaged rudder would lead me to believe that is contributing to your weather helm problem.

Typically if you have weather helm on one tack but not the other is is because the rudders are not symmetrical. The exact shape is not all that important, but if the rudder is not an identical mirror image from one side to the other you will end up with weather helm on one tack versus the other. It does not take much difference (thickness of paint) to result in some level of weather helm.

When I talk about a loose rudder I am talking about movement of the rudder tip fore & aft, not side to side. With the boat on the trailer and the rudder in the full down locked position try moving the rudder tip. If it moves left to right that is not a big deal, but if it moves significantly fore & aft then you can have problems. The issue is that the rudder area is designed to "balanced" around the rudder pivot on the transom, if you end up with too much area behind the pivot you can get weather helm. The typical cause of this either damage like you show in your other photograph or a hugely elongated pivot hole in the rudder. Usually this type of weather helm is equally present on both tacks.


Toe-in is important in that he help to keep one rudder from stalling and keeps the rudders tracking so they don't hunt, similar reasons they do toe-in on the front wheels of your car when they do an alignment.

Hope all of this helps

[jbshu24]

Thanks Matt,
Are the rudders normally symmetrical so it doesn't matter which is left or right?
To adjust rudder rake, would you put a shim behind the rudder gudgeon, or try to adjust some other way?

[Matt Haberman]

Jon,

The rudders are symmetrical and there is NO difference between which blade is used on the port or starboard.

The best way to correct the rudder rake is to make sure the pivot hole is not elongated and that the cam profile is also not elongated. We have repaired and re-drilled rudders to correct for this. Shimming the gudgeon's does not solve the problem so I would advise against that.

[Rhiannon]

Matt,
What is the correct amount of toe in? And where is it measured?

[Matt Haberman]

Check out this discussion: viewtopic.php?f=3&t=313&p=1052&hilit=toe#p1052

It explains how much toe-in and how to do it.