Weather Helm & Lee Helm

[Trim50]

I'm in the process of getting a new genoa made and possibly a second main sail with more roach.

Most boats are designed to have a slight weather helm. This helps in sailing to windward, and is also a safety feature. In case someone accidentally releases the tiller, the boat will simply head up into irons and slow down.

My question is how much is enough and when do you know you have too much?

[Auzzee]

Is inbuilt weather helm still a feature of modern yachts? Mine apparently disappeared when I installed HyDrive hydraulic steering. The boat will still very slowly round up on a reach or close hauled, but the feeling of any tendancy to wander must now come through the deck rather than through the helm.

I enjoy the hydraulic steering and find less need for use of the auto pilot and when running free or goose winged, as long as I have a boom brake set, she will cavort merrily and without interference (from me or Otto) down the face of waves, until China gets in the way.

.....Non of which answers your question Trim.....C'est la vie!

David.

[duckie]

My experience is only with dinghies, but may be relevant.

With too much weather helm,

1. holding the boat straight requires a lot of physical effort on the tiller,

2. the boat slows, as you can feel the drag of the rudder. It is on an angle to the centreline of the boat.

Part of the weather helm comes from teh fact that, in a gust, the centre of effort in each sail moves aft.

However, you can only test these factors after the sail is made and the boat is in the water.

How much can you adjust centre of effort on your boat (and thus lee / weather helm) via rigging after the sail is made?

[redbopeep]

Originally Posted by duckie

My experience is only with dinghies, but may be relevant.

With too much weather helm,

1. holding the boat straight requires a lot of physical effort on the tiller,

2. the boat slows, as you can feel the drag of the rudder. It is on an angle to the centreline of the boat.

Part of the weather helm comes from teh fact that, in a gust, the centre of effort in each sail moves aft.

However, you can only test these factors after the sail is made and the boat is in the water.

How much can you adjust centre of effort on your boat (and thus lee / weather helm) via rigging after the sail is made?

If you have your boat's plans and sail plan, you can actually calculate the shift in coe for the sail as compared to your existing jib/genoa and its impact on the boat handling. If you don't have the boat plans as well as the sail plans, I don't know...

But, I can tell you we've got a 170% genoa on the Rawson 30 and its way! way! too much weather helm. We have a smaller jib that I'd like to put on, but with the particular furling gear on this boat its not as easy as a hanked on jib and we actually need all that sail when we're coming into San Diego harbor at night--there's no wind to speak of. So, sometimes we sail partially furled even though neither one of us likes to do that. If we were cruising, it would be easier to just put the smaller jib on and keep it on for a while assuming we'd have the same wind for more than 6 hrs--but having 2 sail changes a day for a day sail seems a bit much with this boat.

I've been told by a local sail maker that our 170% genoa would better suit my taste for weather helm on this boat if it was more like a 150% or smaller sail. The overlap is quite big on the 170. Who are you having make your sail? They should assist you with this.

[duckie]

acouple of articles that might help.

http://www.myrc.org/Library/centeref.htm

http://www.jutson.com/articles/oct96.html

It seems you could find the centre of effort by cutting the sail shape out in stiff cardboard, using the triangulation method (or a physical balance) to find the centre of effort for each sail, joining the COE for each sail with a light stick or stiff wire, then finding the physical balance point along the stick (COE of combined sails).

Compare this to the COE of your original sail plan, to check that it has not moved significantly.

If your original sail plan caused the boat to have just a little weather helm, then the new one with a similar COE should be OK (or within limits that you can fix with rig trimming).

Of course, your sailmaker may have a groovy computer program to do the same thing in two minutes.

Let us know how you go.

cheers

duckie

[Trim50]

Well, I do know that in 20+knts on the beam, I have to keep around 5 degrees rudder for balance. I have a huge barn-door rudder...so you can imagine it's a lot of unnecessary drag.

[Piotrek]

Finding center of effort of the sails is only the part of the problem. It works if the boat stay upright. As the boat heels center of effort goes to the lee side. The more the boat heels the bigger momentum of the turning force is.

This is the reason, why monohuls tend to point higher in the blow. The only exception are multihuls, where heeling couse weather hull to fly what suddenly moves center of resistance to the lee.

Properly designed boat would keep its course without the rudder. Then, when wind rise she should heel and bear up, spill excess of wind from the sail and strighten. Then center of efford moves closer to the centerline and the boat should bear away.

Then, by adjusting the sails one could be able to change course and even change tack without touching the tiller.

This kind of behaviour was common for two mast, traditional boats, but somehow is rare for modern designs.

Personally I would try to make sails in a way that you can balance your boat at as wide range of courses as possible.

Good luck

Piotrek