Weather Helm Vs Lee Helm – What is it? How to use it?

Posted by Director of Education on June 16, 2010 under Crew, Skipper, weather | Read the First Comment

During the Americas’ Cup campaign in New Zealand in 2003, I saw one of the best explanations of this on a TV interview with the Greg Butterworth, the Tactician for the Alingi Team.

Most of us sort of understand the concept and we’ve been left with the answer of “Well – weather helm is better because it’s safer.” But few explanations go into how it gives your boat a sailing advantage.

The definition of weather helm and lee helm is simple and it is easy to remember which is which. If you have a tiller, weather helm is when you have to pull the tiller to weather (toward the wind) in order to keep the boat going in a straight line. Lee helm is when you push the tiller to lee (downwind) in order to keep the boat going in a straight line. We’ve probably all felt this slight pressure required on the tiller when underway.

Your boat can be tuned to give weather helm or lee helm. Rake the mast forward  and you move the center of effort of the wind forward which causes your boat to want to turn downwind. Rake the mast back and you move the center of effort of the wind back causing your boat to want to go upwind to weather.

When your boat gets rounded up – you just experienced massive weather helm. No matter how much you pull the tiller to weather, you can’t stop the boat going to weather. Dumping the main sail moves the center of effort forward thus reducing the weather helm.

The basic perception of weather helm being safer comes from this effect: if you let go of the tiller, it will automatically go to center because of the water flowing over the rudder and because the rudder is pivoted at its leading edge. Now there is no rudder force to counter the desire of the boat to turn up wind to weather so the boat does exactly that. It turns to weather and rounds up slowing the boat down and reducing forces on the rig. Conversely, lee helm  means that if you let the tiller go the boat will turn away from the wind, heel over more increase forces on the rig.

So from a safety point, weather helm is good. BUT there is another advantage that we’re not generally taught. Holding the tiller to weather means that there is a slight pressure on the rudder to windward. This actually MOVES THE BOAT TO WINDWARD as it slices through the water. And we all know what that means, race advantage!

The Weather Helm Advantage

The Weather Helm Advantage

The illustration shows how the water pressure from weather helm creates a sideways force on the rudder tending to push the boat to weather.

Now Greg Butterworth went on to explain that there are other cool things you can do. One is to put a little trailing edge swinging control surface on the keel.

The illustration below shows this effect too. For us pilots, this is much like a trim tab on a wing of a small airplane. The trim tab creates the ability to adjust the lift at that point on the aircraft and thus create a balance of forces. The issue to remember here is that you’d need to trim the tab the other way when you tack over.

A control surface on the keel

A control surface on the keel

So there you have it. While we’ve all been understanding the lifting effects of the wind over the sail, the other fluid that we’ve ignored is the water under the boat and how we can gain lift from it too.

Next time you’re out sailing on a nice steady 10 knot breeze, come up on a close haul, trim the sails perfectly so that all your tell tails are flying smoothly. Then notice what pressure you’ve got on the helm. Note that if you’ve got a wheel, weather helm will be a tendency to apply downwind turning pressure on the wheel (which is the same as pulling a tiller upwind right?). Ideally you should have slight weather helm. If not, you should probably not jump right in and start raking your mast back. Talk to a mast tuning specialist in your area first.

Weather Helm Versus Lee Helm

Posted by Grant Headifen on March 15, 2009 under Skipper | Be the First to Comment

What are they and what’s the difference? These two terms were established when vessels were fitted with tillers rather than wheels and so the term weather helm refers to having to pull the tiller (helm) “to weather” in order to sail in a straight line. Lee helm is when you need to push the tiller (helm) “to lee” in order to sail in a straight line.

Pulling the tiller to weather (or towards the windwind side of the boat) means that the boat left by it self would tend to turn into the wind. And conversely, lee helm would mean that the boat wants to turn down wind.

Now on a sailboat with a wheel, weather helm is turning the wheel away from the wind and lee helm is turning the wheel to helm in order to hold a straight course. This is because the wheel is opposite the rudder. Don’t get confused here – if you have to go back to fundamentals to work it out each time then just remember that sailing was invented thousand of years ago before the put wheels on boat. “Weather helm is rudder to weather”.

These phenomenons can be fixed quite simply by tilting (raking) the mast forward or aft. To reduce weather helm you’d want the center of pressure of the wind acting on the sail to move forward on the boat. See my last blog on how that works using the floating coke bottle. To reduce lee helm you’d rake the mast backwards.

There are also other things you can do to the sails which are quite detailed in the NauticEd SailTrim Clinic.

One might assume that you’d want a perfectly balanced boat with out any helm at all. Well that’s not quite true.

The first reason that is most often quoted is that weather helm is for safety. Let go the helm and the boat rounds up into the wind. That’s safer than having the boat bare away and speed away from you while you’re laying in the water.

However, the second reason is slightly more subtle yet makes a large difference to your performance. For the tiller to be pulled to weather (to the windward side of the boat) the rudder underneath is turned so that it also is pointing towards the wind. This angle creates a force from the water and the direction is to wards the windward side of the boat as well. This gives the boat “lift” to windward from underneath and guess what that does! It helps you win races.