What are the forces causing weather helm to increase when heeled?

[jibes138]

Can anyone provide information on why sailboats develop a lot more weather helm when they are heeled then when they are upright? At 20 degrees of heel or so it is extremely hard to keep the boat going straight and the rudder drag really slows down the boat, like dragging a series drogue.
Dave

 

[Capt. Kermie]

Beam

A wide beam relative to a shorter length comes to mind!
If the beam width divides into the length less than 3 times you are starting to bet beamy and the boat sails better flat. The curved hull has a tendency to round up into the wind.

 

[sailingdog]

It is usually due to two factors. The first is the asymetrical shape of the heeled hull. Most hulls are only symmetrical when sailed relatively flat. The second is that as the boat heels over more, the center of effort, is no longer above the center of lateral resistance, but outboard of it, since the mast is no longer vertical. This adds a significant lever arm for torquing the boat around the center of lateral resistance and adds to the problem.

Any rudder that is turned more than about 10-15˚ from the direction the boat is headed, is going to stall and act more as a brake than as a rudder. Many boats generate far too much weather helm than is possible to compensate for using the rudder. This is why many boats will actually sail faster and flatter in heavy winds when reefed, since they won't be heeling as much with reefed sails.

 

[Warren Milberg]

In addition to the reasons provided above, some boats that are heeled to 20 or more degrees indicate that they may be carrying too much sail area in the headsail - the result of which is to overpower the rudder. Reducing sail area forward may help reduce weather helm and the tendency of the boat to round up into the wind.

 

[sailingdog]

Wouldn't too much headsail up cause lee helm, not weather helm???

 

[sailaway78]

MY Take on this

While all the above answers may be correct, I think there is something entirely overlooked here. If your boat is heeled over at 20+ degrees, this means the rudder is also "heeled" over at 20+ degrees. It is now beginning to work in an up - down direction, as opposed to just steering the boat.

 

[Joseph Shirley]

The term is "weather couple" and I have described it several times before. It is the 2nd force Sailing Dog talked about.
When a sailboat is designed the center of effort is designed forward of the center of lateral resistance which statically would produce a lee helm. When the boat heals however the center of effort (forward drive), is offset from the center or drag, and produces a torque equal to the forward drive times the horizontal distance to the center of drag that is referred to as the Weather Couple. It opposes the designed lee helm so that beyond 10 degrees or so the boat will have weather helm. As you heel more the weather couple increased and weather helm becomes excessive. To sail straight with excessive weather helm requires to much rudder and slows you down so if you want to sail faster you must reduce the heel.

Have fun

Joe S

 

[Dan Johnson]

Most sailboats...

are designed to sail best around 15 degrees of heel. Sailing with a greater heel begins to create greater leeway as the keel and rudder become less effective from the loss of hydrodynamic lift.

While rail-in-water is more thrilling, sailing more upright is faster (and safer!) and results in higher pointing yielding greater VMG and less distance sailed.

MHO from a decade of racing.

 

[r.w.landau]

I was waiting for the small boat owners to chime in...

I think you will find that Warren's reply is the closest.
It is a result of lift on the sail/s.
Both sails create lift and with good wind they will spin the boat.
Small boat owners know that you can drive with the main with the trimof the sail. It is the lift that the wind creates on the sail that makes that possible.
The genny though a little different, can round the boat up also. I have rounded up on genny only.
The sail over powers the rudder.
r.w.landau

 

[Maine Sail]

Re: What are the forces causing weather helm to increase when heeled?

The simple answer is many factors. These are the ones I find most common:

#1 Operator error
#2 Sail trim / too much sail / not adjusted properly
#3 Rig adjustment
#3 Design of hull


Sail flatter, trim your sails properly and make sure your rig is properly tuned and you can drastically minimize weather helm unless the hull was a poor design..

The old adage "flatter is faster" is still a good one...


Too much head sail or improper head sail trim or an old blown out head sail often leads to increased lee helm.. With the center of pressure forward of the center of resistance of the hull, a "lee" helm will develop. this is generally considered undesirable, if not dangerous. A little weather helm, meaning very little to almost non discernible, can be a sign that you are well balanced..

 

[sailingdog]

Interesting...especially since Warren starts his answer with "In addition to the reasons provided above,"...

I think you will find that Warren's reply is the closest.
It is a result of lift on the sail/s.
Both sails create lift and with good wind they will spin the boat.
Small boat owners know that you can drive with the main with the trimof the sail. It is the lift that the wind creates on the sail that makes that possible.
The genny though a little different, can round the boat up also. I have rounded up on genny only.
The sail over powers the rudder.
r.w.landau

 

[Bill Roosa]

Rounding up

To sail you need sails, a keel and a rudder. If you lean the boat over 45 degrees the sails don't catch as much wind and the keel and rudder loose their ability to resist the sails. The rudder's action begins to be more vertical and less horizontal and so it takes more rudder angle to achieve the same horizontal force. Since you have the tiller more to weather it tends to be the underwater source of lateral resistance. That is to say, the keel is not as effective when heeled and the rudder becomes more of a contributor. Since the rudder is "way aft" of where the designers intended the center of lateral resistance the force is strongly trying to turn the boat into the wind just from where it is applied. Add to that that the keel is not providing as much lateral resistance and you can see that the actual center of lateral resistance tends of move aft and cause weather helm the more you heel the boat.

My personal experience is I don't sail close hauled all that much. You go faster (better VMG) by falling off the wind and easing the sails and tacking more often. The crew is happier too as the boat does not heel as much.

 

[tommays]

Well

For example on a boat like a J24 it is pretty well know what works becasue there are so many sailmakers/racers involved with the and boat trying things to get and edge

The boat was built to allow a LOT of mast movement which has allowed pretty much everything to be tryed

You would be supprised how many tuning guides are out there to help out with what works on a given boat

I find for example that when i am getting close to the edge i can point up a bit during the puff before the boat rounds up IF i dont then i will round up

 

[David in Sandusky]

Reef the main

Reefing the main reduces weather helm in at least two ways:

It moves the center of effort forward (remember that although you pull it down the reefed main reduces sail shape along the leach, the back side of the sail.)

It reduces heel, offering a more balanced hull shape, and making the rudder more effective, since it is more vertical.

If we are struggling with eather helm, Lady Lillie goes faster after reefing because of the improved hull shpe in the water, and less need for the rudder.

 

[sailingdog]

It also moves the center of effort DOWN...which gives the wind a smaller lever to tip the boat with.

Reefing the main reduces weather helm in at least two ways:

It moves the center of effort forward (remember that although you pull it down the reefed main reduces sail shape along the leach, the back side of the sail.)

It reduces heel, offering a more balanced hull shape, and making the rudder more effective, since it is more vertical.

If we are struggling with eather helm, Lady Lillie goes faster after reefing because of the improved hull shpe in the water, and less need for the rudder.

 

[bffatcat]

Weather helm my 2c

I keep an old fashion inclinometer on my compainionway If it shows 20 degrees or more I reef my main. Unfortunately most modern fin keel beamy boats will develop a good weather
helm when heeled in excess of 20 degrees. Another overlooked problem that no one else has mentioned yet is mast rake. Some sailors rake their mast to move the center of effort aft and get the boat to point higher. This unfortunately this causes weather helm. I keep my mast plum

 

[jibes138]

Answer

If the sum of the moments about the central axis are greater than zero than you will have a rotation of the boat. It will not be in equilibrium. So a moment is a force acting over a distance (also known as torque). To solve the weather helm problem we need to understand all the forces acting on the boat and then which ones are variable so we can make the appropriate adjustment. This is a very complex force system. Standing upright you have the center of effort acting on the sails. This is a vector with direction and magnitude. The compnent of this vector acting in the direction of the centerline of the boat is the propulsive force. The component of this vector acting perpendicular to the boat is the heeling force. There may also be a vertical component but lets ignore that, it is either trying to pull the boat out of the water or trying to sink it. The component of this force in the direction of the boat centerline is acting along a distance from the center of gravity, so there is a moment created trying to make the boat turn to weather. The heeling component is also acting on a distance from the CG so it to is trying to rotate the boat. The rudder is trying to rotate the boat , the current , if any, may be acting on the hull to turn it, the wind is trying to turn the boat and for a stiff breeze is a considerable force just on the hull. So summing all these moments is the method to see if you have weather helm. One big one is the distance of the center of lateral resistance to the center of gravity as the force vector acting through the center of lateral resistance is quite large.

 

[Taylor]

Flow to the Rudder

One minor component to windward helm is the flow of the water off the keel and onto the rudder. As the result of leeway, the flow over the keel is not symmetrical, and the keel alters the water flowing to the rudder. Apparently the keel alters the flow of water to the rudder much as a headsail alters flow to the main. According to Stuart Walker (I think I read this in Wind and Strategy) the rudder in a slight header compared to the keel and thus you would expect to have the helm turned to leeward slightly when optimally trimmed.

I would expect leeway to increase as you heel, making this effect more pronounced. But its minor compared with the first answer given.

If you haven't read Walker, consider this: I recall getting a copy of Wind and Strategy 35 odd years ago and thinking that perhaps I was just too young to understand it. But I came back to it last year, and it turns out, I still don't always get it.