By William Mills
Racing Tips 2 explains what weather helm is and how to use the cunningham.
In the yacht club bar after a hard fought race sailors can be heard talking of their exploits on the water.
Recently one young man was overheard saying, ‘I had loads of weather helm.’
Another chipped in with, ‘I had even more than you.’
I had visions of a muscled helmsman manfully wrestling with the rudder in his quest to overcome the forces of nature.
However it’s best to understand and harness these forces rather than battle with them.
So let’s start with the basics.
In diagram 1 above we see the outline of two yachts, one with a headsail, and the other has a mainsail. Neither have a have a rudder.
In diagram 2 the wind blows filling the sail and the bow of the yacht on the left is blown off away from the wind. As in this example the boat doesn’t have a rudder the wind forces the boat to pivot on its keel. The wind catches the rear of one on the right hand side, and again it pivots on its keel, but this time it spins into the wind.
In diagram 3 rudders have been added. The wind fills the headsail trying to force the bow to turn away, however the rudder counteracts this and the force of the wind translates into forward movement.
However as the force of the wind is at the front of the boat the rudder is having to be constantly applied to counteract this thereby causing drag on the rudder.
This is called ‘lee helm’. When the boat only has a mainsail the rudder has to turn it to port to prevent the boat rounding up into the wind. This is called ‘weather helm’.
In diagram 4 the rudder is highlighted. The rudder should always be kept at dead centre in order to reduce drag. The water should flow down either side evenly. Only when a change of direction is needed should any rudder movement be applied.
The rudder has a sharp edge to cleanly cut through the water. When the rudder is turned sideways on to the current, drag is caused.
This turbulence immediately causes the boat to slow down. Huge oil tankers have onboard computers calculating the extra fuel cost every time the rudder is moved.
When a small yacht appears on their radar they calculate the cheapest option for passing it by.
The boat is at its fastest if the rudder is dead centre and the helmsman not touching it.
In diagram 5 both sails are shown. If they are the same size the boat will travel forwards in a straight line without any need for a rudder. The wind in the headsail pushing the bow to leeward is balanced by the mainsail trying to push the boat’s bow to windward.
In diagram 6 the boat has the greatest force on the rear, or leech, of the mainsail. The boat wants to pivot into the wind.
However the force in the headsail at the bow is countering this. But since the mainsail is the larger it’s winning the battle and therefore the helm has to be turned to port.
Although this enables the boat to steer in a straight line, the rudder drag slows the boat.
In diagram 7 the boat has its sails correctly balanced with rudder in the centre causing least drag. This harmony has been achieved by moving the draft forward in the mainsail.
This means that the wind’s force is no longer at the back of the mainsail where it exerts greater leverage to windward.
By applying the cunningham the draft in the mainsail has been moved forwards closer to the mast whereas the force in the headsail has remained the same.
It’s smaller but it’s further away from the mast giving greater leverage.
When the sails are in balance the rudder can be left idle in the centre causing least drag.
Sailing along the tactician should continuously ask the helm; ‘weather helm?’
The helm should remove his hands from the wheel and see if the boat steers itself in a straight line, or has excessive weather helm which is apparent by the boat immediately turning up into the wind.
The alternative is ‘lee helm’. This happens when the superior force is in the headsail. ‘Force’ here means not only the size of sail but also crucially the distance away for the mast the force is, the greater the leverage on the keel.
Here, either the force, or ‘draft’, needs to be increased in the mainsail, or by reducing the power of the headsail.
Usually achieved by firstly moving the sheet car back to spill wind out of the open slot, or ultimately changing down to a smaller headsail.
Weather helm, that’s when the mainsail is over powerful, is cured by moving the draft forwards with the cunningham.
If this doesn’t work and the boat is healing more than 15 degrees to leeward then dropping the traveller and finally reefing will cure the problem.