Under Standing Center of Lateral Resistance & Center of Effort
On January 1, 2012 we had one of the WILDEST Frostbite races in the history of WLSC racing. Winds were 15 to 20 knots with gust up to 40 knots. Most of our sailors and even seasoned sailors had not seen that type of sailing for an entire race in the history of WLSC. It was a very WILD day.
During this race I saw at least three occasions where boats were put in jeopardy due to closeness of land, & by skippers losing control during a tack or gust of wind. Fortunately, no harm came to any of the boats. However, I am sure all of the skippers were highly alarmed at not having control over the situation.
If you will bear with me, I believe under standing the principles of Center of Lateral Resistance & Center of Effort will enable any skipper to handle those situations where you are in IRONS or have lost of Rudder Control. Both of these conditions can occur at any time, and not really related to high winds.
IN IRONS by definition means a boat pointing directly in to the wind and having no rudder control or control of the boat. LOST OF RUDDER CONTROL means just that. Any situation where you turn the rudder and nothing happens. This can occur with the boat in motion or with no way on. This is a common occurrence, and varies from boat to boat. Size of the rudder is a big factor.
The Center of Lateral Resistance is a point on the keel and of the under water profile of the boat that if pushed, would result in the vessel moving side ways with neither the bow or stern preceding the other.
The Center of Effort, theoretically this is the geometric center of the sail plan of the Main and of a 100 % Jib combined. If you collect all the wind forces acting on the two sails in to a single force, this would be its center of effort.
The designer of your boat has control where these two forces interact. Normally with no way on, the Center of Lateral Resistance is aft of the Center of Effort. Thus the bow would be pushed leeward of the wind or down wind. With some forward steerageway, the Center of Resistance moves forward toward the bow, to a point, where the Center of Effort is aft of the Center of Resistance. This causes the bow to turn in to the wind. The boat basically PIVOTS about the Center of Lateral Resistance. This is a safety design feature built in to the boat by the designer. Thus a boat hit by a gust or strong wind, will turn automatically in to the wind, spilling most of the wind with no action from the rudder. This is why most boats have a windward helm.
In application of this knowledge, if when sailing close haul, & you have found that you have no rudder control; if you want to turn into the wind, release the jib sheets so that the jib flies free. Be sure the main sail boom is amidships. The boat will turn in to the wind because you have moved the Center of effort further aft of the Center of Resistance. The boat will in a sense “PIVOT” about the Center of Lateral Resistance depending on which side of it, the Center of Effort is located or pushing. It works just like a SEESAW. The board will go down depending on which side of the PIVOT you are standing on. It is also like a Windsurfer. Moving the sail forward will turn the Windsurfer down wind, and moving the sail aft will turn the Windsurfer windward or up wind.
If you lose rudder control and wish to turn DOWN wind, releasing the main sheet or moving the traveler to Leeward will move the Center of Effort forward of the Center of Resistance and the bow of the boat will turn down wind.
Knowing these principles will allow a skipper to have complete control of his boat regardless of whether the rudder is in or out of control.
Next time you are out sailing, practice these principles so that you have first hand experience of how this knowledge can help you keep control of your boat in difficult situations.
Have fun sailing
John Middaugh
01/04/2012
