Correction

Concerning International 14 gybing centreboards

505-campaigning reader and thedailysail contributor Jesse Falsone points out an error in Friday's International 14 article...

“We are not using gybing centreboards, theoretically I have never believed they work. People claim they generate more lift but that has got to be total rubbish because lift is related entirely to the amount of leverage you are creating so the only way to generate more lift is to create more leverage. However, Trevor Bayliss - who came second at the worlds and set up the programme for the top three boats and I believe everything he says - thinks they gave him a very slight advantage in the lighter stuff,” says Nurton. Evidently Bayliss believes having a gybing centreboard enables a sailor to put the sail plan very slightly more into the wind enabling them to generate more power in the light weather, therefore allowing them to set their boats up for windier weather making them fast in both conditions.


Jesse writes:

This last sentence is incorrect, and I'm sure Trevor was misquoted. It's really just the opposite. People should think of the jibing board as de-coupling angle of attack of the board from the rest of the boat. Since the board is jibed (leading edge to weather), the yaw angle on the hull is decreased, and therefore, the AWA is greater as compared to the same boat without a jibing board. This allows for a better sheeting angle (slightly eased sheets) at the same heading through the water (note here that in theory, the boat with a non-jibing board will have a compass heading that indicated higher point). A boat with a fixed board is not decoupled from the hull and rig, and the leeway angle of the board is the same as it is for the boat.

The other theoretical benefit of a jibing board is that there is less induced drag on the hull (this is drag due to leeway, or the boat 'sliding' through the water). The theory is that the board is a more efficient device for creating lift (in the horizontal plane) than a hull, and therefore, carrying a greater angle of attack on the board than on the hull is beneficial. This theory is probably more relevant for flat-hull dinghies which will not produce lateral lift efficiently, but are, of course, great for producing vertical lift.

In heavy air, the theory for reducing or removing jibe is that the lift force is largely a function of righting moment, velocity, and angle of attack. At some point, your righting moment is maximized (when all of your weight is fully on the wire), but the boat takes on greater speeds. Since lift is proportional to the square of the speed, as speed increases, less leeway is required to balance the righting moment. Therefore, less jibe is required. So, in theory, at higher speeds, a board may be 'over-jibed', leading to an increase in induced drag.