Too much weather helm?

[dvanes_old]

The first thing the "!" moment is although people talk about a CLR center of lateral resistance this would suppose that the centerboard is dragging in the water and resisting lateral forces. This is the wrong way to think about the rudder and centerboard. While the sail is an AEROfoil producing a force LIFT due to the flow of air. The centerboard and if you are trimmed right the rudder are HYDROfoils producing LIFT from the flow of water over them. Water is 750 times as dense as air so as you would expect the "ANTI" foil (Hydrofoil centerboard) compensating for 8 square meters of Aerofoil (the sail) is a lot smaller. The wind comes in over the windward bow - passes over the sails and is turned. Newtons third law says that for every action there is an equal and opposite reaction and a force is produced from the sails to the lee of the bow. The boat slips sideways and forwards; water streams in over the lee bow and over the centerboard and as it is a foil is again turned toward the rudder (back over the lee side of the boat) creating a force LIFT towards the windward stern , LIFTING the boat to windward - not resisting! Now depending on the layout and spacing of centerboard and rudder the stream direction off the back of the centerboard coming over the rudder may be still going to lee. So to have the rudder neutral in this stream the tiller will be slightly to windward but only producing drag! However if you tug it a bit more then the rudder starts acting as a foil and again produces lift to Windward. So the centerboard and the Rudder can be seen to act a bit like a reversed Main and Jib. So if the CE of the rig was set slightly behind the centerboard CLR, when the rudder has windward helm and is lifting as well this can bring the CLR back to match the Rig CE. Everything seems neutral and free and you have that weather helm tug that gives feeling to the boat. Best way is to draw the flows over the sails and the water flow over the boards underneath. So the conclusion is... If you don't have some weather helm then your boat is not trimmed properly! Oh but letting the boat heel to lee makes a huge difference and it seems to be the state of most sailors. So when you are testing for windward helm sail in a nice constant wind and possibly put a spirit level on the deck with gaffer tape to make sure your "feelings" of being upright match reality.
* Page 101 Art and Science of Sails ISBN 0-229-11888-7[/img]

[Pete1177]

and possibly put a spirit level on the deck with gaffer tape to make sure your "feelings" of being upright match reality.

I now have a Silva inclinometer (cost £20) lashed to the mast with cable ties and velcro - very sensitive to boat heel ... every little helps!

Pete 1068
Secretary, Supernova Class Association