Reply To: Mast rake and deck position
I used as Terry said 720mm from the bow and 6100mm for my older mast and 6050mm for my latest very stiff mast. I never sheet to the deck as I think it is slow. The boom was never sheeted outside the sheerline (usually an inch or 2 inside it) with the end about 100-120mm above the deck for moderate/windy conditions…obviously higher (less shett tension) in lighter airs. I would only sheet outside the sheerline when the wind was over 25-30knts, and then only by about 2 inches.
The mast was set up so these nos were achieved with the equivalent of a 19kg tip deflection weight fore/aft.
Your mast position fore/aft will also depend on how full bowed your boat is. I sailed an icebreaker (which having just read another thread I would like to point out was very scientifically designed allbeit back in the mid seventies) which being relatively fine bowed compared with say a delfs has to have the mast as far back as possible without generating excessive windward helm.
A good test is go for a sail, when going upwind your boat should track in a straight line with the tiller centred when it is sailed flat. If you achieve this and your helm still feels heavy there is allowance in the class rules whereby the top and bottom rudder gudgeons can be offset from each other allowing you to rake the rudder tip further forward under the boat. If you do this the rudder lightens dramatically.
So I guess in a nutshell, position your rig as far back as you can (less weight in the bow) without developing excessive weather helm and your boat tracks in a straight line with the rudder centred (or very slightly above the centreline, say abt 5 deg.). At this position when using max sheet tension your boom end should be abt 100-120mm above the deck. The mast tip deflection with the boom sheeted to this position should also correspond to that obtained from hanging a 19kg weight from it. Takes a bit of playing around with some scales and a tape measure on the shore but eventually you get there.
The offsets you get from your mast between the bands with the boom sheeted to this tension I’ve also found were great for getting the sail luff curve right. These were the nos I supplied my sailmaker with when ordering new sails.
Have fun, tuning is about as much fun as racing I reckon.