Mast Rake

By Stephen Jensen:

 
Mast rake is a hotly debated subject in the SJ21 community. Mast rake controls the helm balance called Lee Helm or Weather Helm. To see if you have weather helm or lee helm, let go of the tiller and see if the boat heads up into the wind or falls off. If it heads up into the wind, you have weather helm, if it falls off the wind you have lee helm. The goal is to have a slight amount of Weather Helm instead of Lee Helm. Weather Helm is when the tiller is pulled slightly to weather (3 degrees is a number I have heard as ideal) this gives the rudder enough bite (angle of attack) to create lift.

Mast rake also effects the slot between the Jib and the Mainsail. This is more important with the Genoa than the class 110 jib. The ability to point is also effected by mast rake although I don't understand the dynamics of either of these.

Forestay length is the adjustment for rake. There have been many suggestions for the lengths for the forestay to set the proper amount of rake. One number that is commonly used is 24'4".

I am not sure that one size fits all with our boats. The distance between the forestay tang and the mast base will also effect the rake and with the Clark Boat Co.'s tolerance of "plus or minus some" for deck hardware, it's hard to say that one length of forestay will be the solution to lee helm.

So I have asked skippers to send me the distance from the forestay tang to the aft edge of their masts. This can be done by measuring from the forestay tang to the aft edge of the mast plate pivot pin, then subtracting the distance from the aft edge of the hole in the mast base to the aft edge of the mast.

Once we have some data, we can determine if the mast base position is consistent on our boats.

One thing that I have learned is that masts at the 100.25" position have to loosen their shrouds to remove the mast base pivot pin when the mast is down.