Generally there is no need for more than 50-60cm drift. I have used less than that, but 60-70cm is better on a 50sqm sail.

However, there is a different factor, which may increase the need for longer drift: If the yard is set with a very low angle (peaking angle), there must be enough drift to prevent the angle between the mast and the halyard from becoming too wide. I have used maximum 30° as a rule of thumb on my boats.

In other words, on my sails, like this on Frøken Sørensen, with 70° yards, the sling point sits fairly close to the mast (even with the slingpoint about 4-5% aft of the midpoint) so the drift can be short and still keep the mast-halyard angle within 30° or thereabouts.

Clear as mud, right?

Arne

So let me apologize in advance if this subject has been covered previously. But here is my question as briefly as possible.  How high above the yard does the mast need to be? In PJR it says .3 of your batten length. Meaning if your batten is 16.5 feet you need 4.95 feet of mast over your yard.  Is this correct?  I ask because I notice many pictures on this site that don't seem to support this and it would make my life a lot easier if I could fudge this and get away with a shorter mast and a taller sail.thanks in advance for any input.