Best rope for main halyard

James, what is mast foot pressure a la windsurfers?
At any rate, you can't have it both ways - if the 2:1 system is pulled right to the top, there is virtually no extra length of halyard able to stretch/creep.  If the 2:1 isn't right at the top, then the angle between the ropes is going to be nearly 180 degrees, and therefore the 2:1 will work efficiently.  And what ever extra length of halyard there is, is in parallel, not series, so the stiffness is increased (hence less stretch).

Paul, sorry to say Chewy and me are one and the same - I lost my login details!  Tempted to do the Thornbury regatta though.

A well known mast maker tested this out with weights. The results were astonishing in that the halyard running inside the mast operated under a mechanical disadvantage from kicker, cunningham and mainsheet loads so the the rope in the mast actually holds twice the load of the luff on the sail. If you think about how you rig up a cunningham this does make sense.

In some classes you want this to help de power, but in merlins with the flexible carbon spars the "bow and arrow" effect should cause a power drop just when you want it least, ie force 2 or 3. Halyard locks are becoming popular again, but I opted for a 2:1 halyard but haven't really sailed enough since to draw any conclusions. It looks good on paper though.

Sounds interesting. How does that work?