"double the compression on the mast"
Are you sure about that?
i'm thinking that the down haul pressure on the mast will stay the same no matter how you hold the head of the sail at the top of the mast.
My dad's Shark had a small wire winch at the base of the mast to raise the sail and hold it up.
The Super Cat 20 had a wire halyard with loops swaged into it and a hook at the bottom of the mast. The second loop was to reef.
You need a beefy, well attached mast head fitting that can support full downhaul pressure and a halyard with minimum stretch. Many mast head turning blocks are only designed to take the pressure of pulling the sail up and could break from 8:1 downhaul pressure since normally, the halyard lock takes over once the sail is up.
Absolutely sure.
Look at the mast as a complete system and tension the luff of the sail with it connected at the bottom of the mast and hooked at the top. That's one line of force....let's say 200lbs. Now, don't hook the top of the sail at the top of the mast and run a tensioned halyard back down the mast to somewhere at it's base. That's TWO lines of force that the mast now needs to resist....double that 200 lbs and the mast now has 400 lbs of pressure on it. It's just like any purchase system - but in this case, you aren't getting any more purchase on the sail because it's directly part of the single line of force.
It's the whole reason why we live with the hooks at the top of our masts. The loads are less and the masts can be lighter.
i am pretty sure that i had a conversation with Bill Roberts, Super Cat designer, in 1981 about this. IIRC the force on the luff of the sail, say 200# is a constant(not really constant, because of down haul and mainsheet adjustments) . Each part of a 2:1 halyard system would have half of the force on it. 100# in this example. The loads are spread out differently and mast bend may be slightly different with each system i think.
Weight savings comes from eliminating the wire halyard, and wire could be problematic when used for halyards. Maybe a new high tech sort of line would work with some sort of cleat system at the base like in the example of the retro fitted nacra.
The direct hook at the top first seen on the T in the 60's got rid of any changes in the length of a tradition halyard system during a rough go out. They didn't adjust their downhaul while sailing, so if the top creeped down they would loose downhaul pressure when they needed it most.
If you can solve any problems there may be from just adding a hook lower down on the mast, that is supposed to be a good solution for reefing.
with all the engineers that sail cats the answer to the halyard doubling the force on the mast question, should be easy. a math guy i am not.
