Originally Posted by waterbug_wpb
As to the advantage/disadvantage of the mast hook vs. halyard clutch, that may be better left to those engineering types..

I think there was lively discussion about this on other threads, but I'm still having trouble understanding the physics/forces. I would have thought that the total (down) force on the mast would be the same in either setup...

For instance, if you put 100 kg of downhaul force on the mainsail, the mast would be resisting that 100kg whether it's attached at the top, or runs back down to a halyard clutch.

Instead of comparing the forces to a compound bow, let's look at a 2:1 jib sheet system - which is something we all understand better. Imagine you attach a single block to the clew, and run the jib sheet from the boat through the block, and back to the jib car. Now, if you put 100 kg of tension on the running end of the sheet, you also put 100 kg of tension on the standing end. The force on the turning block, however, is 200 kg. That's the whole purpose of a 2:1 purchase - it doubles the force of your pull.

It may not be obvious at first, but a masthead sheave does the exact same thing with your halyard. When you fasten the halyard and put 100 kg tension on your downhaul, your clutch also sees 100 kg of force. The sheave, however, experiences 200 kg of downward pull. Even though you don't see any movement, a traditional main halyard doubles the compressive load on the mast. A hook or clutch mounted at the masthead, however, does not. Without the turning block (sheave), there is no 2:1 purchase. A 100 kg pull on the downhaul produces only 100 kg of compressive load on the mast.

That is one advantage of a hook over a halyard. The other is that you don't have to contend with halyard stretch. You can use a lighter, cheaper line because it only has to take the load of hoisting/lowering the sail. A traditional halyard, on the other hand, makes for simpler reefing.

Getting back to your original questions though, if your current halyard is class 2 double braid, why switch to a different diameter? You can even get abrasion resistant cover to stitch on where the clutch holds.

I hope that helps,