Illustration 2 - Onohundro Mainsail Halyard Lock Information PDF  | Print |  E-mail
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The drawing above shows the geometry of the Mumm 30 halyard lock. The lock is made from two identical metal plates that are fastened to the masthead crane with a 1/4" gap between the plates.
The main halyard has a wire pennent with a ball swage that is used to engage in the lock and keep the sail at maximum P band.
The rope tail is too thick to run through the halyard lock and is deflected aft of the lock plates. The wire pennent is designed to run between the plates.
As the sail is hoisted, three things will happen.

  1. The rope will run aft of the plates until you get to the wire pennent, then the wire will run between the plates.
  2. The ball swage will hit the plates and be pushed forward by the upper ramp, (A).
  3. When the ball swage is hoisted past the upper ramp, you will hear a clicking sound. This sound is from the swage falling into the lock, (B). If the sail is hoisted too far, the swage will fall off the lower ramp, (C), and will not be engaged. To try again, lower the sail about 12" and rehoist.

To disengage, raise the sail so the ball swage falls off the lower ramp, (C), and then lower the halyard.

A potential problem you may have when lowering the sail is:

When lowering the sail, the rope to wire splice may jam into the lock. To overcome this, hoist the halyard about 6" and keep tension on the halyard as you lower the halyard until the splice is past the lower ramp, (C). This will keep the halyard from being deflected in front of the locking plates and being jammed into the base of the upper ramp, (A).

For initial hoisting of the sail and when hoisting the sail to get off the hook, make sure the cunningham is off, the tack slider is loose, the outhaul is eased and lift the boom. This will make hoisting easier.