Mysterious Sheave on the Mast.

[ClutchCargo]

Hi SN,

I've only just bought my yacht and am working my way through the rigging set-up. There was no user manual supplied with the boat .

I have been able to work out most of the rigging, but there is an odd sheave recessed into the port side of the mast just below the mast head, below the forestay on the forward side. There is a picture below.

I don't think it is a topping lift for the spinnaker pole; that sheave is centre just below the spreaders.

There are 4 sheaves at the base of the mast; main and jib halyards use 2 of these. I guess the spinnaker pole lift uses the 3rd (it's not threaded) and the mystery sheave uses the remaining one.\

Your thoughts or solutions would be appreciated!

Thanks, Mark.

[svHyLyte]

Exit block for a spinnaker halyard that extends to the block on the masthead crane.