Nails it at 13.
ya I thought that but worded it wrong comparing it to a auto pilot. But in all the pictures I seen, that looked like a rigid mount where the horizontal of the weather vane arm meets the sail. there was no evidence of a pivot point. also the wind catch on the vane would be on one side only meaning the tack could only be in the direction of a starboard wind. thats where im thrown...
mann I just noticed it may be in line with the sail!! lol... my total bad.