I need some help finding a cover for a main sail?

Question

The sail boat is a 1970s Venture, 21' long. How long of a mail sail cover would I need to buy?

Answer 1

you need to measure from the front of the mast to the end of the boom; from the bottom of the boom to where the head of the sail lays when its furled, and from the top of the furled sail about mid way to the bottom of the boom...West Marine has diagram in its catalog