Staysail

[Auspicious]

John,

From your description I suspect what you have is a mizzen staysail from a ketch. This is a light-air reaching sail. Depending on how big it is and just how it was cut (mizzen staysails may be tacked to a windward toe rail, at the base of a shroud, or a dedicated deck fitting; the space between masts is all over the map even on similar-sized boats, and mast height varies) it might make a decent spinnaker or reaching sail for you.

On the other hand you may be better off selling it and getting something cut for your Columbia.

sail fast, dave