Examples from the Web for jackyard
A jackyard topsail that requires no topmast can be set, and a spinnaker will be found very useful for running in light weather.
She might well have carried her jackyard topsail going west, and certainly wanted it, coming back with sheets off.Yachting Vol. 2|Various.
One yard ought to serve for both the gaff and jackyard topsail, and these sails should be made the same length on the head.
Jackyard topsails and bowsprit spinnakers preened before it.The Message|Louis Tracy