Capetanios Oz wrote:

On what tack is a sailing boat that's head to wind?

It is considered to be on the same tack as it was before going
head to wind.

Here's a tricky one... if a vessel is sailing along close
hauled, and the wind shifts 90 degrees, forcing her sails across
while the vessel continues on a straight course, has she
'tacked'?

Fresh Breezes- Doug King