When it is not under sail, and under motor power. Then it must follow the powerboat navigation rules. Since you've asked this question, then i recomend taking your state's Boater's Safety Course if it has one. It should be online and it cost about $50. It's expensive but you get a snassy card and you learn lots of things like where to go and where not to go, and things like that.
Any sailing vessel that is operating mechanical propulsion is considered a power driven vessel under the rules of the road, and must maneuver accordingly. This is regardless of whether or not they also have a sail up.
discourteous
Under the Navigation Rules, it is OK to break the rules when it is absolutely necessary to avoid a collision.
When nessasary to aviod a collision
When absolutely necessary to avoid a collision.
insane captain or crew in danger is enough for mutany (MEWT-KNEE)
When absolutely necessary to avoid a collision.
Speed up to pass in front of the sailboat
Do whatever is necessary to stay clear of the sailboat.
(Taken from the USCG Navigation Rules (Inland & International)International & InlandRule3General(C) The term "Sailing vessel" means any vessel under sail, provided that propelling machinery, if installed, is not be used;So the answer is, if a Sail boat is using it's engine, regardless if the sails are being used, now has the responsibility to act as a power driven vessel.
The powerboat should pass to the stern of the sailboat to avoid its wash causing a problem for the sailboat To avoid a collision, the powerboat should avoid crossing ahead of the sailboat.
Discourteous