When a sailboat overtakes a powerboat witch vessel is the stand on vessel?

The boat that overtakes another boat is the give-way vessel. The boat being overtaken is the stand-on vessel.

When a sailboat is the overtaking vessel, she must keep clear of the powerboat. Any vessel overtaking another must stay clear of the vessel being overtaken (Rule 13).

Please refer to the Navigational rules. Specifically Rules 8, 9, 12, 13, 14, 15, 16, 17 & 18. A link is provided below.