Sailboat Right of Way

[rabend]

A 45 foot sailboat is under power moving down the right side of a fairly wide fairway. The vessel under power slows as a 20 foot sailboat tacks from port to starboard directly across its bow. After the small boat passes and is well to starboard, the larger boat speeds up to cross behind the smaller boat's stern. The smaller boat under sail then tacks back across the channel in the opposite direction directly in front of the vessel under power creating immediate danger in a crossing situation. I would appreciate thoughts on who is at fault.

Thanks,

Bob