The white light shining forward is the light to indicate the vessel is under power.
In the case of a sailboat with sails drawing and the forward facing white light on, the vessel is 'motorsailing' and is a powerboat as far as the rules are concerned.
I would be very careful crossing such a boat, as the boat may be under sail alone, and the forward white, 'under power' light may be on in error. In addition, be cautious of sailboats in general, some of their operators think (wrongly) that they have 'right-of-way' at all times.
Note that under the rules, there is no such thing as 'right-of-way'.
There is only the 'stand on' vessel and the 'give way' vessel.
If the 'give way' vessel doesn't maneuver as needed to avoid collision, then the 'stand on' vessel must maneuver to avoid collision.
Always remember that the rules are not there to determine 'right of way' but to 'prevent collisions at sea'.
In the case of a sailboat with sails drawing and the forward facing white light on, the vessel is 'motorsailing' and is a powerboat as far as the rules are concerned.
I would be very careful crossing such a boat, as the boat may be under sail alone, and the forward white, 'under power' light may be on in error. In addition, be cautious of sailboats in general, some of their operators think (wrongly) that they have 'right-of-way' at all times.
Note that under the rules, there is no such thing as 'right-of-way'.
There is only the 'stand on' vessel and the 'give way' vessel.
If the 'give way' vessel doesn't maneuver as needed to avoid collision, then the 'stand on' vessel must maneuver to avoid collision.
Always remember that the rules are not there to determine 'right of way' but to 'prevent collisions at sea'.