Answer:
One Short Blast
Step-by-step explanation:
If the launch approaches you and it sounds two short blasts, it means that the boom intends to allow you to pass them on the starboard side, that is, on the right side.
However, you do not want to do this, and you want to pass on the left side of the boat door. To communicate your desire to the motorboat, you have to sound one short blast. This sign allows you to say "I want to pass on your left side, next to your door and not on the starboard side".