| In case you lose connection in middle of ocean and lose drydock menu:
Goto the spot you want to mark. Gate to shore on same server. Just as your entering gate say either "right" or "left" on the boat. When you come back thru the gate from shore, the boat will have moved out of your way and you can mark. Unfortunatelty, becuase boat is now moving it may take 4 or 5 recalls to get back onto the boat depending on the lag.
Additionally, if you have another boat in your pack you can drydock the first boat in mid of ocean. What you need is to find any other ship in the ocean or other obstacle. Do the above gate trick about 6 tiles away from another ship. The boat will stop automatically when it hits the obstacle. When you go back thru gate onto ocean immediately place 2nd ship and get drydock menu. Now go onto 1st ship and drop anchor. Go back to 2nd ship, gate to shore, and drydock it. When you go back thru gate you can now bring up drydock menu on the original boat.