For an ocean port, best thing I've found is to make a loading/unloading pier with steps (ladders) down into the water. You can stand on a ladder and reach 2m up or down to a container/ship storage/cart etc. After loading or unloading, if you're going to park the boat, move it out about half as far as you can swim and leave it there in deep water with no stones or other stuff nearby.

Haven't lost one like that yet, though I have logged on to find it hanging in mid-air occasionally.

PS: make sure and put a workbench at the end of the pier so you can repair ship.