This is something I've used every time I've had to go from/to booty bay on the boat.
Note: This only works if you can walk on water (Atleast from my experience)
Now, Position yourself like so:
If the boat leaves and you don't move with it (Sort of like in its own gravity), Run to it before it goes to max speed and hug it, I've never failed to do this, Just get close to it, You will sink in a little, keep moving and your camera should zoom and you will be moving at boat speed and you wont even have to move. Like this:
I've used this ever since i got my Bloodsail title.
Tested with night elf/draeni boats, Doesn't work
Haven't tested on wotlk boats but they are pretty much the same so it should work
I would think this is pretty much common knowledge but its useful to me and maybe to others who don't know
enjoy