Sequence 13 port authority mission? help!!!

There are several ways to do this, for some reason some work for some people and not others... This is the way I did it-

1) Dive into the water, either from the rooftop directly (move along the roof to the right of the mission start-point) or work your way down to ground level

2) Swim to the other side of the boat- DO NOT get too close to the boat until you are round the other side

3) Climb up the hull to the right-hand side section of rigging just until you are able to grab the top railing

4) Shimmy across until you are towards the back of the boat, just behind the 2 guards that are over-looking your target

5) Wait until all patrolling guards are away from you (you can try and ledge assassinate some, one of my friends said this worked however it did not work for me)

6) Climb up and immediately drop onto the deck

7) IMMEDIATELY drop a smoke bomb- you should have time to do this just before you are spotted

8) Run past all guards, jump onto the rail above your target, and air assassinate him... DONE!