This has been in my common knowledge for a long long time, didn't find it here, so i decided to post this lol. :b
Get over the wheel, you will see a rope, get on the right rope.
Then, climb up the rope (as the pic shows up), climb high as u can, when you're on the highest spot.. Back off a little, because u cant jump if you're facing the "too hight spot to walk on". And then jump on the thing there.
Now you can go to the both sides of that wooden plank there :>
Warning: Don't jump if you're close to the end of the plank when the boat is moving, it will pop you out of the boat
- Found a similiar post, but it shows how to get on the another plank, didnt find another like this.