Maybe the walkthrough by Malcolm for the original game might help.
Malcolm wrote:
In order to get onto the boat you must first hide behind the nearer crate. To do this, and to get on the boat, you need to wait until the guard has gone around the side. When on the boat, immediately climb up the ladder onto the roof. Wait for the guard to again go round the side, then open the cupboard door and get back onto the roof. As soon as the guard enters the cupboard, close the cupboard door and then jam it by inserting the mop in the handle. Look through the left hand porthole and eavesdrop on Oubier and Karzac.
