The boats are pulled on multiple large rollers. Of course the boats have flat hull.

The rollers..

The winch with the cable. The winch can be operated by two men.

The winch. Guess what is this pulley beside the winch !

The strange pulley beside the winch. Look at the little hole under the pulley...

In fact it is a mobile pulley which must be fixed on the little square between the rollers....

There is a little tooth on the square... the pulley must be positionned on the square with the tooth into the little hole of the pulley. The pulley fixed on the square is used to pull the boat in line with the rollers!

Click to enlarge