immediately after a very simple maneuver to insert the bow 4 of the pusher boat 3 into the notch 2 of the barge 1 until the fender 4a comes into contact with the deepest point of the notch 2 so that the pusher boat 3 may be pushed back as the result of the special configurations of the helmet and the channel to keep a proper clearance between these two watercraft after connection in addition when these watercraft are more or less oscillated by waves small ahead thrust may be maintained by the propulsion means of the pusher boat 3 even after the fender 4a has come into contact with the deepest point of the notch 2 of the barge 1 so that the forward face 21 of the helmet 15 may be forcibly pressed onto the oblique forward side wall 6 of the channel 5 while the former slides on the latter to reduce remarkably the possibility of turning of the connecting pin 12 due to oscillation of the watercraft and thus assure a very stable connection work nowadays almost all ships are constructed by welding and accordingly dimensional and angular inaccuracies due to deformations caused by welding are inevitable for example when the channel 5 together with concavities.