EN
In the paper are presented preliminary considerations concerning the efficiency of water-jet ship propulsion system, as well as the calculation of main dimensions of waterjet channel.The friction and momentum losses of the flow channel have been roughly estimated byusing Fliegner's equations. An important conclusion is confirmed that the summary lossesare inversely proportional to square of ship velocity (~1/u2). On the other hand the shippropulsion power is directly proportional to third power of ship velocity (~u3). Thereforeto minimize ship's hull resistance, hulls of waterjet-driven ships ought to be of a greatslenderness - e.g. L/B = 15, stabilized by sponsons, or of semi-swath hydrofoil-supported construction