The invention relates to a ship having two ship's screws, one of which is fixed to a first screw shaft of hollow construction and the other runs concentrically inside the first screw shaft, a main drive engine for the screw shafts and a differential which is mounted between r the shaft of the engine and the screw shafts and which is able to make the screws rotate in opposing directions and can distribute the engine power dynamically over the screw shafts.

A ship of this type is disclosed in EP-A 0 132 220.

The aim of the invention is to supplement this installation in such a way that too high or too low a torque on one of the two shafts can be compensated for by being able to supply or take off power.

According to the invention, the ship mentioned in the preamble is, to this end, characterised in that the differential is connected via a gear transmission to a second engine or to a power take-off (PTO).

Preferably, use is made of an embodiment wherein a pinion mounted on the shaft of the main drive engine engages with a number of planetary gears which arc connected to one another by means of a coupling element and arc connected via shafts to auxiliary planetary gears which engage in inward-facing toothing on an annular gear with which the hollow screw shaft is in direct connection, wherein the other screw shaft has a direct connection to the coupling element and a gear mounted on the shaft of a second engine or PTO engages in toothing on the outside of the annular gear or of the coupling element.

The invention also relates to a differential for an abovementioned ship.

When a second engine is used, the entire system can be driven by the second engine, it being possible to operate at low power.

The invention will now be explained with reference to the figures.

Figures 1 and 2 show, partially in cross-section, embodiments of drive mechanisms for a ship according to the invention.

The ship's drive shown in the figures comprises an engine 1, an output shaft 2 of the engine, a hollow screw shaft 3 which has a first ship's screw 4 at the rear end, a screw shaft 5 which extends through the hollow shaft 3 and has a second ship's screw 6 at the rear end, and a differential 7 which ensures that when the engine is running the screws rotate in opposing directions and that the power of the engine is distributed dynamically over the screw shafts in such a way that a higher torque or lower speed of the one screw shaft corresponds to a lower torque or higher speed of the other screw shaft.

The differential mechanism according to Figure 1 is of the planetary type and has a pinion 17 which is mounted directly on the engine shaft 2 and engages in at least two planetary gears 18, 19, which are connected to one another by means of a coupling element 11. The hollow shaft 3 is fixed to an annular gear 20. The planetary gears 18, 19 arc connected via shafts 42, 43 to auxiliary planetary gears 18a, 19a, which engage in inward-facing toothing on the annular gear 20. Incidentally, three or more planetary gears can also be present.

Toothing 48 is provided on the outer edge of the annular gear 20, in which toothing a gear 49 engages which, via a shaft 50, cither takes off power from the unit 51 operating as second engine or supplies power to the unit 51 operating as PTO.

In the embodiment according to Figure 2, the gear 49 does not engage in external toothing on the annular gear 20 but in a relatively large gear 52, through which the connecting shafts 41 and 42 extend between, respectively, the gears 19 and 19a and the gears 18 and 18a.

The gear 52 thus connects the planetary gears 18, 19 and in this respect has the same function as the coupling 11 in Figure 1. The shaft 5 is connected to the centre of the gear 52.

With this embodiment as well, the units 1 and 51 can act both as engine and as PTO, the condition being, of course, that when one unit functions as the engine, the other unit

functions as the PTO.

The features essential to the invention are, on the one hand, that the differential is of such construction that neither of the drive shafts 3, 5 extends as far as the engine 1 and, on the other hand, that an additional engine or PTO is integrated. A positive or negative surplus of torque in one of the two shafts can be compensated for by supplying power or taking off power.

If the unit 51 is an additional engine, the entire system can be driven by said engine, in which case, for example, it is possible to operate at low power.