Modern vessels use engines of various types. The most widespread are marine internal combustion engines, and most often they are diesel.

Propulsion devices are designed to assure ship motion by conversion of some kind of energy. They can be active and reactive. Sails are active propulsion devices, others are reactive. Today, the following propulsion devices are in usage:

• vane ones – pulling oar, paddle wheel, propeller screw, cycloidal propulsion unit;
• water-flow – thrust and lesser used water-jet motor.

Propeller screws are used at various vessels. Their disadvantage is need for increasing of screw dimension and weight in order to up-shift of impulse to the vessel. Speed increase entails cavitation which threatens with unwanted consequences – from efficiency lowering to blade destruction.

The cycloidal propulsion unit is a flush-bilge disc with equally spaced propeller-type blades. The disk circles the vertical axis while blades move rotationally oscillatory. Its main disadvantage is low efficiency, main advantage is high ship maneuverability.

Water-jet propulsors are used at shallow-draft vessels. They move owing to volumes of water ejected from nozzles.

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