Propulsion is an important part not only for launching spaceships, but also for navigating (marine crafts) so a destination can be reached.

But how does propulsion work?

First, let's start with a definition of propulsion.

The word propulsion is derived from latin word propellere, which means to propel. The dictionary definition of propel is drive forward or onward by or as if by means of a force that imparts motion.

From the desktop of

Ramses Herrera

In the marine propulsion all movement of a boat in the water has a resistance against  advance to overcome drag, then we needed the propulsion. When saying propulsion, we are not only talking about that one conducted by an engine and a propeller. The propulsion can be also exerted by tow or by action of the wind, it is also exerted by reaction, hydraulic or aerial power, and don't forget the propulsion by oar or with paddle wheels. A single condition is common to all systems of propulsion: the produced push must be equal to the resistance offered to move forward, at this point the object is in dynamic balance with its surroundings, and it will maintain speed, that is the essence of propulsion.

A moving ship experiences resisting forces from the water and air which must be overcome by thrust supplied by some thrust-producing mechanism. In the earliest days this consisted  of manually-operated oars, which gave place in turn to sails and then mechanical devices such as jet, paddle-wheels and propellers of many different forms.

There are now many types of ship propulsion devices. Unusual and  inefficient devices  were invented. Tried and discard. The paddle wheel, which was used successfully on the great western, and many other steamers during the middle of the nineteenth century has subsided into near obscurity as an open-ocean propulsion system. While it still may exist in some remotely located riverboats and special-purpose craft, it has certainly passed its days of significance.

The marine propeller with its many variations is the prime propulsive device of modern ships.

Of the successful types of propulsive devices presently in use, the following may be grouped in four distinct categories:

1) Screw propellers      a) Fixed-pitch propellers      b) Adjustable-pitch propellers      c) Controllable-pitch propellers      d) Shrouded screw working in tunnels or sleeves          (ducted propellers) 2) Paddle wheels, either side or stern mounted with     fixed or feathering blades 3) Jet propellers      a) Water jet through submerged nozzle      b) Water jet through surface nozzle 4) Vertical-axis(cycloidal)propellers      a) Kirsten-boeing propeller      b) Voith-schneider propeller

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