All other types of power transmission generated in the engine room have a more or less hidden part. Here are the four main types to choose from. The advantages and weaknesses of each. We have deliberately avoided mentioning waterjet and surface propellers because of their limited diffusion.
Shaft line transmission
It is the most common type of transmission, by many, it is considered the most reliable, certainly is the one that requires less maintenance. But even in-line transmissions have their weak points, such as the possible misalignment between the propeller shaft and motor-inverter unit; or the wear of bushings and hitch presses. From a practical use point of view they are less docile to maneuver in narrow spaces (this is why the bow thruster and the possible joystick have become so widespread even on medium-sized boats) and the placement of the engine onboard which, moved more to the center of the boat, reduces the living space inside.
Volvo Penta’s IPS transmissions are characterized by the propellers that are drawn towards the bow, so they are more efficient because they do not suffer from foot or axle turbulence and this allows to install, with the same performance, lower power and save a bit on consumption. The optimum is obtained if they are used on a hull designed especially for this type of transmission. In any case, they are also credited with the introduction of the joystick for mooring maneuvers, without touching the gas throttles, which has decreed their success.
Drive train by POD
The response from other manufacturers to the IPS was not long in coming. In particular, Cummins Zeus, ZF Marine POD 4000 and CAT Three60 POD 650 presented three types of propulsion PODs, i.e. with propellers pushing. The main advantage over IPS is the protection that the POD itself provides to the propeller. In both cases the two PODs (right and left) move at different angles to optimize the turning radius and facilitate maneuvering. Often they can also have integrated trim-tabs.
Sterndrives and Axius
In order to answer the question of easy maneuvres, the classic stern driver(also called inboard-outboard) have evolved. There are joysticks that make them work in combination with the bow thruster, while Cummins MerCruiser offers the Axius electronic management system, which allows the stern feet to move independently of each other, with a significant advantage during maneuvers. All naturally with the usual joystick.