Drivetrains

When it comes to buying a boat, the drivetrain factor should not be overlooked, especially as more and more manufacturers are moving into electric and/or hybrid power... Equipment manufacturers offer several choices. A range of different powers, brands and transmission types - which is what interests us today.
When repowering a second-hand multihull, you may also ask yourself the question: shaft drive, sail drive or pod?
Here’s an overview of the available solutions, with their advantages and disadvantages.

Propshaft transmission

This is the oldest and most traditional of transmissions. The principle is simple: a shaft is connected to the motor, positioned either more or less centrally in the hull, while the propeller is at the other, after end of the shaft. The further forward the motor, the greater the efficiency, since the line of the propeller shaft is at the closest angle possible to the waterline.
This system is simple and fairly reliable. It does, however, require a little more maintenance, particularly for the stern gland or stuffing box, and when it comes to alignment.

Advantages

- Reliability
As a simple solution that has been in use for a very long time, the in-line shaft is reliable and durable. The relatively small round hole in the hull limits the consequences of water ingress.

- Maintenance
Once again, thanks to the simplicity of the system, maintenance remains simple and, above all, inexpensive.

- Good long-term performance
Provided you have a sufficiently torquey engine, the in-line shaft offers decent performance when underway, but no dazzling acceleration.

Disadvantages

- Space requirements
To operate efficiently, the shaft must be at the closest possible angle to the waterline. In modern, shallow hulls, this often means installing the motor a little further forward, leaving room for the propshaft, which takes up space on board. A wider angle means reduced efficiency and increased vibration.

- Potentially higher vibration and noise levels
Shaft-driven propeller transmissions are notorious for their vibrations. A problem that can be partly solved with proper installation.

- Precise alignment required
With a propshaft, the engine needs to be perfectly aligned. Failure to do so can result in additional vibration, friction, lower-than-normal efficiency, and even damage to seals or stern glands.

Saildrive transmission

Though an ever-increasingly widespread option, saildrive transmission is also a little more complex than the shaft-driven prop. The motor is connected to a short shaft, which is connected to a gearbox on a vertical shaft outside the hull, which is itself connected to a final gearbox that drives the propeller. This system is in use more and more by boat builders, as it saves significant space on board.

Advantages

- Space saving
This is the main advantage of this transmission. In fact, thanks to the short shaft connected to the motor and the two gearboxes, most of the system is located outside the hull. ...