Tugboats: The source of its strength.
I previously explained what Bollard Pull is, but in order to obtain such towing strength, it is needed a fundamental item, the PROPELLER.
Three categories are common in tugboats, do you know them?
Conventional: The most common on most vessels, it has a fixed shaft connecting the main engine or gearbox to the propeller directly, its steering system is separate and independent. In tugs, it is usual to have Kurt Nozzle around the propeller.
Azimuth: Or Z-drive. It has become the most common propulsion in tugs. Created in the mid-1960s, these systems deliver their greatest power and thrust in 360 degrees, the Z-drive allows for high maneuverability and eliminates the demand for conventional rudders. (Fun fact.: Z because the rotary axes make 2 right-angle curves, resembling the letter “Z”)
Cycloidal: The curious Voith Schneider drive. Developed in the mid-1930s by Voith Schiffstechnik, it offers exceptional maneuverability and simplicity of control, but less power efficiency. Installed at the bottom of the vessel, it is a rotating system of vertical hydrofoils, each of which rotates on its vertical axis, changing the angle of attack. The rotation intensity of the system determines the thrust and the angle of the hydrofoils determines the direction.