Modern ships rely on a growing range of propulsors beyond the conventional shaft-driven propeller. Tunnel thrusters provide sideways force for manoeuvring, steerable thrusters deliver thrust in any direction, podded drives combine propulsion and steering in a single unit, and waterjets power many fast craft. This technical marine engineering course covers the engineering principles, design rules, formulas and selection criteria for each, supported by worked examples. It explains the commercial and operational case for transverse thrusters and how tunnel geometry, forward speed, multiple-thruster interaction, noise and dynamic loads affect their performance. It then covers steerable thruster applications, L-drive and Z-drive arrangements, sizing, propeller and nozzle choices, gearing and bearing life, followed by podded propulsion and the fundamentals, selection and operating performance of waterjets.
Course at a glance: Duration 20 hours · Self-paced online · 9 sections, 39 lessons, a 99-page downloadable course book
What you will learn
- Explain why different propulsor types are selected for specific manoeuvring and propulsion duties.
- Apply tunnel-thruster design rules for tunnel length, inlet shape and grids to assess thrust losses.
- Describe the effect of forward speed, anti-suction tunnels and multiple-thruster interaction on thruster performance.
- Explain noise and fatigue loading of tunnel thrusters, including idling versus powered operation.
- Size steerable thrusters from torque, bending moment and steering moment, and compare L-drive and Z-drive layouts.
- Calculate bearing life and explain the role of nozzles, pitch control and pulling or pushing arrangements.
- Describe podded propulsion and waterjet principles, pump types and operating performance.
Inside the course: a high-level summary, section by section.
The case for transverse thrusters
The course begins with why ships fit transverse thrusters. A tunnel thruster is a propeller mounted in an athwartships tunnel through the hull, able to push water out of either side and generate a sideways force independent of forward speed. The commercial argument is straightforward: lower cost per mile depends not only on efficient passage but also on fast, safe port manoeuvres with less reliance on tugs. Typical applications span ferries, cruise ships, offshore support vessels, research ships and many cargo ships, and product configurations include fixed-pitch and controllable-pitch units with electric, hydraulic or diesel drives.
The tunnel itself has a large influence on performance. A short tunnel keeps friction losses low but may allow turbulent, poorly developed flow to reach the propeller, while a longer tunnel adds friction but can provide some useful thrust augmentation, similar in principle to a nozzle. Design guidelines cover the tunnel length relative to diameter, inlet rounding to reduce entrance losses, the position of the tunnel relative to the waterline and keel, and protective grids with limited blockage.
Tunnel thruster operation
Forward ship speed has a strong effect on thruster effectiveness. As the ship moves ahead, the jet from the tunnel is deflected and a low-pressure region forms on the hull downstream, producing a force that opposes the thrust and can dramatically reduce the net side force at relatively modest speeds. The anti-suction tunnel is presented as one remedy, connecting the high- and low-pressure areas to reduce this suction effect.
Many vessels, particularly large offshore construction and drilling units, carry several thrusters, and interaction between them can reduce net thrust when one thruster’s jet enters another. Non-dimensional performance descriptions allow thrusters of different sizes to be compared. Noise is discussed because tunnel thrusters are often close to accommodation, and dynamic loads explain why a thruster idling in a seaway can still experience significant unsteady blade loading and fatigue, before considering the additional effects of slamming in heavy weather.
Steerable thrusters: applications and selection
Steerable thrusters can rotate through 360 degrees, combining propulsion and steering. The course explains why they are fitted, from tugs and offshore vessels to ferries and dynamic positioning units, and reviews thruster families across their power range. L-drive units have a vertical input shaft and a single bevel gear set, while Z-drive units have a horizontal input shaft and two gear sets. Sizing is based on the torque derived from input power and speed, together with the bending moment on the thruster leg and the steering moment needed to rotate the unit under load, illustrated by a sizing worked example.
Steerable thruster design
The design section compares controllable-pitch and fixed-pitch propellers for steerable thrusters and explains why almost every thruster uses a nozzle: at high propeller loading, such as at bollard pull or low speed, a nozzle significantly increases thrust per unit power. Pulling and pushing arrangements, in which the propeller faces forward or aft relative to the leg, affect inflow quality and efficiency. Mechanical design of the gearing and steering system is reviewed, followed by bearing types and their selection. Bearing life calculations relate the load spectrum and speed to expected service life, and a worked example shows how operating profile influences the result.
Podded propulsion
Podded propulsion places an electric motor inside a streamlined pod outside the hull, driving the propeller directly. The course explains the advantages, including excellent manoeuvrability, flexible machinery layout, good inflow conditions and reduced vibration, together with the engineering issues of power transmission, bearing and seal design, steering loads and hydrodynamic interaction with the hull.
Waterjet propulsion
Waterjet fundamentals explain how a pump inside the hull draws water through an intake and accelerates it through a nozzle to produce thrust, with steering and reversing achieved by deflecting the jet. Efficiency depends on the ratio of jet velocity to ship speed and on the losses in the intake and ducting. The selection section covers pump types, matching the waterjet to the hull and engine, cavitation limits at low speed and high thrust, and operating performance across the speed range, explaining why waterjets are well suited to high-speed craft.
Why this matters in practice
Choosing the right propulsor and installing it correctly has a direct effect on manoeuvrability, efficiency, noise, maintenance and safety. Engineers who understand the physics and design rules behind thrusters, pods and waterjets can specify equipment appropriately, evaluate supplier proposals, anticipate performance losses and diagnose problems in service, rather than relying solely on catalogue figures.
Key takeaways
You leave able to explain why each propulsor type is chosen, apply tunnel thruster design rules, evaluate forward-speed and interaction losses, size steerable thrusters and their bearings, and describe the principles and selection of pods and waterjets.
How you study
The course is delivered fully online and is self-paced, so you can fit roughly 20 hours of study around professional commitments. Lessons combine clear explanation with examples, diagrams and short interactive checks, and the main sections end with graded quizzes (8 in total) so you can confirm you can apply each method before moving on. A 99-page course book can be downloaded and printed for offline reading and later reference.
Course contents
- Course Overview: Course Introduction; What this course covers
- Why Transverse Thrusters, and Basic Tunnel Design: Learning objectives; The case for a transverse thruster; Typical applications and market segments; Product configurations; How the tunnel itself affects performance; Design guidelines for tunnel geometry and grids
- Transverse Thruster Performance – Forward Speed, Interaction and Loads: Learning objectives; Effect of forward ship speed; The anti-suction tunnel; Interaction between multiple thrusters; Non-dimensional performance description; Noise; Dynamic loads: idling versus powered operation, and fatigue
- Steerable Thrusters – Applications and Selection: Learning objectives; Why fit a steerable thruster?; Typical applications; Thruster families and power range; L-drive versus Z-drive; Sizing the thruster: torque, bending moment and steering moment
- Steerable Thruster Design – Propellers, Nozzles, Gearing and Bearings: Controllable-pitch versus fixed-pitch propellers; Why (almost) every thruster uses a nozzle; Pulling versus pushing arrangements; Mechanical design of the gearing and steering system; Bearing types and selection; Bearing life calculation
- Podded Propulsion Systems: Podded Propulsion Systems
- Waterjet Propulsion Fundamentals: Waterjet Propulsion Fundamentals
- Waterjet Selection, Pumps and Operating Performance: Waterjet Selection, Pumps and Operating Performance
Who this course is for
This course is for engineering graduates and practising engineers in marine engineering, naval architecture, offshore vessel design and propulsion equipment supply, as well as superintendents responsible for vessels with thrusters, pods or waterjets. A background in basic fluid mechanics and marine propulsion is helpful.
Frequently asked questions
How long does Marine Propulsors: Thrusters, Pods and Waterjets take?
The course is designed for about 20 hours of study. It is self-paced and fully online, so you can spread it over a few weeks or complete it more quickly.
What is covered?
The course is organised into 9 sections with 39 lessons, moving from foundations to applied methods, as summarised above.
Is there material to keep after the course?
Yes. A downloadable 99-page course book accompanies the lessons for offline reading and later reference.
How is progress checked?
Each main section closes with a graded quiz (8 in total). The quizzes test understanding of the concepts and methods explained in the lessons rather than memorisation, and you can review the relevant lessons before attempting them.
Can I record this study for my own professional development?
Yes. The course notebook includes a self-assessment of the course objectives before and after study, a reflection page and a learning log, which you can use to keep your own record of professional development.
Duration: 20 hours
Related courses: B04 – Marine Propulsion Systems and Thruster Design; B12 – Advanced Marine Propulsion Systems; A14 – Design of Advanced Marine Vehicles; B07 – Propeller-Engine Matching & Ship Resistance
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Study at your own pace and work through the full course material, worked examples and section quizzes. Enrol in B11 – Marine Propulsors: Thrusters, Pods and Waterjets →
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