Many ships need more flexibility than a fixed-pitch propeller can offer. This graduate-level course looks at marine propulsion systems beyond the basic fixed-pitch propeller, focusing on controllable pitch propellers, combinator control, transverse tunnel thrusters and steerable or podded propulsion. It explains where controllable pitch propellers fit and how they compare with fixed-pitch designs from the operator’s point of view, how their hydraulic actuation, oil distribution and failure-safety systems work, and how design points, hub strength, cavitation and efficiency are balanced. It then shows how power-absorption diagrams are used to derive combinator settings and handle tables, before examining tunnel thruster philosophy and components and the performance of pulling thrusters and pods, including stopping, hull interaction and air-suction limits. The course is explicit about the limits of its coverage.
Course at a glance: Duration 20 hours · Self-paced online · 8 sections, 37 lessons, a 149-page downloadable course book
What you will learn
- Explain where controllable pitch propellers fit and compare them with fixed-pitch propellers against operating profile and manoeuvring needs.
- Describe how a CPP is actuated, supplied with oil, controlled and safeguarded against failure.
- Explain how design point, hub strength, cavitation and efficiency are balanced in CPP design.
- Construct and interpret a propeller power-absorption diagram and derive combinator settings.
- Design handle tables and identify operating limits for combinator control.
- Evaluate transverse tunnel thruster configurations, including controllable and fixed-pitch types.
- Assess pulling thrusters and pods using stopping, hull interaction and air-suction evidence.
Inside the course: a high-level summary, section by section.
CPP fundamentals
The course opens by asking where controllable pitch propellers fit. They are valuable on vessels with more than one operating condition, such as fishing vessels that both trawl and steam, tugs that tow and transit, and ships with shaft generators that need constant shaft speed. They also allow engines that cannot easily reverse, such as many four-stroke engines, to provide astern thrust. From the operator’s point of view, a CPP offers fine control of thrust, quick changes of direction and the ability to load the engine fully in different conditions, while a fixed-pitch propeller is simpler, cheaper and slightly more efficient at its single design point.
CPP systems
The second section explains how a CPP works. The system layout runs from the engine through gearbox, shaft coupling, seals, shaft and bearing to the hub, and the remote-control system adds operating modes such as load control, combinator mode and constant speed mode. The actuating principle uses hydraulic oil acting on a servo piston in the hub, connected through a crosshead to the blade carriers so that piston movement rotates the blades. Oil distribution is handled by an oil distribution box, mounted either on the shaft line or on the gearbox, feeding high-pressure oil through the shaft.
Failure safety is treated carefully. In a CPP, safety means preserving the ability to manoeuvre and control thrust during a fault, not only preventing damage. Pressure balance in the hub, maintained by a header tank, keeps internal oil pressure above external sea pressure to prevent water ingress, while a controlled leakage flow supports monitoring of oil condition. The hydraulic power pack and control system are described, together with the alarms, back-up pumps and fail-set strategies that keep the vessel safe.
CPP design decisions
Choosing the design point is the first design decision. Designing a propeller for a lower fraction of maximum engine rating can give better performance across the real operating profile, particularly where shaft generators or part-load operation dominate. Strength and hub design must cope with blade spindle torque and the larger hub required to house the mechanism, which slightly reduces efficiency compared with a fixed-pitch propeller. Cavitation and efficiency are related but not identical goals, and the course explains the levers available, such as larger diameter, reduced tip loading, more blade area, tip rake, skew and refined blade sections. A fishing vessel example shows how these decisions play out.
Combinator control
A combinator curve is a preset relationship between engine speed and propeller pitch, selected by a single control lever. The course explains power-absorption basics: for each pitch ratio, the propeller absorbs a characteristic power at each shaft speed and ship speed. Increasing pitch at fixed power reduces shaft speed. Using course data, you follow a worked method to construct a power-absorption diagram, read the results across different ship speeds and choose a combinator that keeps the engine within safe limits while favouring efficient operation, generally by reducing shaft speed rather than pitch where possible.
Handle table design translates the combinator into lever positions with defined speed and pitch settings. Operating limits, such as engine torque limits, minimum speed for shaft generators and cavitation boundaries, define where the combinator can safely operate.
Transverse tunnel thrusters
Tunnel thrusters are revisited from a design philosophy perspective: their role in manoeuvring and dynamic positioning, their core components and the choice between controllable-pitch and fixed-pitch types. A controllable-pitch thruster runs at constant speed and varies thrust through pitch, giving quick response and simple electrical drive, while a fixed-pitch thruster relies on variable-speed drives. Tunnel design and auxiliaries, including hydraulic units, cooling and seals, are reviewed with maintenance trade-offs in mind.
Steerable thrusters and pods
The final technical section examines pulling thrusters, where the propeller is ahead of the strut, and compares pulling and pushing arrangements. Pod stopping data shows how azimuthing pods can achieve short stopping distances by rotating the thrust direction. Hull interaction explains how the hull and strut affect inflow and thrust, and the air-suction limit identifies the conditions under which a propeller close to the surface begins to draw in air, causing sudden loss of thrust. A worked example applies these concepts to a pod and thruster case.
Why this matters in practice
Controllable pitch propellers, thrusters and pods are found on a large share of modern working vessels. Their benefits depend on careful choice of design point, sensible combinator settings and an understanding of their operating limits. Engineers who understand these systems can improve fuel economy, protect machinery from overload and make better decisions about retrofit and newbuild propulsion. In practice, many vessels operate for years on combinator settings that were chosen at commissioning for conditions that no longer apply; revisiting those settings with a power-absorption diagram and current operating data is often one of the simplest ways to save fuel. Similarly, understanding the failure-safety logic of a CPP system helps crews and superintendents respond correctly to hydraulic faults and plan maintenance that preserves manoeuvring capability.
Key takeaways
You leave able to explain how CPPs are built, controlled and protected, compare them with fixed-pitch propellers, build power-absorption diagrams and combinators, and evaluate tunnel thrusters and pods using real performance evidence.
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 149-page course book can be downloaded and printed for offline reading and later reference.
Course contents
- CPP Fundamentals: Why CPPs Matter; Where CPPs Fit; CPP vs FPP
- CPP Hardware and Safety: System Layout; Actuating Principle; Oil Distribution; Failure Safety; HPP and Control
- CPP Design Decisions: Choosing the Design Point; Strength and Hub Design; Cavitation and Efficiency; Fishing Vessel Example
- Combinator Curves: What a Combinator Does; Power Absorption Basics; Exam Method; Reading the Results; Handle Table Design; Operating Limits
- Tunnel Thrusters: Role and Philosophy; Core Components; CT or FT; Tunnel and Auxiliaries
- Steerable Thrusters and Pods: Azipull Basics; Pulling vs Pushing; Pod Stopping Data; Hull Interaction; Air Suction Limit
- Summary: Key Takeaways
Who this course is for
This graduate-level course suits engineering graduates and practising marine engineers, propulsion specialists, naval architects and superintendents working with controllable pitch propellers, thrusters and pods, including those on fishing, offshore, ferry and naval vessels. A background in propeller hydrodynamics and marine machinery is assumed.
Frequently asked questions
How long does Advanced Marine Propulsion Systems 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 8 sections with 37 lessons, moving from foundations to applied methods, as summarised above.
Is there material to keep after the course?
Yes. A downloadable 149-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: B11 – Marine Propulsors: Thrusters, Pods and Waterjets; B04 – Marine Propulsion Systems and Thruster Design; B07 – Propeller-Engine Matching & Ship Resistance; B02 – Marine Engineering 1
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Study at your own pace and work through the full course material, worked examples and section quizzes. Enrol in B12 – Advanced Marine Propulsion Systems →
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