How much power does a ship need, and how does that power become thrust? This course answers that question by following the full power chain from prime mover to propeller and from hull resistance to installed power. It explains the different power definitions used in ship propulsion, from brake power at the engine to effective power that tows the hull, and shows how efficiencies link them. It then breaks down total hull resistance into frictional, viscous pressure and wave-making components, explains how they change with speed, hull form and operating conditions such as shallow water and fouling, and shows how towing-tank results are scaled to full size using similarity principles and Froude’s law. The course closes with screw-propeller geometry and the operating phenomena that govern thrust and propulsion performance.
Course at a glance: Duration 20 hours · Self-paced online · 7 sections, 20 lessons, a 75-page downloadable course book
What you will learn
- Explain how power is transmitted from the prime mover to the propeller and distinguish BHP, SHP, DHP, THP and EHP.
- Calculate delivered or installed power from stated efficiencies and operating requirements.
- Interpret frictional, viscous and wave-making resistance and how they change with speed and hull form.
- Explain operating factors that increase resistance, including shallow water, fouling and weather.
- Apply similarity principles and Froude scaling to relate towing-tank model results to full-scale predictions.
- Describe how propeller geometry influences thrust and efficiency.
- Explain propeller operating phenomena that affect propulsion performance.
Inside the course: a high-level summary, section by section.
Why power matters
The course begins by explaining why resistance and powering sit at the heart of ship design and operation. Installed power determines the size and cost of machinery, the fuel consumed, the emissions produced and ultimately the commercial viability of the ship. The logic of the whole course is set out early: first estimate how much resistance the hull must overcome, then work out how much power the machinery must produce once all the losses between engine and water are taken into account.
The power chain
Power is defined at several points along the drivetrain. Brake horsepower is the power produced at the engine output; shaft horsepower is the power in the shaft after the gearbox; delivered horsepower is the power arriving at the propeller after shaft-line losses; thrust horsepower is the power represented by the propeller’s thrust and the speed of advance; and effective horsepower is the power needed to tow the bare hull at a given speed. Each stage removes a little power through mechanical, transmission or hydrodynamic losses. Shaft-line losses are small, but gearbox and propeller losses can be significant.
The practical implication is that machinery must be rated with the full chain in mind: the propeller always receives less power than the engine produces, and the hull receives less useful power still. A drivetrain worked example shows how to move along the chain using stated efficiencies.
Effective power and propulsive efficiency
Effective power is the fundamental design quantity before engine selection and propeller matching. In early design, before the ship exists, it is estimated from data and methods, and later confirmed by towing a scale model and scaling the results. The course explains how hull efficiency, which captures the interaction between hull and propeller through wake and thrust deduction, and the overall propulsive coefficient, which relates effective power to shaft or delivered power, connect hull resistance to machinery power. A worked example shows how to size installed power from an effective power requirement, including allowances for losses and service margins.
Hull resistance
Total resistance is divided into components with different physical origins. Frictional resistance arises from the shear of water flowing along the wetted hull surface; it depends on Reynolds number and dominates at low speed. Viscous pressure resistance, captured with a form factor, reflects the additional drag caused by the hull’s shape and the thickening boundary layer. For a given speed, a longer, narrower hull with less displacement reduces viscous resistance, but that advantage must be balanced against stability and cargo capacity.
Wave-making resistance arises because a moving ship creates divergent and transverse wave systems from the bow and stern. As speed rises, wave height and length increase and the energy carried away grows rapidly, so wave resistance climbs steeply. The Froude number, which relates speed to the square root of length, is used to compare ships of different sizes and identifies the humps and hollows in the resistance curve where bow and stern waves reinforce or cancel.
Operating factors add to calm-water resistance. Hull fouling and roughness increase friction, wind and waves add resistance in service, and shallow water has a particularly strong effect. In shallow water the flow under the hull accelerates, raising viscous resistance, lowering pressure under the hull and causing squat, while waves at a given speed become larger. The resistance hump shifts to lower speed, fuel use rises and the risk of grounding increases, which makes shallow-water effects a safety issue as well as an efficiency issue.
Model testing and scaling
Because full-scale testing is impossible during design, towing-tank tests are used. The course explains why: models are affordable, controllable and allow alternatives to be compared before construction. Model results are only useful when the model and ship satisfy geometric similarity, meaning the same shape at reduced scale, and dynamic similarity, meaning the important force ratios match.
Matching both Reynolds and Froude numbers is not possible with water as the test fluid, so Froude’s approach separates resistance into a frictional part scaled using friction lines and a residuary part scaled by Froude’s law at corresponding speeds. The course shows how tank results are converted into an effective power curve for the full-scale ship, with a worked model-to-ship scaling example.
Screw propellers
The final technical section introduces the screw propeller. Geometry, including diameter, pitch, blade area, number of blades, skew and rake, determines how the propeller accelerates water and produces thrust. Thrust and performance are discussed in terms of advance speed, slip and efficiency, and the course explains operating phenomena such as cavitation, which can erode blades, cause vibration and reduce thrust when local pressures fall below vapour pressure.
Why this matters in practice
Powering decisions affect the whole life of a ship. An over-powered vessel wastes capital and may run inefficiently at part load, while an under-powered one cannot meet its schedule or maintain speed in bad weather. Understanding how resistance, efficiencies and propeller behaviour combine helps engineers specify machinery sensibly, interpret model test reports and sea trial results, and evaluate energy-saving measures with a realistic sense of the gains available.
Key takeaways
You leave able to define and convert between the power quantities used in ship propulsion, interpret hull resistance components and the factors that change them, scale model test results to full size and explain how propeller geometry and phenomena affect thrust.
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 (5 in total) so you can confirm you can apply each method before moving on. A 75-page course book can be downloaded and printed for offline reading and later reference.
Course contents
- Drive Train Power Chain: Why Power Matters; BHP to THP
- EHP and Propulsive Efficiency: What EHP Means; From EHP to SHP
- Hull Resistance Components: Total Resistance; Viscous Flow Around Hulls; Wave-Making Effects; Operating Resistance Factors
- Model Testing and Scaling: Why Use Models; Similarity and Froude Law; From Tank to EHP Curve
- Screw Propeller Fundamentals: Propeller Geometry; Thrust and Performance
- Summary: Key Takeaways
Who this course is for
This course is for engineering graduates and practising engineers in naval architecture, marine engineering, ship operations and energy efficiency who need a clear refresher on resistance and powering. It also suits mechanical engineers moving into the marine sector and technical superintendents who interpret speed-power data. Basic fluid mechanics is helpful.
Frequently asked questions
How long does Resistance & Propulsion 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 7 sections with 20 lessons, moving from foundations to applied methods, as summarised above.
Is there material to keep after the course?
Yes. A downloadable 75-page course book accompanies the lessons for offline reading and later reference.
How is progress checked?
Each main section closes with a graded quiz (5 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: A04 – Project Introduction to Hydromechanics; B02 – Marine Engineering 1; B08 – Design of Auxiliary Systems; A12 – Naval Architecture and Ship Production Technology (Part 3 of 4)
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Study at your own pace and work through the full course material, worked examples and section quizzes. Enrol in B06 – Resistance & Propulsion →
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