A sailing yacht must be fast, seaworthy and safe, and those goals depend on a careful balance of stability, hull form, appendages and behaviour in waves. This course covers yacht stability, hydrodynamics, seakeeping and experimental testing. The course looks at the influence of hull shape, appendages, sea state and testing methods on how fast and how safe a yacht is. Topics include judging stability and capsize risk from righting moment and GZ curves, breaking calm-water resistance into its parts and the design moves that reduce each, the effects of heel, side force and leeway, the way waves and weight distribution change speed upwind and downwind, and the merits of systematic series, CFD and tank testing for predicting and checking resistance.
Course at a glance: Duration 20 hours · Self-paced online · 6 sections, 14 lessons, a 73-page downloadable course book
What you will learn
- Explain how righting moment and GZ curves are used to assess yacht stability.
- Explain the factors that govern capsize resistance and re-righting, including beam, freeboard, flare and ballast.
- Analyse the main components of calm-water resistance and the design choices that reduce them.
- Explain how heel, side force and leeway interact with hull and appendage design.
- Evaluate how waves and mass distribution influence yacht performance in head seas and following seas.
- Compare resistance prediction and validation methods, including systematic series, CFD and model testing.
- Interpret towing tank and semi-captive test approaches and their role in design decisions.
Inside the course: a high-level summary, section by section.
Stability and safety
The course begins with righting moment, the moment that returns a heeled yacht towards upright. It is produced by the separation between the centre of gravity and the centre of buoyancy as the hull heels. Initial stability is described by metacentric height, which depends on where buoyancy acts, the contribution of the waterplane through the metacentric radius and the height of the centre of gravity. Beyond small angles, the GZ curve describes the righting lever across the full range of heel angles.
Reading GZ curves is a core skill. The course explains how to interpret the initial slope, the maximum righting lever and the angle at which it occurs, the angle of vanishing stability and the area under the curve. Different hull types produce characteristically different curves. A traditional heavy, narrow cruiser has modest initial stability but a large range of positive stability, while a light, wide-beam yacht has high initial stability but may lose stability sooner and be more stable when inverted, which matters for safety offshore.
Capsize and re-righting are examined in this light. Features that help a yacht recover from a knockdown or capsize, such as a low centre of gravity, freeboard, hull flare and the effect of deck structures, are explained, alongside the trade-offs between stability for sail-carrying power and stability for safety. The use of water ballast to windward is discussed as a way to increase righting moment.
Hydrodynamics and resistance
Resistance prediction methods range from empirical systematic series through computational fluid dynamics to physical model testing. Friction drag depends on wetted surface area and surface finish, while wave drag rises steeply as speed increases relative to hull length. Heel changes the underwater shape and therefore resistance, and the yacht must also generate side force to resist the sideways component of the sail force. Leeway, the angle between heading and course, allows the keel and rudder to produce that side force, but it also adds induced drag. The interplay of heel, side force and leeway is central to upwind performance.
Hull form influences both friction and wave drag, and the Delft Systematic Yacht Hull Series is introduced as a widely used source of resistance data and regression formulas. The course explains how such series allow designers to estimate resistance from hull parameters early in design.
Performance in waves
Sailing in waves raises two connected questions: what the waves are like, which depends on whether the sea has fully developed or is limited by fetch, and how much the yacht slows when heading into them. Added resistance in waves arises from the energy spent creating motion-generated waves, and strip theory provides a method for estimating it in regular and irregular waves.
Results from a systematic series of yacht models show that modest changes to hull shape and weight distribution, including pitch gyradius, alter added resistance and, via velocity prediction programs, race results. Following seas present a very different picture: in the right conditions, waves can add surge and even surfing behaviour, making the yacht faster. A following-seas simulation explores the forces being balanced and how much the wave environment changes performance.
Model testing
Even in the CFD era, physical model testing is treated as the final arbiter of design choices. The course compares towing tanks and wind tunnels and explains how the design question determines the most suitable facility and test campaign. Semi-captive towing tank testing allows the model to respond in some motions while held fixed in others, isolating the effects that matter most, and learners consider which motions are allowed, which are controlled and which quantities are measured.
Connecting stability, speed and seakeeping
A key lesson is that the design parameters examined in each section interact. Increasing beam raises initial stability and sail-carrying power but can reduce the range of positive stability and affect behaviour in waves. Moving weight towards the ends of the yacht changes pitch inertia and therefore added resistance in head seas. Deeper keels improve righting moment and side force but increase wetted area. Good yacht design means balancing these effects for the intended use, whether offshore cruising, inshore racing or ocean racing, and using prediction and testing methods to check that the balance has been struck correctly. Velocity prediction programs provide the framework that ties these effects together, converting stability, resistance and side-force data into predicted speeds across wind angles and strengths, so that design changes can be compared on the measure that ultimately matters to owners and racing crews.
Why this matters in practice
Yacht designers, naval architects and performance analysts need to understand how stability, resistance and seakeeping interact, and how to use prediction and testing methods appropriately. The same principles inform safety assessment, rule-making and the interpretation of velocity prediction results for racing and cruising yachts.
Together these themes give designers a balanced view of speed, stability and seakeeping, supported by sound prediction methods.
Key takeaways
You leave able to interpret GZ curves and capsize resistance, analyse calm-water resistance and the effects of heel and leeway, explain added resistance and following-sea behaviour and compare systematic series, CFD and model testing as tools for yacht design.
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 (4 in total) so you can confirm you can apply each method before moving on. A 73-page course book can be downloaded and printed for offline reading and later reference.
Course contents
- Stability and Safety: Righting Moment Basics; Reading GZ Curves; Capsize and Re-righting
- Hydrodynamics and Resistance: Resistance Prediction Methods; Friction and Wave Drag; Heel, Side Force, and Leeway; Hull Form and Delft Series
- Performance in Waves: Wave Environment and RAW; Yacht Model Study Findings; Following Seas Simulation
- Model Testing: Facilities and Campaign Choices; Semi-captive Testing
- Summary: Key Takeaways
Who this course is for
This course is for engineering graduates, naval architects, yacht designers, boatbuilders and sailing enthusiasts with a technical background who want a deeper understanding of sail yacht design. Familiarity with basic naval architecture concepts such as buoyancy and stability is helpful.
Frequently asked questions
How long does Sail Yacht Design and Technology 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 6 sections with 14 lessons, moving from foundations to applied methods, as summarised above.
Is there material to keep after the course?
Yes. A downloadable 73-page course book accompanies the lessons for offline reading and later reference.
How is progress checked?
Each main section closes with a graded quiz (4 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: A01 – Principles of Naval Architecture: Support, Form, and Stability; A03 – Introduction to Ship Structures Project; B06 – Resistance & Propulsion; A10 – Naval Architecture and Ship Production Technology (Part 1 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 I01 – Sail Yacht Design and Technology →
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