Stuart M Roy
Naval Architect - Yacht Designer
Powerboats, or motor-propelled boats, generally have a much greater speed range than sailing boats and this makes them both challenging and rewarding projects for a powerboat designer. The object is to gain the best possible performance for the engine power available, whilst ensuring that sea-keeping, handling, accommodation and aesthetics meet the client’s requirements, taste and budget. The engineering aspects demand particular attention as the reliability of the propulsion system and the structural integrity of the hull must be assured. The need to design a hull with low wash characteristics is also important to ensure that the boat causes minimal disturbance to the marine environment (unless you are a wakeboarder when the creation of plenty of wash is essential !).

For economical and efficient motor boats, displacement types will suit many owners, providing plenty of accommodation space with good sea-keeping performance. Transitional or semi-planing types can also be very comfortable at sea, whilst providing a good turn of speed for fast passage making. If high speed is important a fully planing hull is essential, either a warped-bottom type for early onset of planing and use on calmer waters, or a deep-V type to cope with rougher conditions dependably, yet this modern type will require more installed power.

The illustration at the top shows a strong and seaworthy displacement type motor cruiser with flying bridge and two helm positions. The photograph in the middle shows the scale model of my design for a fast, stable modern lifeboat which has a transitional or semi-planing hull form. In the illustration it is being prepared for a stability test where the circular ring will be used to apply the heeling moment. Below that there is a line drawing of the hull design for a new fast motor cruiser which will operate in fully planing mode. The blue and red illustration shows the design of a flood rescue boat to be built in aluminium.  For ease of construction the hull panels are “developable” using just cylindrical or conic curvature so that they can be cut from flat sheet material with no distortion or torturing of the material.

The 24’ powerboat on the left, illustrated with superb computer graphics by the client, was designed for automatic cutting out of the hull and superstructure by computer controlled machining (known as CNC). This means that the boat will be made from a “paperless” design with the main components of the boat constructed by machine directly from the computer screen using the electronic design files generated in the design process.  

The self-launching powerboat (shown in bottom photograph) carries its own launching gear in the same way that an aircraft carries its undercarriage and landing wheels. This patented system of hydraulically-powered, lifting tractor units allows the boat to travel up and down steep shingle banks to the sea.  When afloat the tractor units are raised, again by hydraulics, and the hull bottom is sealed by shutting the hydraulically powered “bomb doors”.  The nose wheel is lifted by a winch and the outboard motor takes over.  Powered by a 175 hp 4-stroke outboard motor, the boat achieve speeds of around 35 knots.  More details...

As well as working on the design of a number of motor cruisers and workboats, I have designed a series of traditional river launches and a speedboat in “retro” styling.  I am particularly enthusiastic about new designs based on aesthetically-pleasing classic styles from the past, though I remain keen to utilise modern materials and building techniques where these add to the boat’s safety, longevity and resale value.
 Motor  Boat  Designs  
Yacht & Powercraft Design Services Ltd
Telephone: 44 (0) 1489-583346   Mobile:  07803-724317  
Displacement Motor Cruiser
Lifeboat ready for Stability Test
Hull for Planing Motor Cruiser
Easy-Build Developable Hull Form
24’ Powerboat for CNC Cutting
35 kt Self-Launching Powerboat