Design of a 50 -70 foot Slender Hull motorboat.

The aim of the project is to produce a preliminary design of a medium speed slender hull motor boat with a length between 50 – 70 feet. The boat will be fuel efficient and capable of long passage making at a medium speed. The motorboat will have to be designed to recreational craft directive standards (RCD). The choice of a slender body hull form was chosen to provide a suitable platform to produce an efficiently powered motorboat that is more economical than the current trend of motorboats. The current trend is to produce high volume motorboats with large interiors and reasonably heavy displacement, these requirements do not lend itself to an efficient hull form. Instead huge engines are required to push the boat to a top speed required by the owner, even though when cruising, the boat will not often operate at the top speed because of the cost and limited range. The slender hull motorboat will not be capable of reaching the speeds capable by a planing motorboat but will have a sprint speed capability. The cruising speed of the slender hull is above that of a standard displacement cruising boat which for the size range is below 10kts. The idea is that the slender hull form motorboat can cruise economically at a speed of 0.45-0.5 Froude No (Fn) with a range making it possible to larger distances. The sprint speed is there for short journeys where fuel efficiency is not so important and increases the possibility of travelling to further locations in a short time, which is one of the advantages of a planing motorboat. The motorboat will be designed to be comfy, a stable for offshore cruising, it will have berths to accommodate up to 6 people with separate showers and head for each cabin. With a slender body hull form the volume per length is less this makes the accommodation a factor in the decision of the overall length of the vessel. The project looks at layout options to optimise the interior space and flow, making it user friendly and supplying adequate room. With a slender hull, stability is one of the major issues that have been looked into, RCD have criteria that needs to be met, the project looks at the effect of varying the waterline beam and the vertical centre of gravity and where the limits in the hull form are with minimum beam and VCG being found. With part of the brief being an efficient hull form, resistance and propulsion were another important aspect of the project. Analysis of varying hull forms was undertaken using Wolfson Powering Program to find the key factors affecting the resistance of the vessel. The Final Vessel came to a length of 20.2m overall and beam of 4.75m, it has a cruise speed of 13 knots and a range of 1017nm. It meets the criteria for the both range and speed and also supplies accommodation for 6 people. The vessel also passed RCD stability requirements for Category A.