The Hull

The part of the hull that is in the water is perhaps the most important part of the boat to get right - get it wrong and no matter how good the upper parts of the boat may look, it will not handle nicely nor be a pleasure to use. We undertook a considerable amount of research into hull designs to try and find the most efficient one. Whilst there have been various designs produced in the past, none of them are capable of coping with the varying depths and widths of canals and rivers. Some are efficient in shallow water and others are best in deeper waters.

From our research we concluded that the design of the bow does not have that much effect on the efficiency of the hull in all of the varying conditions in which a narrowboat operates. However, the design of the swim does have a considerable effect on the overall efficiency of the boat and so we put a lot of effort into improving this.

The easiest swim to build is a convex shape coming to a end in a flat plate through which the conventional prop shaft is easily fitted and therefore this is the one that most shell builders will tend to produce. However, from a hydrodynamics point of view this is perhaps the worst way in which to feed water to a propellor. The vortices which are generated by the convex shape of the swim and in particular the flat plate ahead of the propellor, mean that the propellor is working in "dirty" water. To be at its most efficient a propellor needs to be in the smoothest flow of water possible. The ideal position for it would be about 6ft ahead of the bow but obviously this is totally impracticable. If it is to be at the stern then every effort must be made to smooth the flow of water into the propellor and this is where an "S" shaped swim which comes to a knife edge wins. Whilst it is more difficult to build the benefits are tremendous. Not only does it improve the efficiency of the propellor, but the boat becomes more responsive and uses less fuel. Vibration is reduced because of the smooth flow of water through the propellor and this shows in the much reduced turbulence behind the boat when cruising.

Modified Rudder

"S" shaped swim

Another important part of the boat that is in the water is the propellor itself. For "The Laughing Cavalier" it was decided that it needed enough performance to allow it to cope with tidal waterways and fast flowing rivers. With the help of a company that specialises in matching propellors to hulls, the size of the propellor was determined together with the power needed to drive it at the most efficient rpm. From this information we were able to determine the size of hydraulic motor needed and this then gave us the engine power necessary to achieve the performance we required.

So now all of the components in the drive system are matched and operating at their best and give "The Laughing Cavalier" a theoretical top speed of 6.8 knots which is more than enough for her to operate comfortably on rivers etc.

Lastly, "The Laughing Cavalier" has a modified rudder fitted. Horizontal fins are fitted at the top and bottom which improve its performance. The effect is noticeable and the rudder is quite neutrally balanced.

The shell for "The Laughing Cavalier" was built by Reeves Boatbuilders who were selected because of their ability to turn ideas into steel work on time and on budget. They have their own web site at www.reevesboatbuilders.co.uk and may be contacted at julie@reevesboatbuilders.co.uk

RN Narrowboats

Three Acres

86 Chalkshire Road

Butlers Cross

Aylesbury

Buckinghamshire

HP17 0TJ
Phone: 01296 615821

Mobile: 07836 785970

RN Narrowboats - for your boat of the future