A Fast Offshore Cruiser - 9. Hull design details.

The ideas behind the design of the hull are outlined and justified in previous sections. This section will outline items that are particular to this hull design.

All the hull, appendage and deck design work was completed on Multisurf. This program allows quick and easy changes to the design and gives respectable real time renderings that improve the ability to visualise the design as in expands.

The design brief requires that the hull be designed to be fast, undirected by unnecessary racing class rules and comfortable in normal usage conditions.

To achieve this the hull has a very nearly full-length waterline, 96% of the Loa; this produces very short over hangs. The stem rather than being completely vertical has about 5.7° of sweep, to help with the anchoring problem. The transom has a very small clearance over the DWL.

To go with the long waterline the Bwl is narrow giving a small half entry of 14° , compared to typical value of about 22-24° for a normal, short waterline, cruising yacht. This along with an Lcf at 56.3% of the Lwl and a Cp of 0.557 will form the fine forward sections that will produce the comfortable ride by slicing through the waves with minimal bow wave resistance. The after sections are shaped so that the flow of water is smooth and cuts off cleanly so will not want to climb the transom.

The middle and after topsides have a large degree of flare in them this will provide the form stiffness as the hull heels. The flare also allows the water ballast to be further away from the centreline of the hull producing a greater righting moment. The minimal flare at the bow will encourage any spray to cut off and pass to leeward quickly.

Overall the lines have been kept as fair as possible as to minimise the disturbance to the flow of water and keeping wave resistance to a minimum to allow the higher boats speeds to be obtained.

Other aspects need to be taken into consideration during design other than those of designing for operation these include construction. When building in "speed strip", see Chapter 8.1 for choice of construction method, some things are particular to this method need to be considered. The main one here is the difficulty of producing concave plating. It can be done, but with difficulty, the staples used to hold the strips to the construction frames cannot produce a great enough force to keep the strips in place. So from this the author has been careful that there is no concave planking anywhere on the hull.

This hull is fast, this is shown by the VPP plots in Appendix D.4, and will be comfortable in a seaway thanks to its improved wave riding characteristics of the narrow water plane so it will therefore be possible to keep the speed up when the conditions deteriorate. This satisfies the requirement of the design brief to be able out run bad weather.