Design

LOA - 31' 9" (9.5m)

LOD - 30' 0" (9.0m)

LWL - 24' 5" (7.3m)

Max. beam - 10' 8" (3.2m)

Max. draught - 4' 0" (1.2m)

Displacement - 6,830lbs (3,100kg)

AVS - 124°

Category B (offshore)

Design brief:

~ a seaworthy double-ender along the lines of a traditional working boat from the Scottish isles.

~ relatively light and fast.

~ bonnie enough to raise a smile.

~ LOA c. 30'.

~ capable of offshore passage-making.

~ comfortable extended cruising for two, short-term accommodation for up to four persons.

~ easy single-handed sailing.

~ reserve buoyancy built-in.

~ electric auxiliary drive with regenerative battery charging.

~ assymetric double-sided wing sail with progressive reefing system.

Design Process

The hull design was formed in the mind's eye and developed using CAD software. The keel, stem and sternpost were drawn first, along with a sheerline. As the hull was to be built by eye, without the use of molds, the plank lines (rather than waterlines, buttocks, etc.) were drawn in 3D and made as fair as the screen resolution would allow.

The 3D CAD was found to be an excellent 'thinking tool' for trying out details of interior and deck layout. It was also very useful for extracting dimensions for calculating centroids, stability, etc.

The only section of the drawing that was used 'as drawn' was the keel, which was fabricated in steel. The use of fabricated steel in the keel allows the batteries (which power the electric drive) to be fitted as low down in the boat as possible, doubling as ballast.

The backbone (keel, stem, sternpost) was set up more or less in accordance with the drawing - minor departures being made to please the eye.

The planking was developed entirely by eye without reference to the drawing. It is relatively easy to combine the design into the building process when using clinker construction and it has the advantage of skipping the labour of making a construction drawing and the tedium of lofting.

On completion of the planking the hull was measured and redrawn 'as built'. There was noticeable variation from the original drawing around the stern of the boat. The finished article is finer in the quarters and has a much cleaner exit than what was first drawn.

Volumes, masses, stability, etc. were recalculated. The calculated waterline was found to be within 1/2" of where the eye suggested it should be.

The general design of framing, interior and deck layout were established in the 3D drawing but the details were worked out as the build progressed.