Design Specifics



Compass Designer Smith 1934-2008

Designer.  Claude A. Smith Junior, 4 September 1972,  New Zealand.

Capsize Screening Formula: B/cube root of (Displacement/64) = 11/cube root of (16,676/64) = 11/cube root of 260.5 = 11/6.4 = 1.72.  Note: Result should be less than 2

Displacement Length Ratio.  Equals (long) tons/(.01 x LWL in feet) cubed = 7.43/(.01 x 30.67) cubed = 7.43/.3067 cubed = 7.43/.0288 = 258.  Note: Boats with a D/L ratio of more than about 325 are heavy cruisers. A number between 200 and 325 indi­cates a light- to moderate-displacement cruiser, and less than 200 is very light displacement.

On her Hawkesbury River Mooring

Ballast to Displacement Ratio. B/D = 7304/16676 = 44%

Sail Area to Displacement.  SA/D = sail area divided by displacement (in cubic feet) 2/3 = 577/260.5 squared then cube root of result = 577/cube root of 67860 = 577/40.7 = 14.2.  Sail area is size of mainsail plus size of foretriangle (area bounded by headstay, mast, and deck).  To find dis­placement in cubic feet, divide it by 64, then square number and, finally, find cube root.  A SA/D ratio around 12 indicates an extreme under-rigged heavy cruiser.  A ratio double that one is typical of racing boats, and most modern cruisers fall between the two extremes. You can carry all the sail you want for light air (so long as you can reef quickly). Eg Windjammer main is 234’sq and no1 genoa is 504’sq = 738’sq.  SA/D ratio = 738/260.5 2/3 = 738/40.7 = 18.1

Hull speed = 1.34 times the square root of LWL  = 1.34 x square root of 30.67 = 1.34 x 5.54 = 7.42 knots

This report from the NZ Tradeaboat will fill in any technical gaps that I'm bound to have missed.


On the Hard at Oyster Cove in the wonderful Nelson Bay area