S/V Khepri Information

S/V Khepri is a design I found at Paul Fisher’s website. I found it quite awhile ago and fell in love with it’s lines, his design philosophy and the Chinese Junk rig.

As Designed:

  • Length on Deck: 23’7″
  • Beam: 7’4″
  • Sail Area: 257 sq. ft. (Main only)
  • Approx. Dry Weight: 3308 lbs.
  • Max. Headroom: 6’1″

Over the years, I’ve come to appreciate the amount of math and science that goes into designing a boat. Years ago, I stumbled upon a sail calculator designed by Carl Adler that attempted to quantify sailboat design. Since then, Mr. Adler passed away and Tom Dove took up the responsibility of hosting and updating it on his site.

The numbers per the calculator:

  • Name: Selway-Fisher Tasman
  • LOA: 23.58
  • LWL: 18
  • Beam: 7.33
  • Displacement: 5308 (just a guess at full cruising load, as listed – 3308 dry weight)
  • Sail Area: 257 (main only)
  • Displacement to LWL: 406
  • Hull Speed: 5.69 (in knots)
  • Sail Area to Displacement: 13.51
  • LWL to Beam: 2.46
  • Motion Comfort: 29.15
  • Capsize Ratio: 1.68
  • Sailing Category: Cruiser
  • Pounds/Inch: 471

As somebody who wants to cruise, the three numbers I pay attention to are:

1) Capsize Ratio;
2) Motion Comfort; and
3) Hull Speed.

The Capsize Ratio is a number which, arguably, quantifies the tendency of a given sailboat to capsize. According to the calculator:

A value less than 2 is considered to be relatively good; the boat should be relatively safe in bad conditions. The higher the number above 2 the more vulnerable the boat. This is just a rough figure of merit and controversial as to its use.

Carl Adler

Motion Comfort is a method, developed by Ted Brewer, to quantify relative comfort at sea:

Range will be from 5 to 60+ with a Whitby 42 at the mid 30’s. The higher the number the more comfort in a sea. This figure of merit was developed by the Yacht designer Ted Brewer and is meant to compare the motion comfort of boats of similar size and types.

Carl Adler

Finally, Hull Speed represents, in knots, a displacement boat’s designed maximum speed:

This is the maximum speed of a displacement hull. Some racers and lighter boats are able to achieve greater speed by lifting over the bow wave and riding on top of the water,[sic]that is, planing.

Carl Adler

What impressed me most is that these numbers generally reflected my experience across a broad spectrum of boats, from a Columbia 36 I sailed from Long Beach to San Rafael, to playing around in the Bay Area in a Coronado 25, an Albin Vega, a Sparkman & Stevens 39′ yawl and a Rhodes Meridian, to racing a J/24 and 420 and Lark dinghies for the University of Connecticut.