The Slipper 42 Sailboat
Specs & Key Performance Indicators

The Slipper 42, a centre-cockpit ketch, was designed by Robin Chadworth-Musters & Alan Gurney and built in the UK by Tyler Boat Company Ltd.

'Larus', a Slipper 42 Ketch at anchor in Falmouth Harbour, Antigua.A Slipper 42 Ketch

Published Specification for the Slipper 42

Underwater Profile: Fin keel with skeg-hung rudder;

Hull Material: GRP (Fiberglass);

Length Overall: 42'0" (12.8m);

Waterline Length: 30'4" (9.2m);

Beam: 12'3" (3.7m);

Draft: 6'0" (1.8m);

Rig Type: Masthead ketch;

Displacement: 16,500lb (7,484kg);

Designer: Robin Chadworth-Musters & Alan Gurney;

Builder:  Tyler Boat Co. Ltd. (UK);

Year First Built: 1978;

Year Last Built: 1979;

Number Built: 13

Published Design Ratios for the Slipper 42

1. Sail Area/Displacement Ratio: 15.9

  • Less than 16 would be considered under-powered;
  • 16 to 20 would indicate reasonably good performance;
  • Over 20 suggests relatively high performance.

2. Ballast/Displacement Ratio: 43.4

  • Under 40: less stiff, less powerful
  • Over 40: stiffer, more powerful

3. Displacement/Length Ratio: 264

  • Under 100: Ultralight
  • 100 to 200: Light
  • 200 to 275: Moderate
  • 275 to 350: Heavy
  • Over 350: Ultraheavy

4. Comfort Ratio: 26.8

  • Under 20 indicates a lightweight racing boat
  • 20 to 30 indicates a coastal cruiser
  • 30 to 40 indicates a moderate offshore cruising boat
  • 40 to 50 indicates a heavy offshore boat
  • Over 50 indicates an extremely heavy offshore boat

5. Capsize Screening Formula: 1.9

  • Under 2.0 (the lower the better): Better suited for ocean passages
  • Over 2.0: Less suited for ocean passages

read more about these Key Performance Indicators...

Summary Analysis of the Design Ratios for the Slipper 42

1. A Sail Area/Displacement Ratio of 15.9 suggests that the Slipper 42 will need a stiff breeze to get her going. In light conditions, unless you've got plenty of time on your hands, motor-sailing may be the way to go.

2. A Ballast/Displacement Ratio of 43.4 means that the Slipper 42 will stand up well to her canvas in a blow, helping her to power through the waves.

4. Ted Brewer's Comfort Ratio of 26.8 suggests that crew comfort of a Slipper 42 in a seaway is similar to what you would associate with the motion of a coastal cruiser with moderate stability, which is not encouraging news for anyone prone to seasickness. 

5. The Capsize Screening Formula (CSF) of 1.9 tells us that a Slipper 42 would be a safer choice of sailboat for an ocean passage than one with a CSF of more than 2.0. 

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