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. says...

About the Boat:

The Slipper 42 sailboat is a moderate displacement sailboat which is slightly underpowered, but is very stable/stiff and has a good righting capability if capsized. The fuel capacity is good however and she has a good water supply range.

The Slipper 42 started life as the Rancher 41, for which Tyler Boat Works acquired the molds. They raised the topsides about a foot and discarded the bolt-on keel and spade rudder in favor of internal ballast and a skeg rudder. This converted a racing hull into a cruising boat.

The Slipper 42 has two dedicated sleeping cabins with double berths.

About the Designers:

Robin Chadworth-Musters is a yacht designer who has designed several sailboats. One of his sailboats is the Slipper 42 shown here, which he designed in collaboration with Alan Gurney.

Alan Gurney was a British sailboat designer who designed boats the old fashioned way with drafting pencil on velum, using splines and ducks (weights), a planimeter, and a seaman’s eye. He thought like the water through which he had sailed, in England, transatlantic, the USA, both polar regions and much of what lay in between. He was tasked to design a suitable replacement for the famous Herreshoff design Ticonderoga, and produced one of the greatest designs of the past 50 years called Windward Passage.

Here is a list of some of his sailboat designs:

  • Islander 36 (1971)
  • O’Day 27 (1972)
  • Carib 41 (1970)
  • Carib 41 TM (1970)
  • Whitney 41 (1972)
  • Nantucket 33 (1967)
  • Islander 41 (Gurney) (1972)
  • Competition 1000 (1973)
  • Rancher 41

About the Builder:

Tyler Boat Company was founded by John Tyler in the 1960s. The company was known for building fiberglass yachts and sailboats. Tyler's primary business was in the manufacture of pre-fabricated buildings for the housing of livestock. Here is a list of some of the sailboats built by Tyler Boat Company:

  • Tyler Deb 33: A 33-foot sailboat designed by Angus Primrose. It has a long fin keel and a skeg-hung rudder. The boat has a displacement of 11,000lbs and a beam of 10'6".
  • Tyler Custom 62 cutter: A 62-foot sailboat designed by Robert Perry. It has a long fin keel and a skeg-hung rudder. The boat has a displacement of 60,000lbs and a beam of 16'6".
  • Tyler S42: A 42-foot sailboat designed by Ron Holland. It has a long fin keel and a skeg-hung rudder. The boat has a displacement of 22,000lbs and a beam of 12'6".
  • Tyler Victory 40 Ketch: A 40-foot sailboat designed by Angus Primrose. It has a long fin keel and a skeg-hung rudder. The boat has a displacement of 22,000 lbs and a beam of 12'6".

This additional info was drafted by using GPT-4 (OpenAI’s large-scale language-generation model) as a research assistant to develop source material, and believes it to be accurate to the best of their knowledge.

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