The Oyster 625 Sailboat
Specs & Key Performance Indicators

The Oyster 625, a centre-cockpit sloop, was designed by Rob Humphreys and built in the UK by Oyster Marine Ltd.

Red Cat', an Oyster 625 cruising yacht anchored in Rodney Bay, St Lucia in the CaribbeanAn Oyster 625

Published Specification for the Oyster 625

  • Underwater Profile: Fin keel with bulb & skeg-hung rudder
  • Hull Material: GRP (Fibreglass)
  • Length Overall: 63'6" (19.4m)
  • Waterline Length: 56'6" (17.2m)
  • Beam: 17'10" (5.4m)
  • Draft: 9'2" (2.8m)
  • Rig Type: Masthead Sloop
  • Displacement: 73,854lb (33,500kg)
  • Designer: Rob Humphreys
  • Builder: Oyster Marine (UK)
  • Year First Built: 2015
  • Owners Association: Oyster Owners

Published Design Ratios for the Oyster 625

1. Sail Area/Displacement Ratio: 23.2

  • 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: Not published

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

3. Displacement/Length Ratio: 182

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

4. Comfort Ratio: 41.9

  • 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: 1.7

  • 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 Oyster 625

1. A Sail Area/Displacement Ratio of 23.2 suggests that, in the right hands, the Oyster 625 will have enough performance to leave most other sailboats of similar waterline length well astern. 

2. The Ballast/Displacement Ratio of the Oyster 625 has not been published, hence we are unable to comment on this aspect of its stiffness however as much of the ballast is concentrated in a bulb at the foot of her keel, she's likely stand up well to her canvas.

3. A Displacement/Length Ratio of 182, tells us the Oyster 625 is clearly a light displacement sailboat. If she's loaded with too much heavy cruising gear her performance will suffer to a degree.

4. Ted Brewer's Comfort Ratio of 41.9 suggests that crew comfort of an Oyster 625 in a seaway is similar to what you would associate with the motion of a heavy bluewater cruising boat. Pitching and rolling will be well damped - your cup of coffee on the salon table stands a reasonable chance of staying there in most conditions.

5. The Capsize Screening Formula (CSF) of 1.7 tells us that an Oyster 625 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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