The Royal Cape One Design

The Royal Cape One Design, a fractionally rigged sloop, was designed by E G van de Stadt and built in South Africa.

A Royal Cape One Design sailboat approaching Plymouth, UKThe very light and fast Royal Cape One Design

Published Specification for the Royal Cape One Design

Underwater Configuration:  Fin keel with spade rudder

Hull Material: Plywood

Length Overall: 29' 9" / 9.1m

Waterline Length: 27' 10" / 8.5m

Beam: 7' 0" / 2.13m

Draft: 5' 2" / 1.6m

Rig Type: Fractional Sloop

Displacement: 4,020lb / 1,823kg

Designer: E G van de Stadt

Year First Built: 1961

Published Design Ratios for the Royal Cape One Design

1. Sail Area/Displacement Ratio: 22.5

  • 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: ?

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

3. Displacement/Length Ratio: 82.7

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

4. Comfort Ratio: 16.4

  • 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: 1.8

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

read more about these all-revealing numbers...

Summary Analysis of the Design Ratios for the Royal Cape One Design

A Sail Area/Displacement Ratio of 22.5 suggests that, in the right hands, the Royal Cape One Design will leave most other sailboats of her waterline length in her wake. Her very light displacement is largely due to her marine ply construction.

A Displacement/Length Ratio of just 82.7 places the Royal Cape One Design firmly in the ultralight category, making her more suited for racing than cruising. 

Ted Brewer's Comfort Ratio of 16.4 suggests that crew comfort in a seaway is similar to what you would associate with the motion of a lightweight racing boat. Upwind the Royal Cape One Design will slam enough to shake your fillings out with a motion that cruising sailors have no desire to get used to.

Her Capsize Screening Formula of 1.8 tells us that the Royal Cape One Design would be a better choice of sailboat for ocean passage-making than one with a CS rating of more than 2.0. 

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