The Allied Seawind Sailboat

The Allied Seawind 30, a long-keeled ketch, was designed by Thomas Gilmer and built in the USA by the Allied Boat Company Inc.

An Allied Seawind 30 ketch sailboat at anchor in Hog Island, Grenada, West IndiesAn anchored Allied Seawind 30 flying a riding sail from the mizzen mast to keep her head-to-wind and reduce swinging.

Published Specification for the Allied Seawind

Underwater Profile: Long keel with transom-hung rudder

Hull Material: GRP (Fibreglass)

Length Overall: 30'6" (9.3m)

Waterline Length: 24'0" (7.3m)

Beam: 9'3" (2.8m)

Draft: 4'3" (1.3m)

Rig Type: Ketch (a cutter version was also produced with a club-footed staysail)

Displacement: 12,000lb (5,443kg)

Designer: Thomas Gilmer

Builder: Allied Boat Company Inc (US)

Year First Built: 1962

Year Last Built: 1982

Number Built: 161

Owners Association: www.alliedseawindii.org


Published Design Ratios for the Allied Seawind

1. Sail Area/Displacement Ratio: 15.4

  • 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: 34.0

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

3. Displacement/Length Ratio: 388

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

4. Comfort Ratio: 36.9

  • 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: 1.6

  • 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 Allied Seawind

1. A Sail Area/Displacement Ratio of just 15.4 suggests that the Allied Seawind 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 34.0 means that unless the bulk of the ballast is concentrated in a bulb at the foot of her keel, the Allied Seawind will have a tendency to heel excessively in a gust, and she'll need to be reefed early to keep her sailing upright in a moderate breeze. 

3. A Displacement/Length Ratio of 388, tells us the Allied Seawind is firmly in the ultra-heavy displacement category. Load her up as much as you like and her performance will be hardly affected, not that it was ever startling. Few if any sailboats are built to this displacement category these days - but they remain popular with some long-distance sailors.

4. Ted Brewer's Comfort Ratio of 36.9 suggests that crew comfort of a Allied Seawind in a seaway is similar to what you would associate with the motion of a moderate bluewater cruising boat - a predictable and acceptable motion for most seasoned sailors.

5. The Capsize Screening Formula (CSF) of 1.6 tells us that a Allied Seawind 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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