The J40 Sailboat
Specs & Key Performance Indicators

The J40, a performance cruising boat, was designed by Rod Johnstone and built in the USA by Tillotson-Pearson.

'Blue Jay', a J40 performance cruising yacht with bluewater capability

Published Specification for the J40

Underwater Configuration: Fin Keel & Spade Rudder

Hull Material: GRP (Fiberglass)

Length Overall: 40'0" (12.2m)

Waterline Length: 34'0" (10.4m)

Beam: 12'2" (3.7m)

Draft: 6'6" (2.0m) - deep draft version, 5'6" (1.7m) - shallow draft fin keel version, 5'5" (1.6m) - wing keel version.

Rig Type: Masthead Sloop

Displacement: 18,000lb (8,165kg)

Designer: Rod Johnstone

Builder: Tillotson-Pearson

Year First Built: 1984

Year Last Built: 1994

Number Built: 86

'Blue Jay', a J40 for Sale

Although 'Blue Jay' is no longer available, the excellent pics and informative text are retained here for the benefit of anyone researching this popular performance cruiser.

Published Design Ratios for the J40

1. Sail Area/Displacement Ratio: 17.9

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: 36.1

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

3. Displacement/Length Ratio: 204

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

4. Comfort Ratio: 27.9

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: 1.9

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

Summary Analysis of the Design Ratios for the J40

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1. A Sail Area/Displacement Ratio of 17.9 suggests that the J40 will, in the right conditions, approach her maximum hull speed readily and satisfy the sailing performance expectations of most cruising sailors.

2. A Ballast/Displacement Ratio of 36.1 means that the J40 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 204, tells us the J40 is clearly a light displacement sailboat. If she's loaded with too much heavy cruising gear her performance will suffer dramatically.

4. Ted Brewer's Comfort Ratio of 27.9 suggests that crew comfort of a J40 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 J40 would be a safer choice of sailboat for an ocean passage than one with a CSF of more than 2.0.