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
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
read more about these Key Performance Indicators...
Summary Analysis of the Design Ratios for the J40
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.
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