Performance Metrics

The following performance metrics are just one way we decided the Gulfstar 37 would be a good platform for our sailing adventures. The results, below, detail how the Gulfstar is conservatively built as an offshore cruiser, but still has enough spunk to sail 150-mile days.

Specifications (read more about specs):

  • Displacement (Disp): 19500lbs
  • Ballast: 8000lbs
  • Length (LOA): 37'0" (without bowsprit)
  • Length at Waterline (LWL): 32'0"
  • Beam: 11'10" (without solar panels)
  • Draft: 4'8"
  • Sail Area
    • I (height of mast from shearline to sheave): 45.6'
    • J (distance from front of mast to forestay): 15.6'
    • P (distance from top of gooseneck to highest point of mainsail hoist): 39.3'
    • E (distance from aft of mast to mainsail clew): 13.0'
    • Sail Area 100% Jib: 611ft^2
    • Sail Area 150% Genoa: 789ft^2

SA/Disp: 13.55 (jib), 17.29 (genoa) (dimensionless). This is a power to weight ratio calculated with a 100% jib. Most inshore monohull designs range between 16 and 18. Racers can be much higher, full-keel cruisers are lower. The ratio is independent of boat length.

Disp/LWL: 266 (dimensionless). This is probably the most used and best understood evaluation factor. Low numbers (resulting from light weight and long waterlines) are associated with high performance. Cruising designs begin around 200 and can go up to the high 300's. Many racing designs are below 100.

Comfort factor: 33.6 (dimensionless). Large numbers indicate a smoother, more comfortable motion in a sea way. The equation favors heavy boats with some overhang and a narrow beam. These are all factors that slow down the boat's response to violent waves. A value of 30-40 represents the typical offshore cruiser. Racing designs can be less than 20, and a full keel, Colin Archer design could be as high as 60.

Capsize factor: 1.70 (dimensionless). An empirical factor derived by the USYRU after an analysis of the 1979 FASTNET Race. Boats with values greater than 2 should not compete in ocean races. Values less than 2 are "good". The formula penalizes boats with a large beam for their high inverted stability, and light weight boats because of their violent response (low roll moment of inertia) to large waves, which are both very important factors during violent storms

Vhull: 7.58 knots. The highest theoretical velocity for a displacement boat. As a boat's speed increases, the wave it creates becomes longer, creating a trough that moves aft. At hull speed, the trough will be as long as the waterline length, creating a "hole" that the boat just fits. An enormous amount of power (50-100 hp/ton) is required to "climb out" of this hole and transition to a 'planing' movement. This is possible when surfing down large waves.

Vmax/Vhull: 1.01 (jib), 1.09 (genoa) (dimensionless). Vmax is a theoretical maximum speed based on empirical relationships of measurements of the boat. Boats with a generous sailplan and light displacement will have a velocity ratio greater than 1. Under powered or extra heavy boats will be less than 1.

LOA/Beam: 3.14 (dimensionless). This ratio measures the fineness of the hull. Fine hulls, having ratios greater than 3.0, are long and slender which promotes easy motion, higher speeds (via lower drag), and good balance when heeled. Many newer designs favor wider hulls for the larger interior volume, sail flatter, and have high reaching and down wind speed potential.

Roll acceleration: 0.06661G. Roll acceleration has been related to four physiological states: imperceptible, tolerable, threshold of malaise, and intolerable. Malaise starts at 0.1G, intolerable begins at 0.18G. Spending much time under these levels of acceleration reduces physical effectiveness and decision making ability through sleep deprivation.

Roll period: 3.8 seconds. A sailboat’s roll period is inversely proportional to its stability. Tender boats have long periods, stiff boats have short periods. Boats with periods less than 4 seconds are stiff and periods greater than 8 seconds are tender. The roll period is related to LOA and strongly related to the comfort factor.

Random 'best-of' trip reports:

Getting my drink on

 

Crazy jumping bat rays

 

Crossing the Sea of Cortez (nice and calm, eh?)