The rig dimension list is helpful in determining the boat’s approximate sail area. Once you have determined your sail area, the figures can be used to calculate the loads generated by the sails for any given wind velocity. The loading calculations are essential to selecting gear with adequate strength for its intended application.
- Mainsail = (P x E) / 1.8 (1.6 for racing profile mainsails)
- 155% Genoa = (( J x I ) / 2) x 1.65
- 135% Genoa = (( J x I ) / 2) x 1.44
- 100% Jib = ( I x J ) / 2
- Racing Symmetrical Spinnaker = 1.8 x J x I
- Racing Asymmetrical Spinnaker = 1.8 x J x I
- Cruising Asymmetrical Spinnaker = 1.65 x J x I
- “I” is measured along the front of mast from the genoa halyard to the main deck. The main deck is where the deck would be if there were no deckhouse (the sheerline)
- “J” is the base of the foretriangle measured along the deck from the headstay pin to the front of the mast.
- “P” is the luff length of the mainsail, measured along the aft face of the mast from the top of the boom to the highest point that the mainsail can be hoisted or black band.
- “E” is the foot length of the mainsail, measured along the boom from the aft face of the mast to the outermost point on the boom to which the main can be pulled or to the black band.
- “JSP” is the length of the spinnaker pole or the distance from the forward end of the bowsprit (fully extended) to the front face of the mast.
- “ISP” is measured from the highest spinnaker halyard to the main deck. The main deck is where the deck would be if there were no deckhouse (the sheerline)
- “PY” and “EY” are, respectively the luff length and foot length of the mizzen of a yawl or ketch measured in the same way as for the mainsail.
- “IY” is the measurement from the staysail halyard to the deck.
- “JY” is the measurement from the staysail stay to the front face of the mast.
- “LP” is the shortest distance between the clew and the luff of the genoa.
|Comparing the measurements to the Moody 44 – “Enterprise”
- Mainsail = (P x E) / 1.8 = 37.55m² —> actual sail = 33.85m²
- 155% Genoa = (( J x I ) / 2) x 1.65 = 69.11m² —> actual sail = 58.59m²
- 135% Genoa = (( J x I ) / 2) x 1.44 = 60.31m² —> actual sail = 58.59m²
- 100% Jib = ( I x J ) / 2 = 41.88m² —> I don’t have one
- Cruising Chute = 1.65 x J x I = 138.22m² —> actual sail = 115.013m²
|Moody 44 Rig Dimensions:
I = 16.49m = 54’0″
J = 5.08m = 16’8″
P = 14.17m = 46’6″
E = 4.77m = 15’8″
ISP = 16.49m = 54’0″
JSP = 5.08m = 16’8″
Actual Sail Areas on Enterprise:
Roller Genoa = 58.59m² = 630 sq ft
In-Mast Furling Main Sail = 33.85m² = 364 sq ft
Cruising Chute = 115.013m² = 1,238 sq ft
You can use Sailpower Calc – Which is an online calculator that works out the sail areas, forces and moments, when given the rig measurements and wind conditions. It represents, in a simplified manner, the aerodynamic module of a VPP (Velocity Prediction Program), used to predict a sailboat’s performance. Its quite interesting to see the effects on loads for wind speeds from 4 kts to 25 kts to 40 kts….especially when you use / don’t use the “auto depower” setting.