Freeboard Aft, F_AFT, feet*, waterline to top of hull aft

Length of Waterline, LWL, feet *

Maximum Cross Sectional Area, A_max, square feet* (maximum cross sectional area below the waterline, this value may be found on a sectional area curved for the condition under evaluation)

Sail Area, SA, square feet, (total sail area which includes all the fore-triangle, the main, and other normal sails present {like half the area of mizzens on ketches and yawls and all the foresail area on schooners}.  It does not include stay sails nor does it include spinnakers and jibs in the fore triangle.)

Wetted Surface, WS, square feet* (hull surface area below the waterline, including fin, rudder and skeg)

Total Lateral Plane Area, A_LP, square feet,* for full keeled boats this is the longitudinal projected area below the waterline including the rudder, for other boats this is just the projected area of the keel or the centerboard(s)

Weight Density of Water, g, pounds per cubic foot, 64 for salt water and 62.4 for fresh water

Exit Angle of Quarter Beam Butt, q, degrees, a example figure of this angle is provided with the spreadsheet.  This angle is used to determine if the boat is capable of planing or not.

Heeling Arm, HA, feet* (vertical distance from the center of effort of sails to the center of lateral plane of the underwater profile)

Lead, feet* (horizontal distance from the center of effort of sails to the center of lateral plane of the underwater profile)

Half Entrance Angle of Hull, a, degrees* (for waterline under evaluation)

Evaluation Operational Speed, V_OP, knots (the sail boat speed that you want the spreadsheet to evaluate, this need not be the speed that the vessel can go)
 

Waterline Beam, BWL, feet,* maximum waterline beam

Waterplane Area, AWP, square feet* (horizontal area enclosed by the hull at the waterline.  This value may be estimated with the following formula where AWP = 0.67 x LWL x BWL.)

Vertical Center of Buoyancy, KB or VCB, feet,* vertical distance from Baseline to centroid of displaced volume.

Metacentric Radius, BM, feet,* in the transverse direction

Vertical Center of Gavity, KG or VCG, feet,* distance from Baseline

Metacentric Height, GM, feet,* where GM = KB + BM - KG.

Operational Roll Period, T_OP, seconds,* boat full roll period while in operational condition

Prismatic Coefficient, C_P = V / (A_MAXLWL) dimensionless

Sail Area Displacement Ratio, SADR = SA / V^2/3 dimensionless. The SADR is a measure of the power available to push the load (the displacement). Generally, the higher the value the faster the boat, provided the boat is stiff enough to handle the larger sail areas.

Sail Area Wetted Surface Ratio, SA/WS, dimensionless.  This ratio is an indicator sail boat performance in light and medium air.  

Sail Area Lateral Plane Ratio, (A_LP/SA)100 percentage

Ballast Ratio, where BR = W_B/D dimensionless. This is an indicator of stability, but it is not a very accurate one. This is because this ratio does not differentiate between bulb ballast at the bottom of the keel and ballast in the fin keel or hull. Since the location of the ballast is not taken into consideration only boats with similar ballast arrangements should be considered.

Sail Boat Lead % = [(CP - CE)/LWL]100 =  (Lead/LWL)100

Righting Arm at 20 degrees (estimated), GZ₂₀ = (BWL/T)²/14.84, feet

Righting Arm at 30 degrees (estimated), GZ₃₀ = (BWL/T)²/11.00, feet

Righting Arm at 30 degrees (estimated), GZ'₃₀ = 0.03LWL⁴/D, feet

Righting Moment at 30 degrees (estimated), RM₃₀ = the larger of GZ₃₀D or GZ'₃₀D, foot pounds

Screening Stability Value, used for calculating capsize screening value, SSV = (B_MAX/3.28084)²/(BR x (Draft_C/3.28084) x (V/3.28084³)^1/3)

Angle of Vanishing Stability, AVS = 110 + (400/(SSV-10)), degrees

Capsize Risk Factor (or Capsize Screening Factor), where
CSF = BOA / V^1/3 dimensionless.  This parameter is an indication of a vessel's ability to resist capsizing in a violent storm.   This factor is concerned with dynamic stability in which weight and beam are predominate factors.

Roll Acceleration, A_ROLL = 2p(T)²Radius(q_ROLLp/180)/32.2

Stability Index, SI = T /(BOA x 0.3048)

Righting Moment at 20 degrees, RM₂₀ = GZ₂₀D, foot pounds

Heeling Moment at 20 degrees, HM₂₀ = SA x HA x cos²(20 degrees)xP foot pounds, where P is 1 pound per square foot wind pressure

Wind Pressure Coefficient (Type 1), WPC = RM₂₀/HM₂₀ dimensionless

Righting Moment at 20 degrees (Type 2), RM'₂₀ = DGM sin(20 degrees)foot pounds, more approximate than Type 1

Wind Pressure Coefficient (Type 2), WPC = RM'₂₀/HM₂₀ dimensionless

Upright Heeling Moment, UHM = SA x HA x P, where P is wind pressure at1 pound per square foot, results in foot pounds

Heeling Moment for 1 Degree, HM_{1 Degree} = D x GM x Sin(1 degree) results in foot pounds

Dellenbaugh Angle, DA = UHM / HM_{1 Degree}

Roll Period, seconds, evaluate period input value with target values that are presented in this section

Comfort Ratio, CR = D / (0.65 x (0.7xLWL + 0.30xLOA) x B_max^1.333). This term was developed by yacht designer Ted Brewer.  Large numerical values of this parameter indicate a boat with a smoother, steadier and more comfortable motion in a seaway.  Therefore the CR parameter favors heavy sail boats with lots of overhang and a narrow beam.  Since these factors slow down a boats response in heavy weather.  

Waterplane Loading, WPL = (D/2240)/AWP, this is a heave factor comfort check

Maximum Recommended Waterplane Loading, where
WPL_R = a x (D/2240)² + b x (D/2240) + c

Factor of Safety on Waterplane Loading, FS_WPL = WPL / WPL_R values less than one are acceptable
 

C_P versus SLR

C_P versus Fn

C_P and DLR versus SLR

Quarter Beam Buttock Angles