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Advanced Sailboat Parameter Calculations & Checks
(English Units)


Description: This spreadsheet takes you input values for your sail boat and automatically calculates many of your sail boat's numerical characteristics (ratios, coefficients and parameters).  Then this spreadsheet presents various target values allowing you to quickly check and compare your sailboat's characteristics with other similar successful sail boats.  

There are several advantages and benefits to this calculative approach.  Some of these advantages are listed below.

  • First this method saves time.  Many of computations are quickly generated behind the scenes on your input data.   Also to modify, simply change a value in the spreadsheet and it will automatically and immediately recalculates all affected values.

  • Second this approach provides clear and neat documentation. 

  • Third this approach is cost effective because the calculative approach is already developed for you, research time is minimized to the familiarization of concepts when necessary and not to time consuming development activities.

  • Fourth this template is kept simple, it contains no Excel macros and there is no Visual Basic code utilized in it's creation.  Also advanced Excel features such "Goal Seek," "Solver" and "Scenarios" are not used.

  • Fifth, because this is a spreadsheet and not a program, the users can easily modify it to suit their particular needs. 

Electronic Document Type: 
Microsoft Excel spreadsheet           Cost: $50 US funds

Organization and Content:

  • Inputs (all inputs marked with an asterisk * are affected by the vessel condition under evaluation.  This vessel condition may be light condition, half load or full load condition, or some other condition.  All asterisk values must change when the vessel condition changes.)

    • Inputs Sheet 1

      • Weight or Displacement, D, pounds, usually half load condition *

      • Ballast Weight, pounds, WB, in keel and in hull.

      • Draft, Waterline Draft, feet, from waterline to bottom of keel *

      • Draftc, Canoe Draft, feet, from waterline to bottom of hull *

      • Length Over All, LOA, feet (includes spars, bow pulpits etc.)

      • Length of Hull, L, LOH or LOD (for older vessels), feet (length of hull's watertight envelope stem to stern.  This does not include spars, bow pulpits, swim-steps etc., Length on Deck is the same value, except for vessels with reverse transoms, in which case the length is extended to the bottom end of the transom)

      • Length of Waterline, LWL, feet *

      • Hull Beam, Maximum, Bmax, feet (for hull only, does not include rub rails, fenders, etc.)

      • Maximum Waterline Beam, BWL, feet * (this value can be estimated, where BWL = 0.9 x Bmax)

      • Freeboard Forward, FFWD, feet*, waterline to top of hull forward

      • Freeboard Aft, FAFT, feet*, waterline to top of hull aft

      • Length of Waterline, LWL, feet *

      • Maximum Cross Sectional Area, Amax, 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, ALP, 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, VOP, knots (the sail boat speed that you want the spreadsheet to evaluate, this need not be the speed that the vessel can go)

    • Inputs Sheet 2  (these inputs are noted as "optional" and need not have numerical values assigned to them.  In other words this spreadsheet will automatically estimate a value if one is not specified.  If you wish the spreadsheet to estimate this value make sure that the value of the optional input is set to zero!  If you know the actual value, of an optional input, it is highly recommended that the actual value be inserted as an input, so that the spreadsheet does not automatically estimate it.  Remember actual values are superior to estimated values and they will generate more accurate results.)

      • 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, TOP, seconds,* boat full roll period while in operational condition


  • Outputs the following values are automatically calculated by this spreadsheet, in addition definitions, formulas, comments and various target values are normally presented for quick reference on each output.

    • Sail Hull Form Parameters Outputs 1

      • Displaced Volume, V, cubic feet

      • Waterplane Coefficient, CWP, dimensionless

      • Midship's Coefficient, CM, dimensionless

    • Sail Hull Form Parameters Outputs 2

      • Half Entrance Angle of Hull, a, degrees (acceptable target values are presented for this input)

      • Pounds per Inch, PPI, pounds per inch of immersion

      • Moment to Trim 1 Inch, MTI, foot pounds per inch trim of trim, this is an estimated value.

    • Length Ratio Outputs for Sailboat Characteristics

      • Length Beam Ratio, L/Bmax, dimensionless.  High values indicate large form stability, faster speeds (if light boat) and larger interior volume. Low values indicate gentler motions and normally safer blue water performance.

      • Waterline Length - Waterline Beam Ratio, LWL/BWL, dimensionless

      • Overhang Ratio, OR = LOD/LWL, dimensionless

    • Draft Ratio Outputs for Sailboats

      • Length to Draft Ratio, LWL/Draft, dimensionless

      • Length to Canoe Draft Ratio, LWL/DraftC dimensionless

      • Beam to Draft Ratio, BWL/Draft, dimensionless

      • Beam to Canoe Draft Ratio, BWL/DraftC, dimensionless

    • Freeboard Ratio Outputs for Sailboat Characteristics

      • Forward Freeboard Ratio, FFR = FFWD/LWL, dimensionless

      • Forward Ratio, FR = FFWD/FAFT, dimensionless

    • Speed Parameters for Sailboats

      • Operational Speed Length Ratio, SLR = VOP/LWL1/2

      • Recommended Operational Speed, VFN = Fn(g x LWL)1/2/1.689 based on an optimum Froude Number equal to 0.35, knots

      • Recommended Optimum Speed Length Ratio, SLRFN = VFN/LWL1/2

      • Maximum Speed Length Ratio based on DLR, SLR1 = 8.26 / DLR0.311

      • Maximum Speed Length Ratio based on Bottom Exit Angle, SLR2

      • Maximum Speed Based on DLR & Bottom Exit Angle, Vmax knots, this speed based the the lesser of SLR1 and SLR2.

      • Displacement Hull Speed, VHULL = 1.34 x LWL1/2 knots, maximum speed for a normal displacement hulls. This value is based on a speed length ratio (SLR) equal to 1.34. At this speed length ratio the length of the wave generated by the hull is equal to the length of the hull. However, this barrier speed does not apply to all sailboat hulls. Hulls that are very light with flat exit angles and wide beams may exceed this value and go into semi-displacement or semi-planing or even planing mode. Also hulls that are very narrow and light, like racing catamarans, can exceed this speed.

      • Velocity Ratio, VMAX/ VHULL = 1.88 LWL1/2SA1/3/D1/4)/ VHULL based on length, sail area, displacement and hull speed

      • Maximum Speed based on Velocity Ratio, knots, where VMAX =
        (VMAX/ VHULL ) VHULL maximum speed
        based on velocity ratio

      • Sail Boat Speed Maximum Expected based on all above, knots, where VME equals the greater of Vmax and  VMAX

      • Recommended Optimum Speed Length Ratio, SLRFN = VFN/LWL1/2

    • Displacement and Length Parameters for Sailing Vessels

      • Displacement Length Ratio, DLR = (D/2240)/(LWL/100)3, long tons / cubic feet.  Generally the vessel with the lower value will be the faster vessel. But ideal values depend on the speed length ratio range that the vessel is operating at.  Design lanes for optimal DLRs as a function of speed length ratio are given in the references.

      • Length Displacement Ratio, LDR = LWL / V1/3 dimensionless

    • Prismatic Coefficient for Sail Boats

      • Prismatic Coefficient, CP = V / (AMAXLWL) dimensionless

    • Various Parameters Involving Sails

      • Sail Area Displacement Ratio, SADR = SA / V2/3 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, (ALP/SA)100 percentage

    • Ballast Ratio for Sailing Vessels

      • Ballast Ratio, where BR = WB/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.

    • Sailboat Lead Characteristics (check for acceptable values)

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

    • Stability Outputs for Sailing Craft, Sheet 1

      • 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 = (BMAX/3.28084)2/(BR x (DraftC/3.28084) x (V/3.280843)1/3)

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

    • Stability Outputs for Sailing Craft, Sheet 2

      • Capsize Risk Factor (or Capsize Screening Factor), where
        CSF = BOA / V1/3 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, AROLL = 2p(T)2Radius(qROLLp/180)/32.2

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

    • Sail Boat Stiffness Factors, Sheet 1

      • 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

    • Sail Boat Stiffness Factors, Sheet 2

      • 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, HM1 Degree = D x GM x Sin(1 degree) results in foot pounds

      • Dellenbaugh Angle, DA = UHM / HM1 Degree

    •  Sailing Vessel Comfort Factors

      • 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 Bmax1.333). 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
        WPLR = a x (D/2240)2 + b x (D/2240) + c

      • Factor of Safety on Waterplane Loading, FSWPL = WPL / WPLR values less than one are acceptable

  • Informational Sheets

    • Figures Sheet for Sailing Vessel Spreadsheet, one sheet

      • CP versus SLR

      • CP versus Fn

      • CP and DLR versus SLR

      • Quarter Beam Buttock Angles

    • References and Notes, one sheet

    • Instructions, 1 sheet

    • Use Terms, 2 sheets

    • Formulas (these sheets are for interpolations and extrapolations of target data, they are normally not included with printed output) 5 sheets.

Recommended Reading:

  • Books

    • Reference B-A: Arthur Edmunds, Designing Power & Sail, page 193, 1998, Bristol Fashion Publications, Harrisburg, PA.

    • Reference B-B: SNAME, Principles of Naval Architecture, Volumes I and II, 1988, Society of Naval Architects & Marine Engineers, Jersey City, NJ

    • Reference B-C: Dave Gerr, Propeller Handbook, International Marine, 1989, Camden, Maine.

    • Reference B-D: C. A. Marchaj, Seaworthiness, the Forgotten Factor, Chapter 4 - Boat Motions in a Seaway, 1986, International Marine, Camden, Maine.

    • Reference B-E: Edward M. Brady, Marine Salvage Operations, Cornell Maritime Press, 1960, Cambridge, Maryland.

    • Reference B-F: Dave Gerr, Nature of Boats, International Marine, 1995, Camden, Maine.

    • Reference B-G: Howard I. Chapelle, Yacht Designing and Planning, 1971, W. W. Norton & Company, Inc., New York, NY.

    • Reference B-H: Norman L. Skene and Francis S. Kinney, Skene's Elements of Yacht Design, 1973, Dodd, Mead & Company, Inc., New York, NY.

    • Reference B-I: Juan Baader, The Sailing Yacht, Second Edition, 1979, W. W. Norton & Company, Inc., New York, NY.

    • Reference B-J: Lars Larsson and Rolf E. Eliasson, Principles of Yacht Design, Second Edition, 2000, International Marine, Camden, Maine.

    • Reference B-K: Pierre Guttelle, The Design of Sailing Yachts, 1984, International Marine Publishing Company, Camden, Maine.

    • Reference B-L: Robert G. Henry & Richards T. Miller, Sailing Yacht Design, 1965, Cornell Maritime Press, Inc., Cambridge, Maryland.

    • Reference B-M: K. Adlard Coles & Peter Bruce (editors), Adlard Coles' Heavy Weather Sailing, 30th edition, Chapter 2 Sailing Yachts in Large Breaking Waves, pages 11-23, International Marine, Camden, Maine.

    • Reference B-N: C. A. Marchaj, Sailing Theory and Practice, 1964, Dodd, Mead & Company, New York, New York.

    • Reference B-O: C. A. Marchaj, Aero-Hydrodynamics of Sailing, 1979, Dodd, Mead & Company, New York, New York.

    • Reference B-P: Douglas H. C. Birt, Sailing Yacht Design, 1951, Robert Ross & Co. Limited, Southampton, UK.

    • Reference B-Q: Andrew G. Hammitt, Technical Yacht Design, 1975, Van Nostrand Reinhold Company, New York, New York.

    • Reference B-R: D. Phillips-Birt, The Naval Architecture of Small Craft, 1957, Hutchinson & Company, London, UK.

  • Papers

    • Reference P-A: Robert G. Henry and Richards T. Miller, Sailing Yacht Design - An Appreciation of a Fine Art, pages 425-490, SNAME Transactions, Volume 71, 1963 issue, Society of Naval Architects & Marine Engineers, Paramus, NJ.

    • Reference P-B: Richards T. Miller and Karl L. Kirkman, Sailing Yacht Design - A New Appreciation of a Fine Art, pages 187-237, SNAME Transactions, Volume 98, 1990 issue, Society of Naval Architects & Marine Engineers, Paramus, NJ.

  • Articles

    • Reference A-A: Ted Brewer, Is Your Boat Stable?,, Article
      from Good Old Boat magazine: Volume 3, Number 2, March/April 2000.

    • Reference A-B: Ted Brewer, Brewer By the Numbers,, Article
      from Good Old Boat magazine: Volume 3, Number 2, March/April 2000.

    • Reference A-C: Roger Marshall, Design By the Numbers, Motor Boating & Sailing magazine: September 1981.

    • Reference A-D: Roger Marshall, Design Calculatons, The Design Process Part III, Article from Boatbuilder Magazine, November/December 2004.

  • Web Sites

    • Reference W-A: John Holtrup, Several articles including: "Design Basics," Fuzzy Logic," "Estimating Stability," "Plots from Data Base," "Dynamic Stability," and "Best Offshore Cruising Boats" - updated 20 June 2000,"

    • Reference W-B: Michael Kasten, "Sail Area Ratios,", 2001.

    • Reference W-C: Dan Pfeiffer, "Sailboat Design Ratios,", 2003.

    • Reference W-D:, "Angle of Vanishing Stability," and formulas.htm, 2001.

    • Reference W-E:, "Keelboat Course - Design & Stability,", 1999 - 2002.

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Minimum System Requirements: Windows 95/98/NT/2000/XP/Vista/Windows7

Sample: A sample of an output page is shown below.

Similar Sailing Boat Product
There is another Microsoft Excel spreadsheet available that is much more concise.  It calculates the main or primary parameters for multiple sail boats for quick comparison.   You can check this other spreadsheet's characteristics by going to the Sail Boat Parameters Spread Sheet.