Savitsky Planing Boat Calculations (English Units)

Description: This template performs Savitsky planing boat powering calculations.  This Savitsky method is a simple but comprehensive hydrodynamic planing boat power prediction method.  This template also checks the results to see if porpoising instability will be a problem.  Five input speeds are evaluated and the power and trim angle results are automatically plotted on output charts.  The effects of the placement of the vessel's longitudinal center of gravity, LCG, are also computed.   For user experiences with this boilerplate Excel spreadsheet, see the customer comments page.

These calculations are for smooth water performance and are based on procedures for Savitsky's Long and Short Forms that are contained in Reference A.  This template is presently available only in English units.  The effects of slow speed non planing operation, extra powering required for seaway effects, trim tabs, appendage resistance, air resistance are not computed.  Reference B may be utilized to do these additional calculations.

There are advantages and benefits to this calculative method.  First this approach saves time.  Hundreds of computations are quickly done behind the scenes on your input data.  Hours of time are saved since the data does not have to be entered over and over again into the hydrodynamic, iteration and interpolation formulas.  Second this approach provides clear and neat documentation.  Theses computations can readily be submitted to U. S. C. G. or classification societies if requested.  Third this approach is cost effective because the calculative approach is already developed for you, research time is minimized to familiarization of concepts when necessary and not to time consuming development activities.

This Savitsky planing boat template 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" were not used.  Simply change a value in the spreadsheet and it automatically and immediately recalculates all affected values.

Electronic Document Type:  Microsoft Excel spreadsheet           Cost: $75 US funds

Number of Pages: Inputs Sheet 2 pages, Summary Sheet 1 page, Speed calculation sheets 5 pages, Input/Output checks 10 pages, Iteration and Interpolation sheets 5 pages,  References and Figures 3 pages, Bottom Speeds 1 page, Porpoising 1 Page, Use Terms 1 page, Instructions 1 page.   Generally only 8 pages are needed for submittal.  The other 22 pages are required for additional computations, checks or they are instructional in nature.                

Inputs:  

• Two input speeds, knots.  From these two speed the results for five speeds are automatically calculated, these two speeds simply define the upper and lower limits of the speed range evaluated.  However, the user may override the automatic intermediary speeds & calculate five user specified speeds if desired.

• For each speed, two iteration trim angles (upper and lower) are allowed as optional inputs.  Default values are used if iteration trim angle values are not specified.  These default values are normally satisfactory.

• The calculative method needs to be specified.  Simply specify the value of "one" for Savitsky Long Form calculations and set to the value of "two" for Savitsky Short Form computations.

• Hull characteristics

  • Length Over All, LOA, feet (optional input)

  • Length of Waterline, LWL, or Chine Length, feet

  • Beam on Waterline, BWL, feet (optional input)

  • Exit Angle, q_AFT, of Aft Quarter Butt, an explanatory diagram is provided with this template.  This value is critical for proper operation and is therefore checked in this analysis.  For more details about this requirement refer to Pages 12 and 13 of Reference D.

  • Deadrise angle, b, degrees, for vessels with variable deadrise, pages 93 and 94 of Reference A, suggests using the value at the stagnation line.   The stagnation line is shown in the first figure contained in the Reference portion of this spread sheet.

  • Chine beam, b, feet, this is a critical value.  For vessels with variable deadrise, pages 93 and 94 of Reference A, suggests utilizing the value at the stagnation line.  

• Weight information

  • Vessel light ship weight, pounds, without any people, luggage, personal gear, provisions, stores, fluids or cargo on board

  • Weight margin on light ship, percent.  This is optional input, default values are provided.

  • Cargo weight, pounds, can be left at zero default value.  This would include the weight of fish and ice if applicable.

  • Number of crew and number of passengers, integer

  • Additional equipment not included in light ship, pounds

  • Duration of voyage, days, for calculating provisions and stores, can be set equal to zero

  • Personal crew gear and passenger luggage, pounds, can be set to zero

  • Portions of total fluid capacities to be applied in analysis, default values usually 2/3 are provided, however these values may be specified as inputs.

  • Main propulsion engine tank capacity, gallons, and fuel type (diesel or gasoline).  This is a highly recommended input value, if provided an estimate of the vessel's range is automatically computed by this spreadsheet.

  • Auxiliary fuel tank capacity, gallons, and fuel type (diesel or gasoline)

  • Potable water tank capacity, gallons

  • Sewage holding tank capacity, gallons

  • Longitudinal center of gravity, feet, distance forward of transom to center of total weight present.  Initially this value may be estimated.  Weights may need to be rearranged change this value in order to get proper optimal planing boat performance.

  • Vertical center of gravity, feet, distance above hull bottom to center of total weight present.  Initially this value may be estimated.  (Required for Savitsky Long Form calculations.)

• Propulsion Plant Details:

  • Installed brake horsepower

  • Parasitic loads, horsepower, for pumps, generators etc.

  • Continuous operating rpm, percentage, guideline values are given on the input sheet, simply select the applicable rpm percentage

  • Propeller Shaft Angle, e, degrees (required only for Savitsky Long Form calculations for Savitsky Short Form computations set this equal to zero)

  • Thrust moment arm, f, feet, perpendicular distance off shaft line to vessel's center of gravity.  (Required only for Savitsky Long Form calculations for Savitsky Short Form computations set this equal to zero.)

  • Shafting efficiency, ratio, guideline values given, select appropriate value

  • Propeller efficiency, ratio, a default value is present, however another value may be utilized for the calculations

  • Vessel range required, nautical miles, optional input.  If this value is specified this spreadsheet will automatically determine if tanks provided are adequate to make the voyage distance specified by this input.

• Properties of water (fresh or salt) that the vessel is operating in:

  • mass density (Slugs/Ft³) and kinematic viscosity (Ft²/Sec)

  • values are provided on the input sheet, simply select the applicable operating temperature and insert values associated with this operating temperature and the operational water type (FW or SW).  Intermediate values may be interpolated or Reference G may be consulted.

Outputs:  

• For each of the five input speeds the following is output for equilibrium conditions computed by this template:

  • Trim Angle, degrees

  • Drag Force, pounds

  • Effective Horse Power

  • Brake Horse Power

  • Continuous Horsepower

  • Estimated Range, based on tank capacity, nautical miles

• Checks for porpoising instability

• The input and output range of data is checked for applicability as per the limits of the hydrodynamic modeling data utilized.  For details see Reference A.

• The total operational weight is automatically computed based on light ship margin selected, cargo present, persons aboard, voyage duration which affects stores and provisions, selected operational tank capacities and gear on board.

• Supplemental values like the weight density of the water, displacement length ratio, estimated maximum possible displacement speed, speed length ratios, volumetric Froude numbers, equilibrium wetted length beam ratios, equilibrium drafts to keel and a lot of other intermediary values are also computed to obtain the equilibrium values for trim angles and drag forces.

Recommended Reading:

• Reference A: Daniel Savitsky, "Hydrodynamic Design of Planing Hulls," Marine Technology, October 1964 Issue, SNAME, Paramus, NJ 

• Reference B: Daniel Savitsky and P. Ward Brown, "Procedures for Hydrodynamic Evaluation of Planing Hulls in Smooth and Rough Water," Marine Technology, October 1976 Issue, SNAME, Paramus, NJ

• Reference C: Daniel Savitsky, "Chapter IV Planning Craft of Modern Ships and Craft," Naval Engineers Journal, Feb. 1985, Special Edition, American Society of Naval Engineers, Alexandra, VA

• Reference D: Dave Gerr, Propeller Handbook, International Marine, 1989, Camden, Maine.

• Reference E: Dave Gerr, Nature of Boats, International Marine, 1995, Camden, Maine.

• Reference F: Joseph G. Koeble, Jr., "Performance Prediction Chapter," No. 120 Small Craft Engineering Resistance, Propulsion and Seakeeping, Reprinted Oct. 1975, University of Michigan, Ann Arbor, MI.

• Reference G: J. B. Hadler, "Coefficients for International Towing Tank Conference 1957 Model-Ship Correlation Line," Report 1185, April 1958

• Reference H: Alfred D. Isaacson, paper entitled "Sewage Pollution Control: A Guide for the Ship Owner & Design," SNAME Marine Technology, July 1977 issue.

• Reference I: S9086-C6-STM-010/CH-096R1 "Naval Ships' Technical Manual Chapter 096 Weights & Stability," NAVSEA, 2 August 1996.

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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.