Planing Boat Resistance
(Long Form)

This module calculates the resistance of planing boats in both displacement and planing modes.  Planing mode uses a variation of Savitsky's "long form" calculations, taking into account factors such as skegs, rudders, trim tabs, wave heights, and air resistance.  Displacement mode uses a regression technique, developed by Savitsky and Brown, which determines resistance for Froude numbers between 1.0 and 2.0.

This module uses a powerful analysis interface, which allows you to perform a wide range of parametric studies quickly and easily.  First, all input variables are presented in a "spreadsheet-like" form, allowing you to easily modify input values and recalculate the results. 

In addition, you can have the program calculate, print, and/or plot other values calculated from the basic set of input and output values.  For example, you can request that the value of resistance/weight be plotted against Froude number, or resistance plotted against deadrise angle.  Since there are no predefined limits as to what you can print or plot, this program allows you to perform parametric studies on any or all input and output values, including equations based on these values.

The planing boat program uses input such as beam, draft, and deadrise angle to perform all of its calculations.  You do not need an exact description of the hull to perform these calculations.  The results are printed in report format and list all input, results, and intermediate values, to allow you to verify or check any answer.

Displacement Mode - Displacement mode calculates the smooth water (non-planing) resistance of a vessel.  This technique can be used to calculate resistance for Froude numbers (volume) less than 2.0.  It is based on a regression analysis of a wide range of hull forms and uses the method described in:

"Procedures for Hydrodynamic Evaluation of Planing Hulls in Smooth and Rough Water"
Daniel Savitsky and P. Ward Brown
Marine Technology, October, 1976

Planing Mode - For planing mode, a group of equilibrium equations are used to describe the vessel moving at a steady rate.  These equations cover a variety of lift and drag forces, such as hull normal force, friction drag, and spray drag.  Once the input is specified, these equations are solved to find the resistance and trim of the vessel.  Eight pages of input and output can be printed or plotted to allow you to perform detailed optimizations.

The procedure for defining the system of equilibrium equations and hull drag and lift forces is derived from:

"Hydrodynamic Design of Planing Hulls"
Daniel Savitsky
Marine Technology, October, 1964

Additional equations covering appendages, air resistances, and added resistance due to waves came from a variety of other sources.  Contact New Wave Systems, Inc. for a complete list of references used and a complete set of equations used.

Planing Boat Resistance
(Short Form)

This module calculates the resistance of chine hull boats in the planing condition.  It uses a powerful analysis interface, which allows you to perform a wide range of parametric studies quickly and easily.  You may calculate results for a single condition or you may print or plot results over a range of values.

Calculation of the vessel's resistance, EHP, and trim are done assuming that all forces pass through the center of gravity (LCG).  The technique used is one described in:

"Hydrodynamic Design of Planing Hulls"
Daniel Savitsky
Marine Technology, Vol 1, No. 1
Oct. 1964


It is often referred to as the "short form" calculation due to the simplification of having all forces pass through the center of gravity.  In addition to calculating the bare-hull resistance, this program accounts for appendage drag and wave drag.  Another reference about this technique is:

"Small-Craft Power Prediction"
Blount and Fox
Marine Technology, Vol. 13, No. 1
January, 1976.




  Vk    Tau  Taucrit    Rbh        Rt        EHP

10.00    3.7196  17.2000  2296.00    3035.34      93.13 
12.00    4.0625  19.5440  4414.62    5402.15    198.91   
14.00    4.4634  18.1383  5668.45    6864.27    294.87 
16.00    4.8833  15.9557  6421.19    7803.00    383.08   
18.00    5.2459  13.8334  6836.13    8388.89    463.33   
20.00    5.4720  11.9866  6992.83    8704.18    534.16   
22.00    5.5307  10.4395  6967.70    8828.20    595.95   
24.00    5.4462    9.1604  6844.11    8848.57    651.62   
26.00    5.2644    8.1058  6689.49    8836.85    704.99   
28.00    5.0280    7.2349  6545.81    8838.06    759.33   
30.00    4.7667    6.5128  6433.78    8874.84    816.95   
32.00    4.5004    5.9113  6362.16    8957.23    879.50   
34.00    4.2403    5.4076  6332.75    9087.86    948.10   
36.00    3.9927    4.9837  6344.34    9266.16  1023.57   
38.00    3.7604    4.6253  6394.49    9490.23  1106.56   
40.00    3.5444    4.3207  6480.46    9757.88  1197.65 

          Example of Looping Output

All input variables are presented to you in a spreadsheet-like form, allowing you to easily modify their values and recalculate the results.  In addition, you can also have the program calculate, print, and/or plot other values derived from the basic set of input and output values.  For example, you can request that the value of resistance/weight be plotted against Froude number, or resistance plotted against deadrise angle.  Since there are no predefined limits as to what you can print or plot, this technique allows you to perform parametric studies on any or all input and output values, including equations based on these values.

There are 39 input and output variables which can be used to perform looping and plotting.  All of these variables can be displayed, printed, or plotted, along with any algebraic combinations of these variables.

Propeller Selection and Optimization

This propeller module allows you to approach the problem of propeller selection from various directions:


1. If all of the initial data is known, (Diameter(D), RPM(N), pitch/diameter ratio(P/D), and expanded area ratio(EAR)), then you can directly calculate the various quantities related to the propeller, such as thrust and torque delivered, along with the open water efficiency of the propeller.


2. Given that one of the quantities from the input group: D,P/D,EAR,N, is missing then the missing value can be found such that the thrust delivered matches the thrust required.  The required thrust is determined from the input EHP values.  No optimization is done since the one "free" variable is used to match the delivered thrust with the required thrust for the specified velocity.


3. An optimum propeller (with the highest open water efficiency) can be found if two or more values from the group (D, P/D, EAR, N) are not entered as input.

For example, a design process might proceed as follows:

o Enter the maximum allowed diameter.
o Optimize to determine the EAR, N, and P/D of the optimum propeller.
o Use the resultant SHP and N to select an engine and reduction gear ratio.
o Optimize again using the same diameter and the actual
N = N(rpm of engine)/GR (gear ratio).
o Use the resultant P/D and EAR to select a few candidate propellers.
o Compare the candidate propellers at all design and off-design conditions.  Compare how their efficiencies drop off due to increased resistance (from fouling) or when the RPMs are increased over the design condition.


4. The module also allows you to loop (print) or plot anything vs. anything else.  For example, you could print or plot efficiency vs RPM (N) or thrust delivered minus thrust required (Tdel - Treq) vs RPM for a given value of diameter.  The "loop"ing function allows you to display or print these values and the "plot"ting option allows you to display or plot the graph of the values.