PSModel a look inside

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Introduction

Quick Start

Quick Series
Facts

PSModel
Program

Data Input

Data Output

Importing a
Data file into
MS Excel

Main Menu

Main Screen

Printing
Graphs
and Data

Screen Colors
and Fonts

Screen
Graphs

Shortcuts

Working
with Data

Testing:

Test Sheet

Examples

19' Ski Boat

34' Sailboat

41' Utility Boat

Technical

Blade Area
Ratio

Calculating
the Cavitation
Number

Horsepower
Losses

Hull Speed

Kt Breakdown

Propeller
Geometry

Propeller Law

Wake Factors

Glossary

References

Propeller Law:

The Propeller Law is an idealized set of assumptions that can be used for boats operating in the displacement mode below the Hull Speed. These assumptions are:

1) boat resistance is proportional to boat speed squared,

Resistance = C1 x MPH2

2) propeller thrust is proportional to boat speed squared,

Thrust = C2 x MPH2

3) propeller RPM is proportional to boat speed,

Propeller RPM = C3 x MPH

4) propeller torque is proportional to RPM squared,

Propeller Torque = C4 x RPM2

5) horsepower absorbed by the propeller is proportional to RPM cubed,

Propeller HP = C5 x RPM3

The constant, Cn, can be found for any of the equations above if the two other values in the equation are known.  For example, if PSModel predicts a propeller thrust of 50.0 lbs at a boat speed of 8.0 MPH then C2 can be determined as follows:

 C2 = 50.0/8.02 = 0.78125

Once C2 is known, the entire curve representing MPH vs. Thrust can be plotted.

MPH vs. thrust curve from Propeller Law