PSModel a look inside

HOME

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

Kt Breakdown: 

Noncavitating Series such as B and GBL, and subcavitating Series such as GRJ can be used to predict propeller performance when cavitation is present.  The only requirement is that the Advance Coefficient, J, be greater than or equal to the J value at the beginning of Kt breakdown.

Kt breakdown begins when cavitation causes the Kt curve to deviate from the Open Water Kt curve.  Typically, this happens when cavitation covers between 15 and 20 percent of the blade backs.  The point where breakdown begins is called the Kt breakdown point.

The graph below shows Kt breakdown points for a 4 bladed, B Series propeller tested at progressively lower Cavitation Numbers or Sigma's.

B Series cavitation test showing Kt breakdown points

PSModel predicts or estimates the J value at the Kt breakdown point and truncates the propeller curves to J values greater than or equal to that value.  For example, the PSModel screen below shows the propeller curves for the same propeller depicted in the graph above at Sigma = 4.2.  PSModel predicts that the Kt breakdown point occurs at J = 0.69 and the propeller curves have been truncated to J values greater than or equal to 0.69.  Cavitation may still exists on the propeller blades at J = 0.7, but not enough to cause Kt breakdown.  At J values less than 0.69, cavitation becomes more pronounced as the J value becomes smaller.

 PSModel screen showing predicted Kt breakdown point