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

Quick Series Facts:

The following is a description of the various Propeller Series used in PSModel.

Notes:

1) Blade Area Ratio (BAR) as used in PSModel is a generic term referring to either Expanded Area Ratio (EAR) or Developed Area Ratio (DAR).  Normally, the EAR and DAR of a propeller are very close in value.  The tables below show which ratio, EAR or DAR, was used in the published data or reference for each Series.

2) Efficiency curves for all Series in PSModel are calculated from Kt and Kq values as follows:
 Efficiency =  (J × Kt) / (6.28319 × Kq)

3) PSModel uses linear data interpolation for Series that utilize tabular data such as 'GBD', 'GBA', 'NR', 'NV3' and 'NV4'.  In most cases, linear interpolation works fine.  However, in some cases -- such as interpolating Kt or Kq at very low Cavitation Numbers -- linear interpolation may not be accurate.  This is due to the highly nonlinear nature of the data associated with these cases.  Series that are represented by polynomials -- such as 'GBL', 'GRJ', and 'GBR' -- eliminate this problem and also produce smoother propeller curves.  Keep this in mind while evaluating propellers.

4) Use PSModel as a guide only.  Keep in mind that the following items can affect predicted propeller performance:

-- angle of propeller shaft with respect to inflow

-- wake, or flow velocity into the propeller, is usually an approximation

-- pitch and diameter values may differ slightly from values marked on the propeller or advertised

-- the published BAR for a propeller is usually not exact: e.g., 0.70 published, but actual may be 0.69 or 0.71

-- boat speed and RPM need to be as accurate as possible

(B) -- B Series

Description -- A noncavitating Series that uses a polynomial to represent a large body of experimental data.  This Series can be used to evaluate propeller performance on low speed vessels including yachts, recreational boats, and ships.  This Series has a unique geometry but can be used to approximate performance of many commercially available propellers including 2 and 3 blade propellers commonly used on sailboats.

Calculation method used by PSModel -- Polynomial evaluation, see reference 1

Blades  EAR P/D Ratios Cavitation Number Range
2 0.20 to 0.40 0.50 to 1.40 Noncavitating Series
3 0.35 to 0.80 0.50 to 1.40 Noncavitating Series
4 0.40 TO 1.00 0.50 to 1.40 Noncavitating Series
5 0.45 to 1.050 0.50 to 1.40 Noncavitating Series
6 0.50 to 0.80 0.50 to 1.40 Noncavitating Series
7 0.55 to 0.85 0.50 to 1.40 Noncavitating Series

Notes:

1)  The EAR range for the 2 bladed propellers tested is actually 0.30 to 0.38 but PSModel allows 0.20 to 0.40 by extrapolating the polynomial calculations.  This was done because commercial, two bladed, sailboat propellers are available with EAR values less than 0.30.  The value 0.38 was rounded to 0.40 for uniformity purposes.

2)  P/D ranges used by PSModel (as shown in the Table above) are slightly larger, in some cases, than presented in the available literature concerning the B-Series.  This was done to make the Series more uniform.

3) PSModel output is for a Reynolds Number based on chord length of 2x106

4) Propellers being evaluated can have some cavitation present as long as Kt Breakdown has not occurred.

5) Click here for propeller Series geometry details.

6) The most resent version of the B Series can be obtained from the Marine Research Institute Netherland (MARIN) at http://www.marin.nl.

(GBA) -- Gawn Burrill Atmospheric, Digitized

Description --  A 3 blade subcavitating Series used by many to approximate performance of flat faced commercial propellers typically found on small high speed vessels including recreational boats.

Calculation method used by PSModel -- linear interpolation of digitized Kt\Kq curves from reference 2

Blades DAR  P/D Ratios Tested Cavitation Numbers
3 0.50 0.6, 0.8, 1.0, 1.2, 2.0 6.3
3 0.65 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 2.0 6.3
3 0.80 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 2.0 6.3
3 0.95 0.8, 1.0, 1.2, 1.4, 1.6, 2.0 6.3
3 1.10 0.8, 1.0, 1.2, 1.4, 1.6 6.3

Notes:

1) Series 'GRJ' below calculates Gawn Burrill Kt\Kq curves from a polynomial obtained by regression analysis.  A polynomial produces smoother curves and reduces nonlinear errors.  However, the P/D range of 'GRJ' is less than that of 'GBA'.

2) Efficiency curves calculated by PSModel for 'GBA' in some cases do not appear smooth.  This occurs because PSModel calculates Efficiency directly from Kt and Kq values as presented in reference 2,  and does not fair or smooth the resulting curve.  For smoother Gawn Burrill Kt, Kq, and Efficiency curves, see Series 'GRJ' below.

3) Blade section shapes, except near the hub, are segmental (flat face and circular back).

4) Click here for propeller Series geometry details.

5) Experimental work for this Series was funded by the U.K. Ministry of Defence.

(GBD) -- Gawn Burrill Cavitating, Digitized

Description --  A 3 blade cavitating Series used by many to approximate performance of flat faced commercial propellers typically found on small high speed vessels including recreational boats.

Calculation method used by PSModel -- linear interpolation of digitized Kt\Kq curves from reference 2.  To reduce nonlinear errors, linear interpolation is performed both vertically and diagonally.

Blades DAR  P/D Ratios Tested Cavitation Numbers
3 0.50 0.6, 0.8, 1.0, 1.2, 2.0 0.5, 0.75, 1.0, 1.5, 2.0
3 0.65 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 2.0 0.5, 0.75, 1.0, 1.5, 2.0
3 0.80 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 2.0 0.5, 0.75, 1.0, 1.5, 2.0
3 0.95 0.8, 1.0, 1.2, 1.4, 1.6, 2.0 0.5, 0.75, 1.0, 1.5, 2.0
3 1.10 0.8, 1.0, 1.2, 1.4, 1.6 0.5, 0.75, 1.0, 1.5, 2.0

Notes:

1) Series 'GBR' below calculates Gawn Burrill Kt\Kq curves from a polynomial obtained by regression analysis.  A polynomial produces smoother curves and reduces nonlinear errors.  However, the P/D range of 'GBR' is less than that of 'GBD'    

2) Efficiency curves calculated by PSModel for 'GBD' in some cases do not appear smooth.  This occurs because PSModel calculates Efficiency directly from Kt and Kq values as presented in reference 2,  and does not fair or smooth the resulting curve.  For smoother Gawn Burrill Kt, Kq, and Efficiency curves, see Series 'GBR' below.

3) Blade section shapes, except near the hub, are segmental (flat face and circular back).

4) Click here for propeller Series geometry details.

5) Experimental work for this Series was funded by the U.K. Ministry of Defence.

(NV3) -- Navy 3 Blade

Description -- Cavitating Series that consist of commercial, flat faced, 3 bladed propellers typically found on small commercial vessels, yachts, and recreational boats. Blade Area Ratio (BAR) is limited to 0.54.  This Series was tested by the Navy, using 2 ft. diameter propellers on an instrumented boat under actual sea conditions.

Calculation method used by PSModel -- linear interpolation of tabular data, see reference 3

Blades EAR P/D Ratios Tested Cavitation Numbers Cup
3 0.54 1.004 2.334, 3.963, 5.136, 11.692, 16.914 None
3 0.54 1.239 2.396, 3.630, 5.544, 12.939, 18.581 None
3 0.54 1.503 2.729, 4.013, 5.445, 12.359, 18.198 None
3 0.54 0.996 2.741, 3.630, 5.334, 12.050, 17.618, 19.760 Light
3 0.54 1.244 2.729, 3.581, 4.791, 11.173, 17.038, 19.760 Light
3 0.54 1.497 2.717, 4.001, 5.544, 12.828, 19.760 Light
3 0.54 0.996 2.704, 3.605, 5.198, 11.754, 17.865, 19.760 Medium
3 0.54 1.504 2.754, 3.926, 5.433, 12.470, 19.760 Medium
3 0.54 1.00 2.766, 3.642, 4.988, 10.865, 16.593, 19.760 Heavy
3 0.54 1.492 2.717, 3.568, 5.334, 11.840, 17.420, 19.760 Heavy

Notes:

1) Cavitation Numbers used in PSModel are based on inflow velocity to the propeller but Cavitation Numbers reported in reference 3 are based on boat speed.  Cavitation Numbers reported in reference 3 were divided by (1-w)2 [or 0.92 = 0.81]  to obtain the values above.

2) The Michigan Wheel Dyna Jet propellers tested were commercially available and had flat faced, circular back, blade sections.

3) The nominal EAR value reported in reference 3 was 0.50, but reference 4 reported additional details about this Series including measured EAR values which ranged from 0.53 to 0.55 with 0.54 appearing as the average.  Therefore, PSModel uses a nominal EAR = 0.54 for 'NV3'.

4) Click here for propeller Series geometry and cupping details.

(NV4) -- Navy 4 Blade

Description --  Cavitating Series that consist of flat faced, 4 bladed propellers similar to those found on small commercial vessels, yachts, and recreational boats.  Blade Area Ratio (BAR) is limited to 0.70.  This Series was tested by the Navy, using 2 ft. diameter propellers on an instrumented boat under actual sea conditions.

Calculation method used by PSModel -- linear interpolation of digitized data, see reference 4

Blades EAR P/D Ratios Tested Cavitation Numbers Cup
4 0.70 1.058 1.20, 1.80, 2.20, 3.40, 5.50, 11.70 None
4 0.70 1.224 1.30, 1.70, 2.30, 3.40, 5.60, 11.80 None
4 0.70 1.472 1.20, 1.70, 2.30, 3.30, 5.80, 12.20 None

Note:

1) EAR = 0.70 is nominal.  EAR values for test propellers varied between 0.70 and 0.72.

2) The propellers tested were specially manufactured to have an approximate EAR = 4/3 of the 3 bladed propellers used for the 'NV3' Series, but otherwise were similar to the 3 bladed Michigan Wheel Dyna Jet propellers.

3) Click here for propeller Series geometry details.

(NR) -- Newton Rader

Description -- High speed, 3 bladed, cavitating Series based on a unique propeller geometry.  Predictions from this Series should be limited to use with propellers with the Newton Rader geometry.

Calculation method used by PSModel -- linear interpolation of tabular data, see reference 5

Blades DAR P/D Ratios Tested Cavitation Numbers
3 0.48 1.05, 1.26, 1.67, 2.08 0.25, 0.30, 0.40, 0.50, 0.60, 0.75, 1.00, 2.50, 5.50
3 0.71 1.05, 1.25, 1.66, 2.06 0.25, 0.30, 0.40, 0.50, 0.60, 0.75, 1.00, 2.50, 5.50
3 0.95 1.04, 1.24, 1.65, 2.04 0.25, 0.30, 0.40, 0.50, 0.60, 0.75, 1.00, 2.50, 5.50

Notes:

1) The blade section shapes were designed with cavitation in mind; hence, the shapes are unique to this Series.

2) Click here for propeller Series geometry details.

3) Experimental work for this Series was funded by the U.K. Ministry of Defence.

(GBL) -- Segmental Sections, Blount Polynomial

Description -- Noncavitating Series uses a polynomial to represent performance of 3 and 4 bladed, flat faced propellers typically found on slower recreational boats, yachts, and commercial vessels.  The polynomial for this Series was synthesized from published data for other experimental Series.  The polynomial was validated by comparing performance predictions with existing data for commercial, flat faced, segmental section propellers.  

Calculation method used by PSModel -- Polynomial evaluation, see reference 6

Blades EAR P/D Ratios Cavitation Number Range
3 0.50 thru 1.10 0.80 thru 1.40 Noncavitating Series
4 0.50 thru 1.10 0.80 thru 1.40 Noncavitating Series

Notes:

1) Segmental sections are composed of flat faces with circular backs.  This is typical of many commercially available propellers.

2) Propellers being evaluated can have some cavitation present as long as Kt Breakdown has not occurred.

3) Geometry that is representative of this Series is shown by 'GBD', 'NV3', and 'NV4' .

(GRJ) -- Gawn Burrill Atmospheric, Radojcic Polynomials

Description -- Series uses a polynomial to represent the performance of the subcavitating portion of the 3 bladed Gawn Burrill Series: i.e., the portion of the Series that does not show signs of Kt Breakdown.  This Series can be used for higher speed boats with flat faced, commercial propellers with minimal cavitation, i.e., higher speed lightly loaded propellers.  Also see the 'GBA' Series above.

Calculation method used by PSModel -- Polynomial evaluation, see reference 7

Blades DAR P/D Ratios Cavitation Number Range
3 0.50 thru 1.10 0.80 thru 1.80 6.3

Notes:

1) Propellers being evaluated can have some cavitation present as long as Kt Breakdown has not occurred.

2) Click here for propeller Series geometry details.

3) Polynomial was developed by Professor Dejan Radojcic, Department of Naval Architecture, Faculty of Mechanical Engineering, Belgrade University.

(GBR) -- Gawn Burrill Cavitating, Radojcic Polynomials

Description -- Series uses a polynomial to represent performance of the cavitating portion of the 3 bladed Gawn Burrill Series.  The maximum cavitation number is 2.0.  Representation with polynomials minimizes nonlinear problems that can arise when linear interpolation is used as in 'GBD' above.  The P/D range for this Series is slightly less than that of 'GBD'.  This Series can be used to approximate performance of flat faced, heavily loaded, commercial propellers typically found on small high speed vessels, including recreational boats.

Calculation method used by PSModel -- Polynomial evaluation, see reference 7

Blades DAR P/D Ratios Cavitation Number Range
3 0.50 thru 1.10 Minimum P/D =
1.25 − 0.3×DAR − 0.2×(Cavitation Number)
but not less than 0.80,

Maximum P/D = 1.60

0.50 thru 2.00

Notes:

1) Click here for propeller Series geometry details.

2) Polynomial was developed by Professor Dejan Radojcic, Department of Naval Architecture, Faculty of Mechanical Engineering, Belgrade University.