Powering Data - Propeller Design Condition

The optimum propeller is designed at the draught given in the Design Condition on the Loading Conditions page. Various optimization modes may be utilized, and two propeller series are available. In addition, other configurations such as twin screw, noise reduced and controllable pitch are available and may be selected here.

Propeller Design Parameters

The number of entries in the group labelled Propeller design parameters depends on the propeller optimization mode selected and any values not required are greyed out.

Other Propeller Data

• Number of blades - propellers may be designed with 3, 4, 5 or 6 blades.

• Shaft height - height from the keel to the centre of the propeller shaft. Used in the calculations that check for cavitation.

• Minimum effective blade area ratio - you are able to provide a minimum limitation to the actual designed BAR. Note that the propeller series data is constrained by a minimum BAR of 0.4.

• Cavitation safety factor - the actual BAR must be greater than the BAR determined from Burrill's 5% cavitation line, References 12 multiplied by the specified cavitation safety factor. A safety factor greater that 1.0 will ensure greater protection against cavitation than the standard Burrill 5% line.

Propeller Series

There are two propeller series available:

• Wageningen B-series, References 9.

• Gawn-Burrill segmental propeller series, References 10.

The Wageningen B-series is suitable for normal merchant ships, whereas the Gawn-Burrill series propellers are more appropriate for the higher loading conditions of warships.

Optimization Mode

Three different ways to optimize the propeller are provided:

• Given the ship design speed and the rpm of the propeller, determine the optimum diameter, pitch and blade area ratio.

• Given the ship design speed and the diameter of the propeller, determine the optimum RPM, pitch and blade area ratio.

• Given the delivered power and RPM, determine the optimum propeller diameter, pitch and blade area ratio. (An estimated design speed must also be supplied as a starting point for the iteration process.)

Reynold's No. Correction Method

This module also provides three methods to correct the propeller design for the actual Reynold's number:

• No correction.

• Correction according to Oosterveld and Oossanen, References 9. This is the correction related to the Wageningen B-series propeller.

• ITTC78 correction, References 11.

Other

• Twin screw - check this option if the ship has twin screws, otherwise the ship is assumed to have a single screw.

• Controllable pitch propeller / Noise reduced - checking one or both of these options applies a correction to the standard series propeller efficiency to account for noise reduced and/or controllable pitch designs. The correction made is as follows:

  

  where

  correction 0.97 for noise reduced OR controllable pitch.

  correction 0.94 for BOTH noise reduced AND controllable pitch.