Powering Data Dialog - Resistance and Propulsion Tab

Name

This is NOT editable. It is simply a repeat of the condition name as entered on the Powering Data - Loading Conditions. It is simply included here as an aid to you when entering data.

Resistance Method

Select the appropriate prediction method from the list.

Use Ratios

If you wish to incorporate a set of resistance ratios calculated previously, then the Use Ratios check box should be checked.

Note:
Unlike previous versions of Hydro, a different ratio file may be specified and used for each loading condition.

Ratios FileName

If the Use Ratios box is checked, then you should select a file. By clicking in this field, a File Open dialog is displayed allowing you to select the ratio file. The name is then entered into the cell. Note that the file name may not be directly entered.

The structure of the ratios file is given in Powering Files - Ratios File Structure.

Because the resistance ratios are calculated for all resistance methods, the calculated ratios may not be particularly reliable for some of the resistance methods and, in fact, may not even be calculated for others. Therefore, when incorporating a set of resistance ratios into a powering prediction, care should be taken to ensure that the resistance method chosen is applicable to the current hullform and that the resistance ratios in the chosen ratio file are sensible numbers (around 0.8 - 1.5). The resistance ratio file can be viewed as a text file. However, the file is in a fixed format, so editing of the ratio file is strongly discouraged.

Propulsion Factors

Select the appropriate prediction method from the list. If the User Input option is chosen, then the following three entries become available (and are assumed constant across the speed range), otherwise they are disabled, since the values are calculated automatically.

w

Wake fraction.

t

Thrust deduction fraction.

etar

Relative rotative efficiency.

Ship/Model Correlation

Select the appropriate prediction method from the list of two. The Ca x 1000 cell is only enabled if the User Input option is chosen. If Holtrop & Mennen is chosen it must be ensured that all relevant hullform parameters are supplied, as specified on the Powering Data - Loading Conditions.

Ca x 1000

Ship/model correlation value.

Wake Correction

Select the appropriate prediction method from the list of three

• ITTC 1978 method (including FFC) - default option.

• ITTC 1978 method (excluding FFC)

• No wake correction.

Service Allowance

This is a percentage of the smooth water Effective Power (PE) added to allow for service conditions. The propeller is optimized for the increased PE.

Hull Roughness

Hull roughness in microns (mean apparent amplitude). The default value is 120 microns.

Note:
The hull roughness will only affect the correlation allowance (CA) if the Holtrop and Mennen Ship/Model Correlation option is selected. Even then, values of hull roughness less than 150 microns will have no effect since it is deemed to have a minimum value determined by this value of hull roughness.

Form Factor Correction

The Form Factor, k, is estimated using the Holtrop and Mennen formula, References 1 and 2. The form factor correction factor is applied to the value obtained from the formula. This enables the form factor to be corrected or removed altogether by setting the form factor correction to zero. The default value for the correction is 1.0 which applies no correction to the Holtrop and Mennen estimate.

Transmission Efficiency

Determines the shaft power according to the formula

Speed From (knots)

Minimum speed (knots)

Speed To (knots)

Maximum speed (knots)

Speed Increment (knots)

Speed increment in knots.