ShipX

SINTEF has developed a programme for numerical calculation of ship resistance in calm water and speed loss in waves. The programme requires a minimum of input, hence it is very well suited to be used in the early design phase. The programme is integrated in the hydrodynamic workbench ShipX.

The motivation for developing this software was to enable the ShipX workbench environment to provide the user with the ability to calculate calm water performance as well as speed loss in waves within one product. Both of these features were implemented in the ShipX Plug-In “Ship Speed and Powering”. The Plug-In is based on the work behind the SINTEF products EmPower (calm water resistance and propulsion) and Seaway (speed loss in a seaway).

In the development of ShipX Ship Speed and Powering plug-in, a fast to use, easy-to-learn user interface has been one of the main focuses, avoiding manual editing of input files. The speed loss software is integrated as a plug-in in ShipX, and has the same intuitive, easy-to-use user interface as the rest of ShipX.  

Calm water

The calm water part of the programme is designed to predict resistance and performance for conventional ships based on SINTEF's resistance and propulsion database, and other prognosis tools developed at SINTEF. 

The following calculation methods are available for resistance and propulsion data:

• Direct input of residual resistance and propulsive coefficients from model tests or calculations.
• Residual resistance and propulsive coefficients derived from a search in the integrated database
• Residual resistance derived from a comparison ship, where the influence on CR on the difference between the actual ship and the reference ship is calculated using one of the three empirical methods described below.
• Holtrop 84 method.
• Model resistance based on Hollenbach 98.
• Resistance regression derived from SINTEF database using Artificial Neural Network.
• Direct input of resistance curve.
• Miscellaneous high-speed empirical resistance methods.

Ship speed can be predicted by applying data from standard propeller series, including open and ducted propellers, as well as arbitrary open water curves that can easily be read into the programme.

The calm water part of the Plug-In basically consists of three separate sub-programmes or tools, which can be applied separately or together to obtain the information you need (see figure below).   

Results database 

A database containing your model test results of resistance and propulsion characteristics can be included (licensed option). The database functionality includes filtering of vessels with regard to various parameter ranges, such as vessel types, Lpp, L/B etc. in order to select a basis for a performance prognosis for a similar ship. In addition, various reports and plots can be generated based on the filtered vessels. 

The plotting module in the database includes plotting the residuary resistance in a curve fitting toolbox, where a polynomial for the residuary resistance curve can be created and modified based on the filtered vessels. This polynomial can be applied in the performance prediction part of the programme in order to perform performance predictions for a given set of ship data. 

Performance prediction  

In addition to the results database, there is also a performance prediction tool that can be applied to carry out performance predictions based on Holtrop’s method, the Hollenbach 98 method, an Artificial Neural Network regression based on the SINTEF database, or by specifying the resistance and propulsion data directly.

In the latter case, the results database can be applied to find the necessary coefficients, such as residuary resistance and average propulsive coefficients.

There is also a dialog where the required resistance curve polynomial can be constructed from input resistance data. 

Propeller optimisation   

The third component that is included in the calm water part of the Plug-In, is a propeller optimisation wizard, where the propeller diameter and/or pitch ratio can be optimised based on the engine and ship characteristics. As an alternative to the propeller wizard, the propeller characteristics in terms of an open water diagram can be input. 

Together, these different sub-programmes form a basis to carry out complete performance predictions of ships based on empirical and experimental data.

Speed loss

Background

When the ship encounters waves, the total resistance increases and the propeller thrust decreases. As a result, the ship cannot sustain the same forward speed as in calm water.  Involuntary speed loss in waves is a result of a change in point of equilibrium between the total ship resistance and propeller thrust.

Speed loss components included:

• Added resistance in waves (typically from ShipX Vessel Responses plug-in (Veres))
• Thrust loss due to ship motions in waves 
• Wind resistance

Input

Speed loss calculations require a relatively large set of input data. The engine and propeller characteristics must be known, as well as the total still-water resistance and added resistance in waves. If speed loss calculations are to be performed for an irregular sea-state, the wave spectrum defining the sea-state is required input. The ship motions are required for the calculation of thrust reduction in waves. 

The calculation of ship motions and added resistance in waves is done in the ShipX Vessel Responses plug-in (Veres) and the results are used as input in speed-loss calculation.

Use

Running the calculations takes from a few seconds up to a minute, depending on the speed of the computer, and the number of environmental conditions (sea-states and wave headings). As soon as the calculations are finished, reports and plots are available directly from ShipX. Reports and plots can easily be exported to Microsoft Word or pdf for quick and easy report generation.