SHIP PERFORMANCE AND POWERING
Aspects of resistance and propulsion have been discussed in high levels of detail in Chapter 12, but will still be referenced in this Chapter as it does form part of Naval Architecture. However, resistance and propulsion only covers that one aspect, and there are various other aspects that a Naval Architect also must consider as part of ship performance.
Ship Performance and Power Prediction
The purpose of Ship Performance Prediction is to Maximise the ship performance with the minimum power requirement. Factors that the Naval Architect must consider are:
- Ship stability and safety.
- Various ship hydrodynamic performance considerations like:
- Resistance and Propulsion
Ship performance prediction is vital. To understand its importance, consider the following:
- Speed is a contractual design requirement and major penalties can be imparted on the builder and designer for failing to meet this requirement.
- Optimum Power Requirements reduces not only the ship cost, but also the Total Life Cycle Cost of the ship.
- Optimised ship performance will allow for a lower carbon footprint and better fuel
- Reduced fuel consumption increases the vessel’s sustainability.
- Good Manoeuvring Performance increases the vessel’s controllability.
- Better Seakeeping increases the vessel’s operability.
Ship powering is an extremely important aspect of ship design, as various energy losses need to be overcome in order to power the ship through the water. Some indicative losses and their percentages for ships are:
- Combustion Losses -65%
- Transmission Losses -1%
- Appendage Drag -2%
- Hull Form Efficiency -1%
- Propeller Losses -10%
- Wave Drag -8%
- Hull Surface Friction -12%
When the Naval Architect designs for ship top speed, the Naval Architect needs to consider that an increase in top speed results in increase of engine power required, resulting in increased initial cost and higher life cycle cost of the ship. The Naval Architect also needs to design the ship for the required endurance based on the ships required cruise speed. This cruise speed must also be defined at specific loading conditions like lightship or full load. Prior to starting the design, ship speed is usually specified at trial at sea state 2 and a clean hull.