Vessels are usually designed to utilise their maximum engine power (i.e. Maximum Continuous Rating) at their designated top speed, while including some margins on their performance to take into account conditions and incremental change over their life. This has always assumed that vessels will normally be operated at a small range of passage speeds that are close to their maximum, with the engines therefore running at 80% MCR or above.
In current market conditions many ships are now being operated under slow steaming conditions, with some container ships occasionally being run at 10% MCR for extended periods at speeds well below their previous levels. This wish to operate ships at speeds and conditions well away from their nominal ‘design point’, usually in order to reduce costs by saving fuel at the expense of increased passage time, offers an opportunity to re-optimise the hydrodynamic design to further improve the fuel efficiency of the hull at these lower operating speeds.
There are a number of hull features that can be addressed as part of such a design review to improve the fuel efficiency over a wider speed range:
- Re-optimise bulbous bow shape and size
- Re-align/shape hull appendages
- Re design propeller
- Fit energy saving devices, eg Propeller Boss Cap Fin
Efficiency improvements of up to 5% can be achieved from these measures, although the return on capital investment for many of them will be measured in years rather than months.
Many vessels are fitted with transom sterns in order to maximize the usable internal volume of the hull. However a transom hull does have some limitations, including a significant increase in hull resistance if the transom is immersed below the waterline, as many of them are.
MOST Ltd is developing a range of simple, low cost hydrodynamic devices that will offer up to 10% reduction in hull resistance, and hence fuel savings, for some styles of hull (eg Offshore Support Vessels) that will have a return on investment of less than 12 months. If you are interested in fitting this device to your vessels please leave your contact details HERE and we will get in touch with you.
