13 June 2014
Article from Tanker Operator
Conferences on the theme ‘Navigating Ecotankers’ took place in Copenhagen on 27th Mar, 2014 – held by Tanker Operator’s.
KNUD E. HANSEN’s Brian Bender Madsen warned owners and operators to anticipate new fuel regulatory changes going forward and agreed that it was generally cheaper to add fuel saving technologies on a newbuilding, rather than opt for a retrofit solution.
He advised owners/operators to co-operate with a proven design house to ensure high overall efficiency, as the shipyards main focus is on optimised production.
Madsen said that there were many solutions available for old, bad and/or large vessels, but for smaller and newer vessels, few solutions are available to improve their efficiency.
He thought that there basically four methods to improve the fuel efficiency of a vessel:
- Reduce the hull resistance in loaded/ballast condition
- Increase the propulsion system efficiency
- Improve the power plant efficiency
- Improve the crew behavioural and operational efficiency
For newbuildings, a fifth method is the vessel’s operational profile, ie draft, speed, laden/ballast and operation area.
As for hull resistance, the general characteristics of a full-form/high block coefficient vessel, such as a tankers were:
- 60-80% of the hull resistance is in the form of viscous resistance.
- 10-20% can be attributed to wave resistance
- 5-10% to hull roughness
- Up to 5% to air resistance
The largest areas for improvement here lie in optimising the hull form (optimise carrying capacity), applying smooth coatings and keep the hull and propeller clean. For tankers already in operation, hull form optimization has very limited applicability. But on newbuilding it has high value, Madsen said.
There are a range of options available for increasing the propulsion system’s efficiency, all of which are highly customised and designed specifically for each vessel.
Each system has advantages and disadvantages and in some cases combining different devices has been shown to give good improvement, such as the Mewis Duct, which combines a duct and pre-swirl fins. In general the efficiency improvements to be gained are highly dependent on the geometry of the vessel in question, Madsen said.
Generally, the variable frequency drive, waste heat recovery and automation are the key to power plant efficiency, Madsen said.
There are a range of options on the market for systems, which improve the plant efficiency.
In a few cases, mainly on larger vessels and for bad designs, larger conversions could be undertaken resulting in big savings and a quick ROI.
Another feature to consider is the operational efficiency. Trim optimisation can offer reductions in fuel consumption in the range of 1-5%. This can either be verified by model test, or computerised fluid dynamics (CFD) – depending on whether a model is available. Other possible features available for operational efficiency include – route planning (weather, adjust speed according to the ETA).
Crew training and awareness can answer such questions as – do the vessel’s systems operate in the most efficient mode? A lack of maintenance and overhaul increases the vessel’s energy consumption. Other possibilities include slow steaming and taking advantage of the currents and avoiding bad weather and the monitoring of hull and propeller fouling.