Insights: How vessel trim optimisation creates efficiency

A ship’s energy efficiency is determined by its design, its hull and machinery condition – and how the vessel is actually operated in terms of speed, draft and trim.

In the past, ships were optimized for one speed and one draft. But during a ships life time it sees a lot of different speeds and drafts. One only has to think of the shipping industry’s switch to slow steaming over the past years, in an effort to better control costs, as an example of our the “one speed, one draft” concept has gone by the way side.

Hapag-Lloyd has gone to great lengths to improve on this concept and has in turn put a lot of focus on vessel trim optimization which in turn helps reduce fuel oil consumption. And if a ship’s fuel consumption decreases, its emissions also drop.

The trim of a ship describes its floating position in length direction, namely if the bow or the aft of the ship is deeper submerged into the water. The trim can have a significant impact on a vessel’s energy demand for propulsion during sailing. The most efficient trim for a particular ship depends on its design, operational draft and speed.

During the course of 2016 Hapag-Lloyd used trim optimisation software on some 86 ships operated by Hapag-Lloyd (60 owned and 26 chartered).

The software calculates the hydrodynamic resistance for any floating position of the ship considering wave breaking resistance, frictional resistance and viscous pressure resistance. The calculation methods use Reynolds-Navier-Strokes equations (RANSE) representing the state of the art in fluid dynamic calculations.

For each of these ships, the hydrodynamic model is embedded into the Hapag-Lloyd stowage software used by our Marine Operations team. This way a stowage planner can avoid heavy ballast water operations for the ship. The ship has a similar view as the stowage planner as well as a detailed view on the trim efficiency. In both views red and green areas indicate less and more efficient ship operation.

With this uniform view both ship and shore get the same set of information and a mutual understanding by means of efficiency can be gained. Ship and stowage planner both have the same ground for communication in terms of trim. Hence the common goal of efficiency increase can be realised.

Manual Work

At the end of the day trim is not only related to fancy software. Various stakeholders are involved and there is still an amount of manual work that needs to be done and requires substantial working time.

On board, the captain and the chief officer oversee the cargo and ballast water operation and conduct the actual trimming acknowledging the safety and weather conditions.

The Chief Officer, who is responsible for the ship’s cargo and stability, needs to oversee the ballast water operations to achieve an anticipated trim. The focus for trimming is on long ocean legs. Where at the beginning of the voyage leg trim is adjusted on which the vessel can sail for several days without further ballast adjustment.

The stowage planner also has a very detailed role as during stowage planning the trim optimization is already taken into consideration. This is done by positioning the cargo where it is favorable for the optimal trim.

Results

The savings due to trim stand for their own. In general, it can be seen that trimming is an integral part of efficient voyage execution in 2016, Hapag-Lloyd achieved savings due to trim optimisation of about 1.5% of main engine fuel oil consumption.
This saving was achieved despite the fact that the potential for trim optimisation was reduced, due to some vessels of the fleet being retrofitted with new bulbous bows. The new bulbous bow improves the overall resistance of a ship and hence potential for trim savings is reduced.

In addition, a by-product of trim monitoring is to the ability to evaluate a ship’s hull performance. By using the hydrodynamic models from the trim optimisation evaluation and trending of the hull resistance and fouling is possible, followed by inspection and cleaning if required. This gives Hapag-Lloyd vessels improved fuel efficiency and more positive take aways from trim optimization.

Outlook

With trim optimisation being a measureable factor we are able to gain insights into the cost efficiency of this technique and how we can achieve even higher savings. An additional goal is to even better understand if cargo stowage related patterns and technical or nautical issues are obstacles to trim optimisation.

With this knowledge Hapag-Lloyd wants to further extend the coverage of our fleet with trim optimisation. Our chartering department is already working with ship managers across the globe to install trim optimisation software on board their vessels.

With these improvements we foresee a future where our vessels are even more efficient and always enjoy smoothing sailing while at sea.

Source: Hapag Lloyd

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