Der Double Run
The Double Run –
Kai-Uwe Lömker is standing in our office and looking at us full of expectation. “Want to write an article for NSBmagazine again?” he just asked. Basically, we are quickly prepared to – after all, it’s always a good opportunity to advertise for our methods, which frequently also involve extra work for our crews but always have a purpose. The last article on Dirk Hundt on bunker sampling contributed a lot to making the point of these investigations understandable.
Kai-Uwe Lömker then asks: “What about this funny test then that you’re always doing, this Eight …?” The Eight? Ah yes, the Double Run. One of our most important methods for checking the performance of our ships. Yes, it’s a good idea. A Double Run, after all, involves some hours of additional work for the crew – time that also has to be made up for in the schedule. So why this balancing act between the interests? Now that would certainly be an interesting subject for an article from the TOM department – and here it is.
Trust is good.
To begin with, we should explain the actual purpose of the Double Run. As already mentioned, it serves to check the power efficiency of the ships, i.e. the engine performance required to reach a specific speed. This measurement is anything but trivial, as many factors play a role, for example the draught and the weather, which differ for every voyage. Yet the builders have guaranteed a specific performance for fixed conditions, which also serves as a basis for the details in our charter parties. A vessel’s performance can, however, decline as a result of marine growth on the hull and other signs of ageing. The shipyard trials are also carried out under parameters other than the contractually determined ideal conditions and must be subsequently corrected. It has also already happened that on delivery a shipyard has “adjusted a bit upwards” the results of the trial.
To exclude this from the beginning in future and promptly identify performance changes in ship operation, the Double Run was initiated. The Double Runs are based on the speed trials with the shipyard trials. These involve the ship proceeding along a fixed route and back at various speeds. With the joint evaluation of both runs, the influence of wind, waves and current can be worked out. The values are comparable. The conversion between various draughts is relatively difficult. Here the shipyards use the data from model trials, generally available for two or three different draughts. The assessment of intermediate draughts, as they occur for the NSB ships in operation, is very imprecise without a model test. So we try during a Double Run to use if at all possible the draught for which the performance is guaranteed. The other influences are also, if possible, to correspond to the conditions stipulated in the Charter Party, as the more that is corrected, the greater the imprecision.
Solving problems before they arise
The results of the Double Runs are taken, evaluated and collected at TOM for all groups. The diagram shows how such an evaluation can look. If it turns out that a ship may not meet the required performance, the evaluation is initially carried out again more exactly. Things can then definitely become somewhat academic. If the result is confirmed, an attempt is made to find the causes and solutions along with the superintendents.
The newbuildings mostly carry out a Double Run to confirm the shipyard trial trip. The Double Run is also performed if an increased performance requirement is indicated. In future, however, every NSB ship is to undertake such a test regularly – perhaps once a year – to identify problems promptly and enable us better to track developments such as the ageing of the vessels. The Double Run is in any case integrated as Fleet Instruction No. 117 into our quality standard (QDMS).
If the Double Run is taken seriously, regularly carried out and evaluated, it will protect us from nasty surprises and indeed benefit everyone involved.