Weather Data vs. Deck Logs in Speed-Consumption Claims

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Published Sep 29, 2021 9:57 PM by Dr. Arun Kasi

In time charterparties, shipowners will give a speed-consumption warranty. Typically, the warranty will be about the vessel’s speed-consumption capability on sea passages in good weather. Generally, the maximum wind force admitted in the definition of good weather is Beauford scale 4, while it can be higher in the case of tankers. The sea state generally admitted is Douglas sea state 3.

Seldom a vessel will enjoy good weather throughout a sea passage. Hence, the vessel’s performance during a sufficient good weather period on the passage will be taken as the sample. If the sample shows underperformance, the result will be extrapolated to the entire sea passage, including bad weather periods, to find out the loss suffered by the charterer as a result of the reduced capability of the vessel.

In determining whether a particular period was a good weather period, a conflict may come into play between the charterer’s weather routing company (WRC) report and the deck log. Charterparties may provide a resolution to this by preferring one evidence to another, or by requiring the conflict to be resolved by reference to weather bureau data.

Deck log entries

The deck log entries are made by the watchkeeper on the bridge by the authority of the master. They contain data on the weather conditions, including wind force and the state of the sea and swell. They are normally recorded once every four hours, based on the watchkeeper's continuous observation. In this exercise, a watchkeeper usually takes into account the weather data available at that time. Therefore, a deck log entry is subject to errors of human and circumstances. For example, a night observation can be more prone to error than one made under sunlight. An error may happen in recording the observed wind force in the Beaford scale number. The sea waves (caused by local winds) can be mixed up with swell waves (caused by distant winds) in stating the sea state for purposes of Douglas sea state scale.

In London Arbitration 4/12, the deck log entry showed Douglas sea state 4 (rough) for a particular period. The charterer’s weather bureau report noted swell waves of two meters high for the same period. The tribunal held that the watchkeeper must have mixed up the sea and swell waves in recording sea state to be rough, while the true sea state could be Douglas sea state 3 (moderate). The tribunal further commented that watch-keepers usually do not pay attention to separating sea and swell waves. However, an advantage of the deck log entries is that the observations are made from the bridge of the immediate surroundings, which adds to accuracy.

WRC Report

WRC reports rely on the weather information obtained from satellite imagery, weather buoys, etc. The satellite imagery is normally collected at a frequency of once or twice per day, and is therefore less representative of the weather condition for the time in question. Weather buoys measure the conditions for an area covering hundreds of square meters from its position, and are less representative of the weather condition for the ship’s location.

Which one to prefer?

Unless a preference is made in the charterparty, generally deck log entries are preferred (The Evdokia (1980); London Arbitration 6/19). If a charterer wishes to reverse it, the burden is on it to show why the deck log entries should not be preferred (The Dimitris Perrotis (2000) LMLN 533), for example, inconsistencies in the entries, etc.

However, in London Arbitration 4/12, the tribunal seemed to accord generally less weight to deck log entries, saying “log entries are at times made with half an eye on the charter warranties.” This statement must be read in the circumstances of the case. There the conflict was between the Danish Meteorological Institute (DMI)’s findings and the deck log entries. The charterparty expressly provided that an independent weather bureau report was to prevail over the deck log entries. The tribunal found that the watchkeeper must have mixed up sea waves and swell waves in recording ‘rough’ weather, as DMI’s finding was that the swell waves were two meters high. Another case in which the tribunal expressed doubt over the deck log entries, on the factual matrix of the case, was London Arbitration 4/11.

In conclusion, the preference - in the absence of a provision to the contrary - is for the tribunal to determine in each case. In practice, the tribunal gives a good weight to the deck log entries, which is open to the charterer to rebut.

Preference clause

Charterparties may, by a rider clause, prefer one form of technical evidence over another. It may provide that in the event of a conflict, the parties will appoint an independent WRC whose ‘expert determination’ shall be final, as in cl 12(e) of NYPE 2015 form. It may alternatively provide that, where there is a conflict, deck log entries will prevail over the charterer’s WRC report or vice versa – though this is not popular.


Suppose the agreement is that the independent WRC expert determination is final and binding. In such a case, while the arbitral tribunal will accept the technical findings of the WRC, it is not bound to accept that the WRC followed the correct methodology (London Arbitration 15/05; 21/04). Suppose that, as per the charterparty, a favorable ‘current’ goes for the benefit of the shipowner, but the WRC factored a favorable ‘current’ in favor of the charterer. Then, a tribunal may reject the current factor included in the WRC’s calculation.


The process of expert determination is different from that of an arbitral award. In the former, the parties are not heard. In the latter, the parties are heard, which is an important element in the decision-making process (Wilky Property v London & Surrey Investments (2011)). An expert, but not an arbitrator, is liable for negligence (Sutcliffe v Thackrah (1974); s 20 UK Arbitration Act 1996). An arbitral award is statutorily binding (s 58 UK Arbitration Act 1996), while an expert determination is binding only as a matter of agreement between the parties.


Dr. Arun Kasi is an advocate and solicitor in Malaysia. He specializes in charter dispute arbitration under the terms of LMAA and SCMA. He is the author of The Law of Carriage of Goods by Sea (Springer: 2021). For more information, visit https://arunkasico.com.


Dr. Kasi extends his thanks to Mr. Prokopis Krikris, Claims Manager at Meadway Bulkers Athens, and Mr. Georgios Zaponakis, Legal Counsel at Thenamaris Athens, for reviewing this paper.

The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.