Once you have established exactly how much time is allowed and whether particular proportions of that time must be allocated to the loading or discharging operations, it is then necessary to examine the definition of lay time carefully to establish whether lay time runs continuously or whether there are certain periods which, by virtue of the definition of lay time in the charterparty, do not count. It is rarely as simple as adding a fixed number of hours or days to the point at which lay time commenced in order to identify the point at which it expired. Note that exceptions to lay time are treated differently and are dealt with later. The most common interruption specified within the definition of laytime relates to weather. ‘Weather Working Days’: A weather working day is any working day during which the weather does not wholly prevent the working of cargo or would not wholly prevent working if work were intended. If the weather simply interrupts the loading or discharging operation, the day itself is still a weather working day but the charterers are entitled to deduct certain periods for the purpose of the laytime calculation. The amount which they are entitled to deduct must be calculated as it is not necessarily the same as the time lost due to bad weather. The Charterparty Laytime Definitions 1980 provide the following definition: A working day or part of a working day during which it is or, if the vessel is still waiting for her turn, would be possible to load/discharge cargo without interference due to the weather. If such interference occurs (or would have occurred if work had been in progress) there should be excluded from laytime a period calculated by reference to the ratio which the duration of the interference bears to the time which would have or could have been worked but for the interference. This definition has the advantage of setting out how the period of interruption to laytime is to be calculated. In particular, if because of the working practices in the port in question work would not have been carried out over the full 24 hours, then the period of time for which laytime is suspended will not be the full amount of time during which cargo operations were suspended due to bad weather. Therefore, if normal working hours (including time for which overtime is paid) are 16 hours out of 24 and 4 hours have been obstructed by bad weather then one-quarter of the time available for working cargo during that day has been lost due to bad weather. That means that laytime is interrupted for a quarter of the day – that is to say six hours, not the four which have actually been lost due to bad weather. If, on the other hand, the bad weather occurs at a time outside working hours when no work could have been done in any event, the whole day counts as a weather working day and the existence of any adverse weather conditions is irrelevant. Conversely, if the weather was fine during periods when no work was carried out in the port, but prevented work from being carried out during all the working hours of the day, the entire day would not count against lay time. ‘Working Days (Weather Permitting)’. Another way of providing for bad weather is to refer to ‘working days (weather permitting)’. The effect of this formula is to deduct from laytime any time lost due to bad weather. The only distinction, therefore, would appear to be that where the expression ‘weather permitting’ is used instead of simply describing something as a ‘weather working day’, the apportionment described above is not used. The phrase ‘weather permitting’ used on its own is an exception to laytime. ‘Weather Working Days of 24 Consecutive Hours’.As we have seen above a much clearer formula involves a reference to 24 ‘consecutive’ or ‘running’ hours. Thus, if the laydays are expressed to be weather working days of 24 consecutive or running hours, any time during which weather prevents cargo working is deducted. No apportionment is required.