Published: 3 April 2023

Updated: 6 April 2023

The Club frequently encounters cases where there is apparent moisture damage to cargo. This damage may be to agricultural products, or rust damage to steel, for example, due to the formation of ship or cargo sweat. The Club can have difficulty defending these claims due to poorly conducted ventilation and completion of the ventilation log.

Cargo ventilation logs are an important document in order to evidence that the cargo has been properly cared for whilst being carried on the vessel, with routine accurate measurements being taken and ventilation being properly conducted in line with the ventilation rules being applied, where fumigation and heavy weather permit. The correct completion of ventilation logs is crucial as they can be instrumental in the successful defence of a claim for moisture damage. Where ventilation and record keeping have been poorly conducted, we may have difficulty protecting the Member’s position.


Ventilation will reduce the incidence of ship’s sweat and avoid cargo sweat, which can lead to cargo damage claims on both hygroscopic and non-hydroscopic cargoes.


Two rules can be followed when determining whether to ventilate or not:

Dew Point Rule: A cargo hold should only be ventilated when the dew point of the outside ambient air is lower than the dew point of the air inside the headspace of the hold.



  • Accurate if done well
  • Requires less organisation at the load port
  • Requires access to the hold headspace to obtain accurate dry/wet bulb temperatures, which during a voyage is rarely safe/feasible
  • Wet bulb temperature needs to be measured using a whirling or aspirated hygrometer to be accurate. Some vessels may not have this equipment
  • Requires regular measurements and calculations which are sometimes performed incorrectly.


Three Degree Rule: A cargo hold should only be ventilated when the outside ambient dry bulb temperature is at least 3°C lower than the mean cargo temperature at loading.



  • Easier to perform in practice than the dew point rule during the voyage
  • Access to the cargo holds is not required
  • Safer for crew working on deck, particularly at night, as measurements from the hold are not required
  • Complex calculations are not required.
  • A surveyor may need to be appointed at the load port to obtain the cargo temperature for each cargo stow during loading.

Outside of the rules described above, a charterparty may also include general instructions on ventilation. Any ventilation instructions are to be followed at all times. Where the instructions from the charterers are “ventilate whenever possible”, this does not mean ventilate at all times, but rather only when the temperature or dew-point data indicate that it is appropriate and weather conditions are suitable. Any stipulated period for fumigation should be followed and ventilation, as necessary, started thereafter.


In the event of a cargo claim as a result of moisture damage due to the formation of sweat during the voyage, ventilation logs showing that the cargo hold was ventilated correctly and properly cared for may be instrumental in defending any subsequent claims.

Depending on which ventilation rule is followed, the following should be recorded:

  • cargo temperature at loading
  • dew point for outside air at least once per watch, along with dry and wet bulb temperatures
  • dew point for air in each cargo hold at least once per watch, along with dry and wet bulb temperatures
  • whether ventilation is needed
  • seawater temperature
  • time for starting and suspending ventilation in each hold, including reasons for suspension and if this is due to the weather conditions and details of the conditions that preclude ventilation.

If the Dewpoint Rule has been followed, wet and dry bulb temperatures and dew points should be logged once per watch, as well as the sea temperature, as these may change considerably over a short period. This information should be recorded for each hold together with the times of starting, stopping or resuming ventilation and the reasons for doing so.

If the Three Degree Rule has been followed, a record should be kept of the ambient air temperature and the sea temperature once per watch, together with the average temperature of the cargo at the time of loading. Again ventilation details should be documented for each hold.

If bad weather prevents ventilation, the ship staff should record this. If possible, staff should take photographs of the prevailing weather conditions, especially if sea water or spray is being shipped on deck and issue a Sea Protest.


  • Using the least appropriate rule for the given circumstances. For example, the temperature of the cargo on loading could be provided and the holds sealed following fumigation, yet the dew point rule is used.
  • Not commenting in the log that ventilation was not conducted due to fumigation.
  • The rule being followed for determining whether to ventilate not being stated in the log.
  • Ventilation only occurring during the day, with no reason recorded as to why ventilation has not occurred at night. Night time may be the best time to ventilate. However, crew availability and the prevailing conditions may mean it is difficult to achieve.
  • Crew taking the dew point measurement from the hold at the time when fumigation documents state the hold should not be entered.
  • Ventilation logs detailing only one set of measurements a day. This does not demonstrate that the cargo has been ventilated when appropriate.
  • Insufficient notes detailing why ventilation has stopped. Ventilation can occur in the rain, providing the requirements of the rule being followed are met and the ventilation system on board does not allow rain water ingress.
  • Ventilation continuing when the conditions for the rule being followed are not being met.
  • Ventilation start and stop times not being recorded, preventing the length of the ventilation period from being determined.
  • Ambient temperatures not being recorded when not ventilating.
  • Incidences of wet bulb temperatures being recorded as higher than dry bulb temperatures, which is impossible.
  • Large variations in dry and wet bulb temperatures inside the cargo holds, which is unlikely and indicates measurement errors.
  • Inconsistent entries when recording ventilation data in the logbook .

Examples of blank ventilation logs for each of the rules can be downloaded here.

Members requiring any further guidance are advised to contact the Britannia Loss Prevention Department.