Cargo Ventilation and Precautions to Minimise Sweat Loss Prevention Bulletin Claimants typically allege that failure by the ship to ventilate correctly resulted in the development of condensation (commonly known as “sweat”), causing the cargo to deteriorate. It is important to recognise that some commodities may have inherent moisture levels which exceed acceptable limits at the time of loading, making them biologically unstable. Such details may not be known to the ship, and prudent ventilation measures may be insufficient to prevent the cargo from deteriorating on passage. Nevertheless, claimants may still maintain that the ship was at fault. To defend cargo deterioration claims it is necessary for the vessel to produce records showing that customary ventilation routines were followed. Should the necessary evidence be missing or incomplete, it is often difficult for the Club to refute such assertions. General Dry cargo vessels are fitted with either natural or mechanical ventilation systems. In addition to minimising the onset and degree of sweat, ventilation may also serve to remove taint and disperse any gases which some cargoes may emit. The process requires close monitoring throughout the voyage as the moisture content of the cargo coupled with variations in air temperature, cargo temperature and sea temperature can dramatically influence the amounts of water vapour retained by and released into the air inside a hold. “Moisture damage” is the source of a significant number of cargo claims, often involving bagged or bulk agricultural products. Penetration of ventilating air into a bulk stow on a ship is minimal, and so it is only ever possible at best to provide through-surface ventilation. However, ship stability requirements usually dictate that at least the majority of the holds of any bulk carrier carrying bulk cargoes such as grain are loaded fully into the hatch coamings. For a hold so loaded it is unlikely that any significant throughsurface air flow will be obtained. Whilst bagged cargo stows inevitably have some gaps in them, penetration of ventilating air beneath the uppermost layers of bags in the stow is minimal. Bagged cargoes should always be stowed in such a way that ventilating air can pass freely over the surface of the stow. Cargoes at risk Hygroscopic products Hygroscopic products have a natural moisture content and are mainly of plant origin. They may retain, absorb or release water vapour, and excessive amounts of inherent moisture may lead to significant self-heating and “moisture migration” within the cargo resulting in caking, mildew or rot. Examples of hygroscopic products include grain, rice, flour, sugar, cotton, tobacco, cocoa, coffee and tea. Non-hygroscopic products Non-hygroscopic products have no water content. However, certain commodities (e.g. steel) may be damaged if stowed in a moist environment, and others may be harmed if packaged using a hygroscopic material (e.g. wood, paper). By way of illustration a vessel loaded a parcel of glass packed with layers of paper The Formation of Ship Sweat Loss Prevention Bulletin between each sheet. At the discharge port it was found that the paper had absorbed moisture from the air during the voyage, making it impossible for the glass sheets to be separated. The cargo was rejected by the receiver. Types of Sweat Cargo sweat Cargo sweat refers to condensation which may form on exposed surfaces of the stow as a consequence of large amounts of warm, moist air be