RA 06 - December 2009 – One of a series of Steamship Mutual Loss Prevention Bulletins produced by the Ship Safety Trust Page 1 of 1 For further information please contact the Loss Prevention Department, Steamship Insurance Management Services Ltd., Tel: +44 20 7247 5490; Email: loss.prevention@simsl.com Web: www.simsl.com/loss-prevention-and-safety-training.html The Problem The Problem The Problem The Problem of ofof of Sweat Sweat Sweat Sweat Introduction IntroductionIntroduction Introduction The Club continues to encounter claims associated with cargo damage caused by the presence of condensation, known as sweat, forming inside cargo holds either on the cargo itself or the vessel’s structure. Central to the understanding of the problem of sweat is the concept of the dew point. This is the temperature to which a given sample of air must be cooled for saturation to occur with the result that water vapour in the air condenses. Ship Sweat Ship SweatShip Sweat Ship Sweat Ship sweat is formed when the air within the hold is cooled beneath its dew point by the hold steelwork. This could occur, for example, when a vessel loads in a warm climate and proceeds to a colder climate, as the seawater and external temperature cool, the steelwork may be eventually cooled beneath the dew point of the warm moist air in the hold, causing sweat on the hold surfaces. The sweat may affect the cargo by direct contact on the hold bulkheads, by contact on the tanktop where sweat has accumulated after running down the hold bulkheads to the bottom of the hold. Sweat may also drip onto the cargo from above having formed on the underdeck structure and the underside of the hatchcovers. To minimise the possibility of ship sweat damage to cargo dunnage must be properly used to keep the cargo off the tanktop and away from hold sides and structural members. Where appropriate cargo should be covered with waterproof sheeting to protect it from sweat dripping from above. Cargo Sweat Cargo SweatCargo Sweat Cargo Sweat Cargo sweat occurs when warm moist air is introduced into a hold and is cooled below its dew point by the cargo such that condensation forms, this could occur, for example, when a vessel is on passage from a cold climate to a warmer climate and the holds are ventilated with warm moist air being introduced into the holds. The warm moist air is cooled below its dew point by the colder cargo, causing condensation to form on the surface of the cargo. To Ventilate or not to Ventilate To Ventilate or not to VentilateTo Ventilate or not to Ventilate To Ventilate or not to Ventilate The decision on whether or not to ventilate will require careful consideration by the Master and officers. The basic principle is to keep the dew point of the air within the hold below the temperature of the hold structure and the cargo to stop the formation of ship and cargo sweat. The vessel should closely monitor the hold air dew point, the atmosphere dew point and the sea temperature, with recordings being taken on a regular basis. The dew point of the atmosphere can be ascertained by use of the wet and dry thermometers in the Stevenson Screen on the windward bridge wing and reference to a dew point table. Entry to holds should be undertaken in line with the requirements of the vessels Safety Management System with safe enclosed space entry procedures used as necessary. The dew point of the hold air temperature can be found by use of a whirling psychrometer which is a handheld device