Whilst last week many of us were enjoying summer-like temperatures of up to 32°C, the following day the maximum temperature barely reached 18°C—a remarkable drop of some 14 degrees within just 24 hours. Such abrupt changes are exceptional on land, but in shipping, vessels routinely transition between vastly different climate zones in a matter of days. These temperature differences can create ideal conditions for condensation, leading to cargo damage commonly referred to as ship sweat or cargo sweat.
What is condensation?
Air always contains some level of moisture in the form of water vapour. Warm air can hold significantly more moisture than cold air. When warm, moisture-laden air comes into contact with a colder surface, it cools and may reach its dew point—the temperature at which moisture condenses into liquid water.
Within a cargo hold, that moisture may form either on the vessel’s structure or directly on the cargo itself.
Ship Sweat
Ship sweat occurs when moisture condenses on the vessel’s internal steel surfaces—such as cargo hold frames, tank tops, hatch undersides, or bulkheads—and subsequently drips onto the cargo.
This typically occurs when:
- cargo is loaded in a warm climate;
- warm, humid air becomes trapped inside the cargo hold;
- the vessel then sails into colder regions; and
- the ship’s steel structure cools below the dew point of the hold air.
For example, a vessel loading cargo in tropical West Africa and sailing north toward colder European waters may experience rapid cooling of the hold steel, causing condensation to form and drip onto the cargo.
Cargo Sweat
Cargo sweat is effectively the opposite phenomenon. Here, condensation forms directly on the cargo surface rather than on the vessel’s structure. This occurs when cold cargo is exposed to warmer, humid air.
A typical scenario is:
- cargo is loaded in cold conditions (or transported through colder climates);
- the vessel arrives in a warm, humid discharge port;
- warm outside air enters the hold during ventilation or cargo operations; and
- that humid air comes into contact with the colder cargo surface, causing condensation.
For example, steel coils loaded in Northern Europe during winter and discharged in Southeast Asia may develop immediate condensation when warm tropical air enters the hold.
Loss Prevention Measures
Because the causes differ, prevention strategies also differ.
To reduce the risk of ship sweat:
- monitor cargo hold and outside air temperatures;
- manage ventilation based on dew point principles;
- avoid introducing humid air where this may increase condensation risk;
- ensure hatch covers and hold structures are dry before loading; and
- record ventilation decisions in the logbook.
To reduce the risk of cargo sweat:
- exercise caution when ventilating cold cargo in warm, humid conditions;
- delay ventilation where appropriate;
- minimise unnecessary hold openings;
- plan cargo operations with climatic transition risks in mind; and
- consider the sensitivity of the cargo before opening holds.
Ventilation: Helpful—or Harmful?
A common misconception is that more ventilation is always beneficial.
In reality, incorrect ventilation can significantly worsen condensation damage.
As a general rule:
- ventilate when outside air has a lower dew point than the hold air; and
- avoid ventilation where warm, humid air is likely to condense on colder cargo or vessel structures.
In conclusion, condensation claims often develop into disputes over causation, ventilation practices, and cargo condition. Good seamanship, accurate recordkeeping, and a sound understanding of climatic transitions remain essential risk management tools.
With vessels routinely trading between dramatically different climate zones, understanding the distinction between ship sweat and cargo sweat is not merely a technical matter—it is practical loss prevention.
For any questions or assistance, we invite members to contact the NNPC claims team at claims@nnpc-marine.com
