🚢 Why Does “Ship’s Sweat” Happen in Cargo Holds?

 

🚢 Why Does “Ship’s Sweat” Happen in Cargo Holds?

“Ship’s sweat” simply means water forming inside cargo holds because of temperature difference.

It is not leakage.
It is not rain.
It is not necessarily poor cleaning.

It is mostly basic science: warm air + cold steel = water droplets.

Below are the most common reasons.

 

1️⃣ Big Temperature Difference (Most Common Reason)

If:

• Outside air is warm and humid
• Sea / river water is cold
• Ballast tanks are full with cold water

Then the ship’s lower steel becomes cold.

When warm humid air enters the hold (during ventilation or hatch opening), it touches the cold steel and turns into water droplets.

Think of a cold glass of water sweating on a hot day.
Same concept.

 

2️⃣ Heavy Ballast Condition

If the ship is heavily ballasted:

• Steel near tank tops and hopper slopes becomes cold.
• Condensation forms mostly on lower sections of the hold.

This is why sweating is usually seen:

• Along tank tops
• On lower hopper slopes
• Near weld seams

Upper structures may remain dry.

 

3️⃣ Sudden Weather Change

Sometimes holds were dry yesterday.

Then:

• Air temperature rises suddenly
• Humidity increases
• Warm front moves in

Condensation can reappear quickly.

Weather changes are a big trigger.

 

4️⃣ Opening Hatches at Wrong Time

If hatch covers are opened:

• During high humidity
• Early morning (dew time)
• During rain / mist conditions

Moist air enters the hold and condensation increases.

Timing matters.

 

5️⃣ Improper Ventilation Practice

Ventilation should only be done when:

Dew point of outside air < Dew point inside hold

If this rule is ignored:

• You bring moisture inside.
• Sweating increases.

Many junior officers forget this simple rule.

 

6️⃣ Cold Cargo History

If the vessel previously carried:

• Cold cargo
• Was in cold region
• Had refrigerated conditions

Steel may still be cold internally.

Condensation can continue even after cleaning.

 

⚓ What Should Owners & Master Do? (Practical Precautions)

Now the important part — prevention and control.

 

✅ 1️⃣ Monitor Temperatures Daily

Chief Officer should regularly record:

• Air temperature
• Sea / river temperature
• Relative humidity
• Hold steel temperature (if possible)

Understanding difference helps prevent surprises.

 

✅ 2️⃣ Follow the Dew Point Rule Strictly

Ventilate ONLY if:

Outside dew point is lower than hold dew point.

If unsure — do not ventilate.

Better no ventilation than wrong ventilation.

 

✅ 3️⃣ Manage Ballast Smartly (Within Limits)

If condensation is heavy:

• Review ballast plan.
• See if some ballast can be reduced.
• Keep within shear force & bending moment limits.

Even small ballast reduction can reduce sweating.

But safety always first.

 

✅ 4️⃣ Avoid Opening Hatches in High Humidity

Avoid opening:

• Early morning
• During fog / mist
• During high humidity periods

Open during:

• Midday dry conditions
• When humidity is lower

 

✅ 5️⃣ Keep Bilges Clean and Operational

Even if sweating happens:

• Bilges must drain freely.
• No clogging.
• No standing water.

This prevents accumulation.

 

✅ 6️⃣ Document Everything

Very important for Owners & Managers:

• Log weather data.
• Record ventilation decisions.
• Record ballast condition.
• Take photos.

Why?

Because condensation is often misunderstood.

Documentation protects vessel and reputation.

 

✅ 7️⃣ Crew Awareness & Training

Many sweating issues worsen because crew:

• Don’t understand dew point.
• Ventilate incorrectly.
• Ignore early signs.

Training junior officers on cargo care science is crucial.

 

🚢 Simple Rule to Remember

If steel is colder than air dew point →
Water will form.

That’s it.

Shipping may look complex, but this issue is simple physics.

 

🔎 Final Practical Advice

Ship’s sweat is:

• Normal in many trades
• Manageable with knowledge
• Dangerous only if ignored

The best Masters don’t panic when sweating appears.

They:

• Check data
• Adjust ballast if possible
• Control ventilation
• Communicate calmly

Shipping rewards calm thinking.

If you want, I can also create a simple decision-making checklist format that Masters and Chief Officers can keep for grain readiness.