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Cargo Ventilation: A Guide to Good Practice

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Media Book
SKU WS1706K
Publisher Witherby Seamanship International
ISBN WS1706K

This unique illustrated guide for masters, ships’ officers and others associated with the carriage of cargo explains how to avoid problems and disputes arising from incorrect usage of natural and mechanical hold-ventilation systems on cargo ships. Incorrect use of ventilation can lead to cargo damage from ship’s sweat, cargo sweat, rainwater or seaspray.

The guide addresses the key cargo ventilation questions of why, when, what and how, with particular emphasis on the application and pitfalls of the dew-point and three-degree rules. The guide works on various levels, with a quick reference section supplemented by practical guidance and considerations, plus a scientific background for those wishing to understand the underlying principles.

INTRODUCTION

 

Why ventilate?

Safety

How to use this guide

Glossary of terms

 

QUICK REFERENCE

When to ventilate

Cargoes that may require ventilation

 

PRACTICAL GUIDANCE

What is sweat? The simple explanation

Hygroscopic and non-hygroscopic cargoes – know your cargo

Finding the dew point

Three-degree rule – for hygroscopic agricultural cargoes only

How effective is ventilation?

When should cargo be ventilated?

When should ventilation be stopped?

Types of ventilation system

 

PRACTICAL CONSIDERATIONS

Stowage

Dunnage

Recent developments in the rice trade

Cargoes that do not fit the rules

Equipment for measuring the dew point

Myth or truth?

 

SCIENTIFIC BACKGROUND

Air, moisture and relative humidity

Relative humidity and dew point – an example

How much condensation is produced?

Hygroscopic cargoes

Scientific rational for ventilation

 

INDEX

WHY VENTILATE?

There are numerous reasons for ventilating a ship’s holds. Among these are

  • ensuring an adequate oxygen level for people to enter the holds

  • removing poisonous, flammable or fumigant gases

  • attempting to prevent condensation or ‘sweat’ (Fig. 1).

Prevention of sweat is probably the most common reason for ventilating. However, it seems to be the one which causes seafarers and ship operators the most problems, and it is the one on which this guide will concentrate. This guide relates to ships with conventional ventilation systems, both natural and mechanical. It does not apply to refrigerated ships, or to those whose holds are provided with de-humidifiers.

There are also many fallacies about what can be achieved with ventilation on board a ship, such as cooling or preventing self-heating of cargoes. These fallacies, and the limited situations in which ventilation can be used to control cargo temperature, will be outlined. Later sections will explain why sweat forms, and how it can be controlled by ventilation. For now we simply say that, if sweat is allowed to form without any effective attempt to check it, cargo wetting, and expensive claims, can result (Fig. 2). It may not always be possible to prevent the damage by correct ventilation; however, if correct ventilation has been carried out, and recorded, it should be easier to defend the resulting claim.

In the ideal world proper attention to ventilation will ensure that the cargo arrives undamaged at the discharging port. However, this may not always be the case. Even if ventilation is possible, it may be that the cargo cannot be ventilated sufficiently to prevent some sweat forming. It may even be that the inherent moisture content of the cargo is so high that no amount of ventilation will prevent damage. If extensive sweat damage occurs it is likely that a claim against the ship will follow.

To defend such claims successfully, it will be necessary to demonstrate that masters understood the principles of ventilation and that, based on their understanding, they ventilated their ships’ holds during the voyage correctly and as thoroughly as they could under the circumstances.

It may be that weather conditions experienced on passage prevent ventilation for part, or all, of the voyage. If so, masters must still demonstrate that they acted correctly in withholding ventilation and that they did so at the correct times. Therefore, whether the holds are being ventilated or ventilation is suspended because of weather conditions, a detailed record should be kept.

Title: Cargo Ventilation: A Guide to Good Practice
Number of Pages: 48
Product Code: WS1706K
Published Date: August 2019
Weight: 0.70 kg
Author: The North of England P&I Association Ltd

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