Saturday 22 January 2011

GUIDE: Loadlines

Load Lines (or Plimsoll Lines) are markings on the side of ships (amidships) which show the maximum limit of cargo a ship can load. They give different limits based on temperatures of water and salinity, as per the above diagram. 

The logo on the left is the classification society marking. It indicates the ship's classification society by two letters, LR (for Lloyd's Register) or NV (for De Norsk Veritas) for example.

The lines can vary from the standard format on the basis of the ship's trading area and class. The standard format is as per the above diagram but some other examples are below.

Thursday 20 January 2011

GUIDE: Ship Bouyancy


This is a subject which occupies many thousand pages of academic and professional books. However, to the layman there are a few general principles that it is useful to know.

1. Water provides a 'buoyant force' against objects placed in it.
Essentially it forces them upwards. The amount of buoyant force pushing upwards is equal to the amount of water displaced by the object. The more water you push out of the way, the more force pushes back against you.

2. A ship floats when the amount of water displaced by its hull weighs more than the ship itself.
So if a ship weights five tonnes but its shape means that its hull is making a hole in the water equivelent to about seven tonnes of water, then it will float. There is a ´buoyant force´ of seven tonnes pushing the object up and only a weight of five tonnes pushing it down.

3. If you load more cargo on a ship it will sit lower in the water.
This seems obvious but what is happening is that the ship becomes heavier than the water it is displacing, and so starts to sink. However, in doing so the hull goes deeper into the water, displacing more water, and eventually the water displaced again becomes heavier than the ship, so the ship stabilises at a floating level again.

4. Ships sit higher in cold or salty water.
This is a major reason why internationally trading ships have loadlines on their sides. The lines correspond to different climates, fresh and salt water, so you can keep at a safe level throughout transit. Salty water is heavier than fresh water and cold water is heavier than hot water. So a ship´s hull needs to displace less, i.e. sit lower, to float. For example, if a ship sits high in the water at Felixstowe (cold, seawater), the same ship dropped into an African lake (warm, freshwater), would sit a lot lower in the water.

Does the Athens Convention Only Apply to 'International' Carriage of Passengers?

Generally, yes, but in the UK, no.

The Athens Convention 1974 applies to the "international carriage" of passengers by sea. It provides for a two year time limit for bringing claims against the carrier (reduced from 3 years under English law generally).

The Athens Convention was brought into law in the United Kingdom by the Merchant Shipping Act 1979. This applied the terms of Athens Convention to all passengers on international voyages, departing from or bound for the UK.

However, in 1987 the UK government the ‘Domestic Carriage Order’[1] was brought into force, which extended the Athens Convention cover to all passengers on voyages which begin and end within the UK, Channel Islands or Isle of Man.

[1] The Carriage of Passengers and their Luggage by Sea (Domestic Carriage) Order 1987

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