Any boat, ship, barge or floating object will float at different levels depending on the warmth and/or consistency of the water its floating in/on.

If a ship loaded to capacity in, say.., Greenland at a salt water port/harbour and sailed to a fresh water port/harbour in the tropics, there would be risk of it riding too low in the water at its destination and the risk of it sinking.

Also known as a Plimsoll mark, the Plimsoll line was introduced in 1876 in England due mainly to the work of the M.P.

Samuel Plimsoll as part of the package that became the 'Merchant Shipping Act' of that time.

The mark is printed onto the side of cargo ships to indicate the limit to which they can be legally loaded.

Next time you spend a little bit of time down in the docking area have a look. You will see the mark.

At which marking does the water reach? Can you think of all the reasons that the vessel you are looking at might be at that level?