Feature: How deep is the ocean? We know.

When you go out to sea in your boat, you need to trust your chart. You need to know where you’re going, what the potential hazards are and how deep it is. It’s all there on your chart. But have you ever wondered how anyone can tell how deep the water is when you can’t see the seabed?

The answer might surprise you. The process used to find out the depth of the water is similar to that used by bats and marine mammals to navigate and also that used in some medical procedures: sound. 

In the past, of course, it was the old plumb line that was used to work out the depth, but now boats measuring the depth use echo sounders. A sound wave is sent to the seabed - the time it takes for the signal to get back to the boat tells you how deep the water is. It can also give an indication of what the seabed in that place is made of. Sound waves bounce off rock more easily than they do sand.

The work is carried out as part of the Maritime and Coastguard Agency’s running of the UK Civil Hydrography Programme (UKCHP). We use the latest technologies to continually survey UK waters. When the data comes in, it’s processed and checked. Images like this one of Lundy can be made from the data. Although it looks nothing like the charts you use on your boat, it is used to make them.

The MCA pass the UKCHP data to the UK Hydrographic Office which then uses it to make the charts. From a survey being completed to a chart being available to buy takes around 4 months, meaning when you buy one, you have the most up to date information available.


It’s a lot of work but it’s about producing data that can be trusted. And when you’re sailing your boat or trying to bring a container ship into port, that’s something you really need to know.

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