What’s UNDER the Water on a Ship?

There’s heaps to do on modern cruse ships, but most of the passenger areas are found in parts of the ship above the water line. So today, we’re diving into those areas that are below the waterline and discovering what exactly is under the water?

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Chapters:

00:00 What's under the waterline?
00:40 Ship design features
01:01 Technical elements of the ship
02:06 The draft for stability
02:43 Ocean Liner Draft
03:03 What do the hull markings mean?
03:53 Propellers or Pods?
04:33 Anti Fouling Paint
05:25 Inside the ship: Engines and Stores
05:52 Passenger spaces below the waterline
06:24 Conclusion

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About this episode:

The very bottom of the ship is known as the keel. In older ships this was generally the first part of the ship to be built and was essentially the backbone of the ship. The supporting ribs, onto which the hull was built, were attached to the keel and the ship built up from there.

The distance between the waterline and the keel is known as the ship’s draft. The size of the draft is important for multiple reasons. Firstly, the part of the ship that is underwater is critical for the ship’s stability. Too much weight above the water, and not enough below can make the ship unstable or prone to listing.

The depth of the draft has an impact on where the ship is able to visit. The ocean liners of old had deep drafts. This was often due to the large mechanical spaces required to run the ships’ reciprocating engines and the cargo space that was required for them to be profitable. It also helped give them good sea keeping qualities, making them very suitable for running line voyages, but it often made them impractical in a cruising role.

Bow thrusters, and on ships that have them, stern thrusters allow the ship to manoeuvre under their own power. Stern thrusters are generally only installed on ships with traditional propellers, rather than rotatable pods. These ships have a rudder below the waterline which is used to turn the ship when it is underway, but the bow and stern thrusters improve their manoeuvrability in port.

Many modern cruise ships have been built with azipods. These sit below the ship, rather like giant outboard motors and can rotate to turn the ship as needed. These take the place of both the traditional propeller and also the rudder. These pods can be huge, and on the Queen Mary 2, they’re each the same weight as a Boeing 747 jetliner!

Other things found below the waterline are intake and outlet pipes for the collection of water, discharge of waste and ballast. If you’re interested in learning more about these things, please let me know.

The final thing you will probably have noticed about the ship below the waterline, is that it’s a different colour to the rest of the ship. Being in the water all the time, ships attract an array of wildlife and marine growth, that over time build up and cause the ship to become less efficient.


Image References:
Henderson & Cremer Collection - Historic P&O Imagery
Luke Morrison ‪@Boeing_Luke‬ - QM2
Vicki Cross - Costa Victoria
USS United States Keel - Public Domain (USA): https://tinyurl.com/0CVA58
Queen Mary Under Construction - Public Domain (UK): https://tinyurl.com/yckx5jvh
Mary Rose Sinking Engraving - Public Domain: https://tinyurl.com/ytb7z4p2
Mary Rose Painting - Public Domain: https://tinyurl.com/maryrose223re
Imperator (Various) - Public Domain / Library of Congress: https://tinyurl.com/4twpycwz ; https://tinyurl.com/4fe6tsh7 ; https://tinyurl.com/3z5dtbee ; https://tinyurl.com/8whjx85f ; https://tinyurl.com/imperator-eagle
Imperator Interior - Public Domain : https://tinyurl.com/2fwvxtpd
Pods No. 1: Public Domain (USA): https://tinyurl.com/36k8ca77
Pods No. 2: A nice view of the azipods of the Mackinaw - Peter Markham - CC BY Attribution 2.0: https://tinyurl.com/ddmbhtjj
Cleaning USS Bonhomme Richard - Public Domain (USA): https://tinyurl.com/yp23snwy
Ponant Blue Room - Ponant: https://tinyurl.com/ponantship

Tags:
#cruiseship #cruisenews #propeller #pods #azipod #qm2 #qe2 #queenmary2 #cruiseline #oceanliner #engineroom #maritimehistory