Cruise Ship Hull Markings - What do They Mean?

We may have seen them before, but chances are they go relatively unnoticed. That is, unnoticed to passengers and casual onlookers. Rest assured, these odd looking marks seen on the side of the ship's hull are not artifacts from the ship's construction, nor are they some joker's attempt at "nautical graffiti." In fact, they have a serious purpose and are required by regulations to be there. These markings - or "hull markings" - assist those people that need to get close to and along side of the ship such as yard workers, dockside workers, tug boat captains and crew members of other vessels  in identifying sensitive areas that require a certain amount of situational awareness so that damage to equipment and injury to personnel can be prevented. They also assist the crew of the ship itself as a way to monitor the ship's trim, among other things. Lastly but certainly not least, they provide a means for inspectors to determine how safe the ship is as it  rides in the water without the need to board her.

Let's take a look at some of these markings as they appear on various ships:

Here is a close up of Norwegian Breakaway's bow. Notice first off, the ship's bulbous bow with the large protrusion forward and partially submerged. The first marking forward is the depth line. This is a vertical column in numbers that shows the distance from the ship's keel to the waterline. Normally these numbers represent feet. Another depth line is located at the stern. By comparing the lines at both bow and stern relative to the waterline the trim of the ship can be determined. Obviously it would be a good idea to keep the ship level!

Aft of the depth line is the bulbous bow indicator. In the picture the bulbous bow is plainly visible. Should the ship be riding low in the water, however, the "bulb" may be difficult to identify. A small vessel such as a tug would certainly damage it (and itself) if it had come too close.

Following the bulbous bow indicator are three fan-like symbols. These are bow thruster indicators. The thrusters themselves are out of view, under water.

"Norwegian Breakaway 13" by Dickelbers - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Norwegian_Breakaway_13.JPG#/media/File:Norwegian_Breakaway_13.JPG

In the following picture, the Holland America cruise ship Zaandam sits in drydock with her bulbous bow, bow thrusters - in this case, two - and bow markings visible.

"Zadm drydock" by S*anner 06n2ey at en.wikipedia - Transferred from en.wikipedia to Commons by User:Sfan00_IMG using CommonsHelper.. Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Zadm_drydock.jpg#/media/File:Zadm_drydock.jpg 

Below is a variation of a depth line, with Roman Numerals instead of numbers. Before the 1970s depth lines were in Roman Numerals exclusively.

 "Berlin A 1411 - Bug (8729330354)" by flightlog - Berlin A 1411 - BugUploaded by High Contrast. Licensed under CC BY 2.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Berlin_A_1411_-_Bug_(8729330354).jpg#/media/File:Berlin_A_1411_-_Bug_(8729330354).jpg

 Along the middle portion of the hull other markings are visible and are no less important as those found at the bow and stern. Shell doors - service access doors and hatches that provide access to service ways for loading and unloading food, cargo, machinery - are protected with markings such as "No Tug" as seen below on a Celebrity ship.

 Joe Mabel [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Stabilizers, wing-like structures that extend below the waterline perpendicular to the hull that can be extended and retracted - aid the ship in stabilizing roll, the side to side movement as the ship moves through the water. The location of the stabilizers are marked by an ore-like symbol, as seen on the Cunarder Queen Victoria, just forward of the funnel.

By Andrew (Queen Victoria From Snowdrop) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons 

The most complex of the hull markings - and arguably the most important - are the load lines, also known as Plimsoll Marks. Located near the middle of the hull, load lines show how far down a ship's draft (the distance between the waterline and the bottom of the hull) can be legally assuming variations such as water density and temperature. Let us imagine for a moment a large container ship sitting in port, being loaded. As containers pile up and weight increases the ship settles further into the water. Should the distance between the waterline and the top of the hull - known as the freeboard - become too small the ship would be in great danger of sinking. Classification societies survey the ships and determine their load lines. The standard reference load line is known as the Summer Load Line. This is depicted as a horizontal line through a circle. Additional lines indicate the limit after water density and temperature are considered. In each instance of the load line, letters associated with them refer to the classification society (on the Summer Load Line) and various load limits in different waters such as for tropical or North Atlantic operation. Below is an example of a load line:

"Plimsoll-mark hg" by Hannes Grobe (talk) - Own work. Licensed under CC BY 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Plimsoll-mark_hg.jpg#/media/File:Plimsoll-mark_hg.jpg

 The Summer Load Line is marked by the classification letters G and L, indicating Germanischer Lloyd. The letters for the associated lines are: TF - Tropical Fresh water; F - Fresh water; T - Tropical seawater; S - Summer temperate seawater; W - Winter temperate seawater; WNA - Winter North Atlantic.

Markings found at the stern of the hull are similar to those found at the bow. However, many modern cruise ships utilize azimuth pods for propulsion instead of the traditional propellers on shafts and a rudder and therefore have no aft thrusters. A ship displaying a fan-like symbol with thruster symbols would indicate traditional propeller with thrusters.