TRMA Tech Feature of the Month
November 2005

Compass Platform
 

Titanic was constructed with a compass platform on the Boat deck, located amidships between the 2nd and 3rd funnels. Although it seems odd to have a compass located here, away from the bridge, this compass served a purpose somewhat different than the one on the bridge and its position here was determined by certain requirements. The compass on the platform was designed primarily for taking bearings for navigation*. The compass on the bridge was a steering compass: it was designed primarily to be viewed by the helmsman at the wheel. This, along with its position inside the bridge, made it unsuitable for taking accurate bearings. Thus, another compass was needed in a position of superior visibility, and placing one in the center of the boat deck was ideal. Elevating it on a platform out in the open had the benefit of raising it above visual obstructions on deck, and also helped to minimize the magnetic influence of the iron on the ship**.  Being almost amidships, it was found that this was the area of the ship to have the least amount of magnetic interference brought on by the surrounding structures of the hull.  The floor of the compass platform was raised 12 feet above the deck, and the structure was constructed with as little iron as possible to eliminate as much ferrous influence in the immediate vicinity of the compass. A canvas cover was secured over the platform when not in use.

The compass mounted on the platform is listed in Titanic's specifications as a "Kelvin Standard compass with azimuth mirror." The azimuth mirror was a device that allowed an officer to determine the exact bearing of a star, even if it was at some altitude above the horizon. Celestial navigation was highly advanced in 1912 and even today approaches the accuracy of satellite navigation. This compass could also be used to take terrestrial bearings (points on land) with great accuracy.  Also, since this compass was theoretically the most accurate one on the ship (being the most free from magnetic interference from the ship itself), it could also be used to check the accuracy of the steering compass on the bridge. 

For further information on the navigation that would have been done by Titanic's officers, see this fine article by Dave Gittins at
http://users.senet.com.au/~gittins/navigation.html.


*It was not a "backup compass" for steering the ship; there was no telephone link between the compass platform and the bridge, and Titanic was equipped with another compass and a helm at the docking bridge in the event the ship could not be steered from the navigating bridge.

**A compass points north because the magnetized needle - the one that points "North" - is attracted by the faint magnetic pull of the magnetic North pole. However, placing such a compass aboard an iron ship presents problems: the iron of the ship, including the iron of the bridge all around the compass, affects this magnetic pull. For a compass that must be placed inside the ship's structure, there are other ways of compensating for this.



 
Photo courtesy of David Cotgreave

For those building a model of Titanic, the compass platform in the 1:350 Minicraft kit can be replicated with greater detail by using photoeteched brass parts instead of the plastic components from the kit.
 

As a side note: the Kelvin compass is named for Lord Kelvin, who revolutionized the design of the marine compass. Lord Kelvin (born William Thomson) was a professor at Glasgow University in Scotland. He held patents for 70 different inventions, including the Kelvin sounding machine on Titanic. He was made a peer by Queen Victoria in 1892, at which time he chose the title Baron Kelvin.

 

 


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