Saturday, 10 October 2015

CRUISE SHIPS AND TOP HEAVINESS.

The Mercury, Tuesday 19 April, 1910
William Henry Pearson Baker, an ableseaman, residing at Sydney, said he wasa seaman on the Waratah during a voy-age commencing from London on April27, 1909. The vessel had a list to port orstarboard at intervals throughout thevoyage. Sometimes she appeared to be onon even keel, and she rolled more to leeward than to windward. At the end ofthe roll she seemed to hang, the stoppagebeing very much like that of a sailingship under full sail. On the return rollshe would hardly go to windward at all.She seemed to be very slow in recoveringherself from leeward, and it appearedsometimes as if she would remain in thatposition.
If the triple deck superstructure did have an effect (sail area), it seems that this was to catch the wind and hold the Waratah in a list to leeward, lower side. Does this imply that the Waratah was top heavy and unstable? I don't think so, it merely reflects a response to a force. It also explains the slow recovery.
Captain Ilbery had this to say about the Waratah's heeling characteristics:
"Yes, she is a little that way, but you must remember there are many thousands of tons of dead weight to shift. When this once gets in motion, it takes some power to stop it, and, when stopped, it also takes a considerable force to start in the opposite direction."
Captain Ilbery was in effect describing a significantly loaded vessel, not a top heavy one. The following description of cruise ships lends some insight into the issue of top heaviness:
.....considerably increased the overall height of the ships, making them more susceptible to side wind and waves. As a result, there have been concerns about the stability of modern passenger ships especially in heavy weather. Because there is much more ship above the surface than beneath it, modern cruise ships may appear top-heavy to some.
Despite the large superstructure, the center of mass of modern cruise ships is relatively low. This is due to large open spaces and the extensive use of aluminium, high-strength steel and other lightweight materials in the upper parts, and the fact that the heaviest components — engines, propellers, fuel tanks and such — are located in the lower parts of the ship. Thus, even though modern cruise ships may appear top-heavy, proper weight distribution ensures they are not. (wikipedia)
Appearances could be deceiving and in the case of the Waratah an impression of top heaviness was to become synonymous with the ship that disappeared without a trace.




This interesting article also gives food for thought:

http://www.gard.no/web/updates/content/53245/ships-stability-a-cautionary-tale

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