An Allision With An Iceberg
|Although most often it has been referred to as a collision, when Titanic struck an iceberg on the night of April 14, 1912, the event was technically anallision. A collision is what occurs when contact is made between two vessels that are in motion; while an allision ocurrs when a moving vessel strikes a stationary object. Although the iceberg was drifting with the local current, it was stationary relative to the body of water it was floating on.|
The following animation depicts how Titanic’s underwater allision with the iceberg may have taken place. The view is from ahead looking aft. The ship is represented by a set of H&W body plans for Olympic and Titanic. The iceberg, shown in gray in the sequence, is assumed to have an underwater shelf that was struck by the ship as it tried to clear the visible portion of the berg along its starboard side. The waterline is marked by the dark blue horizontal line. The 9 second sequence starts at t=0 when the stem of the ship is in line with the leading edge of the ice shelf. The sequence advances in 36 foot increments, or about 1 second intervals between frames.
Initial contact with the ice would be against the forward end of Titanic’s reinforced bow where the framing and plating was specially strengthened to prevent panting and damage when meeting thin harbour ice. In the first few frames you can see how the bow would tend to cut through the underwater ice as the ship continued to move forward. As the ship advanced, the contact would extend over a greater area along the starboard side and bottom producing both heave and sway force components acting on the vessel as it crushed the ice, as well as a small surge force component directed aft tending to slow the vessel down. The slight heel taken by the ship over to port can be seen as the forward advance continues. This heel was noted by the two lookouts up in crow’s nest when the ship struck. Not only would the ship be damaged by the contact, but the ice would be damaged as well. Most of the known damage to Titanicwould have occurred in the first 6 to 7 seconds. After that, some contact with the ice probably remained possibly producing some small areas of unseen damage (see Where Did That Water Come From?) and allowing ice to be deposited onto some of the ship’s starboard ports as was reported by several passengers. But side pressure against the hull would have been very light once the bow widened out to the full breadth of the ship where it would be moving approximately parallel with the side of the iceberg. We also know that the helm was shifted over hard to port (putting the rudder full over to the right) at some point after the berg had passed astern of the forebridge. This would tend to pull the stern of the ship away from the iceberg as it went aft. We know that the side of the vissible part of the berg came very close tp the aft docking bridge as it went by, and was seen off the ship's starboard quarter before it disappeared from sight by several eyewitnesses.