oscillations of increasing magnitude are commonly associated with the free surface effect, they are not a necessary condition. For example, in the cases of both the and , gradual buildup of water from fire-fighting caused capsizing in a single continuous roll. Mitigation To mitigate this hazard, cargo vessels use multiple smaller bulk compartments or liquid tanks, instead of fewer larger ones, and possibly baffles within bulk compartments or liquid tanks to minimize the free surface effects on the craft as a whole. Keeping individual bulk compartments or liquid tanks either relatively empty or full is another way to minimize the effect and its attendant problems. Hydraulic tankers use water to displace lighter oil to keep the tank full at all times. Tanks or compartments that do not straddle the vessel's centerline are somewhat less prone to destabilising oscillations. Similarly, narrow compartments (aligned bow to stern) and compartments at the extremes away from the centerline are less prone to cause instability. Historical examples Flooding, liquid cargo leakage, or unintended water (from precipitation, waves, or hull damage) in any compartments or on any decks of watercraft, and the resulting free surface effect are often a contributing cause of accidents, capsizes, and casualties e.g. the loss of (Wellington, New Zealand, April 1968), (Zeebrugge, Belgium, March 1987), and (Baltic Sea, September 1994). In the case of the RORO ferry al-Salam Boccaccio 98 (Red Sea, February 2006), improper fire-fighting procedures caused flooding leading directly to instability and capsize. In both the cases of the al-Salam Boccaccio 98 and , severe listing followed immediately after the ship had undergone a hard turn, causing unstable volumes of water (from collision damage in the latter) to surge from one side of the ship to the other. Effects on land and aircraft The free surface effect can affect any kind of craft, including watercraft (where it is most common), bulk cargo or liquid tanker semi-trailers and trucks (causing either jackknifing or roll-overs), and aircraft (especially fire-fighting water-droppers and refueling tankers where baffles mitigate but do not eliminate the effects). The term "free surface effect" implies a liquid under the influence of gravity. Slosh dynamics is the overarching field which covers both free surface effects and situations such as space vehicles, where gravity is inconsequential but inertia and momentum interact with complex fluid mechanics to cause vehicle instability. See also Metacentric height Slosh dynamics References External links Discussion of the