righting arm

English

The center of mass (G), center of buoyancy (B), and metacentre (M) of a tilted vessel; the length of line GZ is the vessel's righting arm.

Noun

righting arm (plural righting arms)

1. (nautical, physics) The horizontal distance between the center of mass of a tilted vessel and the vertical line connecting its center of buoyancy and its metacentre (conventionally taken as positive if the aforementioned line lies on the low side of the center of mass, and negative if the line lies on the high side of the center of mass), measuring the strength of the vessel's tendency (or lack thereof) to return to an upright orientation.
   • 2017 December 12, National Transportation Safety Board, “1.12.10 Postaccident Analysis of Stability, Structures, and Sinking”, in Marine Accident Report: Sinking of US Cargo Vessel SS El Faro, Atlantic Ocean, Northeast of Acklins and Crooked Island, Bahamas, October 1, 2015‎^[1], archived from the original on 15 May 2022, page 156:

     Figure 60 shows the downflooding angles for the downflooding points described above, plus the angle at which the edge of the freeboard deck would have been immersed (about 15°). The downflooding angles are superimposed on two righting arm curves. The upper curve is the righting arm for El Faro in the intact condition on the morning of the sinking, before flooding began and with no wind. The lower curve is the righting arm for the vessel with hold 3 flooded to 20 percent and a sustained 80-knot beam wind. The smaller area under the lower righting arm curve, compared with the area under the upper curve, illustrates the severely reduced energy the vessel had available to right itself after hold 3 flooded and the ship lost power, with hurricane winds on its beam (blowing at a 90° angle to its starboard side).