Rate - The cost, or revenue, for a particular voyage based on a standard of reference, e.g. Worldscale, INTASCALE, ATRS.

Reducer - A short section of pipe, having one end of smaller diameter than the other and having a flange on each end, for connecting a smaller hose or pipe to a pipe of constant diameter.

Registry - A duty imposed on shipowners in order to secure to their vessels the privileges of ships of the nation to which they belong.

Re-Positioning - The movement of a vessel in ballast to shift it from one trading pattern to another.

Restricted Measurement System - A measurement system designed to measure the ship's cargo when its tanks are closed to the atmosphere. During measurements a minimum amount of cargo vapors might escape to the atmosphere.

Relative Density - See DENSITY

ROB (Remain on Board) - The material remaining in vessel tanks, void spaces, and/or pipelines after discharge. Remaining on board quantity includes water, oil, slops, oil residue, oil/water emulsions, sludge, and sediment.

Rogue Wave - An ocean wave much larger than the current wave sequence. This wave may also be outside the current wave direction and may be 100 feet or more in height.

Route - See Deep Water Route, Traffic Route, Two-Way-Route. Means whichever type is appropriate in the context unless otherwise specified.

Routing - A complex of measures concerning routes aimed at reducing the risk of casualties; it includes traffic separation schemes, two-way routes, tracks, areas to be avoided, inshore traffic zones, and deep water routes.

Rudder - The flat or shaped frame hung to the sternpost of a ship, which is used to steer the ship.

Rules of the Road - The rules and regulations accepted by international agreement and enforced by law in marine countries which govern the movements of ships when approaching each other under such circumstances that a collision may possibly ensue.