[RI Swamp Yankee]

With all the comments about "safe speed" I came accross this on boat-ed.com which sounds almost exactly like what I learned in a USCG boating course I took many years ago.

Safe Speed

A safe speed is a speed less than the maximum at which the operator can take proper and effective action to avoid collision and stop within a distance appropriate to the prevailing circumstances and conditions.

In establishing a safe operating speed, the operator must take into account visibility; traffic density; ability to maneuver the vessel (stopping distance and turning ability); background light at night; proximity of navigational hazards; draft of the vessel; limitations of radar equipment; and the state of wind, sea, and current.