RE: Combined shift and throttle levers?
Like flying a plane, it's not at all complicated to do, but it can be difficult at first for a person to visualize WHAT to do. So the twist-your-butt, drive-the-bulldozer, visualize-parentheses analogies are easy ways to convey to an inexperienced boater what to do with the shifters to maneuver a twin-engine boat around.
You only have two choices in a single engine boat--- forward or backward. You have to know about propwalk and you have to know about rudder function and effectiveness but there's nothing fancy you can do with the shifter.
The butt-bulldozer-parentheses analogies work for a three-engine boat. I don't know what the skippers of triple engine boats today do but the skippers of PT boats in WWII usually had the motor mac in the engine room leave the center engine in neutral or shut it down altogether and they'd do all their close-in maneuvering on the two wing engines only. The drawback there was that the three props on a PT boat all turned the same way and the rudders were so tiny they were all but useless at low or no speed, so the boats didn't have nearly the maneuverability you get with a pair of counter-rotating props.
-- Edited by Marin at 19:53, 2008-07-29