Regal 3300 Owner's Manual page 145

Vessel Operation
Gathering Headway
As opposed to a boat with a single propeller, when a twin powered
vessel's engines are put in gear together, the vessel will make headway
without the tendency to pull to the port or starboard. Of course the
throttles must be in the same rpm range as read on the tachometers.
This factor is very basic to this type of vessel having superior handling
and control in tight spaces along with being able to handle wind and
current much more adequately than single screw stern drive boats.
Turning
When maneuvering twin powered boats at slow speeds the steering
wheel is not normally used; the skipper uses the shift and throttle
handles to control the vessels actions.
A vessel's stern may be pushed to one side or the other by moving
ahead or reversing with just one propeller. A bit of headway or sternway
does accompany the turning motion. You can gain the most turning
effect by energizing one drive in forward and the other drive in reverse.
One advantage of twin powered boats becomes evident when you can
turn the vessel in a circle just larger than the vessel itself. As an example,
to turn to starboard, the wheel can be centered, while the port engine
moves forward and the starboard engine reverses.
Begin this type of turn with the engines at idle or in gear at the same
rpm (revolutions per minute). For a starboard turn, insert the port
shifter in forward and the starboard shifter in reverse. When the vessel
starts to turn, it may begin to make headway. This relates to the boat and
propeller design. As a result, you may have to advance the port throttle
somewhat to increase the rpm of the reversing starboard propeller.
When the port engine speed is increased somewhat, the circle is bigger
and the vessel makes headway. If the port engine speed is decreased,
the circle becomes larger, but the vessel goes sternway as the reversing
starboard propeller pulls it around, stern to port.
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