Join Date: Aug 2002
Location: Gloucester, Mass. USA
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Backing and Filling
“Backing and filling” is where you uses the “side thrust” of the propeller to “pivot” the boat into a position, such as when aligning the boat to back into a slip. Done properly, the boat can be walked right around in a circle almost within its own length. While it requires a strong pull from the motor, it’s not a slam emergency thrust that risks pushing everything to the braking point. As with everything, practice makes perfect.
To understand the maneuver, you need to understand that water is more dense deeper down. This means that the lower propeller blade has more “bite” on the water then the upper blade(s) hence, a clockwise turning prop will try to “walk” to the right. On outboard motors, the walking tendency is offset by setting up a zinc tailstock aft of the prop, slightly turned to counterbalance the action. This means that a rudder in the prop’s wash can check and over-ride the action.
Let’s say that our boat has a “right hand” wheel, or one that turns clockwise as the boat is going forward when viewed from astern. With the boat at a stop, cut the rudder well to starboard and keep it there throughout the maneuver.
To “fill”, shift the gear into forward and give it some throttle. The prop’s tendency to walk the stern to starboard will be offset by it’s wash past the rudder and it will actually push the stern to port. Now, just as the thrust is starting to overcome the boat’s inertia or just before she starts to make headway, throttle down and take her out of gear.
To “back”, put the gear in reverse and throttle up. The prop now spinning counterclockwise will check any forward motion and walk the stern again, to port. As she starts to make way astern, throttle down and take her out of gear. Repeat as necessary.