210 seamanship secrets
Twin-Screw Boat-Handling Secrets
Twin-engine boats (or “twin screws”) have the advantage of a second engine to
off set the eff ects of prop walk. Another advantage is that if you lose one engine,
you can still limp home on the other. Here are a few points to remember before
you take the helm of a twin-screw vessel.
Propeller rotation = no prop walk. Most twin-screw boats carry a right-
handed screw on the starboard side and a left -handed screw on the port
side. If you could stand astern and place both engines into forward gear,
you would see both props rotate outboard. With the wheel amidships and
both engines in forward gear, the boat will go in a straight line (assuming no
wind or current). Put both engines into reverse gear, and the screws rotate
inboard. If you place the wheel amidships, the boat will back in a straight
line (again, assuming no wind or current). Th is is because twin-screw boats
have no net prop walk.
Center your wheel. Inside tight maneuvering areas, learn to handle your
twin-screw boat without any rudder. In the boat-handling scenarios in this
chapter, keep your wheel amidships, unless otherwise specifi ed.
Inboard engine vs. outboard engine. On a twin-screw boat, the inboard engine
is that engine on the inside, or closest to the pier, piling, or seawall. Th e
outboard engine is the one on the outside, or farthest away from the pier or
piling. Th is relationship holds no matter which side you dock or undock on.
Your boat is docked port-side to the pier. You are ready to leave and want to pivot
to clear the stern. How do you do this? Go forward on the outboard engine and
reverse on the inboard engine. Both propellers will work in concert to walk the
stern to starboard, away from the pier. You can then back clear of your berth.
Next, let’s try a scenario without reference to a specific side. You approach
a pier at a slight angle. You get your bow up to the pier and need to get your
stern in. How would you do this? Go ahead on the inboard engine and reverse
on the outboard engine. Regardless of whether your approach is starboard side
or port side to, prop walk will pull the stern to the pier.
MASTERING YOUR BOAT’S HANDLING
CHARACTERISTICS
Find a wide-open area to practice these maneuvers.
Straight-line maneuvering. Use only forward or neutral gear. Keep the wheel
amidships. Pick a fi xed object to aim for (such as a pier or buoy). Place both
engines in forward gear and get her moving ahead. If she wanders, put one
engine in neutral for a second or two. To push the bow to the right, use just
the port engine; to push the bow to the left , use just the starboard engine.