Boating and Sailing.pdf - Moja ladja

Tab
Propeller
Let’s run through the parts of the lower unit of an outboard:
Chapter 2: Power to the People—Marine Engines
Anti-ventilation plate
Cooling water pick-up
Lubricant fill hole
Skeg
Bullet or nosecone
◆ Tab. The tab offsets the tendency of a prop to “walk” sideways slightly at some trim
positions and balances the steering force. (Not to be confused with “trim tabs” that
control running trim, usually found on larger boats with inboard power.)
◆ Bullet or nosecone. The bullet or nosecone
houses the forward and reverse gears and prop
shaft.
Boater-ese
◆ Propeller. The propeller grips the water and
propels the boat by pushing water backward.
Three-bladed props are most common.
◆ Skeg. The lowest extension of the lower unit,
the skeg protects the prop from striking obstructions
and also helps the boat track straight.
◆ Lubricant fill hole. The lower unit is full of oil
to provide lubrication. This hole allows draining
and refilling.
◆ Anti-ventilation plate. This flat plate helps
prevent the prop from drawing in surface air and
losing its grip on the water. It is often called the
“cavitation plate,” a usage that is technically
incorrect but common enough to be widely
understood.
◆ Cooling water pick-up. This small intake
allows the water pump to pull water through the
lower unit and up into the cooling passages of
the powerhead. It must be kept free of debris at
all times.
Tabs on outboards and stern drives are usually made of zinc, which acts as a “sacrificial anode”
in salt water. The “sacrifice” it makes is to literally be eaten up by galvanic corrosion
23
The lower unit of an outboard
and a stern drive are
nearly identical. This section
couples the power put out by
the engine to the prop, which
causes the boat to move
through the water.
Power trim is an electrical
and hydraulic system for moving
the lower unit of an outboard
or stern drive in or out relative to
the transom. Trim is used for
minor adjustments while underway
to help improve the running
attitude of the boat. Power tilt is
part of the trim system. It allows
the motor to be tilted to almost
90 degrees while at the dock or
on a trailer.
Boater-ese
The powerhead is the
combustion chamber, ports, and
cylinders where power is made
by burning fuel.