Four winns 318 VISTA, Owner'S Manual, Page: 57 / 236

Owner’s Manual Page Engines, Drives and Instrumentation - Section E
B. Stern Drive
A.stern.drive.or.inboard/outboard.propulsion.system.
has.a.piston.engine.equipped.with.special.marine.
components.mounted.near.the.transom.and.coupled.
to.an.external.outdrive-type.transmission.unit..Shifting.
is.performed.within.the.outdrive.upper.gear.case...
This.type.of.system.is.depicted.in.Figure.E-1.
Figure E-1: Stern Drive
NOTICE
Always return the engine throttle lever to the
extreme low speed position before shifting.
NEVER shift the unit while engine speed is
above 00 rpm.
E - 4 PROPELLERS
Knowledge.of.the.propeller.is.most.easily.gained.
through.better.understanding.of.the.terminology..
used.to.refer.to.the.aspects.of.propeller.size.and.
performance..It.should.be.noted.that.on.most.318.
Vista
®
.models.include.stainless.steel.propellers.
A. Diameter
Diameter.is.twice.the.distance.from.the.center.of..
the.prop.shaft.to.the.extreme.tip.of.a.propeller.blade..
Increasing.or.decreasing.propeller.size.will.have.a.
direct.bearing.on.the.RPM’s.an.engine.will.develop..
This.is.due.to.the.greater.amount.of.propeller.blade.
surface.in.contact.with.the.water..See.Figure.E-2.
Figure E-2: Propeller Pitch & Diameter
B. Pitch
Pitch.is.a.measure.of.helix.angle,.or.angle.of.attack,..
of.the.rotating.blade..Pitch.is.easily.understood.if.one.
imagines.the.propeller.rotating.through.a.semisolid.
such.as.butter.or.gelatin..The.distance.the.propeller.
will travel in one revolution is called “Pitch.” Increasing
or.decreasing.pitch.will.also.have.a.direct.bearing.on.
engine.RPM’s.because.of.the.greater.bite.taken.by.
the.blade.with.each.rotation..See.Figure.E-2.
C. Prop Slip
When.traveling.through.water.a.propeller.is.unable..
to get a complete bite because of the fluidity of water.
“Prop slip” is usually expressed as a percent of the
computed theoretical speed. Twenty-five to thirty-five
percent.prop.slip.is.common.for.a.cruiser-type.boat.
operating.at.cruising.speed.
Changing.either.diameter.or.pitch.will.have.an.effect.
on.engine.speed.and.prop.slip,.and.in.turn,.directly.
effect.the.performance.of.a.boat..The.propellers.
included.with.each.Four.Winns
®
.boat.provide.the.best.
general.performance.based.on.data.obtained.from.
on-the-water.testing.of.that.model..Variations.in.load,.
operating.conditions,.environment,.the.individual.
engine.and.hull.performance.may.necessitate.the.
purchase.and.use.of.another.propeller(s).