dalan zartman crs, ff ii, fi ii, emtp rescue methods 2014 ©
TRANSCRIPT
Outboard MotorsThe outboard motor
selection must begin with the required hp to effectively operate in the prescribed environment with the designated payload.
This is typically driven by the boat manufacturer based on load capacity, application, and boat design.
2 Stroke Enhanced
performance power to weight ratio
SimplisticAcceleration and
TorqueEmission
equivalent to 4 Stroke technology
Fuel economy comparable to 4 stroke technology
4 Stroke More ComplexCleaner
emissions in most cases
QuieterGreater fuel
economy in most cases
Decreased power to weight ratio
Jet drives vs Prop drivesJet Drives
FastShallowResilientInefficientRequire
propulsion to steer
Prop DrivesSlowerEasily
damaged in shallow water
EfficientCan steer
without propulsion due to rudder control
ConclusionTypically speaking, 2
stroke outboard motors with prop drives are optimal for swift water applications due to their weight to power ratio resulting in greater acceleration and reactive maneuverability in all water conditions.
4 BladesGreater torqueSlower tope end
speedGreater
acceleration and maneuverability in all water conditions
Material and design impact performance
DiameterDistance from tip to
tipThe greater the
blade, the greater the water displacement and thrust
The greater the blade, the greater the demand for torque and hp
PitchPitch results in the
theoretical distance traveled per revolution
Low pitch equals fast acceleration but lower top end speed
High pitch equals slow acceleration but greater top end speed
RakeRake impacts the
bow of the craft and its ability to plane out and reduce drag
Increased rake brings the bow up but may result in instability
Decreased rake brings the bow down but may result in increased drag
CupCup maximizes
the efficiency of the blades ability to “grab” the water.
Reduces ventilation and slipping
Increases RakeIncreases Pitch
Trouble ShootingVentilation (often confused with
cavitation) is the result of air pockets which make a prop lose its thrust. This manifests as free climbing RPM’s without gaining speed.
Typically caused by lack of power, high transom mountings, extreme trim, or sharp turns.
Corrective actions:Anti ventilation plate orientationProp Configuration – Increase CupIncrease hp
Trouble ShootingCavitation occurs when a
combination of decreased pressure and increased temperature cause gas bubbles to form which in theory “boil” and vaporize or implode causing pitting and scorching to the prop.
Typically caused by flaws or imperfections and damage to the lower unit or anti cavitation plane. Can also be caused by continuous or excessive ventilation.
Corrective Action: Eliminate ventilation problem Insure lower unit is undamaged
Trouble ShootingInability to plane out will
typically occur when the boat is underpowered, overloaded, or trimmed out inappropriately.
Corrective Actions:Insure weight and load
to power ratio is correctAdjust trimProp Configuration –
Increase Rake