Engine MaintenanceEngine Maintenance

Chapter 6Chapter 6

Inboard Drive SystemsInboard Drive Systems

22

Objectives for the StudentObjectives for the Student

1.Have an understanding of the various drive systems associated with inboard marine engines

2.Have knowledge of the design of marine propellers and how the various configurations affect the boat’s performance

3.Have basic knowledge of how to perform routine maintenance of inboard drive systems

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Reduction GearingReduction Gearing

Optimizes engine speed and Optimizes engine speed and propeller speedpropeller speed

Typically 1.5:1, 1.9:1, 2.1:1, etc.Typically 1.5:1, 1.9:1, 2.1:1, etc.

ExampleExample 2.1:1 means engine is running at 2.1:1 means engine is running at

2,100 rpm while propeller is turning at 2,100 rpm while propeller is turning at 1,000 rpm1,000 rpm

Lower speed means higher torqueLower speed means higher torque

44

Straight Drive TrainStraight Drive Train

The entire drive system is angled The entire drive system is angled to pass through the hullto pass through the hull

55

Angled Drive TrainAngled Drive Train

Output shaft is offset 8-12 Output shaft is offset 8-12 degreesdegrees

66

Vee DriveVee Drive

Permits engine to be placed Permits engine to be placed further aft in hullfurther aft in hull

77

Inboard Performance Inboard Performance SystemSystem

88

PropellersPropellers BladesBlades

number of blades generally increases with number of blades generally increases with power requirementspower requirements

DiameterDiameter outside edge to outside edge across centeroutside edge to outside edge across center larger diameters need more torque to drive larger diameters need more torque to drive

themthem PitchPitch

distance of advance for one revolutiondistance of advance for one revolution Other characteristicsOther characteristics

shape, cupping, rakeshape, cupping, rake

99

Propeller PerformancePropeller Performance

Boat speed and engine speed Boat speed and engine speed are keyare key Optimize both!Optimize both!

Best speed is the rated boat Best speed is the rated boat speed at wide open throttlespeed at wide open throttle

1010

Jet DriveJet Drive

Flush mounted for shallow Flush mounted for shallow water operationwater operation

1111

Specialty Drive SystemsSpecialty Drive Systems

Trolling motors are electric Trolling motors are electric motors used for low speed motors used for low speed applicationapplication

Bow and stern thrusters are Bow and stern thrusters are used for close-in maneuveringused for close-in maneuvering

1212

Routine MaintenanceRoutine Maintenance

Oil levelOil level Transmission fluid levelTransmission fluid level Impeller pumpImpeller pump Transmission oil cooler (may clog Transmission oil cooler (may clog

with impeller bits)with impeller bits) Water intake strainerWater intake strainer Hoses and clampsHoses and clamps

1313

Vee Drive MaintenanceVee Drive Maintenance

Same as standard inboard, plus…Same as standard inboard, plus… Keep an eye on the transmissionKeep an eye on the transmission

1414

Propeller MaintenancePropeller Maintenance

Inspect for chips, nicks, dents, Inspect for chips, nicks, dents, etc.etc.

Check for cavitation damage Check for cavitation damage (small pits)(small pits)

1515

Jet Drive MaintenanceJet Drive Maintenance

Same as standard inboard, Same as standard inboard, plus…plus…

Special manufacturer’s Special manufacturer’s requirements for the drive unitrequirements for the drive unit

1616

Winter StorageWinter Storage

Prevent freezingPrevent freezing Haul outHaul out Run potable antifreeze through raw Run potable antifreeze through raw

water systemwater system Warm the engine, then change the Warm the engine, then change the

oiloil Maintain transmission fluidMaintain transmission fluid If hauled out, disconnect the drive If hauled out, disconnect the drive

shaft couplingshaft coupling

1717

Spring ServiceSpring Service

Check stuffing boxCheck stuffing box If hauled over the winter:If hauled over the winter:

Allow the boat to sit in the water for Allow the boat to sit in the water for five daysfive days

Reconnect drive shaft coupling and Reconnect drive shaft coupling and check alignmentcheck alignment

Replace raw water impellerReplace raw water impeller Check stuffing box againCheck stuffing box again

1818

Remember…Remember…

You should be able to You should be able to identify problems and identify problems and explain them to a mechanicexplain them to a mechanic