Conditions Affecting Operation; Weight Distribution; Bottom Of Boat; Cavitation - Mercury D4.2L Manual

Hide thumbs Also See for D4.2L:

Service manual (878 pages)

Table Of Contents

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

Table of Contents

CA7

Weight Distribution

Positioning of weight (passengers and gear) inside the boat has the following effects:

A. Shifting weight to rear (stern) will:

•

Generally increases speed and engine RPM.

•

At extremes, can cause boat to porpoise.

•

Causes bow to bounce in choppy water.

•

Increases danger of following wave splashing into boat when coming off plane.

B. Shifting weight to front (bow) will:

•

Improve ease of planing on some boats.

•

Improve rough water ride.

•

At extremes, can cause boat to veer back and forth (bow steer).

CA8

Bottom Of Boat

To maintain maximum speed, the following conditions of the boat bottom should be observed.

A. Clean, free of barnacles and marine growth.

B. Free of distortion; nearly flat where it contacts the water.

C. Straight and smooth, fore and aft.

Marine vegetation may accumulate when boat is docked. This growth must be removed before operation; it may

clog water inlets and cause engine to overheat.

CA9

Cavitation

Cavitation occurs when water flow cannot follow the contour of a fast-moving underwater object, such as a gear

housing or propeller. Cavitation permits the propeller to speed up, but the boat speed to reduce. Cavitation can

seriously erode the surface of the gear housing or propeller. Common causes of cavitation are:

A. Weeds or other debris snagged on propeller or gear housing.

B. Bent propeller blade or damaged gear housing skew.

C. Raised burrs or sharp edges on propeller or gear housing.

CA10

Ventilation

Ventilation is caused by surface air or exhaust gases which are introduced around the propeller resulting in pro-

peller speedup and a reduction in boat speed. Excessive ventilation is annoying and usually caused by:

A. Drive unit trimmed out too far.

B. A missing propeller diffuser ring.

C. A damaged propeller or gear housing, which allows exhaust gases to escape between propeller and gear

housing.

D. Drive unit installed too high on transom.