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Almanac

Marinas

Events

SailingAlamancwhite1a1 Dipping Lights Navigation Menu

Lighthouses are indicated on a chart with the height of the centre of the light (in metres) above MWHS. Be mindful though that both the lighthouses below are 40m high, but the yacht on the right might be expecting to see a tall tower from the lighthouse on the left.

Lthoheight1

All lighthouses are given a nominal range (in miles) in ideal conditions, but of course weather, pollution and haze etc will often than not reduce this range. In addition to this, the curvature of the earth and the height of the viewer above the earth's surface can influence this range. Below we can see that the lighthouse is blind to the yacht whose view point is almost at sea level, but the bridge of the ship next to the yacht can see the light because the view point is much higher. We can see therefore, that at the point where the light just sits on the horizon, we can tabulate a relationship between the height of the light and the height of the viewer's eye to work out the viewers distance from the light - this is referred to as the dipping distance.

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When dipping a light, try not to get confused with the light's loom, (as shown on the left) which has a wider span across the horizon and can be seen at a much greater range, where as the real light will be a sharply focused light just above the horizon (as shown on the right).

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DISTANCE FROM DIPPING LIGHTS
IN NAUTICAL MILES

Height of eye in feet

Height of light in metres

6

7

8

9

10

20

2

57

60

62

64

66

81

3

64

66

68

70

72

87

4

69

72

74

76

78

93

5

74

77

79

81

83

98

6

79

81

83

85

87

102

7

83

85

87

89

91

106

8

87

89

91

93

95

110

9

90

92

95

97

98

113

10

94

96

98

100

102

117

11

97

99

101

103

105

120

12

100

102

104

106

108

123

13

103

105

107

109

111

126

14

106

108

110

112

114

129

15

108

111

113

115

116

131

16

111

113

115

117

119

134

17

113

116

118

120

122

137

18

116

118

120

122

124

139

19

118

121

123

125

127

142

20

121

123

125

127

129

144

21

132

134

136

138

140

155

22

141

144

146

148

150

165

23

159

161

163

165

167

182

24

174

177

179

181

183

198

25

188

191

193

195

197

212