This may mean that it is prudent to proceed at less than full speed, some times a difficult decision on a sailing boat!
Part (a) (iv) of this rule, reminds us that when approaching well lit areas, it may be difficult to pick out unlit or poorly lit vessels and objects such as large mooring buoys. It is also very difficult to see past the backscatter of lights on the bow of a vessel in conditions of high humidity, the navigation lights tend to produce a diffuse glow of light which is impossible to see through.
Part (b) of this rule, implies that if you are using radar you should be familiar with its operation and limitations. It is probably a good idea to become familiar with its use before it is really needed.
Part (b) (iv) of this rule, reminds us that by comparing what can be seen visually, with the ranges from radar, a good indication of visibility can sometimes be obtained.
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