On 1 Mar 2005 01:24:24 -0800, "Dan"
wrote:

AFAIK the horizon is 22 odd miles away. A ship moving at 22kts would
therefore take about an hour to get to you.

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That's way optimistic, even for a good radar. Good sized boats
disappear from view on my flybridge at around 8 miles, small boats at
2 to 4 miles.