500 metres
They have standby vessels - more than likely field standby vessels these days - covering a number of platforms. These are tasked to keep other vessels clear, plus manned platforms have radars if situated close to deep water routes etc.
You should not have any need to go closer than this exclusion zone.
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No a genuine question...done lots off west coast of Scotland but pretty sparse on oil riggs!!!! never crossed North Sea yet though and highly infected with the damm things.
We sailed too close to a rig at night a few years ago. Black uniformed guards armed to the teeth in a black RIB buzzed us then boarded us. We managed to convince them we were not IRA (this was well before 9/11). But they theatened to report us to the MCA for prosecution. In th end we heard nothing more but it was bloody fightening at the time.
Better to keep well clear; the vessels around a rig or platform may be undertaking maneovres which you are not aware of, such as running anchors or snatching cargo, and they may be restricted in their ability to manouevre. Around big platforms the wind may fluke unexpectedly and there is always a tide to think about.
One thing to be sure of, in the present day climate since 9/11, is that there is a good chance you are been monitored from afar.
On the other hand they make good way points (500m offset in case of asleep on watch with autohelm engaged!)
stay at least 500 metres away from us, you will see "U" being flashed all the time, "you are standing into danger", if you get too close, you will be hailed and told to go away. Have your VHF on channnel 16 and do as you are told. otherwise you will some hairy arsed roughnecks feeling yer' collar. A standby boat may also buzz you, basically stay away, we smell awful anyway.
I resemble that remarks about looks and smells!!!!
We have been working just off Israel on and off since mid 1999 and if you think 500 metres is a long way then think again. We were 6 miles off the coast and our own supply boats used a harbour about 10 miles from us. Before they left port they had to get clearance from Israeli Navy to leave port and then were tracked all the way to us. They then had to report in to them when coming within 1 mile.
Italy was different cos the wee boats used to come out and circle the rig at the weekends - the wee boats with their young ladies with even weer bikinis. It was a good summer that year and we did not try to enforce the exclusion zone.