Trying to find exact terminological definitions is not easy. Just as distances to the horizon differ based on observer height, the ability to see the shore is affected by, say, the height of a boat. The inshore lifeboat may still be able to see the shoreline that the panicking 'offshore' surfer in distress can't. Some old texts tried to set a mileage; up to six miles, inshore, up to 12, offshore, over that, at sea.
Nowadays clarity over choosing your correct emergency flare has shortened the distances.
Inshore- up to three miles is the guideline for having a reasonable hope someone on the beach (at sea level) should be able to see a red hand flare or an orange hand smoke flare burning on a boat.
Offshore- over seven miles from shore. A boat will normally be over the visible horizon. In these circumstances a rocket flare that projects up to 350 metres is the only distress flare that could attract attention from over the horizon.
Which throws in another zone that includes inshore, the coastal zone- up to seven miles from shore.This is the distance of the visible horizon on a reasonable day with reasonable visibility. A hand flare being used on a boat between 3 and 7 miles from shore *may* not be visible to a person stood on the beach due to the curve of the earth and the sea conditions. In the coastal zone a combination of hand flares and rocket flares normally increases the chances of being seen.
All of which again helps to muddy the waters for believing a bird to be 'in-off'; cutting between (to them) visible distant headlands may well just be a coasting movement rather than a crossing.
Inshore/offshore fishing? That allegedly has a different measure, a water depth division- 30 metres. How easy is that for us to judge? Not easy at all. 'Sea-ducks' can do it.
'Seawatching', the standard laybirder's name for watching coastal waters, can be a bit of a pedantic misnomer, especially around our shallow Kent coast. Never going to get replaced of course, but it really is worth some birders considering their seawatch totals more as coastal movements. Helping to answer birder murmurations as to why we never get the same seabirds as other coastlines.
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I've been told not all comments are publishing. There seems to be a problem between Blogger and Chrome, and I'm being told if you have a problem you should try a different search engine.
All a pain in the proverbial. Sorry! I'm a luddite/technophobe (still won't even have a mobile phone) so much else is beyond me..
If still doesn't work, pls send me a DM/post to my twitter a/c @dunnokev to let me know- thanks! Kev 18/12/21