Units of measurement & Posh cars.

[Matthew_]

Andrew,
To answer your question, nautical miles are variable because they are measured by one minute of latitude and latitude is variable according to where you are in the world: by definition. So one minute of latitude at the equator is different to one minute in the UK or indeed, from Truro to Stornaway. You can standardise by using one minute measured at the equator, but for navigation purposes, we always use the latitude scale where we are. I know what you are going to say now, because you will be thinking: does this mean that 10 kts is faster in Egypt than it is in Eccelston? The answer is no because you are still moving at the same speed over the ground.
If you are battling against a heavy sea, you are just going slower. If you are doing 6 kts on the North coast of Scotland where there are 10 kt tides, you are either doing 16kts or 4kts backwards or something in between, depending on the resultant vector.
Divers are mostly mad as opposed to brave. Its one of those jobs, (I am a mine clearance diver) that everybody thinks must be very dangerous but its not dangerous when you are properly trainied and equipped. There are risks but at the end of the day, I still more likely tobe hurt in a RTA than blown up or drowned

[Andrew MacLean]

Okay, so do you measure Nautical Miles according to the "minute of latitude" even if you are sailing north - south?

I have a cousin (actually it the son of my cousin) who used to dive in the North Sea. He now runs a yacht in the Red Sea where he charges wealthy tourists more than they can afford to spend time doing chores on his yacht and "swimming with sharks". I think the Red Sea is famous for having rather aggressive sharks, so he employs local divers to put themselves between the paying guests and harm's way.

As you can guess I have no idea about navigation at sea, although I do always know which way is North. this makes it far easier not to get lost on land.

Andrew

[Matthew_]

Hmmm, till you run out of land that is and lets face it: there's a lot more land south of us than there is to the north.
I've been up as far as you can go and its very cold!

Latitude anyway is measured the same in both directions as the earth curves roughly at the same rate in both directions. (That's not true actually but close enough -another assumption / fudge).
Red Sea is full of sharks as you say but I wouldn't say aggresive, particularly. Sharks get very bad press as far as this is concerned,lots of myths surround them. I would be more worried about trigger fish. Out of 350 species of shark, only 7 are known man eaters. There must be Aussie opinion on this. I wouldn't mind betting they have some super sharks! In the Red Sea there are Hammer Heads which have been known to be a bit aggresive. Mostly though its Reef Sharks, which are territorial but not normally dangerous.
Your friend has the right idea I think, sat diving in the north sea for lots of money or diving in the red sea for lots of money, tricky decision?

[Andrew MacLean]

What ever you do, please do not tell my cousin's clients that the sharks in the Red Sea are not aggressive. I think he charges them extra on the pretext that they are.

My ability to know which way is North seems to work in all circumstances, at sea, in the southern hemisphere, on all continents and in cloudy conditions. I can just orientate myself to the North and work out from that which way is South, East, West, etc. When walking in the hills (and running, but I don't do that anymore because I am old) I found it more useful to know which way was North than to know which way was up or down You can run out of path if all you know is which way is down.

My son has the same sense of North, although he always carries a compass in order to check his orientation against Magnetic North. My wife and daughter have no sense of direction at all.

Andrew

[Matthew_]

My wife has reverse orientation. Whenever she goes anywhere on foot, she always goes exactly the wrong way. If was just going in a random direction, then she would go the right way at least some of the time. Yet, she is brilliant at navigating in the car.
As far as walking in the hills goes, I usually go with friends from work who are much better than me at that. One in particular is a Royal Marine, so we leave the map reading to him! The weakness in this plan was when he fell and split his head open in the Mamores, then we had a casualty and an orienteering task together! Fortunately, he was OK and we got him stitched up at Fort William. The good news was that with Marines, you don't need anaethesia! Well OK, you do really.
As far as sharks are concerned, I am sure if cousin's clients are diving in the Red Sea, they are getting the real deal and don't need to worry about the authenticity of the experience! The sharks are plentiful and swimming with them is an awesome experience whether they actually decide to have a nibble or not! Aldrenaline will happen!