Shipwreck survival

[Agemegos]

Originally Posted by Vynticator

I understand on a clear day you can see the coast 7 miles away from sea level, I am told by the inter web. So if they head broadly the right way and the storm clears after half an hour or so, they may see shore soon after that.

That sounds more like standing at sea level (i.e. with any eye height of five and a half feet) than immersed at sea level (i.e. with an eye level only a few inches above the waves).

[Anthony]

Originally Posted by Agemegos

That sounds more like standing at sea level (i.e. with any eye height of five and a half feet) than immersed at sea level (i.e. with an eye level only a few inches above the waves).

Horizon distance is typically given as 3.57 km * sqrt( height / 1m ), so 7 miles is too far even for someone standing up, and for someone swimming would be more like 1-1.5 km. However, you can see things that are over the horizon if they're tall enough -- if we assume 1.3 km horizon from swimming, and 10 km for the target (total 11.3 km, or 7 miles) the object needs to be about 8 meters tall to be visible, which is a decent-sized tree but not impossible, and mountains would be visible quite a bit farther, probably out to the range at which atmospheric haze wipes them out.

[Vynticator]

Originally Posted by Anthony

Horizon distance is typically given as 3.57 km * sqrt( height / 1m ), so 7 miles is too far even for someone standing up, and for someone swimming would be more like 1-1.5 km. However, you can see things that are over the horizon if they're tall enough -- if we assume 1.3 km horizon from swimming, and 10 km for the target (total 11.3 km, or 7 miles) the object needs to be about 8 meters tall to be visible, which is a decent-sized tree but not impossible, and mountains would be visible quite a bit farther, probably out to the range at which atmospheric haze wipes them out.

Thanks for this helpful formula. There's a rocky headland at the northern edge of the bay which is 41m above sea level.

[Anthony]

Originally Posted by Vynticator

Thanks for this helpful formula. There's a rocky headland at the northern edge of the bay which is 41m above sea level.

Sea-level air often has pretty poor transparency, so you can certainly justify quite a lot shorter vision range, but that gives a maximum range.

[Tuk the Weekah]

Originally Posted by Vynticator

Thanks for this helpful formula. There's a rocky headland at the northern edge of the bay which is 41m above sea level.

With a headlands that high, the swimmers may see the sea birds playing in the wind currents created by the headland before they sight land itself.