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[BazaJT]

Watched a war film yesterday about a submarine,so strange questions popped into my head[it's weird what occurs to me at times ]When submerging to any given depth form where on the sub is the depth measurement taken?Presumably it's at or very near the top of the sail?What method/instrument is used to ascertain depth?

[flyer 0712]

Dosent it measure the difference between the pressure inside the sub against the sea pressure outside..as the depth increases the pressure rises and the gauge then determines the depth....i think in feet....or something like that.

[Entwood]

I asked a ex-submariner friend of mine exactly that question several years back.. his answer was the "lowest point of the boat" .. the reason .. the hull is stressed to be able to take a certain pressure, which they refer to as the "maximum depth", thus the lowest point of the boat is the part under maximum stress.

I also asked why subs are called boats and not ships .... surprisingly simple answer ..... 

[zirk]

Depth Gauge, pressure, bar etc, feet can easierly be calculated from bar(s) thats how bar measurement is calculated as a unit, in feet.

Theres more than one on a sub, quite a few, top middle, bottom, bow, back etc. Also one on the periscope for sticking your eye out of the water without being seen.

[106pete]

Yup just large depth gauges, yet apparently nothing to tell you about the big tanker your about to hit 

[Entwood]

They have lots of kit to tell them lots of things .. but for many, many reasons they don't always use it all of it all of the time!! and sometimes they use very very little of it ..

Have a read of The Silent Deep by James Jinks & Peter Hennessey, some very interesting stuff going on out there !!!

[zirk]

Yup just large depth gauges, yet apparently nothing to tell you about the big tanker your about to hit 

Ping.....

[Bigron]

Nige, tell us Nige, please Nige - WHY are they called boats and not ships?

Ron.

[STEMO]

Nige, tell us Nige, please Nige - WHY are they called boats and not ships?

Ron.

Who knows? 

https://www.theguardian.com/notesandqueries/query/0,,-197783,00.html

[Entwood]

Nige, tell us Nige, please Nige - WHY are they called boats and not ships?

Ron.

as STEMO says .. originally navy had "submersibles" .. carried on the deck of a mother ship, so as a ship carried them they were called "boats", as they got bigger and became submarines the Navy tradition of calling them boats stayed...

[Bigron]

I learn something new every day!   
Thanks, Nige.

Ron.

[Diamond Black Geezer]

For further reading/watching, the excellent drama 'Das Boot'.

A fascinating documentary about the footwear manufacturing industry of Northampton. 

[Shackeng]

Dosent it measure the difference between the pressure inside the sub against the sea pressure outside..as the depth increases the pressure rises and the gauge then determines the depth....i think in feet....or something like that.

Just got this from a Polaris submariner:
Depth is referenced to the keel of the sub. So the bottom of the sub. is zero meters/feet and periscope depth is around 60ft.(submarine class dependent).
Measurement is by pressure gauge both mechanical and electronic. Echo sounders would give a subs position away. If all that fails they could always swing the lead!!
 

[Andy B]

Nige, tell us Nige, please Nige - WHY are they called boats and not ships?

Ron.

as STEMO says .. originally navy had "submersibles" .. carried on the deck of a mother ship, so as a ship carried them they were called "boats", as they got bigger and became submarines the Navy tradition of calling them boats stayed...

 ..... and submariners call ships 'targets' 

[106pete]

I thought the difference was more to do with a ship had sails or something along those lines, I work on subs but that's about all I can say, I don't know how people go away on them for months with little contact with family and no idea where they are (except for about 3 people on board)