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Old 09-29-2010, 07:28 PM   #10
ak_aramis
 
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Join Date: Jun 2010
Location: Alsea, OR
Default Re: Seaplanes & Submarines

Quote:
Originally Posted by copeab View Post
Well familiar with it ;)

There are also the submarine cruisers, such as the Surcouf and (unbuilt) Type XI U-cruiser.



As malloyd said, the battery life is the real problem. However, with snorkels a sub can run just under the surface and still use the diesel engines. Only when it has to run deeper than periscope depth does it need the batteries.
DE subs had 4 key depths noted:
Surfaced Draft
Periscope depth
Snorkel depth - the snorkel wasn't always on the periscope
Crush depth

But there's one more: weather depth. Surface weather has deeper effects than the wave height.
21. Can you feel the waves on a submarine when it's under the water?

It depends on how big the waves are at the surface and how deep is the submarine. During normal weather conditions, a submerged submarine will not rock with the motion of the waves on the surface. In fact, during even moderate storms the submarine stays perfectly level at its submerged depth while the waves crash above. In extremely violent storms like hurricanes and cyclones, wave motion can reach 400 feet or more below the surface. Though not as violent as on the surface, these large waves can cause a submarine to take 5 to 10 degree rolls.
(http://www.navy.mil/navydata/cno/n87/faq.html item 21)
http://www.seafriends.org.nz/oceano/waves.htm notes that deepwater wave depth scales to 0 at half-wavelength below midline of the surface wave. It also notes that wavelengths of 100m are not uncommon... and few subs will have 50m of even flexible snorkel... let alone the additional height needed to avoid breakers.

In a wholly ocean setting, you'll need to account for weather depth, and realize motion at depth is very roughly wave height times (Wavelength-(2*depth))/wavelength. And weather depth on such a setting are gonna be anywhere from 1m inside some archipelagos to 50m+ in deep wide ocean.

If your goal with subs is avoiding weather, then it's pretty safe to assume a need for 50m depth, plus 5m above surface, as needed for snorkel, so a safety margin of 5m for 60m snorkel, of which 10m is probably rigid.

If, instead, you go with a nuke, you can get electrolysis, don't need batteries (which were, at the time, lead-acid, heavy as heck, low energy density), and can cruise for months, or even years. And, to be honest, it's only a decade past your envisaged era.
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