The bottom of their hulls handle their weight in dry dock, but that is probably a very even distribution.
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German subs were said to “sit on the bottom” near NY harbor during the day to shoot at transports during the night. I imagine they floated just above the sea floor rather than actually sitting on the bottom.
Absolutely correct, of course, and I should have been more clear here.
Agreed.
Nitpick…a submerged submarine doesn’t change its buoyancy by “letting go of a lot [of] air.”
Instead, a sub has main ballast tanks, which are either full of seawater (when submerged) or full of air (when surfaced). A submerged sub controls its fine buoyancy by use of its variable ballast tanks, in which seawater is flooded in or pumped out (or in some cases, expelled with high pressure air).
For what it’s worth, submarines in drydock have no trouble supporting their weight (on blocks). The uneven seafloor might be an issue, though.
Well, I did say that “they have lead ballast in the bottom of the boat or in the keel itself.” Per wikipedia: “A secondary purpose of the keel is to provide ballast. Keels are different from centreboards and other types of foils in that keels are made of heavy materials to provide ballast to stabilize the boat.”
These are all military unit awards. The crew earned the award. All crewmembers assigned to the unit for the time period in question get to wear the unit award.
Blind Man’s Bluff actually tabulates all of the unit awards earned by U.S. submarines during the Cold War. The Navy Unit Commendation (NUC) that we earned while I was onboard my sub is listed.
And they’re very easy to capsize. They stay upright by the crew hanging their weight off the windward side. But any monohull sailboat that’s too big to keep upright using your weight will have ballast of some sort.
The Finn has a steel centreboard. Brute of boat that. But suited to heavy and tall sailors. It was designed explicitly for the Olympics and has been an Olympic class ever since. Whether you class the centreboard as a keel is a bit of semantics. It is fully retractable, and does not have a bulb, but neither of these disqualify it from being considered a keel. In general however it is normally considered as a dingy.
The Star class was an Olympic class, but was dropped very recently. That has a more conventional keel.
What is perhaps more pertinent - it is easy to capsize a Finn, and it isn’t self righting. Even then, all keel boats can be capsized as well. In principle they should self right, but even this is not guaranteed. All configurations have an angle of vanishing stability - ie the angle at which they continue to roll over rather than roll back, and upside down is always somewhat stable. Modern wide flat racing yachts can be a significant problem.
Also, the paralympic classes for disabled sailors are keeled. Usually at least partially retractable. These boats are designed to be uncapsizable.
Hydrodynamic forces on the keel/centerboard are designed to provide a lateral force that counters the force of the wind on the sails. This allows a boat to sail into the wind (or nearly.) When sailing downwind it is usual to retract a centreboard of one can. When at an intermediate angle it is common to drop the centreboard partially to gain a little stability. Modern centreboards and keel fins are long thing wing sections. This force is in the direction to add to the force rolling the boat - and so is exactly wrong to help right the boat.
Modern high end ocean racers take things to another level again. These have a canting keel - one that can be swung from one side to another, and it is common to see one sailing with the keel actually horizontal in the water - for maximum righting moment. (Classes such as the IMOCA 60, the VO 70and VO 65.) This then requires the addition of centreboards to provide lateral forces to counter leeway due to force on the sails - and thus make the boat go forwards when sailing into the wind. Keels on these boats are now actually angled so that they develop vertical lift, and the latest is to angle the centreboards so that they do as well. With the ultimate expression being centreboards whose main design goal is lift as well - but still needing to provide lateral force as well. A canted keel provides righting moment, but angling to provide lift causes hydrodynamic forces to counter some of this - but overall it is a win for boatspeed.
https://www.youtube.com/watch?v=y4loB_UGxw8From my sailing classes and books, I was under the impression that keels had both a fin or generally some surface to resist moving sideways thorough the water along with a lot of weight to lower the center of gravity of the boat. You see older ships from 300 or 400 years ago without big fins sticking out below but they did had weight down low in the ship and a generally long narrowing of the boat to resist slipping sideways.
Smaller boats had center boards (that went down through of middle of the boat) or leeboards off to the side. These boats are easy to overturn. Whereas keel boats are hard to over turn because the keel is heavy and sticks out far below the main hull.
The Navy is not alone in these sorts of awards. The other DoD services and many other countries have similar things. See Unit citation - Wikipedia for more.
In the case of USAF & US Army, they don’t (usually) paint a replica of a service ribbon on the side of the building in the way the Navy often does on their ships. Though I have seen such things painted inside hangars, gyms, etc. The official award emblem is a cloth ribbon a couple feet long and a couple inches wide which is attached to the staff carrying the official unit flag. It has the same color striping as the ribbon worn by the people. See Guidon (United States) - Wikipedia for more.
A unit with a long and distinguished history may have a dozen of these things trailing off the ~8 foot pole with the ~3x5 foot flag that is carried by the color guard in parades and ceremonies. In this photo you can see many such ribbons hanging from each service’s guidon. Flags of the United States Armed Forces - Wikipedia. Those seem to me to be the extra large flag size with extra long unit award ribbons. Lesser unit’s flags aren’t quite that big.
Simon Lake’s Argonaut traveled with wheels on the sea bottom. The crew hauled up crustaceans into the boat to eat during a long voyage.
The idea of wheeled travel on the sea floor for subs seems to be resurfacing.
A U.S. nuclear sub rests overnight on the ocean bottom in shallow waters off Bremerton, Wash. in Nevil Shute’s 1957 novel On the Beach. It does so to avoid high surface radioactivity after WWIII.
An earlier thread on turning a sub upside down: Can a submarine turn upside down? - Factual Questions - Straight Dope Message Board
The same issues apply to non-aerobatic airplanes & helos. The key to successfully rolling one (e.g. Kelly Johnson in the -80 prototype) is to maintain positive G throughout the maneuver. Which requires what pilots call a “barrel roll” rather than an “aileron roll”.
The problem in a sub is that they can’t make a large enough corkscrew fast enough for centrifugal force to more than offset gravity during the 180 degrees of roll when they’re more upside down than right side up.
The good news is that because of more or less neutral buoyancy, unlike an airplane/helo, they don’t have to worry about falling out the bottom of the maneuver.
I see what you did there, young man. Do you think your mother would be proud ?
Thinking about this, I picture those spectacular (killer) whale breaches, where they shift their plane in such a way that just before they crash back down they’ve corkscrewed almost half way.
Don’t subs breach – is that word ever used – most rapidly, do they point upwards sometimes? And then at some small level handled somehow by marine engineering, corkscrew the same?
Ie, The differing ballast/center of gravity points necessitate, as a matter of basic mechanics, angular momentum when the entire thing goes vertically rapidly under power, yes?
My hydrodynamics knowledge is following up on the sum total of my aerodynamics knowledge, which is airplanes can’t just turn up, down, left, or right with out banking, i.e., a corkscrew, if you will.
That’s all confused.
Whales are trying to scratch their back. So they zoom upwards and as they’re breaking the surface, try hard to roll onto their back by twisting their fins, curling their tail, etc.
When subs make that maneuver, they’re trying very hard to stay upright. They have no desire to corkscrew. So they don’t. Here’s a not-so great article with a not-so great pic. But the point is the topside is staying on top throughout the maneuver. You can probably find some YouTubes pretty easily.
For either whale or subs, by and large they travel through the water aimed where they’re going. They’re not going sideways, or moving vertically while aimed horizitonally. At least not much.
It must be a Virginia-class link. I can neither see nor hear it.
:smack: Emergency main ballast tank blow - Wikipedia
Nice joke though. Thanks.
nitpick : that’s one possible explanation - but the truth is, we have no clue why (some) whales breach.
[QUOTE=wiki]
Ultimately, the reasons for breaching are unknown; however, there is evidence to support a range of hypotheses. Whales are more likely to breach when they are in groups, suggesting that it is a non-acoustic signal to other group members during social behaviour. Scientists have called this theory “honest signalling”. The immense cloud of bubbles and underwater disturbance following a breach cannot be faked; neighbours then know a breach has taken place. A single breach costs a whale only about 0.075% of its total daily energy intake, but a long series of breaches may add up to a significant energy expenditure.[10] A breach is therefore a sign that the animal is physically fit enough to afford energy for this acrobatic display, hence it could be used for ascertaining dominance, courting or warning of danger.[6] It is also possible that the loud “smack” upon re-entering is useful for stunning or scaring prey, similar to lobtailing. As breaching is often seen in rough seas it is possible that a breach allows the whale to breathe in air that is not close to the surface and full of spray, or that they use breaching to communicate when the noise of the ocean would mask acoustic signals.[11] Another widely accepted possible reason is to dislodge parasites from the skin.[11] The behaviour may also be more simply a form of play.[11] Breaching is therefore undoubtedly a very important part of socialising in cetaceans, and is learnt by all cetaceans at an early age from conspecifics.
[/QUOTE]
Do submarines always surface horizontally if they can help it? (Forget about the bank/corkscrew.)
We know they don’t want to scratch their backs… 
What is the energy expenditure/wear and tear equation when–in those stunning photos from the Arcitic, a sub just all of a sudden is there…it looks like it came up from the ice horizontally (all though I suppose it may have surfaced on an angle, settled down, and then the snow gathered for a flat horizon.
How does it do it?
Come to think of it, if it needs/wants to surface under-and-through an ice sheet, it matters a great deal if the ice is a few inches or 20 (?) feet deep, doesn’t it?
Does the bridge (where the Skipper stands…not sure if thats called the bridge) gauge that ahead of time, maybe by sonar pings differing on the density of the ice mass?
(Lotta questions with lotta assumptions. Forgive me.)
That was Tex Johnston (with a T). Kelly Johnson has already claimed enough credit for things he didn’t do, we don’t need to be giving him any more. 
In the Arctic, the ice isn’t uniform thickness. Since it is moving all the time, areas open up and then freeze over. These are the areas you look for to surface in. Subs that surface in the ice have strengthened sails to punch through without damage. They go straight up from a standstill. Still, once up there, you have to keep an eye out that the pocket doesn’t close up with you in it.
Good catch. :smack: Thanks.