not offended at all but not everyone is an experienced sub mariner so opinions do happen lol.

all i was trying to point out is, since it is near impossible to get absolute true neutral boyancy without some margin of error, so this "small" margin of error was IMO (theres that dirty word again) going to be on the negative boyancy side of neutral.

what they called neutral boyancy really wasnt, it was just as close as you could get within the small margin of error.

EDIT: i have reversed my position on this subject, i now believe any margin of error was on the positive boyancy side to allow survival in case of loss of power. i failed to consider this before.

If your neutral buoyancy is perfect now, in 10 minutes it will no longer be. Most captains took a trim dive a day. Since they didn't plan to stop completely anyway, close was close enough.

I was at an airshow watching a different kind of submarine, the Fuji blimp, trying to get off the ground. This was a mini blimp and there was a rail around the outside of the gondola. They asked me to help them launch, so I walked over. First, they dropped ballast until we judged the blimp weighed about 20 pounds or so. The captain got on the speaker and said, "Now everyone hold the blimp as far over your head as you can. Then jump up use your whole weight to slam it into the ground!"

So about 15 of us body slammed the blimp into the ground. Turned out there was a kind of pogo stick on the bottom of the gondola that shot the blimp up in the air, the pilot gunned the engines and took off, easily generating 20 pounds of lift by forward motion and angle of attack. It all took a shorter time than it took to type this. Amazing!

No single post in this thread hit the mark exactly, but when combined together, this question was answered pretty well! :up:

A couple of nitpicks:

Submarines flood water in or pump it out to adjust buoyancy, not depth. Depth is controlled strictly by the planes.

Consider this: Take a submarine that is level on the surface and tilt it downward at a 25 degree angle. A submarine's point of tilt is amidships, not at the stern. What happens? The bow up to the conning tower fairwater is submerged, but the stern is sticking up into the air. What is at the stern? The propellers and the stern diving planes! It is true that you can flood the negative tank to gain negative buoyancy, but most of the dynamic force necessary to submerge a submarine is provided by propulsion, assisted by the diving planes. Stick the propellers up into the air and you have lost a great deal of that dynamic force. You would also loose nearly all the control over your angle as it is the stern planes that control the angle!

The bow planes are used to control depth and the stern planes for angle. Submariners live in fear of a casualty called a "jam dive" on the stern planes. That is a mechanical failure of the operating mechanism that causes the planes to go to full dive and stay there. This is what happened to the Chopper and is what came within a hairsbreadth of causing her loss. A submarine will go out of control faster than you can believe in this situation. It happened to me a few times and it is scary as hell.

What am I getting at? Yes, you can take a larger down angle when diving, but there is a point of diminishing return. All of the factors have to be considered. 40 second dive times for a boat as large as a Fleet Boat is pretty damn fast already. Large down angles while diving are possible to do, but are not desireable until the boat is completely submerged, and even then you have to be careful. A really fast dive time doesn't mean squat if you lose control and exceed collapse depth.

Torpedoes are neutrally buoyant. Once they are expelled, water floods the tube. The torpedo is the same weight as the water. Once the outer door is shut, the tube is drained into the Water Round Torpedo (WRT) tank. Therefore, the compensation does not change. Even still, the planesman, Auxiliaryman of the Watch (who runs the Trim and Drain manifold), and the Diving Officer have to really pay attention to buoyancy and depth control when shooting fish.

Dave

USS Darter SS-576 1984-87

www.pigboats.com

Oh yeah - this discussion reminds me - we had what we called the Safe Operating Envelope for the boat... What it did was effectively limit the speed of the boat at shallow and deep depths to prevent unsafe depth excursions in the event of a casualty such as a stern planes jam... An unwanted broach can be as bad - well almost as bad - as exceeding test/crush depth... We practiced the jam dive drill all the time... First action - BACK EMERGENCY...

Wow, Scott! That wouldn't be good for the heart there.:eek::eek:

May be of interest:

From:
http://www.fleetsubmarine.com/diving.html

and
Happy Hunting!

Art

Ewwwwww! That's some kind of oversimplification because the trim ballast system and negative tank have to have some water in them. The boat would have to have a fair amount of reserve buoyancy with the main ballast tanks full or it couldn't carry any cargo or people. Once a tank is empty, you can't make it any lighter.

I think the statement is probably correct with full MBTs and a default amount of water in the trim and neutral buoyancy systems. Davey? What's your take?

I should know better than to 'dance' with you again RR ..... lol - however I didn't want to quote the entire page. They go into greater detail on the website. The weight of the boat would of course include 'cargo & people'

http://www.fleetsubmarine.com/dynamics.html is also helpful.

Happy Hunting!

Art

thats an equally good point, i was only thinking of accidentally being detected if something went wrong yet like you say to survive you dont want to sink either so being detected on the surface gives you a better chance to survive than crush depth. :up:

Main ballast tanks are always completely empty or completely full. Their purpose is to provide or eliminate the overriding postive buoyancy that holds the boat on the surface. The trim tanks are used to regulate the buoyancy of the boat.

While in port between patrols, a careful accounting of how much fresh water, fuel oil, lube oil, hydraulic fluid, torpedo alcohol, stores, etc., etc. is brought on board and the weight of all this is used to figure the initial compensation. One of the first things that is done after clearing the harbor outbound is to conduct a trim dive. It is not uncommon for the boat to have trouble submerging or maintaining depth at this time. As much time as is needed it taken to properly adjust the ballast compensation by flooding water into or pumping it out of the trim tanks. The goal is to obtain perfect neutral buoyancy so that a minimal use of the planes will maintain depth. The whole time the boat is at sea, a running tab is kept on consumables useage and the compensation is periodically adjusted as needed. Trim dives usually took place once a day.

In reality, on the fleet boats, perfect neutral buoyancy is virtually impossible to achieve. The manually operated trim and drain system, while a very good design, was just not sensitive enough to get to that point.

From a submariners standpoint, if you can't get to neutral buoyancy you would default to a slight positive buoyancy. Contrary to popular belief, true crash dives did not happen all that often with our boats (radar gave you enough warning). If you had to go down quickly you could flood the negative tank and you would go down like a rock. I heartily agree with the other posts that it is far better to broach (although obviously not desireable) than to sink. You at least have some chance at survival if you broach, but if you exceed crush depth you WILL die.

Dave

www.pigboats.com

Dave,

love your posts, some of the very best I have read here. Keep educating us, this stuff is great!

tater

Agreed. It's great to hear from a real submariner who knows what he's talking about.:up:

Thanks guys. I really appreciate it. For a real world example of the importance of proper ballasting, surf over to http://pigboats.com/dave5.html when you have a chance (insert shameless self-promotion here!) :lol:

Dave

Thanks for the detailed description on how these beasts swim Davey. Informative site too. :up:

I wish the sim had things like trim dives, equipment malfunctions, (that aren't related to battle damage) training crewmembers, etc. There's so much more to a patrol in a sub than a leisurely cruise between ship sinkings.

I agree that a random equipment malfunction feature should be added. It shouldn't be too hard to do and would add an extra level of realism to the game.

Thanks for the kind words on the site. My partner Ric Hedman does all of the grunt work, I just do the writing.

Dave