How to maintain depth with zero speed

[Subject]

Or - you go get the "Neutral boyancy mod for GWX" to get rid of that modelling.

Some like to play that the crew is there to handle the boat and obey orders

[melnibonian]

If I remember correctly in the new version of GWX the reduced positive buoyancy will be default. Until then just use the optional "Reduced Buoyancy Mod".

[seafarer]

Originally Posted by Subject

Or - you go get the "Neutral boyancy mod for GWX" to get rid of that modelling.

Some like to play that the crew is there to handle the boat and obey orders

If reality is your desired goal in the game though, even the best crew could not keep a boat at constant depth without forward momentum and use of the control surfaces (planes). A submarine in a state of neutral bouyancy is a delicate balancing act and practically impossible to acheive with mechanical means. Sure, you can pump water in and out of tanks, shift water between trim tanks and such, but true neutral bouyancy is a knife's edge state that you will keep slipping off of.

The boat, for one thing, is not stationary. It is subject to currents. Those currents will move it through water with subtly varying temperatures/salinity, hence subtly varying density. As it sinks, it's hull compresses, so it's volume changes slightly, so ballast needs to be released. So, true neutral bouyancy is fine in theory, but impossible with real life machinery.

Plus, pumping out water at depth takes a lot of power, as you have to pump out against the external pressure. It's also thus difficult to percisely meter pumping out very small amounts of water to maintain neutral bouyancy and level trim.

It's one of those classic instances where the theory is relatively straightforward, but engineering a 1000+ ton machine that can exactly implement the theory is the challenge.

[Chock]

Unfortunately, SH and pretty much every other sub sim is not totally realistic in this area, as it would probably require a supercomputer running all sorts of chaos algorithms to model it at least well, if not truly realistically. So the reduced buoyancy in the sim is about the best simple comprimise.

As seafarer notes, if you ever bring a boat to a halt out on the open ocean in real life, the amount of drift you get on currents is absolutely frightening, and you can quite easily drift a mile or more in ten minutes near estuary outflows, which extend fo many miles. So in theory your sub shouldn't even be able to remain laterally stationary either, as it would require thrusters to pull that off. And that drift would put you in water with altering densities, as the temperature, salinity, etc fluctuated.

Real U-Boats, and modern subs for that matter, will drive dynamically to the depth they want, and then try to maintain that depth by altering trim, but some fluid movement over the planes is the simpler and more desirable method, and the problem gets even worse if you launch a torpedo and suddenly lose all the weight of it as it leaves your sub, subs being equipped with compensating tanks which flood to aleviate the problem a little.

This is why most WW2 subs would perform a daily 'trim dive', to give the chief an idea of what was a likely setting required for maintaining position at various depths given the sub's altered weight from food consumed, oil and lubricants used, ammo spent etc, all of these changes alter the calculation. Even the sub itself gets smaller as it dives deep and is compressed by the water pressure!

I was reading the other day that when the Pittsburgh was launching Tomahawk cruise missiles in the Gulf War, even though in theory it can launch them in a matter of minutes, the skipper actually started the countdown to launch twelve hours beforehand, and elected to slowly approach the launch point from the start of that countdown, so that he would be able to ensure he was at the correct point and depth at the right time, and that's a modern nuclear sub with computers assisting the trim calculations!

So if it's a bit tricky to maintain depth in the sim, that's definitely realistic, even if it is simplified.

Chock

[Subject]

You do not need speed to dive to 180 meters. Maintaining depth do require constant monitoring and a lot of work, but that's why your boat is full of men
Please don't spread myths.

[floundericiousWA]

Perhaps your easiest way to quietly maintain a depth is to set your speed at an extremely low number (click between 0 and 1)...that will maintain some positive pressure over the surfaces and mean you're doing less sea anchor duty!

[Peto]

Historically : "Hovering" was very difficult for the simple reason that the ocean is dynamic--varying temps/salinity/currents which impact the effort. To do it, it was typically nessecary to pump water aft, forward, here, there etc, which made noise--something that a hunted submarine was trying to avoid. Not to mention that a submarine having a dc go off while it has no momentum was a recipe for disaster as it could leave you galloping for the surface or the ocean floor. That would require HUGE amounts of noise to compensate/get the boat under control again.

A skipper might order for all stop but he was still counting on forward momentum to be sufficient for the planemen to keep the boat under control. I've never read any account of a submarine attempting to hover in a combat situation...

My 2 cents (but probably worth much less ).

Peto

[PapaG39]

Man, you guys have brought up a whole bunch of interesting sea stuff to this old army guy.

Heck, I didn't know what the "Reduced Buoyancy Mod" was actually for.

Other things I am aware of such as, water temperatures, salinity and currents but I never even thought of them in this game.

You can only put so much into a $50 CD.

I was reading on some sub background material which stated that at the beginning of WWII the men who went into the German sub service had ***five years*** of training prior to entering the submarine.

When these guys went to sea they knew their boat backwards & forwards.

We pickup a shiney CD with a cool picture on it & plop it into a computer & try to make some sense out if it...

[seafarer]

Originally Posted by Subject

You do not need speed to dive to 180 meters. Maintaining depth do require constant monitoring and a lot of work, but that's why your boat is full of men
Please don't spread myths.

What myths? Lots of web sites by ex-submariners talk about the fact that true neutral buoyancy is impossible to acheive in a submarine. Practically speaking, the machinery, no matter how masterfully manned and handled, is not capable of such refined control of ballast and trim.

I've done a number of dives in small, 3-man deep diving submersibles. With state of the art, solid-state electronic controlled trim and ballast pumps, it was never possible to acheive and maintain true neutral buoyancy for more then brief periods of time. The Alvin pilots are some of the best trained submersible operators you'll find anywhere in the world, but no amount of artful control inputs from them could acheive precise depth maintenance for anything more then a few minutes without the use of the thrusters. And this in a vessel that only displaced a few tons, not thousands of tons.

The environment is the issue, and the environement is not stable, so you are in effect chasing a constantly moving target. For a submarine, at war, and with finite power reserves, that chase is costly - in terms of power, a ridiculous strain on the crew who must ultra-micro-manage a maze of buoyancy controls, and it makes noise running pumps and such.

As mentioned, much better off just slipping along at 1 knot or so, and let the dive planes do what they are intended for - depth and trim control.

A quote from a US Naval Officer and an engineer who served on the USS Loggerhead (SS-374, a Balao class boat) in WWII:

Lt. HARRISON W. SIGWORTH

Modern United States Submarines

In Engineering and Science Monthly (California Institute of Technology), Volume 9:8, August 1946
...<snipped the first portion of article>
...
SUBMERGED OPERATION
The achievement of neutral buoyancy is a practical
impossibility. It can be approached by pumping
water out of the trimming tanks or flooding in; but
true neutral buoyancy in which the boat will stay anywhere
it is placed below the surface without sinking
or broaching is impossible. Depth can be maintained
within a foot for hours at a time, however, by propelling
the boat through the water and using the
diving planes. These are horizontal, tiltable, planing
surfaces olaced at the bow and stern to control dewth
and ang-l e of the boat.
... <article continues>

the whole paper is here