maintaining depth at stop

[tater]

Real subs didn't automatically broach if stopped. It was trim dependent, but trim varis from moment to moment, someone walks from one part to another of the sub, the water temp changes, etc, ad naseum. Unfortunately, the two solutions to hack this behavior into SH3 don't seem to work in SH4 (making the sub slowly surface all the time without down-planing, or having it slowly sinking without up-planing).

The simple solution for the gamer is to not stop the sub, or only rarely and for a very short time period, and never shoot while stopped. Easy enough to not cheat, really

[Rockin Robbins]

There was an interesting exception to the rule that a sub had a lot of trouble maintaining depth at all stop. If the thermocline was enough different in temperature, there was a layer of dense cold water below a less dense layer of warm water. A submarine could set ballast to sink in the warm layer but still have enough positive buoyancy in the cold layer to sit there for a couple of days without power if they wanted to. A couple of times during the war that saved the subs' cookies, giving them the opportunity to shut everything down and affect repairs without worrying about depth-keeping or running out of battery power.

we all know subs pump water in or out to control depth

so think about it, if you were the skipper and you life depended on stealth, would you rather have negative boyancy so your sub sinks at all stop or positive boyancy so your ship will rise at all stop and get your head blown off.

positive or negative boyancy is not designed in, it is a setting chosen by the captain. plus if you want to dive faster like all subs do, then positive boyancy is going to be fighting you as you try to dive.

IMO all subs made sure they were at some level of negative boyancy any time they werent surfaced

[Blood_splat]

What about firing torpedoes, would they have to adjust the trim to compensate before firing?

[Soundman]

Originally Posted by WEBSTER

we all know subs pump water in or out to control depth

so think about it, if you were the skipper and you life depended on stealth, would you rather have negative boyancy so your sub sinks at all stop or positive boyancy so your ship will rise at all stop and get your head blown off.

positive or negative boyancy is not designed in, it is a setting chosen by the captain. plus if you want to dive faster like all subs do, then positive boyancy is going to be fighting you as you try to dive.

IMO all subs made sure they were at some level of negative boyancy any time they werent surfaced

I completely see your point, but on the other hand, if something goes badly wrong, I wouldn't want to sink to crush depth either.

[scott613]

Don't know much about WWII subs - but - in modern subs - it was relatively easy to maintain depth without forward motion... The DOW and COW had to pay attention though... The newer subs even handle hovering automatically... Then there was always the infamous "TRIM PARTY" to indoctrinate a new officer into the wonderful world of depth control...

[SteamWake]

A common misconception.... "Hover" does not indicat a full stop, more rather a few (1-3) knots, just enough to keep some flow over the planes to maintain depth and attitude yet not disrupt the launch of the unthinkable.

[Rockin Robbins]

Scott, were you ever in a sub that floated on top of the layer? That sounds like it would be pretty amazing to do.

Originally Posted by Soundman

I completely see your point, but on the other hand, if something goes badly wrong, I wouldn't want to sink to crush depth either.

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.

[DaveyJ576]

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

[tater]

Dave,

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

tater

[Rockin Robbins]

Originally Posted by WEBSTER

IMO all subs made sure they were at some level of negative boyancy any time they werent surfaced

Webster, not to be offensive or anything, but we're not talking about opinion. We are talking about actual practice as verified by the people who actually ran the submarines.

In actual practice there was a tank called the negative buoyancy tank. Once per day the submarine took a "trim dive." Sub jockeys, check my accuracy here and keep me straight. In the trim dive, you dive the sub, slow it way down and with fore and aft trim tanks you level the boat. Somewhat simultaneously you fill or pump negative until the boat is at perfect negative buoyancy. The tank (in WWII anyway) is then marked at the level of neutral buoyancy. Fore and aft trim tanks are calibrated to know how bow or stern heavy the boat is. When a torpedo is fired, ballast equivalent to the weight of the torpedo being fired must be immediately added to the fore or aft trim tank to compensate for the lost weight and still leave the boat in balance.

Part of the diving procedure was to flood negative to the mark. Yes, you remember that, I see. "The mark" would be that neutral buoyancy level established in the trim dive earlier in the day. That way, subject to any changes to conditions since the trim dive, the boat dove adjusted as closely as possible to neutral buoyancy.

Now I will speculate just like you :rotfl:, making an educated guess based on many books I have read by World War II submariners. If a submariner did something that departed from "the book," that would have been remarkable and noted in any of the books I have read. None of them have mentioned flooding negative to a level above the mark.

To me, that means that this part of the procedure was one that maybe was not required, but was one that captains were very reluctant to depart from, just like maintaining under a 10º dive angle, even though after the war the guppies successfully used dive angles that were much greater and speeded dive and surfacing times. Nonetheless, in spite of possible gains from changing the practice, during the war, captains were very precise about adhering to the official guidelines for diving and surfacing procedure.

[tater]

RR, I don't know much about the guppies, but might it be fair to say the slower dive times in fleet boats were doctrinal, rather than hardware limited? Ie: they could go down faster had they put more than 10 degrees on the planes?

[Rockin Robbins]

Yeah, you can say that again! Read Gallant Lady: A Biography of USS Archerfish for a FULL rundown on that. Matter of fact, that's EVERYBODY's reading assignment to read a book that's altogether too much fun to hold all that information. Their job was to find the real limits of the design and they did it to the point of hurting people because of the steep angles. They were among the first to really violate the guidelines, which were not orders, but were treated that way during the war.

Put yourself in the place of a sub captain. You choose to dive at 25º (which turned out from Archerfish's tests to be perfectly reasonable) but something unrelated went wrong and you lose some crewmembers. It's inquest time and they start asking questions. "Did you exceed the guideline of a 10º down bubble on the dive?" If you answer "Yes" the inquest is over and they have their scapegoat. Bend over. I see military people smiling and shaking their heads to that one.:rotfl:

[tater]

How did that change the crash dive speed?