"Driftdown problem" (neg. buoyancy when submerged) addressed?

senjorlossi · 03-15-10, 01:57 PM

Hi Guys,
just a quick question, since I can´t find anything about it here in the forum:

Has the problem of the negative buoyancy (sub tends to sink deeper and deeper when submerged) already been addressed in any way? I can´t see anything so far.

Good hunting,
Stefan.

GoldenRivet · 03-15-10, 02:03 PM

im not sure about this SH5...

but in SH3/4 this was an issue when crash diving while already submerged.

i have not noticed this bug nearly as much in SH5 as i did in SH3

Juliano · 03-15-10, 03:18 PM

I think he´s having problem after a normal dive
same problem here

sometimes I have to set speed higher than 2-3 knots to keep the same depth at 100 meters

still, I don´t know how to help or if there´s a mod to fix that (if I remember right, in real life the extra speed is indeed needed to keep depth at 100m or below, but I may be wrong)

Ducimus · 03-15-10, 03:31 PM

http://www.subsim.com/radioroom/show...6&postcount=25

Problem was worse in SH4, you had to go to flank.

Conrad von Kaiser · 03-15-10, 03:38 PM

Silent running at 100 feet depth gives me a very slow decent. Maybe 1 foot per minute. Not a big drop if you're sitting and watching it, but at time compression it could build up pretty quick.

senjorlossi · 03-15-10, 04:54 PM

Yes, when you go deeper than 80 m the sub keeps on sinking deeper unless you command a new depth of around 60 m or less. Even at around 80 m you can see that the dive planes are in the "up" position.

I thought that it might be connectet to the "silent running" status, as water would not be pumped out of the sub to prevent any noise, but it is not.

OK, I am not a submariner in real live, but I think a well trimmed sub should be able to stay at any depth, even at low speed. Of course there is always some water leaking in, the deeper the more, as the outside water pressure rises. But it´s the Chief´s duty to pump it out at times.

Frederf · 03-15-10, 05:49 PM

It's a complex issue but, no I don't think it's been fixed in any patches. Someone would have mentioned it.

Standard procedure, at least near the surface, is to set the buoyancy purposefully negative so the boat has to be moving to plane up to periscope viewing depth. This way if anything goes wrong you simply sink a little deeper instead of broach, get spotted, and die.

Keeping exact trim is rather difficult. The overall buoyancy that keeps the boat at 60m and 65m are rather close. With time and effort one can "dial it in" more or less. With surface swells near the surface it's like trying to make a house of cards with the fan on.

Sinkikng down and then hovering at 0 kts to exactly 100m would take a lot of fiddling with the trim tanks and you might wobble up and down 10s of meters as trim was changed. Speed and planes help you get to a precise depth quickly. However there's no chance that at 0 kts and 100m the boat would inexorably sink out of control as the buoyancy can be changed.

There is a point of no return for submarines known as the critical depth where maximum available buoyancy authority is insufficient to achieve positive net buoyancy but that would be well below 100m in a Type VII.

03-15-10, 01:57 PM	#1
senjorlossi Seaman Join Date: Jul 2005 Location: Germany Posts: 42 Downloads: 49 Uploads: 0	"Driftdown problem" (neg. buoyancy when submerged) addressed? Hi Guys, just a quick question, since I can´t find anything about it here in the forum: Has the problem of the negative buoyancy (sub tends to sink deeper and deeper when submerged) already been addressed in any way? I can´t see anything so far. Good hunting, Stefan. __________________ Best regards, Stefan.

03-15-10, 02:03 PM	#2
GoldenRivet Subsim Aviator Join Date: Mar 2007 Location: Texas Posts: 8,726 Downloads: 146 Uploads: 0	im not sure about this SH5... but in SH3/4 this was an issue when crash diving while already submerged. i have not noticed this bug nearly as much in SH5 as i did in SH3 __________________

03-15-10, 04:54 PM	#6
senjorlossi Seaman Join Date: Jul 2005 Location: Germany Posts: 42 Downloads: 49 Uploads: 0	Yes, when you go deeper than 80 m the sub keeps on sinking deeper unless you command a new depth of around 60 m or less. Even at around 80 m you can see that the dive planes are in the "up" position. I thought that it might be connectet to the "silent running" status, as water would not be pumped out of the sub to prevent any noise, but it is not. OK, I am not a submariner in real live, but I think a well trimmed sub should be able to stay at any depth, even at low speed. Of course there is always some water leaking in, the deeper the more, as the outside water pressure rises. But it´s the Chief´s duty to pump it out at times. __________________ Best regards, Stefan.

03-15-10, 03:18 PM	#3
Juliano Helmsman Join Date: Apr 2009 Location: Cruising by you with "EXTREME SPEED" Posts: 101 Downloads: 139 Uploads: 0	I think he´s having problem after a normal dive same problem here sometimes I have to set speed higher than 2-3 knots to keep the same depth at 100 meters still, I don´t know how to help or if there´s a mod to fix that (if I remember right, in real life the extra speed is indeed needed to keep depth at 100m or below, but I may be wrong)

03-15-10, 03:31 PM	#4
Ducimus Rear Admiral Join Date: May 2005 Posts: 12,987 Downloads: 67 Uploads: 2	http://www.subsim.com/radioroom/show...6&postcount=25 Problem was worse in SH4, you had to go to flank.

03-15-10, 03:38 PM	#5
Conrad von Kaiser Helmsman Join Date: Mar 2010 Location: New York Posts: 105 Downloads: 19 Uploads: 0	Silent running at 100 feet depth gives me a very slow decent. Maybe 1 foot per minute. Not a big drop if you're sitting and watching it, but at time compression it could build up pretty quick.

03-15-10, 05:49 PM	#7
Frederf Seasoned Skipper Join Date: Apr 2005 Posts: 665 Downloads: 79 Uploads: 1	It's a complex issue but, no I don't think it's been fixed in any patches. Someone would have mentioned it. Standard procedure, at least near the surface, is to set the buoyancy purposefully negative so the boat has to be moving to plane up to periscope viewing depth. This way if anything goes wrong you simply sink a little deeper instead of broach, get spotted, and die. Keeping exact trim is rather difficult. The overall buoyancy that keeps the boat at 60m and 65m are rather close. With time and effort one can "dial it in" more or less. With surface swells near the surface it's like trying to make a house of cards with the fan on. Sinkikng down and then hovering at 0 kts to exactly 100m would take a lot of fiddling with the trim tanks and you might wobble up and down 10s of meters as trim was changed. Speed and planes help you get to a precise depth quickly. However there's no chance that at 0 kts and 100m the boat would inexorably sink out of control as the buoyancy can be changed. There is a point of no return for submarines known as the critical depth where maximum available buoyancy authority is insufficient to achieve positive net buoyancy but that would be well below 100m in a Type VII.