Steeper dive angle in the control room please

only in crash dive or emergency surface would a sub be at such a steep angle

[oscar19681]

Originally Posted by WEBSTER

only in crash dive or emergency surface would a sub be at such a steep angle

Yes i,m aware of that but i dont see these angles in sh-3 or sh-4 in crash dive or emergency surface

[Letum]

Originally Posted by WEBSTER

only in crash dive or emergency surface would a sub be at such a steep angle

What kind of angles are you thinking of?

If a uboat managed 40° it's bow would be more than half way down to crash dive depth before the stern had gone underwater!

At 25° the sub only has to travel 6 times it's own length before it reaches crush depth.

A undamaged uboat doesn't have a very steep dive angle.

[IanC]

Originally Posted by Letum

What kind of angles are you thinking of?

If a uboat managed 40° it's bow would be more than half way down to crash dive depth before the stern had gone underwater!

At 25° the sub only has to travel 6 times it's own length before it reaches crush depth.

A undamaged uboat doesn't have a very steep dive angle.

From what I've read in Buchheim's Das Boot, the dive angles were definitely steep, especially with 'all men forwaaaard!'.

This from U-boatarchive seems sensible to me;

"(iii) Diving Angles.
During a normal crash dive, the angle tower increases from roughly 2 at the commencement to 10° as the bridge screen dips. Thereafter the angle down is normally from 12-15°, though angles up to 45 have been reported, after complete submersion."

http://www.uboatarchive.net/KTBNotes...iveEdition.htm

[Letum]

Well, here is a scale diagram of a 45deg. dive:


I haven't any facts of figures, but it looks far too dramatic to me.
At no point does the boat have any chance of a constant dive rate
and that's going right down to the absolute maximum depth.

The klauen would have the be utterly nuts.

[IanC]

That animation is kinda funny lol...
But I don't understand your point, you saying a boat diving at 45 degrees will reach 220 meters in 6 seconds?

edit: btw you sure that boat animation is at 45 degrees? Looks a little steeper to me.

[JU_88]

I presume a submarine must gain speed in steep dive, just like an aircraft gains airspeed in this way.
Gravity is slightly reduced in water, but not by all that by much.

Is this modelled in SH3/4? I have never thought to really monitor My boats submerged speed while diving or accending.

Does the boat accellerate and still continue at a higher than normal speed after levelling off (having gained momentum), then gradually reduce speed down to whatever RPMs your electrics are driving?

IN SH3/4 I never noticed the effects of gravity or physics simulated in thii way, but then I was never looking for it.....
Then again, maybe my theroy is wrong?

Originally Posted by JU_88

I presume a submarine must gain speed in steep dive, just like an aircraft gains airspeed in this way.
Gravity is slightly reduced in water, but not by all that by much.

Is this modelled in SH3/4? I have never thought to really monitor My boats submerged speed while diving or accending.

Does the boat accellerate and still continue at a higher than normal speed after levelling off (having gained momentum), then gradually reduce speed down to whatever RPMs your electrics are driving?

IN SH3/4 I never noticed the effects of gravity or physics simulated in thii way, but then I was never looking for it.....
Then again, maybe my theroy is wrong?

not really, in a dive its a momentum (or inertia) vs resistance thing which follows the same patterns as aircraft but they are different. the effects of gravity are much less effective on submerged objects containing an air pocket because the floatation cancels out gravity to a large extent. if anything IMO the opposite is true, it would lose speed in a dive due to the increased resistance forces against it trying to push against the forces of resistance, floatation, and pressure changes.

a boat never really levels off, it has a bowl like action as it bottoms out its dive but bouyancy is all part of it too because the dive planes putting force against that bouyancy is what gives you the control or you would forever be in flux going up or down constantly

[Letum]

Originally Posted by IanC

That animation is kinda funny lol...
But I don't understand your point, you saying a boat diving at 45 degrees will reach 220 meters in 6 seconds?

edit: btw you sure that boat animation is at 45 degrees? Looks a little steeper to me.

Yes, it is precisely 45 degrees at the steepest point.
It's not about the speed. Even slowed down to the correct speed, the
dive still looks utterly crazy.
I only have it going fast because no one wants to watch a .gif for 10 mins.
As soon as the boat reaches 45deg. it needs to pull up at an
impossible rate or it would go straight down to crush depth.

Originally Posted by JU_88

I presume a submarine must gain speed in steep dive, just like an aircraft gains airspeed in this way.

No, gravity does not give a uboat much speed at all because the u-boat
never has much weight.
Even with all tanks flooded it will only weigh about 10 tonnes.

It might get a knot or three of extra speed on the way up because the
VIIC can have a positive buoyancy of exactly 102 tonnes when the
basalt is all blown.
Come to think of it, that much positive buoyancy could really rocket it
upwards.

ed: going to do the math...
ed:2

Wow!

This is all just calculated guess work, so don't take it too seriously...

If we assume that the motors and dive planes can only give enough
thrust in the vertical to counteract vertical drag. (they can at low
speed, but this is very optimistic as the speed rises)...
And we assume that the VIIC can blow all it's basalt and get into a
climb angle instantly (Ha!)...

Blowing basalt from 220m gets us about 14knots of vertical speed
when the boat breaks the surface.
However, the dive planes and motors, even at a 45 degree climb,
can only counteract drag up to the speed of ~4.5 knots (half the
underwater top speed at 45 degrees).

I don't have enough info to work out the drag forces, but it's a safe
bet that it will take off a lot of the speed above 4.5 knots.

A top vertical speed of 8 knots seams to be in the ball park. This is in
addition to the ~4.5 knots of horizontal velocity. that gets the VIIC
from crush depth to the surface in just under one min.

Of course, the VIIC can't blow all 102 tonnes of basalt instantly and it
can't get to a 45 degree climb angle instantly, but even with the most
conservative figures, you can expect a good knot or two of vertical
climb if all the basalt is blown.


I ran the calculations for a sinking u-boat and the effect of the ~10
tonnes of basalt that the VIIC can take on top of the neutral
buoyancy load gives it less than 1 knot of extra sink as it passes
220m.

ed3: removed some mistakes.
ed4:

As a calculated guess it would take 18-24min to sink a VIIC to 220m
without dive planes.

[Sailor Steve]

Originally Posted by WEBSTER

only in crash dive or emergency surface would a sub be at such a steep angle

Or in a faked picture.

"Hey, guys. Lean way over and I'll tilt the camera!"

On the other hand it's interesting that the bow planes are apparently at full down while the stern planes are almost flat.

[BlueFlames]

On the other hand it's interesting that the bow planes are apparently at full down while the stern planes are almost flat.

Damaged/malfunctioning boat out of control, perhaps? Might be time to tell the DC team to be more aggressive.

[Ducimus]

Old PR Kreigsmarine photo. I recall reading somewhere, that that photo is staged. Heck, Nazi Germany's PR ministry made several full length PR fillms, let alone still photo's. You'll find PR photo's on both sides of the war, some of them are rather amusing. I particuarlly like the ones on the US side. I think one is on the book cover of Silent Running. Nice crisp uniforms, they tilt their hats back and up their collars to try and look like they've been busy. Officer at the periscope wearing a Tie.

Originally Posted by Sailor Steve

Or in a faked picture.

"Hey, guys. Lean way over and I'll tilt the camera!"

On the other hand it's interesting that the bow planes are apparently at full down while the stern planes are almost flat.

The pic may or may not be posed but thinking about it for a second and the zero angle on the aft planes makes perfect sense for the initial stage of the dive.

With both sets of planes at hard-dive the boat should tend to pitch down rotating around the centre of gravity (or perhaps the center of pressure which one would think would start forward and move aft to the CG as the boat achieves equilibrium in the dive.*) This might well cause the entire stern to come out of the sea and result in losing control of the rudders, aft planes and now free-spinning props. Good arguments to avoid big angles.

On the other hand with aft planes at or near zero, they should become the pivot point and so the props and control surfaces stay safely submerged.

If you can get hold of Submarine Commander by Paul Schraatz, he goes into great detail about the problems and pitfalls associated with big-angle dives in diesel boats.

<*My background is in ballistics not hydrodynamics so this is a guess and anybody familier with pitch behaviour of vessels in water may freely debunk as necessary.>

[Sailor Steve]

Good points, and I wasn't actually suggesting that it was posed - just that it was one of many possibilities.