Going deep - cavitation effects

[CruiseTorpedo]

Another question came up when I was reading Clear the Bridge, they mentioned that their propellors won't make any noise to be heard at the surface when they're down deep, around 500ft as cavitation doesnt occur at those depths traveling even at their maximum underwater speeds up to 10 knots!! So they could go deep, manuever around at 10 knots with a convoy overhead and not worry about being detected!! What the heck! In SH3 anytime I go deep and run ahead full even in 1940 the destroyers hear me without any problems. Is this just a game limitation or will this work in SH4? Anyone know why this doesnt work in the atlantic?

[flyingdane]

Huh:

[Morts]

Originally Posted by CruiseTorpedo

In SH3 anytime I go deep and run ahead full even in 1940 the destroyers hear me without any problems.

maybe they are pinging you with sonar ? maybe thats why they detect you

[fatty]

Just because you are not cavitating does not mean you are totally silent. Cavitation is the rapid formation and collapse of bubbles caused by a spinning propeller at certain RPMs and pressures. As you can imagine this is quite noisy. In its absence, however, you still have your motors etc creating sound for the ASW vessels to pick up on.

[Subnuts]

Even without cavitation, there's still the noise from your electric motors, pumps, generators, etc., plus the flow noise from the conning tower, deck guns, and fittings. That, and submarine propellers back then were basically the same design as merchant ship propellers, without much regard for quieting.

[AirborneTD]

500ft (?) Seems a bit "too" deep for WWII boats. Maybe not.

[Torplexed]

500 feet equals 152.4 meters. Not too deep.

[Takeda Shingen]

By modern standards, the WWII Silent Service was not really all that silent. Flow noise due to hydrodynamic drag was a major contributor to detection.

[Crosseye76]

500 feet should put you below the layer. Without VDS, you can be pretty noisy and a Surface ship won't be able to hear you, or Ping you.

I don't think SH3 has the layer, but I think I read somewhere on the forum that SH4 will have a basic one.

[Egan]

Originally Posted by Crosseye76

500 feet should put you below the layer. Without VDS, you can be pretty noisy and a Surface ship won't be able to hear you, or Ping you.

I don't think SH3 has the layer, but I think I read somewhere on the forum that SH4 will have a basic one.

Much more importantly, 500 feet is going to put you under the silt in all those shallow seas.....

[CruiseTorpedo]

Originally Posted by Morts

maybe they are pinging you with sonar ? maybe thats why they detect you

No they can't ping me when I'm at 160m in 1940, asdic doesnt go that deep in grey wolves till later in the war.

In the book I mentioned it's mid 1943 fighting the japanese and they still had a pretty decent number of escorts who definitely had radar units on some of the ships. O'Kane's first or second convoy he encountered on their first patrol he attacked at night, was in front of the ships but saw a destroyer heading right at them. That's when they went to 500ft listening to the merchants in the convoy which changed course 30' so they accelerated to 10knots stating their props won't cavitate at that depth even at 10knot speed and as mentioned in an earlier post they were under the thermal layer. So they accelerated over and came back up to the surface sinking one of the merchants with 4 torps and quickly left the area on the surface getting setup for another run on the other merchant or two the escorts were protecting.

I'm in SH3, year 1940, running at 2 knots, silent running engaged submerged to 160m and there will be two escorts running over me dropping charges occasionally and they're very accurate! I'll be twisting and turning, changing direction but they'll stay on top of me for a good 2 hours before leaving. Also I dont submerge after they've spotted me on the surface, I'm going after a convoy at periscope depth undetected, hit a ship or two with torps, still running slow and silent engaged, tell them to go down to 160m and the escorts find me! This is even using electric torps that are wakeless! Day or night doesnt matter. Just wondering why they're so good?

In this time period I usually do surfaced attacks and the escorts come right after me once I fire electric torps but I can usually escape running at flank speed up there. I'm just comparing the game to how it really was wondering about the differences.

I know I'm comparing the allies to the japanese who werent the greatest at ASW but in the book it was 1943, the Japanese had radar units, sonar equipment, surely in a better position to detect submarines than the allies in 1940!

[Takeda Shingen]

Originally Posted by Crosseye76

500 feet should put you below the layer. Without VDS, you can be pretty noisy and a Surface ship won't be able to hear you, or Ping you.

I don't think SH3 has the layer, but I think I read somewhere on the forum that SH4 will have a basic one.

SH3 does not have layers modeled. However, depending on the sea state, climate, current, time of year, or any number of other conditions, you can have a very deep thermal boundry, sometimes in the neighborhood of 1000 feet. In some cases, you just can't be under the layer.

[OneTinSoldier]

Originally Posted by CruiseTorpedo

Also I dont submerge after they've spotted me on the surface...

I'm not real sure what you meant by that(i'm sure i'm misunderstanding) but I know I submerge pretty quickly after being spotted on the surface! if they are a good ways off I might, punch it, put them at my 180, then get up to full speed(turning causes a little loss in speed), and then submerge. But I certainly submerge.

As for the rest, how well they can hear you seems to depend on how good of a crew they have, and in 1940 there are some Elite crews. Those guys and perhaps one notch below elite can hear you at 2 knots(in GWX) if they are close enough. You need to make sure you've issued Silent Running, and then go to 1 knot! As it's been said already, the faster the speed you have commanded the more noise your engines make, and in GWX 1 knot is truely 'silent speed', whereas 2 knots still make a enough noise for a good crew directly overhead to be able to hear you, even in 1940. In 1940 there's just fewer of the really good crews, and although rare, there are some!

I once had a couple of guys doing just what you describe for a good while, running directly over me, dropping charges occasionally. Im like, man... I'm running at 1 kt occasionally putting it back up to 2 for just a bit after I 'hear' them pass by overhead. Ocassionally I would change course by 30 or 40 degrees. But man, they keep coming directly overhead! Wth!?! I look around... DOH! I had secured from Silent Running to pump out a little flooding and do some repairs and had forgotten to reissue silent running!




After I reissued silent running and ran at 1 knot they began to lose me right away. But I could tell one of them had an Elite crew(hence my need for repairs), and this was early in the war.

Cheers

[CruiseTorpedo]

Originally Posted by OneTinSoldier

I'm not real sure what you meant by that(i'm sure i'm misunderstanding) but I know I submerge pretty quickly after being spotted on the surface! if they are a good ways off I might, punch it, put them at my 180, then get up to full speed(turning causes a little loss in speed), and then submerge. But I certainly submerge.

Oops, I meant I go under to periscope depth long before I'm spotted.

I tried something different, I dismissed all of my lower ranked petty officers and crewmen and spent renown on a better set. I still have a good 6 or 10 crewmen that are at the 1 stripe level but all my petty officers are 2 dots or better now. I met a convoy in AL67 area and did my usual setup. Coming into the convoy from about 30 degrees off their bow. They had a destroyer in front and smaller escorts on the sides and something in the rear. Light fog was in effect as usual so I was watching with my binoculars manually to see the ships in time. With decks awash I saw the lead destroyer at 7km away (normal crew eyes wouldnt say anything till 4.3 or so, stupid fog). So I ducked under the waves, silent engaged, and went ahead at 2knots. Once I was inside the escort I turned around to make my ship going ahead part of the convoy only much slower so they could overtake me and I could fire my torps. Things went as normal at this point, I looked around with my scope and picked out some big ones and fired. This time though after the torps went off the escorts didnt know where to go and the one nearest to me kept it original course!

I dont know if it was the crew or like you said I was running into very good escorts. I'll find out in my next few encounters if the escorts find me like a neon sign in the night or if they're guessing as to where I went.