Back Emergency to Slow down
 

So when Your going across the Big map moving to mission areas and run into an unexpected enemy at 20 knots it takes a bit of time to slow down and for the sensors/sonar to work. I can slow down in a hurry by going to back emergency, I been on boats where this has been done and it makes big wakes, disturbances, and air bubbles. Anyone know if Im setting off signal flairs and laying out the welcome mat for the Russians doing this? With the new update I am still doing alright with subs but surface encounters are still giving me trouble so its hard to tell, I dont get cavitation warnings, anyone know?

Thanks
Jay

You're not giving away yourself. You are rapidly decelerating so your flow noise and engine noise will decrease quickly.

I'm sure one of our resident submariners could give us a definitive answer, but you'd think going all back emergency would make a heck of a racket. After all, the screw is only optimized to turn one way, and the pumps would probably shift to high speed.

I guess it depends. :hmmm:
Real world, its not like you're shifting gears from the helm.
All you're doing is turning the dial on the announceator which makes the pointer move on a similar dial back in Maneuvering.
Its up to the throttleman to see the new order and turn the "big wheel" to drive the screw, just like when you give a spoken order to "make turns for X knots".

So, I guess you can assume that you have a sharp throttleman back aft who knows you want to slow down fast. :D

In thinking about it more the screw is attached to a electric motor and with an electric motor you can use induction to instantly reverse the polarity, which then works like a giant brake on the motor at the expense of heat generation ( I think? going off of my very limited knowledge of how trains work and driving a Prius :up: ) just flip the switch on the side of a ceiling fan when its spinning on high to see what Im referencing, now image if your ceiling fan blades were in water, consider how quickly they would slow down. Im sure with some testing at a place like the The Navy's Acoustic Research Detachment in Idaho they could work out a chart which got me down below 10 knots with the best risk vs reward for noise crated vs the disturbance I made in the water. Of course it would probably be contained in a chart with a million curves and lines for each 25 feet of depth and each 2 knots of speed I was going and require the use of a slide rule to decipher but thats part of reward of being a sub captain!

Yes.. it makes one HELL OF A LOT OF NOISE. HUGE "HERE I AM" TRANSIENT NOISES.

In reality you slam the forward throttle closed and open the astern throttle rapidly without regard to cavitation. You do not shift pumps unless ordered. You will answer the bell to the maximum limit of the current plant lineup.

This spins the screw in the opposite direction creating HUGE amounts of cavitation. The idea is that you are gonna hit something anyway and you can at least try to cut down on the damage done in the collision.

While I am on this tangent, if you want to slow down you ring up all stop. The boat will continue in the water but the screw will act as a brake. It is still turning but the drag of the water will slow the boat down. Think of it as coasting in a car. Drag will slow you down. You never, NEVER, NEVER open the astern throttles unless you are in an emergency, docking, or are in restricted maneuvering operation.

But hey.. its a game.

It sounds like we're both talking about "Crash Backs". :D

I had a buddy who was standing throttleman watch after we finally got good old Ustafish out of a long overhaul.
Our skipper had been talking about doing crash back drills so up in Control it wasn't that big of a surprise when the OOD ordered a backing bell while we were cruising along.
I guess the skipper didn't like the reaction time (putting it mildly) and he set a speed record sprinting from Control to Manuvering. :timeout:

Allegedly, our skipper took control of the throttles manually while he chewed out my bud and the RO. :timeout:

Now, anyone who ever stood watch back aft or made it through quals in general can say, "Hey, that part of the story IS REALLY MESSED UP!!" and you would be right. :yeah:

Getting back on topic, yeah you could order a backing bell IRL if the situation is dire enough but we're talking about a game where the whole point is to beat the Devs. :haha:

Beat the devs.. yeah... that is a good way to put it. If we could make this game even 40% consistent with actual ops people would lose their minds.

To give more detail for those who are wondering:

There are two sets of throttle. One controls spinning the screw in ONE direction, one turns it the other direction.

I can not go into the physical plant layout but I can tell you this with 100% certainty. You do not EVER open the astern throttles to slow down. The ONLY time they are opened is to spin the screw in the opposite direction.

As an aside. If you are streaming the tail and you answer a backing bell then you can with almost 100% certainty loose the tail. Bad day in the sonar shack.

Well, to go even deeper- :D

The OP mentioned electric motors as a kind of justification but even that is shaky.
My first boat was the Barbel. Three standard navy diesels that turned generators which fed the battery wells which then fed two large electric motors coupled to a common shaft. No reduction gears and you still wouldn't want to just chuck it into reverse. :o

The best way to torture an electric motor is to do what's known as a Blocked Rotor Test. The motor sees the maximum possible amperage load and if the windings, cables, and brushes don't burn or blow up- you've got a good motor. :up:
Now imagine the stress of reversing the field while the motor is running near its rated speed (at some point you'll also block the rotor for a couple of seconds). :o

Add the additional force of the screw as it is moving through the water thus making want to continue to spin in the same direction. You are adding to even MORE counter torque than just stopping the shaft and reversing it. Take your blocked rotor test and double the amount of stress due to counter electric motive force.

Not in any of the US boats we have in game. In most nukes the prop is spun by the turbines through the reduction gear. Or directly in the case of Narwhal.

Well that makes sense. Steam turbines only work in one direction so if you wanted to spin the shaft both ways you would need backing turbines in addition to ahead turbines, each with their own throttles, and you would not want them fighting each other.

During my time in the surface fleet, back emergency was only allowed to be called by the CO.

Normally, the axle would rotate at 80rpm at minimum and with pitch control of the blades, you'd get your propulsion from changing pitch in those conditions where the 80rpm and little pitch was enough for you. When exceeding these limitations, the axle rpm would be increased to max 200 or so.

When ordering back emergency, the pitch of the blades would be rotated to their reciprocal pitch leading to immense pressure on the screw blades, we didn't reverse the axle spinning direction.

Ahhhhh so more like a variable pitch prop on an aircraft! Well that was an obvious answer I should have picked up right away.

No, you're telling the crew back aft to slow the boat as rapidly as possible without blowing up the gears and seals. :yep:

Many people have no idea how "hands on" this stuff is IRL. :03:

You're ordering an approximation of something you and your crew have practiced in the past, you just don't remember doing it. :salute: