Critical Speed Range

It's magic.

LOL!!

It's programmed.

Reason why during maneuvering, in E/R control and local, the engineer needs to do this himself.

Can be tricky sometimes, as you'd need to let the engine pick up momentum before making the jump.

Otherwise the whole ship is gonna continue dancing until the engine clears that band!

This may be particular to the specific engine and controls package on whichever vessel it is. Engine + fuel delivery + governor + wheelhouse/local controls. Probably too many variations for a forum-type answer.

It could have a flywheel that gives boost through the critical speed range...but probably just giving it more fuel...Is it a digital readout, it may be a digital control...

Propulsion engine critical speed is logged during ship trial and is programmed into engine control system.

Generator engine have same challenge too, however, that is normally way below its normal operating speed.

i.e.: you feel it during startup, that too for a brief moment.

Your tagline is incorrect. Lawyers are the oldest profession. Even before God got hold of the place, the world was Chaos, without form, and void. Just who do you suppose created the Chaos?

!!Almost everything discussed in engineering, and by direct association CR4, would always have precedent - think steam turbine and Hero.
I started looking for ways to cover my behind...... when that tagline zapped right across ethereal space before me !!
Epiphany moment ?Hell yeah !!
Chaos, linked directly to lawyers ?Too much credit to them.
Chaos Theory is deep science which I've very interested in.

I always thought it was 'hunter-gatherer' that was the oldest profession.

Finding food was first then processes of argue or trade services for it came later.

I was trying to do humor, rather than cultural anthropology!

Shaman...

No, 'Gold-Digger' is the oldest 'profession.'

Hunting and gathering is base-line survival; It doesn't count as a 'profession' until you're hunting/gathering enough so that each hunter/gatherer is supporting several others (aside from children) who are NOT hunting/gathering.

We've already seen in studies of various primates in controlled conditions and in the wild that there are females that will forgo the 'searching for food' task the others are doing, and they aren't doing anything 'productive' during this 'not going to forage' time; They're not caring for the group's kids (babysitting), they're not clearing debris and refuse from the group's home turf (housekeeping), they may sit and groom each other, but that could have been done when the whole group was together doing grooming/flea-picking. What they *DO* to is offer -ahem- 'playtime' to the returning males in exchange for a share of the gathered food.

'Shaman' came later, when one of the males thought, "Hey, these gals get food just for f--king the food-bringers, perhaps there's some way *I* could f--k the tribe and get food for free too."

Not all Shaman are male....there are nurses too....

I see many kinds of expensive medications in your future.....

True.

But I seldom let the facts get in the way of a good off-color joke, or even a bad off-color joke.

Isolate the RPM meter - sit it on a pillow. It may be vibration. Been there.

Good joke!!!

Hi Johnny, you have good memory!!

Programmed delay before jumping Critical Speed is to allow turbo(s) to settle and ship to gain momentum.

Alternatively, you could hit 90-110% throttle, for a straight-through - no pause required !

(Just be sure you're alone when pulling that off!!)

Bridge/Engine Room control - electronic.

Local - electro-pneumatic(solenoid valves)

Emergency Control - literally sitting on the engine while controlling it, - Full pneumatic.

There's normally a pneumatic diagram plate attached to the emergency control station.

Can be fun though, electronic controls failing every now and then, especially going up Misi-ziibi!!!

Forgive my ignorance but what is the 'critical speed' in this context?

Why is it important?

Is it the ship knots through the water, propeller rpm, or engine rpm, or what?

If I knew, it might help me appreciate the value of some of the CR4 replies.

Just wondered.

In this context, a critical speed is one at which a resonance can develop and vibration become severe. Either by calculation or experience, one can determine what speeds to avoid, and set up "skip bands" in the control system.

The OP seems to be dealing with a large marine engine.

Ever have a car with the tires out of balance?

At a certain speed,there is very much shaking.

Above or below that speed it is fairly smooth.

Car engines have a harmonic balancer on the front of the crankshaft to compensate for this effect.

Large engines have the same problem with harmonics,but a harmonic balancer would weigh tons,and be impractical,therefor they simply skip past the harmonic zone instead.

I have coffee to prevent this.

It usually occurs after about 1 hour from my last cup,and knowing this,I try not to go that long without a caffeine fix.

If I do,I begin to "un-shake",which is a prelude to shake.

Like when you slow down with the unbalanced tires,it is worse than speeding up.

The un-shake zone is much worse,and is out of phase with the shake zone,tending to

make one zig when they should zag,and visa versa.

Do not try slalom skiing or skate boarding in this state.

I have left DNA on trees and concrete,so take my advice.

Thanks 19# & 20#. Now I understand. I am not aware get of a critical fast speed for my narrowboat diesel engine (is it only diesel?) but I know if tick over is adjusted too very slow, the engine tries to leap off the shock-absorbers - which doesn't do the rigid prop-shaft much good - so minimum speed is a bit high to avoid it.

Its the RPM that might severely damage the engine, it would start to shake itself to bits.

I don't have huge onboard diesel experience, but all had an area marked in red on the RPM gauge, many years ago..

It was 109 revs on one diesel ship I was on, I believe it was a WW2 liberty ship!! It was still in service with the RN in the 60s...Pistons almost a yard across.....8 cylinders.....

At a particular speed, about 70 RPM plus or minus 3 or 4 RPM, the entire engine (looking down the length of the engine from the control room) appeared to serpentine along it's length. Maybe it was my eyeballs vibrating but the ship wasn't a pleasant place to be right then.

They had a spare piston hanging from the girders - about 3 feet in diameter. This was a six cylinder from memory - a MANN.

"Maybe it was my eyeballs vibrating but the ship wasn't a pleasant place to be right then."

So either A) the drive shaft was twisting in disconcerting ways, or B) your body was being vibrated so strongly that your own eyes were producing optical illusions. Both those scenarios seem to have the same solution: Get the heck out of that room and adjust the throttle to move the engine's RPM out of that 'strange/cursed frequency.'

Everything that rotate can, and will have a critical speed range.

When starting up stationary genset, pay attention to that way out of norm "bbbrrrrr", whereby the whole engine 'shudders', while on it's way to normal operating speed/rpm.

That's you critical speed.

It's just that, especially, for slow speed marine engines, this happens to be in it's normal operating range, i.e.: usually between 30-55 rpm.

Critical speed is normally logged 'on site', i.e.: as fitted on a given hull, since this is a global phenomenon, i.e.: hull it's on contributes to its critical speed behavior.

Didn't they have this problem on Avro Vulcan, for the same reason?!!

Apparently, the engines "rang like a bell", at the particular rpm when the plane is about to take off.

That's critical speed - at its deadliest !!

"When starting up stationary genset, pay attention to that way out of norm "bbbrrrrr", whereby the whole engine 'shudders', while on it's way to normal operating speed/rpm."

Ah, that explains my Jeep's tendency to "growl" at idiots driving too slow on the highway.

1. I have to brake when coming up behind them, which drops my transmission to a lower gear.
2. When accelerating after changing lanes, the vehicle goes from it's 'crusing' RPM of 2,000 to around 3-4,000 as the automatic transmission lags in responding to the engine.
3. The 'critical speed' for my engine looks to be around the 3,250-3,500 RPM range, which the vehicle reaches right about the time the engine compartment is even with the driver's door.
4. By the time I have pulled up where my rear bumper is even with the other driver's door, the transmission has caught up and shifted back to the 'highway gear,' and the engine has dropped back to 2,000 PRM.

way back I read about a boat racer that used a Ford inline 6 in his racer. He wrote to Ford about his successes with it and told them he was turning it to 7,000 RPM. They replied that that was impossible because the engine went into destructive harmonics(that snaps the crankshaft) at 5 thousand and some RPM. He replied that it went through that RPM range so fast it did not have a chance to vibrate!

Austin Healey Sprites of the 50s and 60s had a similar problem with the cast iron, only 3 bearing crank in many A series engines.

Luckily there were steel ones reasonably priced that held better....not from BMC!!