[Sawyer]

Originally Posted by Thad E Ginathom

I have seen a single-cylinder small-boat engine of the simple diesel kind. To start it, you open a valve so that there is no compression. You turn it by hand until the flywheel has enough momentum to turn against the compression and close the valve. Boom, it fires, and, hopefully, goes on firing.

Yes, but does it do this while connected to the prop or is there some kind of clutch in the middle to disconnect the load? Else doesn't that get too much of a load for the hand to turn over? Cars started this way in the past by a handle, but when left in neutral. Or was that just so it did not run over you when the engine started?! That would be a Laurel and Hardy moment. Or if it ran away from you if left in reverse.
PS: sorry, did not think. A car in gear won't budge, so I can't see anyone being able to start it with a handle either. Not even Ollie! So will a boat engine?

[Brumby]

@sawyer the props are direct drive on low speed diesels, as mentioned they work in a yielding medium, there is very high slippage. We just make sure that before starting the engine the prop is clear and the ship is ready to sail.

[Sawyer]

Got it; so what you are saying is that the slippage between the water and the propeller acts like a fluid drive auto box instead of like a manual clutch.

[Jeroen]

Originally Posted by V.Narayan

Interesting. So the Master doesn't say 'Chief Engineer give me 18 knots' instead he says 'Chief Engineer maintain 120 rpm'. Did I get that.

Well, sort of. On most modern ships the engine(s) will be directly controlled from the bridge. So there is no calling to the engine room. At best a command to whoever moves the Throttle handles on the bridge.

The first ship I sailed on (1979) still had a proper old fashioned telegraph. So the bridge would 'ring' for "half ahead", slow astern etc. etc. That showed up in the engine control room and we would manually adjust the engine settings. We had two levers for the engine. One determines ahead or astern (as we discussed earlier) The other one was starting and engine speed.

If the bridge gave an order on the telegraph, eg. slow ahead, you first had to acknowledge that on the telegraph by moving a lever. There was mechancial interlocking between the telegraph and the engine controls. If the bridge asked for ahead, you had to acknowledge ahead. If the engine ahead/astern lever was still in astern you could not start the engine. To start you moved the other lever to the start position. Then you watched the RPM needle and listened to the sound of the engine. Took a bit of practice and experience. But as soon as it moved through 40 RPM you moved the lever further which meant fuel would be injected and air starter valves were closing.

Even these days with full bridge control you find modern versions of telegraphs. Just in case the bridge control system breaks down, the engine room will take over, based on the telegraph as in the old days. And the captain can still call the Chief engineer at any point in time as well of course!

I'm not sure but calling for a certain number of revolutions is more a navy thing then a merchant navy thing, I think. Not sure, maybe others could chip in here.

Originally Posted by V.Narayan

. Why do warships (those which are diesel powered) have medium speed diesels that run (I think) at say 1000 to 1200 rpm. What factors/needs lead to a medium speed diesel being a more appropriate choice for a naval frigate.

There are various factors to be considered. But one of the most important one is the size of these low speed engines. They are absolutely huge!So you need a lot of space to accomodate them. No problem on a big tanker or container ship. Quite a bit of a problem on something a bit sleeker.

You will find medium speed engines on just about all ocean going tugs, supply vessels, anchor handling tugs, RoRo vessels, ferries and quite a number of war ships.

It means the engine room can be kept quite low. It also provides redundancy as they typically have two or four main engines. It allows for having two propellors, which again is more redundancy and makes for better manoevrability.

One other thing is that these huge slow speed engines dont do well with quick changes in loading, especially at the high end of their specfiication. It could take several hours of slowly increasing the RPMs from what is known in maneuvring full speed to cruis full speed.

Medium speed engines tend to accomodate this much better/quicker.

Ferries often sport four medium speed main engines and you will find they might have different power outputs, usually per pair. So they might have two 10.000HP and two 6.000HP engines. So they have 32.000hp in total, but depending on what speed they need to sail they might only run the two 10,000 or two 6.000HP engines. A lot more efficient. Especially if you go diesel/electric this becomes even more relevant.

Hope this helps. And all current marine engineers, please jump in. My knowledge and experience is dated at best!

Jeroen

[V.Narayan]

Originally Posted by Jeroen

Well, sort of. On most modern ships the engine(s) will be directly controlled from the bridge.
The first ship I sailed on (1979) still had a proper old fashioned telegraph. So the bridge would 'ring' for "half ahead", slow astern etc. etc. That showed up in the engine control room and we would manually adjust the engine settings.
One other thing is that these huge slow speed engines dont do well with quick changes in loading, especially at the high end of their specfiication. It could take several hours of slowly increasing the RPMs from what is known in maneuvring full speed to cruise full speed.

....might have different power outputs, usually per pair. So they might have two 10.000HP and two 6.000HP engines. So they have 32.000hp in total, but depending on what speed they need to sail they might only run the two 10,000 or two 6.000HP engines. A lot more efficient. Especially if you go diesel/electric this becomes even more relevant.

Jeroen

Dear Jeroen, thank you for that detailed answer. Filled my needs in full. Regards, Narayan

[Thad E Ginathom]

Originally Posted by Sawyer

Yes, but does it do this while connected to the prop or is there some kind of clutch in the middle to disconnect the load? Else doesn't that get too much of a load for the hand to turn over?

No, but probably not. Small craft have gear boxes with forward, neutral and reverse gear. The weight of the prop and shaft might not be that much, but why add work. My dad taught me to depress the clutch when starting any car engine. Two reasons: safety, and slightly less load on the starter motor. Looked at the other way, you can run the engine slowly, in gear, without putting much strain on your mooring lines.

Cars started this way in the past by a handle, but when left in neutral. Or was that just so it did not run over you when the engine started?! That would be a Laurel and Hardy moment. Or if it ran away from you if left in reverse.

I'm so old that I remember there being a starting handle under the seat. Pre-alternator days, and less reliable stuff generally, flat batteries were not that unusual. I don't recall it getting much use, but I did get a demonstration. According to my Dad, the biggest risk was a broken wrist if the engine started driving the handle. There was a knack; I've forgotten it.

PS: sorry, did not think. A car in gear won't budge, so I can't see anyone being able to start it with a handle either. Not even Ollie! So will a boat engine?

Famous WW2 film: Guys getting a broken-down truck across a desert. getting the thing up hill... backwards, (reverse is the lowest gear) by turning the starting handle.

I was going to add that you cannot push start a boat. Of any size. Sounds clever! But wait, the water motion past the propeller of a boat can make it spin. I don't think it can start the engine though. I have never, ever heard of such a thing being done. I have never ever read of it being done. I did a lot of reading back then, and remembered a lot of handy hints and emergency stuff. It made me a useful crew member

[Sawyer]

Originally Posted by Thad E Ginathom

the biggest risk was a broken wrist if the engine started driving the handle. There was a knack; I've forgotten it.


I was going to add that you cannot push start a boat. Of any size. Sounds clever! But wait, the water motion past the propeller of a boat can make it spin. I don't think it can start the engine though.

Just like one can sprain - or break - an ankle kick starting a Bullet of the old style. One has to learn to feel which stroke isn't the one to kick against or through - or more accurately, which of the four is.

As to the boat, I suspect the slippage issue spoken of earlier here will mean that the speed of the water past the prop via the motion of the boat has to be fairly high to get it to move and getting there via pushing the boat may be not achievable.

[Brumby]

The main reason for warships using either medium speed engines or gas turbines is quick manoeuvrability, war ships are more about quick movements, slow speed diesels take a long time to stop and change directions due to a large amount of inertia (momentum). Medium speed four stroke engines are usually equipped with gearboxes and CPP, controllable pitch propellers, the engine continues to move in the same direction and reversing the propellers does not cause undue stresses on the engine components. As mentioned by Jeroen, space is a big constraint on warships.
The marine engines have changed a lot in the recent years and have gone camless with the peak pressures coming in early due to the ability to control the fuel injection timings electronically. The marine 2-strokes, have further moved to used natural gas as fuel.
There's a lot about the latest technology being used in marine applications and how the marine engine rooms have changed over time from being rusty and dirty to spic and span, engines using the residue in the distillation process of crude oil and still meeting the requirements to prevent air pollution.

[Brumby]

Originally Posted by Thad E Ginathom

No, but probably not. Small craft have gear boxes with forward, neutral and reverse gear. The weight of the prop and shaft might not be that much, but why add work. My dad taught me to depress the clutch when starting any car engine. Two reasons: safety, and slightly less load on the starter motor. Looked at the other way, you can run the engine slowly, in gear, without putting much strain on your mooring lines.
I'm so old that I remember there being a starting handle under the seat. Pre-alternator days, and less reliable stuff generally, flat batteries were not that unusual. I don't recall it getting much use, but I did get a demonstration. According to my Dad, the biggest risk was a broken wrist if the engine started driving the handle. There was a knack; I've forgotten it.


Famous WW2 film: Guys getting a broken-down truck across a desert. getting the thing up hill... backwards, (reverse is the lowest gear) by turning the starting handle.

I was going to add that you cannot push start a boat. Of any size. Sounds clever! But wait, the water motion past the propeller of a boat can make it spin. I don't think it can start the engine though. I have never, ever heard of such a thing being done. I have never ever read of it being done. I did a lot of reading back then, and remembered a lot of handy hints and emergency stuff. It made me a useful crew member

The engines do spin due to the motion of the ship. Ships with two or more propellers (even with a slow speed 2-stroke engine) are fitted with a clutch to dis-engage the shaft in case one of the engines develop a problem, e.g. loss of lube oil pressure. A propeller turning due to the momentum of the ship is called as free-wheeling.
If the main propulsion engine trips while the ship is moving at its rated speed, the prop keeps turning for a while, if the reasons for the trip are restored and reset within this time the engine starts and maintains the rpm as per the command from the control system. No starting air is required in this case.
These large 2-stroke diesels do not have any accessories which are engine driven like in four stroke medium speed diesels or automobile engines. The lube oil pump, cooling water pump, fuel supply pump etc are all driven by electric motors which run on the power generated by the diesel generators.
There are marine applications where in an alternator is a part of the transmission shaft and is called shaft generator. Shaft generators are available for connection to the switch board after a certain rpm has been reached and at a time when the ship is out at high seas and will continue to maintain certain minimum rpm. Once the shaft generator is connected to the electrical systems the main engine becomes self sufficient, but it cannot start from a blackout condition like the auxiliary generators can.

[Jeroen]

Originally Posted by Brumby

The engines do spin due to the motion of the ship. Ships with two or more propellers (even with a slow speed 2-stroke engine) are fitted with a clutch to dis-engage the shaft in case one of the engines develop a problem, e.g. loss of lube oil pressure. A propeller turning due to the momentum of the ship is called as free-wheeling.

If n.

I have sailed on dozens of ships with two engines or one but none had a clutch. Obviously the medium speed engines all have gear boxes, but none of the ships I sailed on had main engine clutched. They did have pitch control propellers so in theory you could minimise drag when one failed. But even then it turned and you needed to keep the lub oil pumps running. Still not very advisable for prolonged period of usage.

I have never seen a clutch for a large stroke engine even when used in dual configurations such on container ships.

On ships with multiple engine configuration as I described earlier I have seen ways on clutching engines in and out. But I have never sailed wit these.

What kind of clutch would a 60.000HP slow speed engine have? Any references or examples we can look at?

Thanks Jeroen

[Brumby]

I agree that you must have sailed on a twin screw ship without a clutch but there must have been an auto slowdown function on the engines in case one trips. As a recent experience, if one engine is running at slow ahead, there is not enough drag to cause rotation of the other shaft.
Regarding the clutch, it's two splined shafts engaged through an internally splined sleeve kept in place through hydraulic pressure. Once disengaged, it's a real pain to engage them because the clutch won't engage until they are perfectly aligned.
The reasons for providing this clutch is to have manoeuvrability even if an engine has a breakdown. You can even carry out piston de-carb while the ship is still sailing at a reduced speed.
If a ship moving at say 30 knots, just imagine what will happen to the bearings and the crankshaft if the lube oil pump trips and the stand by pump did not start. We are looking at wiped out bearings and a crankcase explosion due to high oil mist density.

[Jeroen]

Originally Posted by Brumby

I agree that you must have sailed on a twin screw ship without a clutch but there must have been an auto slowdown function on the engines in case one trips. As a recent experience, if one engine is running at slow ahead, there is not enough drag to cause rotation of the other shaft.

Regarding the clutch, it's two splined shafts engaged through an internally splined sleeve kept in place through hydraulic pressure. Once disengaged, it's a real pain to engage them because the clutch won't engage until they are perfectly aligned.

The reasons for providing this clutch is to have manoeuvrability even if an engine has a breakdown. You can even carry out piston de-carb while the ship is still sailing at a reduced speed.

If a ship moving at say 30 knots, just imagine what will happen to the bearings and the crankshaft if the lube oil pump trips and the stand by pump did not start. We are looking at wiped out bearings and a crankcase explosion due to high oil mist density.

No, output shaft from the engine connected to the gearbox. Output shaft from the gearbox connected to the propellor shaft. Nothing else.

Only a variable pitch. These vessels would not be doing 30 Knots, more like 12-14 knots maximum. Ocean going tugs, AHTs, supply vessels are rarely build for speed.

Jeroen

[Brumby]

As you said Sir, those were medium speed engines and usually are not reversible because they have CPP. The other thing is the speed which again as you mentioned, is not high in the crafts that you mentioned, so the example which I gave was for ships with slow speed diesels, which can do more than 15 knots, fitted with twin engines and do not have CPP.
There are so many exceptions and have their own reasons and explanations. I have sailed on a single screw pure car carrier with a reversible slow speed diesel engine and still had a CPP (LIPS control).

[Jeroen]

Originally Posted by Brumby

. I have sailed on a single screw pure car carrier with a reversible slow speed diesel engine and still had a CPP (LIPS control).

I have come across similar set ups. The early so called A/series AHT/Supply vessels of SmitLLoyd had reversible engines and CCP, also Lips.

Not quite sure why . But these ships were designed and built in the 70s. Most marine engine were reversible as standard and CPP was relatively new. So I guess they felt it was easy and provided a little bit of extra guarantee on having reverse power, no matter what.

to your earlier post, I have sailed on a few vessels with shaft generators. They, obviously, have clutches. Once, the clutch broke and we could not unclutch it anymore. This was a problem. If the generator would be run for extended period of times with no load it would damage the gear box. So we had to actually find a way to remove the whole of the clutch. I can t quite remember the details, other than it was a real PIA. Took us close to 12 hours of continuous work with 4 engineers to get it out.

But if it worked it was a very good setup. No aux engines running, very efficient.

Just came across this little video. Tug Holland during manoevring. You can clearly hear the starting air and see/hear the engine picking up revs and then start to run on fuel

https://www.youtube.com/watch?v=5whJG3S99uM

Jeroen

[Brumby]

Shaft generators have changed a lot and are a part se the transmission shaft, no more clutches. The rotor starts rotating the moment engine is started. These type of generators are available after a set minimum rpm. They generate higher AC voltages, converted to DC and then again converted to AC. Thyristors are used for the purpose and it eliminates the troubles with change in frequency due to change in rpm of the main engine, they can even run in parallel with the auxiliary generators.
I do remember working on a ship with a shaft generator which had a clutch & gearbox and could be used over a very short range of the rpm.