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Twin Screw From A Single Engine


FlyingFortress

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A friend has just sent me a link to a boat for sale that is the same as his.

The point of the link was just how much it was up for compared to what he paid for his earlier this year.

The strange thing was that it had twin screws running off a single engine. Now I can see how that can work with 2 hydraulic pumps but I have never heard of it before.

Has anyone else?

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11 minutes ago, FlyingFortress said:

A friend has just sent me a link to a boat for sale that is the same as his.

The point of the link was just how much it was up for compared to what he paid for his earlier this year.

The strange thing was that it had twin screws running off a single engine. Now I can see how that can work with 2 hydraulic pumps but I have never heard of it before.

Has anyone else?

There was a Sancerre for sale a few years back at Jones’ St Ives which had a similar arrangement , originally it was twin engine but when they died it was refitted with a 90hp beta engine with hydraulic drive to two props , apparently very successfully.

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35 minutes ago, CambridgeCabby said:

There was a Sancerre for sale a few years back at Jones’ St Ives which had a similar arrangement , originally it was twin engine but when they died it was refitted with a 90hp beta engine with hydraulic drive to two props , apparently very successfully.

Interesting 🤔

So not unheard of then.

Would the engine have to run at constant RPM to supply Sufficient pressure for the varying demand? Such as turning short round it has always, in my experience required more power on the astern engine than the ahead one if you don't want the vessel to gather headway.

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I've always wondered if that was an option for when I'm too knackered for sea and diesel is too expensive, I'm used to twin engines and have barely driven a single engine on shaft at all.

A single of about 90hp sat transverse in mine and smaller fuel tanks would give me a mass of space for a beer cellar....

Did the control levers work the same do you know?

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12 minutes ago, Smoggy said:

I've always wondered if that was an option for when I'm too knackered for sea and diesel is too expensive, I'm used to twin engines and have barely driven a single engine on shaft at all.

A single of about 90hp sat transverse in mine and smaller fuel tanks would give me a mass of space for a beer cellar....

Did the control levers work the same do you know?

There were 2 fairly standard looking control levers in the pictures.

With normal single screw hydraulics the first click (clutch in) starts the prop turning then by increasing engine revs the pump gets faster and prop rotation speeds up. Virtually impossible to tell the difference to a shaft drive.

I would assume this twin screw setup works the same.

So maybe the engine senses demand and increases revs accordingly. If that is the case then a pretty sophisticated set up for a Broads Boat.

Just wondered if anyone else knew more 

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Back in 1993 Jones at St Ives had for sale a boat they built  for a director of Handley Page it had two engines and three props two in wing housings that were hydrolic powered by a four cylinder Perkins and a six cylinder  Perkins that laid on its side driving a single prop though a gear box i nearly bought it, it was incredibly quirt and well fitted out someone bought it and moored it at The Waverny River Center it was called Gelder somthing. It was built to use on the French canals where the wing props where used the large centa prop for sea use. The reason i didn't buy it was you banged your head when at the galley sink and cooker due to a curved deck. John

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4 hours ago, Cheesey69 said:

From my plant days, variable valve? Engine stays at set rpm and solenoid detects how much fluid to flow by how far control moved
A bit like a 360 digger. All or none cylinders can be very accurately controlled.  
final speed by engine rpm of control movement. 

Thought it must be something like that.

Can not be good for fuel economy though.

Again at the risk of boring some people.

The CPP ( Controllable Pitch Propellor) ships that I worked on would have 2 modes of operation.

Combinators or constant speed .

Combinators were used when the ship was underway as the pitch of the prop increased so did the engine revs.

When working you need power available with no delay as in the engines spooling up so you run the engines up to max RPM and then the pitch controls could be operated without consideration.

If you went into the engine room you could actually see the engines moving on their beds as the turbo blowers spoiled up when the engines came on load.

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17 minutes ago, FlyingFortress said:

Thought it must be something like that.

Can not be good for fuel economy though.

Again at the risk of boring some people.

The CPP ( Controllable Pitch Propellor) ships that I worked on would have 2 modes of operation.

Combinators or constant speed .

Combinators were used when the ship was underway as the pitch of the prop increased so did the engine revs.

When working you need power available with no delay as in the engines spooling up so you run the engines up to max RPM and then the pitch controls could be operated without consideration.

If you went into the engine room you could actually see the engines moving on their beds as the turbo blowers spoiled up when the engines came on load.

That should have read spooled up.

It was known as Black Staking it 

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I once built a display panel in the Engine Control Room with interface to the CPP System on a channel ferry, because the Chief Engineer wanted a visual indication of what the bridge officers were up to on the telegraph and how the CPP system responded.

I was told that the CPP would automatically respond slowly to a change in bridge telegraph setting, so going from zero to full ahead on the bridge would result in the actual pitch slowly increasing unti it reached full pitch. Amongst other considerations, this is apparently to stop the sudden load from stopping the engine!!!  (Actually they had a total of 4 engines driving 2 shafts).

We all had a good laugh when I got it working.

As I recall it would take something in excess of 10 seconds to add the full pitch (maybe more, my memory is hazy now).

On the bridge they were using the telegraph just like they used to in the old days where a bridge telegraph just sounded bells and duplicated their settings on a readout in the engine control room. So we had the full ahead / full astern / ahead again movement on the bridge, followed by the gradual increase in pitch and before it had finished they were at it again and the CPP never reached it's set pitch until they stopped fiddling with the telegraph.

 

 

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54 minutes ago, TeamElla said:

I once built a display panel in the Engine Control Room with interface to the CPP System on a channel ferry, because the Chief Engineer wanted a visual indication of what the bridge officers were up to on the telegraph and how the CPP system responded.

I was told that the CPP would automatically respond slowly to a change in bridge telegraph setting, so going from zero to full ahead on the bridge would result in the actual pitch slowly increasing unti it reached full pitch. Amongst other considerations, this is apparently to stop the sudden load from stopping the engine!!!  (Actually they had a total of 4 engines driving 2 shafts).

We all had a good laugh when I got it working.

As I recall it would take something in excess of 10 seconds to add the full pitch (maybe more, my memory is hazy now).

On the bridge they were using the telegraph just like they used to in the old days where a bridge telegraph just sounded bells and duplicated their settings on a readout in the engine control room. So we had the full ahead / full astern / ahead again movement on the bridge, followed by the gradual increase in pitch and before it had finished they were at it again and the CPP never reached it's set pitch until they stopped fiddling with the telegraph.

 

 

I can believe that 😳

I was always a big fan of CPP until I became a pilot. The OSV's I worked on the response time from moving the levers to actually putting on the pitch was very very fast as when we needed power we needed it now. Hence the Black Stacking I mentioned above as the load came on and the blowers struggled to keep up.

When I became a pilot I found that the response time was excessive and sometimes even slower than waiting for an air start of a fixed prop. There is a different mentality in the offshore world to more conventional vessels as you are at real danger when working that close to an oil rig so the engines were seen as more consumables when the entire vessel was at risk.

With normal ships the engines themselves are better protected.

On many offshore vessels there was a function at the helm to override the automatic shutdown of an engine and run the engine to destruction if it would save the vessel. 

I was warned by engineers not to expect the phone to be answered if I ever activated this 😳🤣🤣

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The beauty, apart from safety, that is, of twin prop for me is one ahead and one astern, can it do that?

My father's Fairey Huntsman going back to the 60s could spin in her own length and leave a crowded Poole Quay as if she had modern thrusters,

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1 hour ago, ChrisB said:

The beauty, apart from safety, that is, of twin prop for me is one ahead and one astern, can it do that?

My father's Fairey Huntsman going back to the 60s could spin in her own length and leave a crowded Poole Quay as if she had modern thrusters,

I think that was the question I was asking but you put it better than me. 😳

If you can't split the props then I see little point. Two engines, now that is a real safety advantage 👍

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1 hour ago, ChrisB said:

The beauty, apart from safety, that is, of twin prop for me is one ahead and one astern, can it do that?

My father's Fairey Huntsman going back to the 60s could spin in her own length and leave a crowded Poole Quay as if she had modern thrusters,

Pretty much the bit I was wondering about.

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