Author Topic: Chris's Build of Battleship Ohio Engine  (Read 123673 times)

Offline crueby

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1215 on: May 22, 2023, 04:05:14 PM »
It took me a little while to work out why the slot is at a funny angle to the arm. It is quite a subtle piece of geometry. It appears to be designed so that the cylinder can be 'linked-up' running ahead, but the adjustment has very little effect on the timing when running astern.

If the slot were at right angles to the arm radius, as one might at first expect, then any adjustment for running ahead would result in over-travel of the expansion link when moved across to the astern position. Or someone would have to frantically un-twiddle the knobs before yanking the reversing handle.
Yes - here is the page from the Naval Machinery book that talks about it:


Offline crueby

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1216 on: May 22, 2023, 06:25:15 PM »
The keyways for the crank arms are made and everything assembled:


A video to show it in action:
<a href="https://www.youtube.com/watch?v=hGraLgOEDsM" target="_blank">http://www.youtube.com/watch?v=hGraLgOEDsM</a>

And when I left the room for a minute the shop elves decided to invent the 'Boss-a-pult'   :lolb:
<a href="https://www.youtube.com/watch?v=wbi_wPoai4s" target="_blank">http://www.youtube.com/watch?v=wbi_wPoai4s</a>

The reverse engine is done, next time will move on to the eccentric arms and the reverse links!

Offline tghs

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1217 on: May 22, 2023, 06:52:53 PM »
standard treatment of the FNG...
what the @#&% over

Online Kim

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1218 on: May 22, 2023, 08:02:19 PM »
That is very slick, Chris!  Love the boss-a-pult!  :ROFL:

Kim

Offline cnr6400

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1219 on: May 22, 2023, 08:20:25 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:

re the boss-a-pult : "It was only then that Stu Pervisor realized he'd (messed) up."   (translated from toolroomese cause it's a family show)  :Lol:
"I've cut that stock three times, and it's still too short!"

Offline derekwarner

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1220 on: May 23, 2023, 02:07:29 AM »
That piloted reversing system in action looks spectacular Chris....'so little effort to achieve the movement of such mass'  :stickpoke:

A credit to the original designers ......[over linkages & fulcrums & linkages]

Question.......have viewed all of the postings, but unsure if I have missed.....'can the engine be reversed without coming to zero revolutions?'  :headscratch:

Derek
« Last Edit: May 23, 2023, 02:51:42 AM by derekwarner »
Derek L Warner - Honorary Secretary [Retired]
Illawarra Live Steamers Co-op - Australia
www.ils.org.au

Offline crueby

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1221 on: May 23, 2023, 03:51:22 AM »
That piloted reversing system in action looks spectacular Chris....'so little effort to achieve the movement of such mass'  :stickpoke:

A credit to the original designers ......[over linkages & fulcrums & linkages]

Question.......have viewed all of the postings, but unsure if I have missed.....'can the engine be reversed without coming to zero revolutions?'  :headscratch:

Derek


In the video that Michael posted they did exactly  that, though I  would  think that  doing so at high speeds would  put an awful lot of  strain on the parts, the mass of the prop as well as the engine is a lot! 

Offline Michael S.

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1222 on: May 23, 2023, 09:58:06 AM »
In the video, a maneuver to cast off the ship is being carried out. They say the machine only runs at 20 to 40 revolutions. It doesn't seem to be a big strain on the machine.
I once read that the Titanic took more time to turn back. It could be that she didn't have the cylinder to reverse but a rotary machine as drive. For ships of war it has to be faster.

Michael

Offline internal_fire

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1223 on: May 23, 2023, 03:50:26 PM »
In the video that Michael posted they did exactly  that, though I  would  think that  doing so at high speeds would  put an awful lot of  strain on the parts, the mass of the prop as well as the engine is a lot!

I thing if the timing is correct and perhaps with a bit of luck an instant reversal can be done without damage. It would get one's attention, however, since the prop would be rotating against the vessel motion. Lots of noise and vibration at the least.

The primary problem is likely the introduction of high pressures in the low-pressure parts of the engine, such as the intermediate receivers and pistons.

The Handbook for the Care and Operation of Naval Machinery says,

"Reversing. When reversing, the throttle should first be closed ,
and engine then reversed ; but when the emergency signal is received
(that is, a signal to back full speed when going ahead) , the engine
should be immediately reversed , even at a risk of breaking something.
This signal should never be given from deck unless it is an emergency
signal."


https://books.google.com/books?id=6rQ3AAAAMAAJ&dq=Handbook+for+the+Care+and+Operation+of+Naval+Machinery&printsec=frontcover&source=bl&ots=CvVxydp74M&sig=jAoSe_dxumddbp0Um-emhG6gjPw&hl=en&sa=X&oi=book_result&ct=result#v=onepage&q=Handbook%20for%20the%20Care%20and%20Operation%20of%20Naval%20Machinery&f=false

Gene

Offline crueby

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1224 on: May 23, 2023, 04:40:19 PM »
In the video that Michael posted they did exactly  that, though I  would  think that  doing so at high speeds would  put an awful lot of  strain on the parts, the mass of the prop as well as the engine is a lot!

I thing if the timing is correct and perhaps with a bit of luck an instant reversal can be done without damage. It would get one's attention, however, since the prop would be rotating against the vessel motion. Lots of noise and vibration at the least.

The primary problem is likely the introduction of high pressures in the low-pressure parts of the engine, such as the intermediate receivers and pistons.

The Handbook for the Care and Operation of Naval Machinery says,

"Reversing. When reversing, the throttle should first be closed ,
and engine then reversed ; but when the emergency signal is received
(that is, a signal to back full speed when going ahead) , the engine
should be immediately reversed , even at a risk of breaking something.
This signal should never be given from deck unless it is an emergency
signal."


https://books.google.com/books?id=6rQ3AAAAMAAJ&dq=Handbook+for+the+Care+and+Operation+of+Naval+Machinery&printsec=frontcover&source=bl&ots=CvVxydp74M&sig=jAoSe_dxumddbp0Um-emhG6gjPw&hl=en&sa=X&oi=book_result&ct=result#v=onepage&q=Handbook%20for%20the%20Care%20and%20Operation%20of%20Naval%20Machinery&f=false

Gene
The thing I was wondering about was the stresses on the engine/crankshaft when reversing at speed on a large ship due to the massive weight of the propeller spinning in the one direction and the engine trying to reverse all of a sudden. The forces from a multi-ton prop on a large ship must be enormous. On a little steam launch that would not be a big issue, but on a full size battleship it seems like a great way to shear something off, a huge flywheel-type mass being reversed by an 8000hp engine...

Offline internal_fire

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1225 on: May 23, 2023, 05:17:09 PM »

I am not sure the available torque would be more than in normal operation. The engine reversal might be slowed by the prop inertia, but it is not clear the forces and torques would be greater.

Gene

Offline cnr6400

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1226 on: May 23, 2023, 05:48:19 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:

Chris, I think an additional factor to consider is hydrodynamic forces acting on the prop / transmitted through the machinery during an engine reversal. The hull would continue to move through the water by inertia, although decelerating. The wash passing the prop as it starts to turn backwards after engine reversing could result in some very large twisting forces in the prop and also a large torque in the shaft I think. No idea how to calculate these forces, but there may have been some rules of thumb among the naval architects and engineers about this. This info may or may not have been widely published as it may have been considered trade secrets by the various shipyards or possibly strategically important by the various Navies worldwide.

It could also be that the naval architects and engineers did best calcs they could then applied the standard rule of railway equipment design - "if it looks good and strong, double it"  :Lol:

(I used this approach to design my 1" wide 8" long gasket scraper in 3/8" thick gauge plate) :Lol:
"I've cut that stock three times, and it's still too short!"

Offline crueby

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1227 on: May 23, 2023, 06:54:45 PM »
Well, whether or not it could happen on the real ship without leaving the prop behind on the harbor floor, on the model it should be possible to reverse with the engine running. I won't be trying it too fast though! 

Offline crueby

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Re: Chris's Build of Battleship Ohio Engine
« Reply #1228 on: May 23, 2023, 07:00:17 PM »
Got a start on the reverse link bars today. Found some 1/16" thick stainless stock on the shelf left over from a previous model, and cut narrow strips for the arched link bars. A hole was drilled at either end of each for the end spacer bolts eventually, but to hold it to the milling fixture first. I will be machining the bars in pairs, one pair per set, four sets needed. Also drilled a center hole after they were mounted to the fixture, that will eventually get the bar that will hold the links back to the reverse cranks already made. The radius of the arc is 4.844", so the tooling plate on the rotary table needed an extension. Made it out of some aluminum previously used as a cylinder turning jig. Here is one of the sets bolted down and ready to start shaping.


and after the first cuts on the outer arc. The ends will step down more past where the slider will operate, then I'' start on the inner arc.


Offline uuu

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