Chris's Build of Battleship Ohio Engine

[derekwarner]

Chris......

I think you mentioned no evidence of keys in the crankshaft sections, and there  is no larger diameter hub at each coupling, so could each of the crank pins have been machined from a forging to include the length of the pin + the larger section which was machined as the coupling half?

I am not sure why any single section of the crankshaft would need to be removed in the vessel life [excepting at major refit with the entire engine jacked up and the complete crankshaft removed]

If sections of the crankshaft were designed to be removed, my previous comment of interference shrink fitted bolts at the couplings would be invalid

Propeller shafts with bolted couplings is far less of an integrity problem, as the forces are [generally] acting in a single direction. The crank pin engine couplings however are subject to two opposite reaction forces at each revolution

Just out of interest, are these two crank pins the same length?

Hollow propeller shafts are common  as the hollow section is stiffer and stronger than a solid shaft [of the same weight], however I am not sure in the use of hollow engine crank pins? 

....courtesy Google ......... https://www.mechanicalfunda.com/2017/03/hollow-vs-solid-shaft.html#:~:text=The%20material%20at%20the%20centre,the%20same%20weight%20solid%20shaft.

Derek


 

 

[crueby]

John, there are automatic oilers on the bearings and con rod ends.




Derek, there are four identical sections of crankshaft assembly, each bolted to the next at larger diameter flanges. Each section is flipped end for end from the one next to it, and also rotated some multiple of 90 degrees.

[Mcgyver]

'Steamer' Dave very kindly gave me a copy of the set of plans he has of the engine from this ship.

Where do these drawings come from?   I doubt I'll tackle this project, but Chris, I share your enthusiasm for just getting to pour over the drawings.  They'd have to be out of copyright at this point....if they only exist in they physical form, I'd happy to volunteer to produce large format high res PDF's and make them available; I'd just like to see them.

They came from a big old book he has, most of its missing but for the plans. A friend of mine has a large format scanner, I'm going to be seeing him this weekend and will ask if he can scan my copy of the prints, if that's ok with Dave?

I recently got a big cannon printer/scanner, like the kind does up to D or E sheets.  I think it does 600 dpi, but the cool part is its colour so you can photoshop out yellowing etc.  If it was of help, I'd assist.

Really liking the CAD progression!

[tghs]

another source is the, transactions society naval architects and marine engineers  many volumes can be found searching digital libraries.. but most of the plan fold-outs were not.. have had mine hands on hard copies but at the time I was more interested in full ship plans..sample below

[internal_fire]

Propeller shafts with bolted couplings is far less of an integrity problem, as the forces are [generally] acting in a single direction. The crank pin engine couplings however are subject to two opposite reaction forces at each revolution

I do not think that is correct. The applied rotational force (torque) from each cylinder varies from zero to maximum twice per revolution, but it does not reverse. If it reversed during each revolution the engine would be quite ineffective.

Gene

[Vixen]

Propeller shafts with bolted couplings is far less of an integrity problem, as the forces are [generally] acting in a single direction. The crank pin engine couplings however are subject to two opposite reaction forces at each revolution

I do not think that is correct. The applied rotational force (torque) from each cylinder varies from zero to maximum twice per revolution, but it does not reverse. If it reversed during each revolution the engine would be quite ineffective.

Gene

I would agree with that Gene. This is a steam engine, not an internal combustion engine, so there is no compression stroke.

Mike

[Admiral_dk]

Not only is it a Steam Engine where each Piston both Pushes and Pulls - but look at the Crank - 90 degrees Offset from Cylinder to Cylinder ...!!!...
Minima - Yes - But no Zero Power part of the Rotation ....
Where two Cylinders are approching the end of their Power-Stroke - the other two are taking over.

In that sense, it is actually not different from a two cylinder Double Acting Steam Engine with a single 90 degree offset - that is why they are Self Starting (as there are no dead spots)

I Do understand the problem with an IC Engine - about Opposite Forces - but besides bringine the Piston to a Complete Stop @ each end of the Stroke ....  I honnestly do not know the actual forces involved in such a Steam Engine - newer seen an analyze .... but I expect it to change quite a bit with regards to the Timings of the Valves.

Per

[crueby]

Not only is it a Steam Engine where each Piston both Pushes and Pulls - but look at the Crank - 90 degrees Offset from Cylinder to Cylinder ...!!!...
Minima - Yes - But no Zero Power part of the Rotation ....
Where two Cylinders are approching the end of their Power-Stroke - the other two are taking over.

In that sense, it is actually not different from a two cylinder Double Acting Steam Engine with a single 90 degree offset - that is why they are Self Starting (as there are no dead spots)

I Do understand the problem with an IC Engine - about Opposite Forces - but besides bringine the Piston to a Complete Stop @ each end of the Stroke ....  I honnestly do not know the actual forces involved in such a Steam Engine - newer seen an analyze .... but I expect it to change quite a bit with regards to the Timings of the Valves.

Per

When he mentioned the zero to max, he specifically said the force from one cylinder. He is correct in that. You are talking about the force at the end of the crankshaft, also correct. Both right, but talking about different things!

[Charles Lamont]

Most steam engines have 'line-on-line' exhaust. This means that as one end opens to exhaust, the other end closes.

Most engines also have admission lap in order to provide the economies of expansive working.

Lap means the timing has to be advanced to provide inlet 'lead' at top dead.

This means the exhaust point occurs well before the dead centre.

Releasing the exhaust a bit early ensures the back pressure is reduced to a minimum before the piston has got far into the exhaust stroke.

Advance also means that, at the other end of the cylinder, there is a simultaneous compression point. The purpose of compression is twofold:

Firstly it brings the pressure of the small amount of exhaust steam trapped in the cylinder up to a pressure approaching steam-chest pressure, ensuring that there is    not a wastefull sudden inrush of steam at the admission point, and

Secondly, it provides a cushion to arrest the momentum of the reciprocating parts.

Ideally this results, at normal revolutions, in a fairly smooth change of thrust on the crankpin from one stroke to the other.   

[derekwarner]

Gents......my apologies......my word opposite as used is absolutely incorrect .............

At any set speed, the forces are more like a constant harmonic running in one direction

Derek 

[Admiral_dk]

Chris - I stand corrected - interesting subject none the less.

Charles - I kind of knew, but thanks for clarifying - that said, it still means that the Timing has a big influence on the outcome ....

Derek - I completely agree on a Steam Engine - but it was also mentioned that things are different in an IC Engine, where the Compression Stroke has an opposite force on the Crank (braking) ....

Per

[internal_fire]

I spent a lot of time studying Liberty ship engines. Most of those had segmented crankshafts, and they did have large dowel pins as part of the couplings.

Of course there are lots of other differences as well.

Gene

[crueby]

I spent a lot of time studying Liberty ship engines. Most of those had segmented crankshafts, and they did have large dowel pins as part of the couplings.

Of course there are lots of other differences as well.

Gene

Before getting the Ohio engine plans I had been looking at the Liberty Ship plans, that also looks like an interesting engine. Do you have any plans for one? I was able to find partial ones, but not enough to build from.

[crueby]

I spoke with my friend with the large format scanner, he is going to scan these for me, they will be great to bring up in a window next to the CAD app, I had been using pictures I took of the sections of the sheets. Steamer Dave, any objections if I make the scans available to others? Not my plans, that decision is yours and I will abide by it without question.




Spent the day out at the pond with a large group of RC sub nuts from all over the place, US and Canada, awesome time. Well not the whole day, only 11 hours!! We are back at it tomorrow, got the battery chargers all busy now. Great to see a lot of them that we haven't been together with since pre covid, so many jokes and puns backlogged...

[internal_fire]

Before getting the Ohio engine plans I had been looking at the Liberty Ship plans, that also looks like an interesting engine. Do you have any plans for one? I was able to find partial ones, but not enough to build from.

Live Steam had an extensive series back in 1980 or so on the Liberty ships, including a lot of details about the engine. Quite a few detailed prints included, but not really a full set.

I built a triple based on the well-known OB Bolton plans as modified by J. P. Bertinat, with some further modifications based on the Liberty ship drawings. No castings used. All bar stock.

Gene