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Marine Engine Flywheel Fixing

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SillyOldDuffer19/01/2021 15:23:09
6878 forum posts
1539 photos

Had a look at my American Marine Engineering Book circa 1945.

Volume 1 describes the US Maritime Commission Engine of 1940 in considerable detail. Quite interesting - it's the Triple Expansion Steam engine used to power Liberty Ships. Rationale almost engineering firm could make them, and reliable simplicity, not high-performance or fuel economy. Goes on to describe Woolf Engines, Lentz Engines, Steam Turbines and Maritime Diesels. None of these engines have flywheels.

However, Volume 2 has a section on vibration, and mentions flywheels as a way of controlling it. My idea of a flywheel is a hefty beast designed to store a lot of energy to deal with varying loads. Not how this book sees them. Small, if used at all, and intended to deal with resonances.

Looking at the engine plans in Volume 1, although they don't have separate flywheels, they do have heavily weighted cranks. Although the main purpose of the weights is balance, they would also have a flywheel effect, maybe sufficient to not need a separate flywheel at all. There are also features like the engine / propeller-shaft couplings that must act as small flywheels. The reduction gearbox on a steam turbine looks like a hefty flywheel - might take a turbine ship a few miles to stop!

Mill engines and pumps see varying loads and for them a big flywheel must be very helpful. Maritime engines don't have the same need for a flywheel because they deliver power into a steady load for weeks on end. I suppose a ship engine's worst nightmare is when the propeller dips in and out of the sea during a storm.


Ramon Wilson19/01/2021 20:25:47
1051 forum posts
205 photos

Guys - my thanks again for your continued interest in my question.

I have no real knowledge as such of full size marine engines to call upon and just assumed from the wheel fitted to this design clearly described as a Marine Condensing Compound that they would have one fitted.

I can see now that this is not, or very rarely the case. I mentioned the 'Monkey' triple produced by Elliot and Garrood as having quite a substantial one but this was part of the design as said and acted as part of the crankshaft make up. During the research carried out with my sorely missed friend on this engine one thing that came to light was - with the 180 degree cranks how difficult it was for the driver to go from forward to reverse when having to manoeuvre the vessel. That bears out Noels input for sure.

I have the Spooner book but did not consider it because this is more on land based machine design though having checked it out there is a description of a marine coupling further on using fitted tapered bolts.

So mulling all this over today between machining ops on the base I've concluded this engine will be statically displayed without a flywheel but with flange couplings at each end. When - if - it is run for display then a flywheel can be temporarily fitted to smooth the slow speed out.

Sounds good? - I hope so

Regards - Tug

PS - Jason , I did spot the Thornycroft last night.yes

And as you would expect by now JB Weld will feature a fair bit on this build but maybe not quite as you suggest wink

Edited By Ramon Wilson on 19/01/2021 20:28:41

John Olsen20/01/2021 00:39:29
1147 forum posts
92 photos
1 articles

I see I'm a bit late to this party, but I would confirm that the majority of full size marine engines would not have a flywheel, at least not as such. The length of shaft and the big propeller would usually provide all that is needed.

I mostly recall shafts being plain with keyways rather than flanged. Thrust bearings can be multiplate or the later Mitchell type. Sometimes the thrust bearing has been incorporated in the engine bed plate, but I think not usually.

Modern small steam launches do usually include a flywheel. This is I think because the relatively smaller prop and shaft don't provide a lot of inertia. It is also sometimes convenient to be able to pull the engine over a little, although I would not advise this since it can be a bit hazardous. Crankshafts are usually 90 degrees for a twin to give self starting. On mine, each crank has balance weights, effectively attempting to balance each cylinder as it it was a single. You can't really balance a 90 degree parallel twin of course. The self starting feature is more important than balance at the sort of revs we use in steam launches anyway, and a compound should have a simpling valve fitted to allow giving the LP a shot of steam to move the HP off top dead centre. This is not a full simpling arrangement usually.

Even with a 10 inch diameter by three inch wide flywheel, my Leak compound can reverse faster than the eye can see, so the inertia in the setup is not a great deal of concern. It takes a lot longer to overcome the inertia of over two tonnes of boat! I think the same probably applies with full size turbines, where even though the reversing turbine is usually smaller, the real problem is the inertia of the hull, not the gears.


Ramon Wilson20/01/2021 10:00:33
1051 forum posts
205 photos

Thanks for that further input John - it all adds to the info.

I'm pretty relaxed now about not fitting one as my last post. From the outset I thought that the diameter as drawn was rather excessive anyway.

It is my intention to have a thrust bearing installed and possibly a stub shaft with a propeller fitted but that's a long way off as yet.

The engine parts are being machined from cast iron bar stock and like the double ten cylinder done some time ago will be of composite construction using JB Weld to hopefully create the effect of castings. Here's the major parts roughed out ready to go

marine compound (14).jpg

I made a start this week beginning with the base - from a solid slab of cast this was after yesterday's session

marine compound (20).jpg

There's a fair bit of swarf come off of there so far and still some to come!

Regards - Tug

derek hall 120/01/2021 14:25:39
136 forum posts

Although your question Ramon refers to marine reciprocating engines. I served an apprenticeship in a shipyard in the 1970's, where we installed marine diesel engines and they all most definitely had flywheels.

The flywheel was separate from the engine and bolted onto the crankshaft via a machined matching spigot and with fitted bolts. A short tail shaft was then fitted between the flywheel and the thrust bearing (a Michell bearing). From the thrust bearing the prop shaft and the prop was fitted.

I guess steam engines would have had a similar layout but I am sure there would have been some sort of flywheel fitted for the small turning engine to engage with to rotate the engine manually prior to starting...but marine steam was a bit before my time!

Regards to all


Ramon Wilson20/01/2021 18:29:49
1051 forum posts
205 photos

Me too Derek - Apprentice welder, Richards Shipyard in Lowestoft - 1960. Long gone as most are and now an Asda supermarket!! They were still riveting hulls at that time but for the most part superstructures were being welded.

If I have little, if any, knowledge on marine steam engines I have even less of diesels but I do have two ME friends who served apprenticeships as fitters at AK Diesels in the same town - I'll see what they say.

I intend to make the flange that the temporary flywheel will attach to of a reasonable size and with barring holes as you point out - it would only be much larger engines that had barring engines I'm sure.

Thanks for your comments


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