The Ship Model Forum

USS Monitor turret drive machinery
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Author:  mcg [ Sun Jan 02, 2011 9:00 pm ]
Post subject:  USS Monitor turret drive machinery

Made a beginning on a part of the USS monitor that I have not seen modeled in much detail: the turret drive mechanism. I am using Rhino3D. Line drawings of the various components were scanned from the book, Drawings of the USS Monitor, by Capt. Ernest W. Peterkin.
File comment: USS Monitor decking is aligned with the long (roll) axis of the ship
monitor turret clutch small.jpg
monitor turret clutch small.jpg [ 20.27 KiB | Viewed 9388 times ]

The monitor was planked with 7"-thick pine, and the above sketch shows the how the turret drive mechanism penetrated this deck. The brown oak deck beams run beamwise, and the turret support beam is shown aligned with the long axis of the USS Monitor.
File comment: view with the deck layer turned off, showing oak beams
minus the deck small.jpg
minus the deck small.jpg [ 27.94 KiB | Viewed 9388 times ]

If we subtract the pine planking as shown above (by turning off the layer) the cast bearing and its oak beam supports become more clear. The bearing was cast in one piece, and mortised into the oak deck beams. It was further secured by bolts through the deck beams.
File comment: view of machinery with deck beam layers turned off
minus oak beams small.jpg
minus oak beams small.jpg [ 20.54 KiB | Viewed 9388 times ]

Finally, if we turn off the oak beams, the bearing and drive can be seen whole. Note that the toothed drive "clutch" appears to cradle, rather than lock or rigidly secure -- the turret beam. The turret contained two 8-ton Dahlgren guns, and these were on rails to permit recoil and running out. It appears to me that with so much mass in motion, Ericsson may have decided to simply let the turret rock a bit. The outermost rim of the turrret was supported on a brass bearing ring.

The gear itself is sized and toothed per the drawings and specs, but the spokes are conjectural.

Next step is to finish drawing the central bulkhead and the fittings that supported this whole system.


Author:  mcg [ Sun Jan 02, 2011 9:30 pm ]
Post subject:  Re: USS Monitor turret drive machinery

Here are two views of the cast bearing viewed in isolation:
File comment: casting seen from above
bearing from above small.jpg
bearing from above small.jpg [ 29.79 KiB | Viewed 9384 times ]
File comment: casting as viewed from below decks
bearing from below small.jpg
bearing from below small.jpg [ 31 KiB | Viewed 9384 times ]
Notice the horizontal and vertical flanges. The flanges, and the front of the bearing "cup" were mortised into the oak deck beams.

Author:  rtwpsom2 [ Sun Jan 02, 2011 9:57 pm ]
Post subject:  Re: USS Monitor turret drive machinery

Very interesting subject. I would like to see more when you have it.

Author:  DrPR [ Mon Jan 03, 2011 4:25 pm ]
Post subject:  Re: USS Monitor turret drive machinery

Excellent illustrations. I have read descriptions of this mechanism, but they were pretty sketchy. This build will help a lot in understanding how it worked.

Also, this is an excellent example of the use of CAD modeling to document the construction details of an historic ship.

Author:  mcg [ Mon Jan 03, 2011 6:41 pm ]
Post subject:  Re: USS Monitor turret drive machinery

Thank you for your encouragement. To put this in context, here is a sketch of the turret bulkhead.
File comment: Turret bulkhead, forward side
master bulkhead small.jpg
master bulkhead small.jpg [ 41 KiB | Viewed 9352 times ]

The casting for the turret bearing, shown in the posts above, was bolted to the middle of the oak deck beam backing the bulkhead. The turret shaft descended on this side of the bulkhead.

The oak deck beam was flat under the turret, then tapered off slightly toward the edges of the deck to form a mild turtle deck. The cutout in the top of the bulkhead is for the main turret gear. The "butterfly" flanges flank the turret drive shaft. The butterfly structure is one of those features that is shown in many drawings of the USS Monitor, but I didn't quite understand what it was until I worked it out in 3D.
File comment: Shipyard tracing of Ericsson's plan
Rowland tracing small.jpg
Rowland tracing small.jpg [ 38.42 KiB | Viewed 9328 times ]

This model is being assembled on a contemporary shipyard tracing of Ericsson's original plan. Thomas Rowland was co-owner of the shipyard (the Continental Iron Works), and the tracings were kept by his family. In general, they are sharper and more legible than Ericsson's work, particularly in the legends and captions.

The turret gear train two small steam donkey engines that drove it were mounted on frames suspended below the Monitor's kitchen ceiling, just on the other side of this bulkhead.

In addition to Capt. Peterkin's book there is another very helpful resource for modeling the USS Monitor. This is an article by Stephen C. Thompson, "The Design and Construction of USS Monitor." It appeared in Warship International, No. 3, 1990. Ericsson made extensive use of angle irons of various sizes in designing the Monitor. The profiles of the angle irons are included in the Peterkin book, but the Thompson article tells you which one goes where. I will need to revise the angle iron placement on this bulkhead somewhat because I made it before the Thompson article came in. I found it on Abebooks.


Author:  mcg [ Tue Jan 04, 2011 7:14 pm ]
Post subject:  Re: USS Monitor turret drive machinery

Here is the turret drive shaft and bearing box in position, mounted at the bulkhead.
File comment: Bulkhead viewed from below, looking aft.
from below looking aft small.jpg
from below looking aft small.jpg [ 34.21 KiB | Viewed 9321 times ]
File comment: Seen from above, from the kitchen side of the bulkhead
from above kitchen side small.jpg
from above kitchen side small.jpg [ 25.98 KiB | Viewed 9321 times ]
File comment: The bearing box was notched and bolted between two oak deck beams.
bulkhead with bearing box small.jpg
bulkhead with bearing box small.jpg [ 24.72 KiB | Viewed 9321 times ]

The oak deck beam seems like a large clear span in these screen captures, but it was additionally braced by two columnar stantions mounted just outboard of the doors.

Noticably missing is an anvil-like fitting Ericsson mounted at the narrowing of the butterfly flanges. This fitting supported the turret shaft -- and could be used to jack the turret slightly off the deck. It is an intricate chunk of machinery and I am still working on it.

In general, the materials and methods of 150 years ago are very different from ours. They integrated wood and metal in interesting ways. The wood was milled in sizes and shapes we don't often see any more.

It reminds me a bit of the machinery in an old cider mill I visited many years ago.


Author:  mcg [ Wed Jan 05, 2011 6:52 pm ]
Post subject:  Re: USS Monitor turret drive machinery

The basic shape of the Dahlgren, generated from coordinates.
File comment: The 11-inch Dahlgren
11-inch Dahlgren small.jpg
11-inch Dahlgren small.jpg [ 90.95 KiB | Viewed 9295 times ]

The Monitor's Dahlgrens were raised from the wreck and are being restored at the Mariner's Museum:

This photo is published on their riveting blog.

Author:  mcg [ Tue Jan 18, 2011 7:08 pm ]
Post subject:  Re: USS Monitor turret drive machinery

When the USS Monitor was under tow the whole turret was lowered so that it sat solidly on the deck. The turret had to be jacked up slighly off the deck to enable it to turn freely.

Here are some sketches of the turret jacking mechanism.
turret jack - basic small.jpg
turret jack - basic small.jpg [ 20.13 KiB | Viewed 9217 times ]

The components include a boxed bearing that supports the turret shaft. It is poised above an anvil-like casting, and between these two parts slides a long wedge. The wedge is pulled to the left by a threaded shaft 2 inches in diameter. I have not yet filled in the threads. Notice in the drawing above that the wedge slides within, and is positioned and guided by, a square hole cut in the butterfly flange.
vertical slot for shaft small.jpg
vertical slot for shaft small.jpg [ 20.88 KiB | Viewed 9214 times ]

Note that behind the jacking nut there is an elongated vertical slot, shown here viewed from the bulkhead side of the assembly. This slot allows the shaft to rise slowly in the plane of the wedge as the nut is tightened. The top of the wedge stayed horizontal. The height of this slot puts a limit on how high the turret could be jacked up off of the deck. If you make the measurement in CAD, the full range of vertical motion appears to be 1.75 inches, but from the resting position as drawn by Ericsson (with the turret decked) it is slightly less. Maybe 1.5 or 1 5/8 inches.

The bearing box for the turret shaft is positioned by a massive V-block casting, shown here from above.
Casting from above small.jpg
Casting from above small.jpg [ 19 KiB | Viewed 9217 times ]
In working out castings like this one in Rhino3D, I find it is easier to draw the plug first, as if to make a model of the mold. Then do a Boolean subtraction from a simple V-block solid to achieve the look of a casting. It is a process that is sort of similar to the work they did in crafting the original molds 150 years ago.

Here, finally, is a view of the assembly flipped upside down.
upside down small.jpg
upside down small.jpg [ 21 KiB | Viewed 9217 times ]

The jack appears from the drawings to have been a one-way device. Rotating the nut clockwise raised the turret, but rotating it in the other direction just backed out the nut. To lower the turret (that is, drive the wedge to the right) I think I read somewhere that the sailors used a sledgehammer.

Author:  DrPR [ Tue Jan 18, 2011 7:40 pm ]
Post subject:  Re: USS Monitor turret drive machinery


This is really interesting! How much of the ship are you going to model in CAD?


Author:  mcg [ Tue Jan 18, 2011 7:59 pm ]
Post subject:  Re: USS Monitor turret drive machinery

Thank you. The USS Monitor engine has already been done beautifully by Rich Carlstedt, who carried the CAD work through to CNC and hardware.

For this project I am trying to concentrate on the turret drive machinery, partly because I don't think it has been completely worked out. The turret itself has been salvaged from the wreck site, but the small turret engines and drive train are, I think, still underwater.


Author:  Cadman [ Tue Jan 18, 2011 11:09 pm ]
Post subject:  Re: USS Monitor turret drive machinery

fascinating. I look forward to seeing the machinery come together.

Author:  mcg [ Wed Jan 26, 2011 9:59 pm ]
Post subject:  Re: USS Monitor turret drive machinery

The turret elevating wedge, which Ericsson called the "key", has a 2-inch diameter shaft, and it is threaded at 3.75 threads per inch. I cut these threads using an old Acme profile, because it looks something like threads on a part the divers have brought up. But this thread profile is conjectural.
3.75 threads per inch small.jpg
3.75 threads per inch small.jpg [ 28.87 KiB | Viewed 9140 times ]

Here is an overall view of the turret bulkhead frame. The 1/2-inch bulkhead sheet is turned off for better light.
turret bulkhead framed xmall.jpg
turret bulkhead framed xmall.jpg [ 40.66 KiB | Viewed 9140 times ]

Finally, here is a detail shot of the massive V-block casting as mounted to the bulkhead. Each of the 8 main bolts securing it to the butterfly flanges is 2 inches in diameter.
turret shaft & butterfly flanges small.jpg
turret shaft & butterfly flanges small.jpg [ 32.98 KiB | Viewed 9140 times ]

Author:  middle_watch [ Sat Jan 29, 2011 10:20 am ]
Post subject:  Re: USS Monitor turret drive machinery

Now that is what I call detail, looking great.

Author:  DrPR [ Sun Jan 30, 2011 4:29 pm ]
Post subject:  Re: USS Monitor turret drive machinery


How did they turn the screw? Was it done by hand (if so, how many men were needed to turn it) or was there a power-driven mechanism?

Author:  mcg [ Sun Jan 30, 2011 8:30 pm ]
Post subject:  Re: USS Monitor turret drive machinery

Thank you middle_watch.

Phillip, it was a long handled wrench, used to rotate the huge nut shown here:


As I understand it the screw itself was fixed, integral with the wedge. It looks like the leverage was provided by the jack screw, the inclined plane of the wedge, and the long wrench handle. Plus impulses from the sledgehammer.

Starting to work on the aft side of the bulkhead, where the turret drive mechanism was suspended from the ceiling. There are good, welll conserved drawings of the machinery forward of the bulkhead, but as we move back into the galley, the drawings are not very good.

There are a few hard numbers to work with, however, in a table describing the individual gears in the gear train. The table provides pitch circle dimensions, numbers of teeth, and a few other specs for the four gears. My thought is to create the gear train first, working from the numbers rather than drawings, and then superimpose it on the very sketchy drawings that have survived.
galley gearbox small.jpg
galley gearbox small.jpg [ 31.15 KiB | Viewed 9091 times ]
This one was acquired in the early 1960s (apparently by a private collector, a Dr. Lunderberg) from the Swedish War Archives in Stockholm. It was subsequently published in Capt. Peterkin's catalog of Monitor drawings. It has a nice detail of the short, vertical crankshaft. This was the common crankshaft for a pair of donkey engines, essentially arranged as a big V-twin bolted just beneath the deck beams.
harpers galley small.jpg
harpers galley small.jpg [ 135.78 KiB | Viewed 9089 times ]
This slightly surreal drawing of the turret drive on the ceiling of the galley appeared in Harper's Weekly magazine. It is propaganda, perhaps -- one of a set of Monitor illustrations in which every space below decks appears to be the size of a ballroom. In fact the galley was a smallish room sandwiched between the two boilers (on the right) and the turret bulkhead. Yet this is the only contemporary perspective drawing of the turret drive gearbox I have come across. The real, exact structure is a mystery that will only be resolved when they salvage the components.

Author:  mcg [ Tue Feb 01, 2011 12:08 pm ]
Post subject:  Re: USS Monitor turret drive machinery

This is an overhead view from the shipyard's tracing of Ericsson's layout. The drawing is near final and the basic dimensions are as built.
shipyard dims small.jpg
shipyard dims small.jpg [ 58 KiB | Viewed 9056 times ]
I drew the oak deck beams as an array. They are spaced at 3-foot intervals, if we use the face of each 10" deck beam as a marker. If we dropped a plumb bob from the face of a deck beam, then directly below it, spanning the bottom of the ship, was positioned a floor "timber." These timbers were in fact iron sheets transformed into I-beams or C-beams using angle iron. They were also positioned at 3-foot intervals.

The ship's outline is perfectly symmetrical. I drew only one arc and mirrored it to draw the hull. Parenthetically, there were two 12-inch oak beams at the pilothouse. I don't see that these two heavier beams altered the 3-foot period of the beam spacing, however.

The beam spacing makes it possible to "good eye" the spaces within the ship, since the oak beams form a ruler marked off in 36" increments. The galley space we are now concerned with was rather like a tunnel, shy of 8' from the bulkhead wall to the boiler backs. But it was a long tunnel, spanning almost the full width of the vessel. The curved lines behind and outboard of the turret are the walls of the ship's coal bunkers. There were two passages running along these bunkers between the galley space and the engine room, one on either side of the boilers.

Author:  mcg [ Thu Feb 03, 2011 10:59 am ]
Post subject:  Re: USS Monitor turret drive machinery

Here is a view of the turret gear train, seen from below. The bulkhead has been turned off for better visibility.
sketch of drive train small.jpg
sketch of drive train small.jpg [ 28.24 KiB | Viewed 9030 times ]
. Here is the same machinery seen from overhead, with some deck beams turned off for better visibility.
drive train from above small.jpg
drive train from above small.jpg [ 24.61 KiB | Viewed 9030 times ]
Basically the drive train is just four gears, two spurs and two pinions. Power is to be applied at the crankshaft by a pair of "donkey" engines. The two cylinders were mounted in the form of a "V" just above the 2nd spur gear. The engines have not yet been sketched in. Quite a bit of other detailing to come, including spokes for the second spur, hubs, more precisely trimmed shaft lengths, pillow blocks, gearbox structure etc. But this is the core layout. As noted the gears were recreated from a table of specs. There is a free plug-in for Rhino3D that makes gears out of specs, so this was a straightforward job. Michael

Author:  rtwpsom2 [ Thu Feb 03, 2011 11:11 am ]
Post subject:  Re: USS Monitor turret drive machinery

I much prefer SolidWorks, but I do envy Rhino users because of some of the nice little add-ins that you can get for it.

Author:  mcg [ Sun Feb 06, 2011 5:47 pm ]
Post subject:  Re: USS Monitor turret drive machinery

CAD modeling of the USS Monitor is almost a genre. Here are links to three significant efforts. ... 1269901772 ... 1269901772

There is a picture of the galley on the Nova version of the USS Monitor that is similar in perspective to the cartoon like Harpers' Weekly sketch shown in an earlier post in this thread. The Nova CAD illustration shows the boilers well, along with some artfully hung pots and pans. However the online tour does not show the turret engines. Evidently they were working from Capt. Peterkin's book, and this book does not include a crisp representation of the turret engine.

The CAD work presented in San Francisco actually depicts the turret engines, in a schematic way (no valve gear, no steam chest). But there is a mechanically implausible connecting rod between the portside turret cylinder and the crankshaft axle.
conf-jons-fig10.gif [ 31.72 KiB | Viewed 9006 times ]
Maybe the CAD artist saw the crankshaft as a bicycle type, but it seems clear from published drawings that it had just a single throw.

V-configured engines are such a commonplace of internal combustion that we barely notice them, but in the age of steam it seems a V-twin engine was an unusual choice -- not at all typical. Some of them had a quite specific purpose.

I have learned that V-twin steam engines were, in the 1850s and later, a favored choice for powering the rolling mills in an iron works. (Imagine an iron plate rolling back and forth and back and forth.) Apparently this was because the V-twin steam engines were readily reversible, and could be made to run without a flywheel. The two cylinders would never hit bottom dead center or top dead center simultaneously. The V-twin could not stall for any geometric reason.

It was said of John Ericsson that his "second home" was the Delamater Iron Works in New York. He was building propellor driven iron vessels (barges, tugs, and Hudson riverboats) from 1839 on, and when he wasn't at the drafting board he was prowling the iron works. Rolling mills and their V-twin engines were clearly in his technical repertoire.

Here is an illustration from a handbook of steam engine practice published in the late 19th century.
rolling mill small.jpg
rolling mill small.jpg [ 36.28 KiB | Viewed 9004 times ]
The V-twin engine's quality of quick and reliable reversing may have encouraged Ericsson to use one to turn and to quickly reverse the Monitor's turret. The V-twin was made for the USS Monitor at the Clute Brothers' Foundry in Schenectady, NY. It would be interesting to learn if they also manufactured and supplied engines for rolling mills and, above all, if they published an illustrated catalog. For CAD, an actual picture of a similar engine from the same manufacturer would be a great help.

From a 1927 patent (Helena) describing an improved rolling mill engine, there is critical description of V-twin steam engines typically used in rolling mills.
Helena - prior art small.jpg
Helena - prior art small.jpg [ 64.81 KiB | Viewed 9004 times ]
I am leaning toward the idea that this patent's description of the "prior art" is also a fair description of the V-twin steam engine suspended from the kitchen ceiling of the USS Monitor.

Author:  mcg [ Sat Feb 12, 2011 9:34 pm ]
Post subject:  Re: USS Monitor turret drive machinery

It turns out the Mariners Museum has done some computer enhancement of an important Continental Iron Works tracing of the USS Monitor. If possible I am going to try to obtain a copy of this crisper art work to work from. Meantime, just doing detailing, adjusting the shafts, hubs and gearworks to fit the drawings now in hand, filling in spokes, etc.
detailing gear train.jpg
detailing gear train.jpg [ 83.07 KiB | Viewed 8950 times ]

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