Roman cranes

[Wander]

I'm considering making a scale model of a Roman crane -- you know the kind, with the slaves walking in the hamster wheel for lifting power. I have a few questions for anyone who knows the details:

Do we have any documentation or evidence showing a ratchet mechanism to lock the wheel? It seems so logical that they must have done it (and ratchet mechanisms on catapults, etc, support this idea), but I'd prefer that it be documentable if possible.

How about a swivel mounting? A crane is much more useful if it can swivel -- otherwise it's limited to lowering and raising the boom to change the point of lift.

Finally: How about wheels? If not to move a lifted load, at least to move the lifting apparatus -- do we know if they were ever mounted on wagons or the like?

I'd be grateful if anyone can point me toward pictorial evidence -- preferably primary source. (I have one showing a complex block and tackle in use, so that's covered.)

Thanks in advance

[Eleatic Guest]

Start here: http://en.wikipedia.org/wiki/Crane_(machine )

Hans-Liudger Dienel, Wolfgang Meighörner, “Der Tretradkran,“ Publication of the Deutsches Museum (Technikgeschichte Series), 2nd ed., München 1997 has AFAIR a detailed scheme for constructing a medieval crane.

[Wander]

Wow, sometimes Wiki has really good stuff!

I learned a few things from that useful link, thank you. Unfortunately, it doesn't address the questions of ratchets, swivels, or wheels. The reproduction crane shown in Germany seems to have none of those features, but it gives a very clear idea how it might have worked.

And I may be able to find the Deutsches Museum publication through a local university library, but it's still about a medieval crane. (But the medieval treadwheel crane shown seems to have a swivel base, and it looks like the treadwheel itself acts as the counterweight.

On further thought, it becomes clear that a swivel crane demands a counterweight. The polyspastos shown in the German reproduction uses guy lines to secure it rather than a counterweight. If that's the standard construction, that would pretty much rule out swiveling.

Good start. Any further knowledge?

[Eleatic Guest]

Thx. The article, at least the history section, was mine. :mrgreen:

I can send you the museum publication along with a small bibliography.

Evidence for ratchets, swivels, or wheels on ancient cranes, though, is largely or even entirely absent.

[Wander]

Much as I appreciate your generous offer, Stefan, the fact that it's a medieval crane suggests that it wouldn't be worth my slogging through it with my poor German skills. I'd probably wind up building a medieval crane instead!

My compliments on the Wiki article, however. It made me realize that I'd want to consider the load lifted in designing it. I was thinking of a diorama showing a stonemason's yard, with keystones for arches or capitals for columns waiting to be loaded onto a wagon for transport. Unless they handled really huge stones, a modest-sized one-man crane could probably do most of the work.

Of course, building the treadwheel two men wide would offer the option of doubling the lifting power when needed. And they could most likely get the locking effect of a ratchet by simply inserting a beam between the treadwheel spokes in such a way that it locked against the supports. That seems a likely and reasonable conjecture.

[SMC]

Hi Wander
Have a quick look at this link. I saw similar models in the museum in Regensburg many years ago but failed to find them on the web. However these look similar.

http://tribus.bonn.de/texte/englisch/roemkr15.htm

[D B Campbell]

The prototype crane reconstruction (afaik) is the one in Xanten Archaeological Park, which I saw there in 1984.

Vitruvius describes two types of crane -- this may be in Stefan's Wikipedia entry (apologies ... I haven't read it yet) -- and there's the famous sculpture of the Haterii (here, courtesy of Indiana University web site).


As far as swivelling is concerned, it wasn't the crane that turned -- as you correctly observed, the guy ropes keep the crane stationary. For situations requiring swivelling -- chiefly unloading ships on a quay --, a stationary upright would have a boom (sometimes called a tolleno) connected by a device called a carchesion (literally "little cup"), which Marsden translated as "universal joint" -- basically it was a tilt-and-swivel mechanism.

[Wander]

Wow, a lot more good info.

First, Stephen, thanks for that link. The models look useful, though I wonder if they might be inferring generalities from specific examples. (For example, stating that each treadwheel had 13 spokes -- just because we see such a wheel doesn't mean they're all like that -- but that's what I'll go with just to be safe.)

A number of details spring to the eye -- like the fact that the larger, farther crane in the lower picture has a double treadwheel for increased lifting power. Seems quite likely; do we know of any documentation?

I also like the way the boom includes a set of climbing rungs so people can climb up and mess with the load in a really unsafe way (as shown in the Haterii sculpture, thanks, Duncan!). I can't see that getting approved today!

Do we have any depictions of the carchesion? The "little cup" suggests a cuplike socket, and the boom may have been shaped in a sort of ball joint, probably sheathed in bronze and oiled to reduce friction. This would then require careful coordination of lateral support lines to control unwanted pivoting.

I'm also curious about the support rigging that controls the boom's tilt. The Haterii sculpture seems to suggest two outlying support points and a lot of mechanical advantage, based on those blocks in the rigging. Probably a couple capstans secured to the ground nearby, triangulating the load.

Wow. This is bigger than I expected -- but it's cool.

P.S.: I'm gonna have to start calling them "gaius ropes". Just can't resist.

[Eleatic Guest]

As far as swivelling is concerned, it wasn't the crane that turned -- as you correctly observed, the guy ropes keep the crane stationary. For situations requiring swivelling -- chiefly unloading ships on a quay --, a stationary upright would have a boom (sometimes called a tolleno) connected by a device called a carchesion (literally "little cup"), which Marsden translated as "universal joint" -- basically it was a tilt-and-swivel mechanism.

Interesting. I did not know about that. But did the guy ropes nonetheless prevent the crane from swivelling?

Sources for Roman crane reconstruction (the one in Bonn, Germany):
- W. Meighörner-Schardt, „Zur Rekonstruktion eines römischen Bockkranes.“ Journal of Roman Military Studies 1, (1990) 59
- Meighörner, Wolfgang und Heinrich Blumenthal: Räderwerk Römerkran. Zur Rekonstruktion eines römischen Baukrans, Bonn 1989

[D B Campbell]

But did the guy ropes nonetheless prevent the crane from swivelling?

I believe the idea was to secure the basic A-frame using guy ropes. By loosening the guy ropes, the crane could move its load forwards (and backwards) over a short distance. So some limited fine-tuning was possible.

The swivelling cranes used on the quayside followed a different design. Here, a single upright was secured by four guy ropes. A carchesion near the top allowed a boom, or spar, to extend outwards in any direction.

[Wander]

It's becoming clear we're talking about two basically similar crane designs, differing in the boom design. The A-frame type would have no swivel capability, but could vary its tilt based on tension in supporting guy (gaius) lines. The two "feet" of the "A", along with a single gaius line, could safely triangulate the load.

Alternatively, a simple one-piece boom, with a carchesion ball-and-socket joint at its base, would allow a limited degree of swivel from side to side, as well as tilt of the boom. Both of these could be closely controlled by gaius lines triangulating the load, anchored behind the crane on either side. The wider they are anchored, the more side-to-side movement they allow. The further back they are anchored, the greater the control over tilt.

Obviously the engineer in charge would locate the anchor points carefully, depending on the space available and the type of ground conditions on the site.

One of the sources I've come across researching this mentioned the spar as a medieval innovation on cranes -- I'd be curious what documentation we have for it in Roman usage. Vitruvius, maybe? Unless it's counterweighted, I can see it posing a real safety hazard in managing the load forces involved.

Thanks again for all your input!

[Eleatic Guest]

I believe the idea was to secure the basic A-frame using guy ropes. By loosening the guy ropes, the crane could move its load forwards (and backwards) over a short distance. So some limited fine-tuning was possible.

That is how I understand it, too.

The swivelling cranes used on the quayside followed a different design. Here, a single upright was secured by four guy ropes. A carchesion near the top allowed a boom, or spar, to extend outwards in any direction.

The existence of ancient (harbour) cranes with swivelling mechanism is news to me. To what source(s) do you refer exactly? Perhaps Marsden was only conjectural here.