Saturday, May 09, 2020

Trireme question

When I see pictures of a trireme (and most other similar boats) I see a sharply up-peaked stern--and usually it curved back over the body of the boat.

In the images, there's nothing tied to it, so I assume during normal sailing nothing was.

I know they had a tensioning rope running down the middle to hold the planks tightly together from end to end, and I know the boats had to be dragged ashore for refitting very regularly--and they were light enough that it wasn't a big deal.

I'm puzzled why the Greeks and the Carthaginians (very different cultures) both used that same curved-back peak. (The Romans did too, but I gather they borrowed Greek technology here.). I figure there had to be some good reason for the curve-back. It's quite an extra complication to be simple decoration, though it did get decorated frequently.

A high peak might be easier to sling ropes around to drag it in/out of the sea, and maybe a little back-curving would be helpful for when the stern's peak bent under the force of the ropes. But that much?

Alternatively, maybe they hung ropes on it when refitting, when trying to release the tensioning rope, or for strapping other things in place when replacing planks.

My preliminary search didn't find out anything conclusive. I vaguely remember reading something about it decades ago, but my memory fails me here.

Does anybody know?

UPDATE: maybe a bit of an answer?


Laura said...

I think there is something tied to it-- the triremes had a pair of heavy cables, called hypozomata, "undergirding", running from bow to stern. They were considered the critical piece of technology for building a trireme by the Greeks, and their exact details were considered a state secret (death penalty for revealing the specifics or exporting one). They were expensive and hard to make, and every trireme carried spares because it was combat-ineffective without them.

I believe that the purpose was to hold the hull under a lot of compression force, so that it could absorb the blow from the ram without its own hull planks popping loose under the impact. Also, it would help to prevent hogging, that is, the keel bowing up out of shape. To be very maneuverable, the trireme would need to be slightly concave (deeper at the center than at either the stern or bow)-- you may have seen this design in a canoe,* for example, where you have to specify the "rocker" you'd like based on how you want it to handle. But wooden ships tend to hog, that is, bend up in the middle, because their center of buoyancy is there. But mainly, I think, to absorb the blow from ramming another ship.

* At least, for whitewater canoes; canoes designed primarily to keep Grandpa from falling out of them while fishing in the lake, might be completely flat on the bottom!

james said...

When they tried to build a replica, they tried using steel cables for the hypozomata, but the flexing of the boat would alternately release and restore tension. The steel didn't react the way hemp did--they were afraid the cable would snap and kill people. In the replica it was attached to prow and stern portions below the level of the deck, not quite at the bottom of the boat. I guess you get better distribution of compression that way. Without it, the natural hogging of a boat would open and close joints between planks (I'm quoting the sources here) which could cause wear and leaking.