Your link made my case. Quoted abstract of paper: “According to the CTX tanker casualty database, machinery failures are an important cause of tanker oil spillage. This paper argues that the current large (over 10,000 deadweight) tanker fleet is experiencing at least two full losses of power or steering per day, and probably more than ten. If this fleet were twin screw, properly implemented, this number would be cut by a factor of one thousand. At the same time, tanker low speed maneuverability would be improved dramatically. All this could be done for a net cost of less than that of the double hull.”
All this talk about tugs costing less than mules ignores the fact that the tugs can’t maneuver in the locks. One or two or even three tugs might be cheaper, but if they were useless you might as well put that money in a barrel and burn it. As for stopping the ship in an emergency you would be wrong to rely on the stern tug. The times I’ve experienced an engine failure on a final approach there was no time for the tug to stop the ship by itself. I was lucky enough to have a bow tug or thruster that pulled the bow away at the same time the stern tug backed. We overlapped, but didn’t touch. That option is not available in the confines of a lock.
When a builder creates a subdivision of 100 houses the extra cost per house to pre-treat the ground for termites, to use modern concrete foam blocks instead of 2x4 stick framing, to use vinyl siding instead of Hardi-plank, to use pvc instead of pec piping and to use double glazed windows are all small percentage points of the final cost of the house, but seldom done around here even though the final product would be infinitely better. Relying on simple initial cost factors ignores long term benefits.
Kennebec made an observation about “piston effect”. I have gone through the canal a couple times on a 500’ vessel and didn’t notice it. I have talked to captains of Panamax ships and Panama pilots who confirm it is real, but it only applies to vessels whose beam approaches the width of the lock. The OOCL Utah appears to have room around the sides for water to flow freely.
Kennebec also made the excellent observation that European locks don’t use mules. I think that’s a good question. It occurred to me that the lock gates there might be a design that’s easier to repair/replace, but I couldn’t find that information in the time I was willing to spend searching.
Lastly Ausmariner noted that the video stopped just when it was about to show contact between the ship and the lock doors. Excellent question - maybe edited by somebody’s lawyers before posting?
