Mike, I’m very interested to see the primacy you give to the tonnage: capacity ratio as the index of merchant ship efficiency, and I agree that getting maximum use out of limited docking capacity is an important consideration. From this perspective, I think you are absolutely right to be thinking in terms of canned cargo convoys, by which I take you to mean groups of standardised TF’s, the TF’s in each group having the same ship composition and being optimised for the ports they are to ply between.
I have been looking at Japanese merchant marine efficiency more from the perspective of fuel expenditure, and have now completed an initial run of tests upon TF’s mostly composed of a single ship. I am posting a graphic to show the results of this test, but will also upload the full spreadsheet so others can play with it as they see fit.
The test covers a range of voyages, for some of the tankers between Fukuoka or Takao and Dalian/Port Arthur, with the remainder of the voyages being between Honshu ports and Truk. I noted both fuel expended and hexes travelled each day, so the tests reflect actual rather than predicted performance. I may have made a one-hex error in distance travelled in one day with the Akasi Maru class ship. A better test would have been to send the big whale factory ships to Truk; their voyages are a bit short to make the test results as reliable as I would like.
One anomaly in the tests was the first day’s travel: in all cases save the Yusen S TF the ships seem to have moved only half the usual daily distance travelled on day one – 7 December 1941. The exception – the Yusen S design – travelled a full 9 hexes on its first day, but this was due to it having to restart its voyage on December 9, as I mistakenly set it on its way at full speed, obliging a return to Yokohama and restart at cruise speed. This suggests something anomalous is happening with TF travel in the first turn of the game.
The results permitted calculation of an average expenditure of fuel per hex, which in turn made possible a calculation of a ‘Cargo Miles per Fuel Ton’ figure as an index of fuel efficiency relative to amount of cargo carried.
The tankers come out on top in terms of fuel efficiency, but I suspect that may just reflect differences between wet and dry cargoes. As to the dry cargo ships, I think the figures make a case for using the modern designs (Kyushu Maru’s and NYK N, S and A designs) on the long haul routes (probably Truk and the SRA ports), on grounds of both fuel economy and speed. Not only do they carry more cargo per fuel ton, but they also do so faster. Faster rates of advance = shorter cycle times over a given route = greater cargo hauling efficiency.
A pity the Standard A’s are not available until June 1942: it would have been useful to see how they stack up in fuel efficiency terms.
The figures in my own tests if anything reinforce the conclusion I drew from Mike’s figures, namely that the most significant class of all remains the Aden Maru’s. By my reckoning there are 189 of them, far more than any other class, and they are the ones that I think will have to form the backbone of the Yellow Sea/Sea of Japan services bringing resources in to the Home Islands’ industry.
For me, there are two questions still unanswered. First, can the Standard A’s plus the Lima Maru’s take over from the fast ships as the prime hauliers from the SRA? Doing this would free up the fast ships to enhance Japan’s strategic sealift capability, something that I think will be required if she is to exploit her advantage of interior lines. Second, what to do with the Kawasaki tankers, the Type N TL’s? They are precious vessels since you only get 8 of them, and they can either be converted into fast oilers to supplement the 4 you start with, or they can be converted into Tonan Whalers with their high capacity and fuel efficiency. Or you can just leave them alone. Difficult choice.
