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[MatthewB]

I am working on a digital application that can be used to run campaigns, or a campaign driven Grand-Tactical, or Theatre-Level strategic game, using digital devices like iPads, Microsoft's Surface/Surface Pro, or Cell-Phones to keep track of the Strategic Movement and Supplies/Logistics.

But in researching the various Merchant ships, from places like Navsource, Pacific War Online Encyclopedia, and other WWII Era sources that friends have found at NARA, I am confused about the way that Merchant ships are treated.

For instance.... The use of GRT and NRT for the ships themselves seems to diverge from these sources, as does the Cargo Capacities of the various ships. The MSS says that the Ship Combat Log is based upon "Volume" rather than tonnage as a weight.

In the sources mentioned, the AKs for the USN are listed as carrying around 4,000 to 5,000 tons of Cargo, and generally having between 350,000 cubic feet and 600,000 cubic feet of Cargo Space.

My problem comes from in researching these ships that the weight that they can carry (in Tons) far exceeds the Tonnage in Volume that is given in the MSS, and in keeping track of things all of the various War Materiel I am researching is listed only in DWTs or "Weight," and calculating the volumes of these things is a rather enormous task (for the various levels of play, where at the "Advanced" you would need to keep track of many very specific types of cargo). At the "Basic" level the problem isn't so difficult to resolve, as the abstraction involved allows for a lot of hand-waving away the problems of things like the differences in size and weight between USN Mk. 13 Aerial Torpedo and the Mk. 18 Submarine Torpedo.... or the IJN Type 91 Torpedo vs the Type 93.... And so forth for other things like food, water, toilet paper, or Marston Matting (for that matter).

In the Basic system, these are easy to abstract away. You just have a single "Supply" category that is built up over the average of all freighters in operation (and can only be disrupted by the complete elimination of one category of essential freighter - Say Oilers capable of UnRep).

But even getting into the Intermediate System, where the basic components are:

• Dry Cargo (including dry Food)
• Refrigerated Cargo (Including Frozen Food).
• Water.
• Oil / Diesel / Gasoline (which includes AvGas).
• Ammunition.
• Troops.

As are indicated by the basic Campaign System.

Here problems begin to be encountered in dealing with the fact that the number of holds on the Merchant Ship Combat Logs no longer really corresponds to the actual capabilities of the ships in terms of the tonnage they can carry in weight, which often far exceeded their volume (Carrying a shipment of Type 93 Torpedoes, for instance, quickly overwhelms a 1C Class IJN Cargo ship's Volume. It has ample "room" left in its holds, but carrying further "Weight" in Cargo risks swamping the ship in heavy seas).

This presents at least two main problems in accounting:

1) How to account for where this stuff is in the Holds on the Ship's Logs (and thus what is lost if a Hold is destroyed)
2) How to account for how much "stuff" is in one of these holds.

This is even more apparent when looking at the Oilers, which could carry tens of thousands of Tons (Weight) in Oil, Diesel, or Gasoline. (The Cimarron-class, such as the Neosho, could carry 147,600 Barrels of Fuel Oil, which translates to between 16,000 and 22,000 tons of Oil/Gasoline).

Yet the AO Logs show only 7 Tanks for Petroleum Products. That would be between 2,500 and 3,000 tons of Oil in these holds in Weight as opposed to the system of Volume.

And I am having trouble finding a consistent means of tracking this difference, considering the demands of the ships in refueling (I can find nothing to show a similar means of abstracting the Bunkerage of each ship from DWT to Volume that results in a consistent equality to the Oilers' or Colliers' supply).

Does anyone have any idea in how to account for this discrepancy, or can shed light in how the values for NRT and GRT for the various ships were chosen given their divergence from that found in the sources I have?

MB 

Edit: And this does not even get into the "Advanced" system, where individual ammunition, crew/troops, fuels, food, and cargo types will be tracked.

Edit: I think that I found the relevant information on the conversion of Weight (Tonnes) to Tonnage (Volume). But it does mean having to work out storage volumes for different stores (Naval Gun Ammunition, Different torpedo types, Oil / Diesel / Gasoline / AvGas, Depth Charges, Spare Tires, Airplane Propellers, Rope, and, of course, Toilet Paper) and then keeping track of every ship's Weight limit as well as its internal volume limits.... 

But the Wikipedia article read on Gross Tonnage at the same time as reading the MSS and Campaign Tables helped to sort things out. 

This does lead to another question, though:

Why use NRT instead of Weight?

I see that this does make for more Compact Ship Logs, where you have fewer "Holds" to keep track using Volume/NRT than using Weight.