Primer on Capacity

[JWE]

Ok, enough with the pms about your favorite website and your favorite numbers. What part of the discussion with Brother Buck, don’t you understand? The people who write that stuff are not Naval Architects, and don’t understand what the word “ton” means in its many permutations. So here’s a primer on “tons”, based on the USMC specs for a C2-S/F/T.

Gross Register (GRT) -- 8,015 (Cu-ft/100)
Net Register (NRT) -- 4,612 (Cu-ft/100)
Bale Capacity -- 4,398 (Cu-ft/100)
Grain Capacity -- 4,424 (Cu-ft/100)
Measurement Ton capacity -- 10,995 (Cu-ft/40)

So gross tons is clearly a crock. It’s a tax measurement. I mean, how much did you really earn last year, and what did you report to the IRS – yeah, right – same same. Net is similar. Bale capacity is physical – how many 1 cubic foot boxes can you stack in the holds. Grain capacity is also physical – how many cubic yards of stuff (expressed in cubic foot ton units) can you pour into the cracks and crevices between the bale boxes. Measurement tons are a military measure and are the Bale capacity expressed in units of 40 cubic feet, instead of 100 cubic feet.

When you think in terms of weight tons, things begin to become clear, but once again, different people use the terms in different ways, so you need to know how the industry uses them, and how they relate to one another. That way, you can read a number, go to a couple other numbers, and say “aha, that’s what he means by …” So here’s the weight numbers for the C2-S/F/T.

Loaded Displacement -- 13,910 Long Tons
Light Displacement -- 4,250 LT
Total Deadweight -- 9,660 LT
Max Cargo DwT (max) -- 7,485 LT
Net Cargo Dwt (design) -- 4,900 LT

Fuel Capacity (all tanks) -- 1,640 LT
Water (steam + reserve) -- 376 LT
Accomodation allowance – 944 LT

So add up all the stuff and you get 2,960 LT which, when subtracted from 9,660 Total Dwt leaves 6,700 Long Tons for cargo, max, before you sink. You can get to 7,485 max CDwT by leaving the deep fuel tanks empty and overloading. There is a 30% design load margin, required by insurance underwriters and, accepted by anybody who has been to sea, as a critical difference between safe delivery and Russian roulette.

The game uses 5,600 LT for a C2-S (subsuming the F and T designs as well).

Historians are not naval architects, so they are sometimes caught up in the vagaries of terminology. Many confuse Total Deadweight with Cargo Deadweight. It’s probably the industry’s fault because some consider everything that sits on top of Dspl (Lt) as technically cargo, but there is a big difference between DwT and “real” NCDwT. The industry folks get it, because it’s just a matter of looking at a couple other numbers to understand what’s really meant, but others don’t have that coup d’oeil.

I hope this helps a bit. Internet websites really suck when it pertains to merchant ship capacity, but sometimes they (unknowingly) have some info from which reality may be extracted. The above shows how it’s done.

[Dili]

Thanks

[JWE]

You are very welcome, Dili. I know, in the past, you have asked questions on this subject and I hope my answers were informative.

I realize the post is a bit sharp, but those of you who 'get it' know exactly where I'm coming from. You, Dili, and Buck, and several others, 'get it'. I'm glad that the primer is helpful to ya'll. I was just shootin at the "numbers penus's" out there. Them of you out there what's got a clue, please ingore the sharp stick; I just try to present what is, and relate that to what we got in the game.

Ciao. John

[Buck Beach]

From a HyperWar link:

" It was dark by the time the Enterprise came alongside for her turn. No heavy ship had ever been fueled in the open sea at night, but the carrier had to have oil for the fast run-in. Smoothly and steadily, Capt. George Murry eased the carrier toward the Platte to a position close abreast "as if it were a summer noon in Long Island sound." The seamen and engineers did the rest. Below decks the "oil king" and his helpers on both ships directed the flow of
oil from one tank to another as the two ships steamed side-by-side for five and a half hours. As the gap between the two vessels widened and contracted the topside crew tended the lines and hoses making sure that none parted, though ironically, other men stood by with axes to cut everything away in the event of enemy attack or other emergency. Replenishing Enterprise's depleted bunkers or for that matter any large ship while under way at sea was, as it continues to be today, an exacting task that demands superb seamanship. The dynamic forces involved when a 30,000-ton (or larger) aircraft carrier and a 25,000-ton oiler are maneuvering at 8 to 12 knots within 50 feet of each other are difficult to comprehend or image. Yet the two vessels had to steam at identical speeds within 20 to 70 feet of one another for hours while a trickle of black oil flowed through 6-inch rubber fuel hoses suspended from saddles rigged to booms projecting over the oiler's side. Quick, skilled hands and precise judgment were necessary to keep the two ships separated. It may have looked easy, but itwasn't, and although collisions did not occur often, they could have disastrous effects. On one occasion, Kaskaskia lost every one of her portside booms and had to put into Pearl for emergency repairs after being sideswiped by the Yorktown."

A so what share. Old Buck has been there and done that. I never will forget the only emergency break away that happened while I was aboard the AO-22 in 1963. We we're unrepping an AE (Ammunition ship) late one night and I was relieved to go to my bunk a couple of decks below. I was really sawing some Zzz when the ships whistle sounded five blasts (IIRC) for an emergency break away due to the ships giro going out. I flew up the ladders to deck level not knowing what to expect, but found that we had allready broken away with our gear (hoses and connections) being lost but we were parting our parallel paths rapidly, and safe.

There were many swabies with puckered parts that night.[:D]

As I read this back I saw I was really off topic here. Sorry.

[Don Bowen]

I rode the old Cacapon from Subic out to the Gulf of Tonkin to join a ship on station. There were a couple dozen of us "passengers" assigned to various ships on station. As we came alongside each ship, the Cacapon's crew managed the fueling without incident. Each time a passenger's ship was being refueled, all the remaining passengers would man the lines for high-lining the guy over. Fun, fun, fun.

My own ship was standing North SAR One - the furthermost ship on the Search and Rescue picket line. Approximately off Haiphong. Cacapon ran out of oil a few ships before mine and the last few of us got highlined to a destroyer, then picked up by a mail helicopter and ran to out ships.

Two weeks on station and Rickmond K Turner was relieved and ran all the way to Sasebo (refueling from another oiler on the way). You know, the Navy could have just sent me directly to Sasebo to wait for her and I would have been just as happy.

[Buck Beach]

Question withdrawn you tried to explain it under the other thread Mariners Capacity. I will have to study it some more.

[Zebedee]

ORIGINAL: JWE
Historians are not naval architects

Very true. And of course, vice versa.

Really interesting insight into putting new hauling capacity into the game while staying within guidelines for existing ships. Much appreciated.

[Shark7]

I think I get it.

Total displacement is obviously the maximum tonnage of the ship that if exceeded would likely put the ship into Davey Jones' locker.

Light Displacement would be the structural tonnage of the ship. IE the steel, wiring and engines.

All you do is subtract the structural from the total, which gives you the total deadweight tonnage. Take away the bunker, water and living spaces and you get a total on the max actual cargo tonnage...this is the bulk cargo max...bulk being such as coal, ores etc.

And just because you have a 5000 ton bulk cargo capacity doesn't mean you can necissarily carry 5000 tons of other cargo, since they may take up more volumetric space.

It is nice to see how you come up with the numbers though. This is why people get confused when you say a Liberty ship is a 10,000 ton ship...that is the total displacement, not the cargo capacity.

[JWE]

ORIGINAL: Shark7
I think I get it.

I think you do, too.

Total displacement is obviously the maximum tonnage of the ship that if exceeded would likely put the ship into Davey Jones' locker.

Yep. Defined as the total amount of water displaced by a fully loaded ship, floating on her design waterline marks. You could overload, and folks often did, and some types more than others, but everybody in-game plays to the same rules, i.e. design displacement.

Light Displacement would be the structural tonnage of the ship. IE the steel, wiring and engines.

Yep. But there's 4 different versions of Dspl(lt), so 'grain of salt city'. We used Maritime Commission design light ship tons (LST(d)).

All you do is subtract the structural from the total, which gives you the total deadweight tonnage. Take away the bunker, water and living spaces and you get a total on the max actual cargo tonnage...this is the bulk cargo max...bulk being such as coal, ores etc.

Yep. Which is why consistency is so important in specifying Dspl(fl) and Dspl(lt).

And just because you have a 5000 ton bulk cargo capacity doesn't mean you can necissarily carry 5000 tons of other cargo, since they may take up more volumetric space.

Yep. Just think of a cargo of 1/4 ton weapons carriers. Don't weigh all that much, but take up a lot of room.

It is nice to see how you come up with the numbers though. This is why people get confused when you say a Liberty ship is a 10,000 ton ship...that is the total displacement, not the cargo capacity.

Pretty much, but a Liberty was 10k and a skoosh 'deadweight'; about 14k or so Dspl(fl). We got them at about 6750 Net Cargo. Actually pretty darn close to the C2-S/F/T described, above. Not surprising, since Liberty was an 'emergency' C-2 design, thus the EC-2 designation.

Think ya pretty much 'got it' Shark.