Ocean Steam Navigation and the Ocean Post - Thomas Rainey

Showing the mutual relation of Displacement, Power, Speed, Consumption of Coal, and capacity for Cargo of vessels of progressively increasing magnitude up to nearly 30,000 tons of Deep-draught Displacement, employed on a passage of 3,250 nautical miles, without recoaling: showing also the prime cost Expenses per ton of Cargo conveyed.

Mean or Mid-passage Displacement.	Speed.	POWER.		Assumed weight of Hull and Engines.	PASSAGE 3,250 N. M. DIRECT.
Mean or Mid-passage Displacement.	Speed.	Nominal H. P.	Indicated h. p.	Assumed weight of Hull and Engines.	Time.	Coal.	Cargo.	Deep Displacement.	Expenses per Ton of Cargo.
Tons.	N. M.	H. P.	h. p.	TONS.	D. H.	TONS.	TONS.	TONS.	£	S.	D.
	8	109	436	1109	16.22	369	1209	2684	2	1	10
2,500	9	155	620	1155	15. 1	466	1112	2733	2	7	8
2,500	10	213	852	1213	13.13	577	999	2788	2	16	11
	11	284	1136	1284	12. 7	699	867	2849	3	11	3
	12	368	1472	1368	11. 7	830	717	2915	4	14	5

	8	172	688	2172	16.22	582	2537	5291	1	16	1
5,000	9	245	980	2245	15. 1	737	2386	5368	1	19	7
5,000	10	336	1344	2336	13.13	882	2223	5441	2	4	1
	11	448	1792	2448	12. 7	1103	2000	5551	2	13	1
	12	581	2324	2581	11. 7	1311	1763	5655	3	5	1

	8	276	1104	4276	16.22	934	5257	10467	1	12	3
	9	388	1552	4388	15. 1	1168	5028	10584	1	13	10
10,000	10	536	2144	4536	13.13	1407	4760	10703	1	16	9
10,000	11	712	2848	4712	12. 7	1753	4411	10876	2	2	1
	12	928	3712	4928	11. 7	2094	4025	11047	2	9	4
	13	1180	4720	5180	10.10	2458	3591	11229	2	19	5
	14	1472	5888	5472	9.16	2848	3104	11424	3	14	3

	8	436	1744	8436	16.22	1476	10826	20738	1	9	0
	9	620	2480	8620	15. 1	1866	10447	20933	1	9	11
20,000	10	852	3408	8852	13.13	2236	10030	21118	1	11	4
20,000	11	1136	4544	9136	12. 7	2797	9466	21398	1	14	9
	12	1472	5888	9472	11. 7	3322	8867	21661	1	19	1
	13	1872	7488	9872	10.10	3900	8178	21950	2	4	11
	14	2340	9360	10340	9.16	4528	7396	22264	2	13	1

Mr. Atherton gives this table, which shows the following facts:

That, as the various sized vessels named, increase in speed from 8 to 12, or from 8 to 14 miles per hour, their horse power, as well consequently as their coal, increases:

That, as the speed increases, so does the weight of the hull and engines:

That, as the speed increases, with the consequent increased coal and engine weight, the cargo decreases: and

That, as the speed increases, with the other necessary conditions noticed, the expense per ton of cargo also increases in a rapid ratio. In the four cross columns ships of different sizes are considered; of 2,500, 5,000, 10,000, and 20,000 tons. There is also given the working or indicated horse power, and the nominal horse-power, or that of 33,000 lbs. raised a foot in a minute, which is the general basis of making contracts. It is a fact, however, that engines generally work up to three or four times their nominal horse power; so that the word horse power has no positive or useful meaning. Vessels called one hundred nominal horse-power have been known to work up to six hundred.

Let us take a ship of 5,000 tons. We find that at 8 miles per hour the horse power is 436; but at 12 miles it is 1,472, nearly four times as great. At 13 miles, it would be nearly 1800 horse, and at 14 it would be above 2100. So, also, with the weight of engines, boilers, etc. At 8 miles per hour they would weigh 1,109 tons; but at 12 they would have to weigh, to be large and strong enough, 1,368 tons. At 14 miles, they would weigh nearly 1,600 tons.

Now, see the columns "cargo" and "coal," and observe how rapidly that of coal increases, while that of cargo decreases in the inverse ratio of the coal, the engine, the boiler, and the hull weight combined. The cargo has come from 1,209 down to 717 tons; and if the speed were increased to 13 or 14 miles per hour, the cargo would be so reduced as to be unworthy of notice.

The next column shows how much greater the quantity of water displaced as the speed increases. This extra displacement requires extra power.