THE numbers in the last two figure columns of the Table show approximately the relative excellence, in respect of speed, of the forms of the various vessels, conjointly with the relative efficiency of the propeller, as adapted to each of them.

The formula by which the calculations are made are founded on the assumption that the resistance of a vessel varics as the square of her velocity, and therefore that the power required to produce that velocity varies as the cube, and that the useful effect of the engine, that is, the effect which remains after deducting the power absorbed in overcoming friction, working air-pumps, &c., bears a constant ratio to the power developed in the cylinder, known by the term "Indicated Horse Power." The resistance is, in the first of these columns, assumed to vary, cæteris paribus, as the area of the midship section, and in the last column as the square of the cube root of the displacement.

None of these assumptions, however, more especially the last two, are absolutely correct, but probably they are not so far from the truth as to render useless and uninteresting a comparison, of which they are the basis,

made between the performances of any two screw vessels; while between two vessels which do not materially differ in engines and displacement, or in the area of their midship sections, such a comparison is not only highly interesting, but it may prove of great value in pointing out the forms of vessels and proportion of propellers which ought to be adopted. In some striking cases it is scarcely necessary to make any other comparison than that of speed. For example, as may be seen in the table printed in 1850, the Teazer, after her form had been improved, went above a knot an hour faster with 40 horse engines than she had previously gone with engines of 100 horse power. Again, these engines of 100 horse, when transferred to the Rifleman, a vessel approaching to double the tonnage, drove her, after her form had been altered, as fast as she was previously driven by engines of double the power, and nearly two knots faster than the same engines drove the smaller vessel before the alteration of her after-body.

Admiralty, August, 1856.

Do.

Do.

868 11-201 3 July, 868 11-476

Do.

868 11-603

FORTH

Do.

1228 1228

8.6

GLATTON, Battery 1535

4.5

HANNIBAL

3136

HARRIER.

HASTINGS

1763

HAWKE

1754

1856 Stokes Bay 200 0 30 4 10 8 3 July, 1856 Stokes Bay. 200 0 30 4 10 8 3 July, 1856 Stokes Bay. 200 0 30 4 10 8 31 March, 1856 Plymouth 159 0 42 2 16 O 9.384 16 May, 1856 Stokes Bay. 159 0 42 2 17 7 4 July, 1855 Nore 172 6 45 24 8 4 8.6 12 April, 1854 Nore 217 6 58 1 20 6 747 8.32 24 Oct., 1854 Stokes Bay. 160 0 31 10 13 8 6.702 5 April, 1855 Stokes Bay. 176 10 48 6 19 9 6.525 126 April, 1855]Stokes Bay. 176 1 48 5 20 10

22222

3300

1047

22222

30 2 6114

100

576-6 13 2 19 11 3 0

308-810 011 9 20 350 1302-3 11 0 21 4 3 0 6105 350 1154-9 11 0 21 4 306 1061 30 7 350 1166-813 2 19 114 3 0 350 7436

76

60

20 350 1016-3 13 2 19 11 3 0 350 1160-6 13 2 19 11 30 200 814 12 010 0 1 8 200 833-6 12 0 10 0

62 150 693.4 6 214 0 450 1071-2 17 0412 6

20 100 360 10 011

65 200 597-3 12 0 12 3 1 11111

50 7456

8117

1 8 7 8 11 1

2 3365

2

1 11 9

13 1 10 7 6

12 0 9 6

1 7 7 10 11

Calm

Spare propeller, with wooden sphere attached to boss.
Same propeller as on the trial of the 16th July, 1853.
Common propeller (uncut). Calm. [Wind No. 3 to No. 4.
Common propeller, 1 foot cut off each corner of each blade.
Bomerang propeller. Wind No. 2 to No. 4.

Bomerang propeller. Wind No. 1. [ler. Wind No. 3 to No. 5.
Common propeller, surface reduced to that of Bomerang propel-
Do. and edges of blades bevelled. Wind No. 1.
Strong breeze, with swell. Trial not considered satisfactory.
Wind No. 3.

PROPELLER, (Continued.)

Slip.

RATIO OF

Indicated

power.

Vessel's length to
breadth.
Screw's pitch to
diameter.

Midship section to screw's disc.

To midship. section.

To displace

ment 3

Speed'x Mid. Sec.
Indicated Power.
Speed3x Dispt.

Indicated Power.

12.133 1-133

Knots. Knots.

9-344.16 1.14

3-21 2.25

12-739 1-496 11-744-16 1.14 4.17 2.14 13-573 2-703

9-5450-545

8-882 1.082

19-916-35 1-45 2:48 3:07 5.71 3.65 0.82 4.64 1.06 12-18 5.32 0.81

6:02 1-10

8-623 1-800

9.163 0.517

5.64 4.37 0.98 3.24 1.26

61-5 12-588 3.42527-515-30 1.70 4.02 1.31 12:429 3.210 25-835-30 1.67 4.16 1-26 10.979 3:40 1.24 4:30 1:39 14-007) 2-698 19-26 6-85 1.23 6-33 4.18 17-044 4.581 26-886-85 1-49 6:33 4.21 16-843 4-583 27-216-85 1.51 6.33 4-06 9-87 544-1186-7 John Penn and Son 17-060 4.923 28-866-851-51 6:33 4:11 10.00 435 1 1787 John Penn and Son 21-038 11-152 53-016-85 3:01 2.77 2.86 6.96 337.8 138.8 John Penn and Son 17-110 5-411 31-62 6-85 1.31 3.22 3.90 9.49 410-9 168-8 John Penn and Son 22-749 11-823 51-976.85 2.54 2.96 3.84 9.36 339-6 139-3 John Penn and Son |26-124 14-466 55-37 ||6-85 2.54 3.51 4.49 10.95 352-8 144-8 John Penn and Son 16-332 3.299 20-206-85 1.33 2.97 4.88 11-87 453-6 186-5 John Penn and Son 17:293 4-023 23-266-85 1.27 2:55 4.88 11.87 478-7 196-9 John Penn and Son 15-967 2-738 17-156-85 1-22 2.60 4.78 11.69 484-3 1981 John Penn and Son 19-975 6-759 38.846-851-58 2.75 4.84 11.77 477-2 1960 John Penn and Son 9-272 5:03 1.07 2.93 1·11 3.53 17-255 5-670 32-866-59 1.94 2-96 4.63 12.30 16-727 5-429 32-466-59 1.94 2.88 4.21 11.10 14-765 3-029 20-516-59 1-52 2:00 4:29 11-29 11-615 1-692 14-576-59 1.52 2.03 2:08 5.50

Wind No. 5. to No. 6.

Horizontal. Tk., Hgh. Prs. Wind No. 1.

4.22 587-9 182-1 J. Scott Russell and Co. 4.07 622.1 192-7 J. Scott Russell and Co. 5.14 Maudslay, Sons, and Field 10.17 346-0 142-1 John Penn and Son 10-25 459-9 188-9 John Penn and Son

[the weather. Speed not ascertained in consequence of the boisterous state of Wind No. 6 to No. 7.

Horizontal, Trunk
Inclined, Oscillating
Inclined, Oscillating
Inclined, Oscillating
Inclined, Oscillating
Horizontal
Speed not ascertained in consequence of strong wind.
Vertical, Oscillg., Geared Scott's propeller. Calm.
Vertical, Oscillg., Geared Griffiths's propeller. Wind No. 3.

Calm. Ship fully rigged.

Griffiths's patent screw propeller.

Griffiths's patent screw propeller. Wind No. 2.

Griffiths's patent screw propeller. Wind No. 2.
Common propeller. Wind No. 2.

[Wind No. 4.
Vertical, Oscillg., Geared Common propeller, cut with blades like Griffiths's propeller.
Vertical, Oscillg., Geared Common propeller, same as 24 Dec., 1853, with sphere attached
Vertical, Oscillg., Geared Lowe's propeller. Wind No. 7. [to the boss. Wind No. 4.
Vertical, Oscillg., Geared Bomerang propeller. Wind No. 4.
Vertical, Oscillg., Geared Lowe's propeller. Wind No. 4.

Vertical, Oscillg., Geared Lowe's propeller, but six inches less in diameter. Calm.
Vertical, Oscillg., Geared Fisher's Venetian propeller with flange.
Vertical, Oscillg., Geared Griffiths's propeller. Wind No. 1.
[to No. 2.
Vertical, Oscillg., Geared Common propeller cast at Portsmouth in 1850. Wind No. 1
Vertical, Oscillg., Geared Lewsey's blades fitted in boss of Griffiths's propeller.
[from the Eastward.
Vessel not taken to Stokes Bay, the wind being No. 8 to No. 9.
Wind No. 3.

11-245 1-861

5.65

Horizontal, Tk.,Hgh. Prs. Fresh breeze and a little swell.
Horizontal, Tk.,Hgh. Prs. Wind No. 3 to No. 4.
Speed by common log.

[Negative slip.

Speed by common log. Launching cleets not removed. Wind. No. 4.