NOTE. - Diameters are calculated to nearest eighths of an inch with a fibre stress of 5,000 lbs.

Rudder Stock per Germanischer Lloyd Formula.

This rule is a much more correct one than Lloyd's Register, using, as it does, truer factors. It is given here converted for

English measure as well as for metric.

Let

Then,

d diameter of stock in centimeters.
F= area of rudder in square meters.

r = distance from centre of gravity of area to axis of
stock in centimeters.

V speed in knots.

For English measure let

Then,

d = .42 / Fr V 2.

British Corporation Formula.

The "B.C.," or British Corporation, Rule is slightly different from the foregoing, but, like it, takes the true factors into account, and gives a more correct result than either of the foregoing formulæ.

d = .26 rAV2

NOTE."" is here taken in feet.

PROPELLER STRUTS.

SIMPSON'S FORMULA.

Propeller "A" brackets or struts are not dealt with in any of the classification societies' rules, and in deciding on a suitable area of section for these, it is the invariable practice to base it on experience. Such being the case, a great divergence is found in the

proportions and dimensions of them in vessels of similar size and power. To insure greater uniformity in their design and weight consistent with ample strength to meet the stresses to which they are subjected, the writer has prepared the formula following, based on the results of a varied experience with struts for all sizes of vessels with a range of I.H.P. of 10 to 7,000 per shaft and revolutions of 70 to 600, and from observation of some which were actually carried away. It should be stated that the smaller powers were not for twin screws but for small craft with cut-away deadwoods necessitating a bracket to support the outer end of shaft. From the formula given, the area is obtained, and with it the following proportions determined :

SECTION OF ARM

Let

Then,

R=revolutions of engines per minute.

P indicated horse power.

outboard length of shaft from stern tube outer bearing to centre of boss, in inches.

k = coefficient = .0633 R.

RX PX 1
k

area in square inches.

Of course the horse power is that transmitted through one shaft only, and the area obtained is for one arm. The proportions of the pear-shaped arm are as under.

For the lesser powers and for brackets intended for wood or composite vessels, the brackets should be of gun metal or bronze, and for higher powers and steel ships of cast steel.

Spectacle Frames.

For the larger classes of twin screw steamers what are known as spectacle frames are bolted to body post to take the outer end of shaft, and the shell plating webbed out to enclose what otherwise would be the outboard length of shafting, as described in the chapter on design. These frames are of cast steel and semi-pearshaped in section. The area of this section may be found from the same formula as if the ship were to be fitted with "A

Bossing adds 34% to wetted surface and .84% to displacement.

30°

C.L. OF SHIP

FIG. 39.

brackets and the result multiplied by 2. This greater area is accounted for by the fact that there is only one arm and the greater breadth of same required to permit of working the shell plating and also obtaining the necessary section modulus. The weight, however, will be found to approximate very closely to the open struts. Experiments have shown that better results are obtained by inclining the spectacle frame downwards at an angle of about 30° from the horizontal.

The outside diameter D of the boss will be fixed in conjunction with the engineer.

THE TRANSPORT OF CATTLE.

In arranging the ship for the transport of cattle in conformity with the United States Department of Agriculture, care should be exercised in first providing for the main cattle gangways. A good location for these would be at the ends of engine or boiler casings opposite which the cattle doors should be placed. The webs, webframes, and any other structural obstructions should be arranged with a view to working them in as boundaries for blocks of 4 cattle if practicable, and if the ship be a new one, the frame spacing should be fixed to work out with the legal dimension for cattle pens to obviate waste of space, unsuitable pillaring, and division boards coming off beams. If the ship be of such dimension as to require 30′′ spacing ordinarily, then by increasing this to 30", a very good arrangement of pens will be obtained. Coaling ports, mucking ports, and all thwartship passages in connection therewith, should next be located, bearing in mind, in arranging these, the 4-cattle blocks previously mentioned. The stalls may be then outlined, followed by the pillars, which, of course, will be placed to suit these, working downwards from the cattle deck to the other hold pillaring.

The following are the dimensions of cattle spaces required by the Department of Agriculture :

Cattle per head on upper, spar, or weather decks:

8' 0" long × 2′6′′ wide x 6'0" high in the clear.

Cattle loaded under decks will require 2 inches more width unless in regular cattle ships with satisfactory ventilation.

Pens must be arranged for 4 cattle, unless at the ends of a row of pens, where 5 may be stowed.

Special permission must be obtained to carry cattle on lower deck, and in all cases where this is granted, the width allotted must be 2′8′′, the ventilation sufficient, and no animals are allowed on hatches.