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appended is a table giving the value of these angles for various speeds and lengths of vessels obtained from actual well-known ships of the best form.

On the construction lines of the body plan and profile, a mean water line is drawn half way between keel and load line, as shown

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D

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By referring to the table of angles, a is selected for the length of vessel being designed and the tangent of the same spotted on the half-breadth plan. This will give the outline of the mean water plane.

Two diagonals, D and D1, are struck in on the after body plan, the former intersecting the centre line at half the draught, as well as the base line at a distance equal to the half-breadth of the ship, and D1 intersecting the load water plane at centre line as well as the half moulded breadth construction line at the mean water line height, as shown in Fig. 55.

The angles ẞ and are obtained from the table and transferred to the half-breadth plan representing the half planes of D and D1 respectively.

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Campania. 1st Class Ocean

Liner, T.S.

Manchuria 1st Class Interme

600 65 041 6 26 10 19,336 .644 .667 .976

diate Liner, T.S. 600 65 043 333 2 26,514 .715 .762 .942

Normannia 1st Class Ocean

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Jupiter. Sound, P.S.

Greyhound Channel, P.S. Tynwald. Channel, T.S. Sandy Hook Sound, T.S. Mayflower. Yacht, T.S. .

Yacht, T.S.

Yacht, Auxiliary Composite Yacht, Auxiliary Steel.

160 26 6 17 0 11 6

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157 27 0 17

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011 6 136 22 6 13 9 8 9 21 6 11 0 6 6 19 0 10 6 6 6 15 6 8 9 50 11 9 7 34 0 86 10 7 5 10 2 9

Princess

Maud*

S.S. Customs Launch,

S.S.

65 12 0 7 0 4 3

55 12 0 6 8 4 6

* Designed by the Author.

1,508 .58 .594 .976 1,165 .417.5 1.82 2,414.535 .612.874 1,862 .505.498 .904 568.407.59.682

552 .3968.6 .664 332 .428 .59.73 303 .482.626.773 202 .439 .594 .74 100 .407 .610 .667 41 .412 .662.622 30 .43 .625 .687 41.437 .585 .757

37 435 .56.776

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1,538.493

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.837 2,827.426 1,167.1758 3,995 .6019 627 9,065
.875 3,891.463 637 .0764 4,528 .539 731
.847 2,125.472 531 .118 2,656.59

.868 1,210.388 328 .105

3,844 98 13.93 306

8,390 3,535 75 12.8 245

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SECTION II.

STRENGTH OF MATERIALS.

CHAPTER I.

STRESSES.

It is by the application of the known strengths, as derived by experiment, of the various materials used in shipbuilding to the physical properties possessed by their geometrical sections that we are enabled to calculate with accuracy the loads they will bear with a predetermined margin of safety when subjected to either of the four simple stresses of tension, compression, shearing and torsion.

Ultimate Strength is the direct stress producing rupture of the material.

Working Load is the stress applied in practice, and its ratio to the ultimate strength varies with the nature of the stresses applied, viz.: (1) tension with a dead load; (2) tension with a live load, or (3) a live load working alternately in opposite directions (see Table).

Many of the fittings in shipwork come under the third category, as in rudders, derricks, etc. In derricks the inertia of the load has not only to be overcome, but also the jarring and surging. For this reason a very common factor of safety for these details is ten times the ultimate strength.

Proof Strength is the test load to which cranes, davits, derricks, chains, cables, etc. are subjected, and is usually a multiple of the working load or ultimate strength. Careful measurements should be taken before applying this load, and these checked after the load has been removed, to discover, if any, the amount of permanent set.

Stress and Strain.-Stress is the measure of the internal force or resistance in a bar due to the load applied tending to produce

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