NOTES ON ANCHOR CRANES. The most suitable radius of crane to efficiently fish the anchor having been determined, this dimension in feet multiplied by the weight of anchor including stock, will give the moment in footcwts., to which reference must be made for the corresponding sizes of parts. N.B. These cranes are in accordance with Lloyd's requirements per Table 12, but for convenience the moment is given, which will be found much easier of application, and the table has been extended to deal with the heaviest anchors. Of course where the ship is not classed to Lloyd's, the crane should be figured out with a factor of safety of eight, when it will be found that the sizes in this table, being empirical, may be considerably reduced. The heavier sizes of cranes may with economy be built up with structural sections, or the post and jib may be formed with angle sections having lattice bracing. It will also be found more economical to step the crane post or anchor deck in preference to housing it and making it revolve with the jib. BRONZE SHIP'S BELL. Copper 13, Tin 4 parts. Directions for Laying Out. — Divide diameter of bell into 24 parts. Arc A G, drawn with rad. of 3 parts from K, wherever that may fall, the rest of curve laid in by hand. Rad. of crown 17 parts may be 16 to 19; thickness of beil at B, parts waist, sound bow = diam. = QP. = Part of bell above bis. laid in as a cylinder. BALANCED ARMORED HATCH. Determination of Counterweight. — Weight of hatch and fittings complete W1 = 540 lbs. = 30 lbs. Moments about centre of upper gear segment: 373 X 24.8 = P2 × 5.375 ins. Strength of Teeth for Gear Segments. — Lewis formula: = Distance between bearings 1730 X 8 8 = 1730 in.-lbs. Maximum bending moment Mь π 32 = d3 Xf; ƒ = 10,000 lbs. per sq. in., 8 6650 X 32 π X 10,000 = 1.9", make 2" to allow for keyways, etc. |