3.1.3 The thickness of the screw shaft coupling flange is to be not less than 0.25 of the diameter of the intermediate shaft as required by Section 2.1 based on the screw shaft material.

3.1.4 The fillet radii at the base of the flanges are to be not less than 0.08 times the diameter of the shaft at the coupling. The fillets are to have smooth finish and are not to be recessed in way of nuts and bolt heads.

3.2 Separate Couplings

3.2.1 Where couplings are separate from the shafts, provision is to be made to resist the astern pull.

3.3 Flexible Couplings

3.3.1 Where flexible couplings are fitted, full details are to be submitted for consideration including the name of the manufacturer, type and method of securing the couplings is to the shaft.

3.4 Tap or Clearance Bolts

3.4.1 The major diameter of tap bolts or of bolts in clearance holes at the joining faces of couplings is to be not less than that given by the following formula: Diameter of coupling bolts =

(d) For bearings which are white-metal lined, oil lubricated and provided with an approved type of oil sealing gland, the length of the bearing is to be approximately twice the diameter required for the screw shaft and is to be such that the nominal bearing pressure will not exceed 0.8 N/mm2 (8.1 kgf/ cm2). The length of the bearing is to be not less than 1.5 times its diameter.

(e) For bearings of cast iron and bronze which are oil lubricated and fitted with an approved oil sealing gland, the length of the bearing is, in general, to be not less than four times the diameter required for the screw shaft.

(f) For bearings which are grease lubricated, the length of the bearing is to be not less than four times the diameter required for the screw shaft.

4.2.2 The bearing in the stern tube is to be secured to prevent rotational and axial movement. 4.2.3 Where screw shaft bearings and tube shaft bearings are made of lignum vitae or approved plastics materials, they are to be so designed as to ensure adequate water lubrication Depending on the location of the bearing, it may be necessary to supply water to the bearing from a circulating pump or other pressure source.

4.2.4 Stern tubes are to be carefully fitted and well secured to the hull of the craft. The stern tube, propeller brackets and fastenings in wood craft are to