Steam Tug Wattle was built as a harbour tug in 1933, a steel ship built to Lloyds scantlings. Forty-four steel angle frames, at 20" (508mm) centres from bow to stern, are clad with riveted steel plate of thicknesses varying between 5/8" (16mm) and 3/8" (10mm).
Steam is supplied from a two-furnace Scotch Marine wet-back boiler, 10'9" (3.28m) diameter and 11'0" (3.35m) long. The boiler was originally fired with dewatered and filtered waste oil, but has recently been converted to burn distillate for environmental and maintenance reasons. Total bunker capacity is 10 tons in port and starboard tanks. The boiler operates at a pressure of 120–130 psi to power a two-cylinder (compound) engine.
The high pressure cylinder is 13.75" (349mm) in diameter and the low pressure cylinder is 31" (787mm) in diameter. The stroke is 20" (508mm). Steam-assisted reversing gear (Stevenson's link) is fitted. The engine turns a four-bladed propeller, 7'6" (2.29m) in diameter with a pitch of 9'4" (2.84m).
The ship is recorded as having achieved 10.8 knots at 132 rpm, 287 IHP, during first trials in light condition (118 tons). (Some records say 9.82 knots at 134 rpm and a boiler pressure of 128 psi). Wattle generally steams at about 8 knots (85–90 rpm).
Wattle was not originally equipped with a steering engine but the ship was found to be very difficult to steer, so the auxiliary steering engine was fitted on the main deck, abaft the Engine Room skylight. To meet current safety and amenity standards, a 19kVA diesel generator was installed in the aft storage compartment in 2016.
81'3" (24.76m)
17'6" (5.33m)
9'3" (2.82m)
99.8 tons (101.4 tonnes)
Launched at Cockatoo Island on 27 June 1933 by Cockatoo Docks & Engineering Co. Ltd. (CODECO) on order from the Commonwealth Shipping Board.
80'8"
17'3"
9'3"
10 knots
120 tons (132 tonnes light)
36 hours / 360 miles at 300 IHP
Single screw, compound two cylinder (HP and LP). Indicated horsepower (IHP) 300 at 134 RPM.
Return tubes main type, 2 × Deighton withdrawable furnace — 3'0" diameter × 7'10" long. Heating surface 1196 sq ft. Boiler 10'6" diameter, 11'0" long, working pressure 130 lbs.