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Variable pitch screws
Variable pitch screws have attracted more and more attention in recent years. This is explained by the fact that they make it possible to maintain a constant number of engine revolutions without stopping them or reversing, if necessary, reducing the speed, stopping the vessel or reversing it.
An example of installing variable pitch propellers on a large marine vessel is the Swedish motor ship Sweden, with a length of 140 m and a speed of 17 knots above 7,700 tons of deadweight. The ship is a twin—screw, with two six-cylinder diesel engines of 3,500 hp at 125 rpm.
The screws are mounted in a "Kameva" type with rotatable blades in the hub by means of a hydraulically controlled servo motor. Control columns are installed on the bridge, with the main column on the starboard side. The speakers have only control levers and indicators showing the position of the blades. There is a control column in the engine room, similar to the column on the bridge.
A pneumatic telemotor is used for transmission from the levers on the column to the valves of the blade rotation servomotor. Compressed air is used for this purpose from starting cylinders with pressure reduction from 25 to 2 atmospheres.
During the tests, when the vessel was in ballast (6,000 tons displacement), the time for stopping the vessel was set at 2 minutes. The speed at 7,000 hp was 18.75 knots.
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Tugboats built in recent years in England
During the Second World War, several types of tugboats were built in England. These tugs are single-screw and can be divided into 5 classes:
1) "rescue": length — 48 m, width amidships — 10.2 m and side height — 4.95 m, power — 1625 hp, speed — 13 knots;
2) "long-distance navigation": length - 40.5 m, width — 9 m, side height — 4.8 m, power — 1125-1250 hp;
3) "coastal navigation": length — 31.5 m, width — 8 m, side height — 4 m, power 850-1000 hp.;
4) "port": length — 27.6 m, width — 6 m, side height — 3.1 m, power — 500 hp.;
5) "dock": length — 19.5 m, width — 5.1 m, side height — 2.4 m, power — 220 hp.
Tugs of classes "1" and "2" are designed to operate on the high seas. Their boilers are heated with fuel oil. These vessels have a one-month fuel supply. The Class 3 tugboats were initially equipped with coal-fired boilers, and then many of them were equipped with oil-fired boilers. They, like the tugboats of the first two classes, are also equipped with powerful fire and rescue pumps.
Class 4 tugboats are designed to operate in ports and on the roadstead, but were used for towing in coasting. Some of them are equipped with Court nozzles.
Tugs of class "5", sectional assembly, with mechanisms manufactured in mass production, and boilers supplied by various companies.
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New gas appliance
A new 22.5 kg gas apparatus for cutting metal was successfully used by the Americans during the war in the Pacific Theater. The gas cylinders in the new unit are installed in such a way that they can be easily and quickly replaced in case of gas consumption. The supply of acetylene and oxygen is automatically regulated.
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