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THE ICE-BREAKER "KRISJANIS VALDEMARS": Bow VIEW.

NOTES.

THE ICE-BREAKER “KRISJANIS VALDEMARS."

The ice-breaker Krisjanis Valdemars, which was launched on the 9th June by Messrs. William Beardmore & Co., Limited, at their Naval Construction Works, Dalmuir, to the order of the Marine Department of the Government of Latvia, will constitute a very important addition to the facilities of the port of Riga. The vessel is intended to operate in the Gulf of Riga, so as to ensure that the port will be accessible to shipping at all seasons of the year, and she has also been equipped for salvage purposes. The following are the leading particulars of the ship:

Length on waterline, feet and inches.
Breadth on waterline, feet and inches..

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185-0

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As will be seen from the photograph reproduced, the ice-breaker has a specially designed stem with considerable rake under the waterline and a stern of cruiser type, both stem and stern-post being of cast steel, reinforced as necessary for ice-breaking purposes. The framing, which is on the deepframe principle, is exceptionally strong, the spacing of the frames being 18 inches amidships, reduced to 12 inches at the ends of the hull. The shell plating is also much in excess of the usual requirements of the Bureau Veritas, with whom the vessel is to be specially classed. The ice belt from about 6 feet above the waterline to about 9 feet below is 1 inch in thickness fore and aft, and the end plating down to the keel line is practically of the same thickness.

In addition to the heavy, closely-spaced transverse watertight bulkheads, there are on each side of the vessel, for about three-fourths of the length amidships, longitudinal watertight bulkheads forming coal bunkers and water-ballast tanks. The whole system of subdivision is so arranged as to enable the ship to obtain the special mark assigned by the Bureau Veritas to vessels which are capable of remaining afloat with any two compartments open to the sea. By rapidly transferring water from the end tanks forward to the end tanks aft, or vice versa, the ship may be quickly trimmed either way. Similarly, by transferring water from tanks on one side of the vessel to those on the other, she may be rapidly heeled, and by these means she will be able to free herself when locked in ice.

Special arrangements are made for taking another ship in tow, a recess being provided in the stern of the ice-breaker so that the stem of the following ship may be drawn into it and held in that position by means of a large towing winch, of exceptionally powerful type, fitted on top of the after deckhouse.

Electric light is installed throughout, the generating plant consisting of two engines and dynamos each of 20 kw. and 120 volts. Wireless telegraphy, two flood-light projectors and a powerful searchlight projector are also fitted.

An electrically driven submersible salvage pump, with a capacity of about 200 tons per hour, is provided, with arrangements for transferring it to a vessel in tow or alongside so as to render assistance in case of damage.

The living quarters of the vessel include two large staterooms and a comfortable saloon for directors. The remaining accommodation throughout is ample and roomy; and the arrangements for heating and ventilating, and the insulation of the sides of the ship, bulkheads and decks in way of all living quarters, are such as will ensure the maximum comfort for the officers and crew compatible with the most trying climatic conditions which will be encountered on the service for which the vessel is intended.

PROPELLING MACHINERY.

The ship is provided with two sets of triple-expansion steam engines, which, together with the boilers, have been constructed by the shipbuilders. One set, for driving the after propeller, has cylinders 264, 424 and 69 inches diameter, by 432 inches stroke; while the other set, working the propeller at the fore end of the vessel, has cylinders 162, 26% and 432 inches diameter, by 20 inches stroke.

Steam is supplied to both sets of engines by four single-ended coal-burning boilers, each 15 feet 9 inches diameter by 11 feet 10 inches long, working under Howden's system of forced draught. Smokebox superheaters of the Sugden type are also fitted to provide a moderate amount of superheat.

The construction of the machinery throughout is very massive in character, in view of the extremely heavy stresses which will have to be borne on service. The shafting and propellers are of special nickel steel, which, together with the whole of the other steel materials-plates, bars, forgings and castings-for both the hull and machinery, have been supplied from the various departments of the shipbuilding company.

The principal functions of the after engine are to propel and maneuver the vessel, and it is capable of developing about 4000 I.H.P. for these purposes. The forward engine, driving the propeller at the fore end of the vessel, is used to assist in propulsion, and this engine is capable of developing about 1500 I.H.P. When working together, it is anticipated that the two sets of engines will give a speed of about 141⁄2 knots.

The forward propeller, however, is primarily fitted to assist in icebreaking, so that when the stem of the vessel is on the ice the propeller acts as a suction pump, sucking the water from under the ice and thus withdrawing its support. The weight of the ship, assisted by any water ballast transferred from the after to the forward end, will then break down the ice, enabling the vessel to forge ahead and clear a passage.

The very complete equipment of auxiliary machinery provided includes independent air pumps by Messrs. G. & J. Weir, Ltd., Glasgow; circulating pumps and forced-draught fans by Messrs. Matthew Paul & Co., Ltd., Dumbarton; feed pumps by Messrs. A. G. Mumford, Ltd., Colchester; and two large centrifugal pumps, each capable of discharging about 900 tons per hour against a head of about 50 feet, by Messrs. Henry Watson & Sons, Ltd., of Walker Gate, Newcastle-on-Tyne. The last-named pumps are used for transferring a large quantity of water ballast from the forward to the after tanks, or vice versa, and from tanks on one side of the ship to tanks on the other, in about 10 minutes. "The Shipbuilder," July, 1925.

A SUGGESTED METHOD OF INCREASING THE EFFICIENCY OF THE SCREW PROPELLER.*

By WALTER POLLOCK.

It is well known that the water flowing from a ship's propeller moves tangentially and axially as in the upper view in Figure 1. The object of the "Star" contra-propeller is to convert the tangential flow into an axial flow and so increase the propeller efficiency. This is effected by means of guide blades, which may be fixed either forward or aft of the propeller, or both. These blades are so formed as to divert the flow of water as it leaves the propeller blades in a direction more or less perpendicular to the face of the blade into a direction parallel to the line of the ship's course, as shown in the lower view of Figure 1. If, however, the contra-propeller is fitted forward of the main propeller, the water flowing through its blades has its direction changed before it reaches the main propeller, as shown in Figure 2.

PROPELLER WITHOUT CONTRA PROPELLER.

CONTRA PROPELLER

MAIN PROPELLER

-MAIN PROPELLER

PROPELLER WITH CONTRA PROPELLER

TR

FIG. 1.-COMPARATIVE WATER ACTION DIAGRAMS WITHOUT AND WITH CONTRA-PROPEeller Abaft tHE MAIN PROPELLER.

The blades are so curved that just sufficient change of direction is given to prepare for and to counteract the rotary motion ordinarily given to the water by the main propeller. Since the one change of direction is just neutralized by the other, the water is thrown off the main propeller blade in a direction parallel to the course of the ship. That the object aimed at has been achieved has now been proved, not only in experimental tank tests but in ships in actual service. The practical results obtained in actual service go to show that there is a very definite advantage to be gained. Hitherto, however, the variations among different types of ships in coefficient of dis

Abstract of paper read at the Spring Meetings of the Sixty-sixth Session of the Institution of Naval Architects, April 2.

placement, and in the formation of the stern frame and aperture for any given tonnage, have made it difficult to ensure a uniform gain in efficiency, but recent tank experiments have furnished information which will enable that difficulty to be overcome in the future. The "Star" contra-propeller can be built in a large number of forms, and a great deal of the success of an application will depend upon the correct selection of the type to be adopted, which must vary according to whether the vessel is an existing one or one to be built, whether she is to have twin screws, and so on.

PROPELLER WITHOUT CONTRA PROPELLER

MAIN PROPELLER

MAIN PROPELLER

PROPELLER WITH CONTRA PROPELLER

CONTRA PROPELLER

FIG. 2.-WATER ACTION DIAGRAMS WITHOUT CONTRA-PROPELLER AND WITH CONTRA-PROPELLER FORWARD OF MAIN PROPELLER.

In general, the dimensions of a contra-propeller are governed by the dimensions of the main propeller, the stern-frame aperture and the indicated horsepower, which must vary considerably with the type of ship and the particular views of its designer. For this reason it is impossible to standardize the device as regards dimensions and weight. Each case must be dealt with independently except where the vessel under consideration is a sister ship to one which is already fitted. In this case it might be possible to use the same drawings for the second vessel, making the necessary alterations in the process of fitting. The diameter of the contra-propeller may be taken to be approximately 55 per cent of the diameter of the main propeller. One of the chief objections which may be raised to the contrapropeller is the weight, and it is quite true that no shipowner would fit a device weighing several tons, as it may do in a large vessel, unless he could see some substantial advantage. It is therefore desirable to reduce the weight as much as possible so that the very slight decrease of the deadweight cargo capacity may be reduced to a minimum, and also that the stresses on the stern frame and stern plating may not become excessive. The weight is governed by two factors-the stern-frame aperture and the indicated horsepower. It is also obvious that, besides the weight to be carried, the contra

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