Marad Design C4-S-1a "Mariner-Class Vessels"

Introduction

The arrangement of the Mariner class vessels is much like that of many modern general cargo ships. There are two complete decks in the hull, and one partial deck forward, two partial decks aft. A Continuous double bottom extends from the fore-peak bulkhead nearly to the after-peak bulkhead. Propelling machinery and accommodations are amidships. A rather long forecastle extends from the stem over the full length of the forward cargo hold. There are seven holds for general cargo, four forward of the machinery space and three aft. Deep tanks fitted to carry fuel oil are provided in the lower parts of Holds 1 and 7, and similar deep tanks which alternately may be used for dry cargo, if desired, in Hold 6. The double bottom is arranged to carry fuel oil or water ballast; the fore peak and aft peak are for water ballast only; while fuel-oil settling tanks and fresh-water tanks are placed at the sides of the machinery space. 'Tween decks in the wings of No. 5 hold are insulated for the stowage of refrigerated cargo. Refrigerated stores are carried in insulated spaces below the 'midship house, on the port side of the second deck. A deckhouse of four levels amidships provides accommodations for 12 passengers and the entire crew of 58 officers and men, together with space for the wheel house and for navigating and radio equipment. Small houses on the main deck between cargo hatches provide space for fans, motor generator sets for winches, and other equipment. Tops of these houses serve as platforms for the winches. A small house on the main deck aft is used for shelter, the access to the steering gear room and to storerooms aft, for the ship's office, and for an office for the cargo checker. The vessels are built in conformity with requirements for steamers of the shelter deck type. There is a tonnage hatch on the main deck aft, and tonnage openings are provided between the main and second decks in all transverse bulkheads except the fore-peak bulkhead. Except tor these openings, all transverse bulkheads are watertight to the main deck, while the fore-peak bulkhead is watertight to the forecastle deck, provisions which will greatly simplify the conversion of the vessels to "full scantling" ships, should this change be desired in order to permit operation at greater draft.

Structure

Scantlings of the Mariners are suitable for a draft of 31 feet 6 inches, although, as shelter deck vessels, the assigned summer freeboard draft is 29 feet 10 inches. The vessels are transversely framed, and have solid floors on each frame. There are nine principal transverse bulkheads. In the double bottom, there are four longitudinal girders and a center girder, each continuous, and two intercostal girders. Longitudinal girders, located at the sides of the hatches on each deck, are continuous through the holds. Framing, girders, brackets and inner-bottom structure are welded. Flush welded butt joints are used for shell, deck, and inner-bottom plating, except for the seams at the top and bottom of the turn of the bilge, which are lapped and riveted. There is also one strapped, riveted butt seam in the main deck, each side, just outboard of the hatches. The gunwale bars are riveted. Main bulkheads, machiney foundations and other principal structural parts are generally of welded construction. Trunks and coamings in general are worked with rounded corners; rectangular openings in decks are rounded at the corners; half-rounds or split pipes are fitted on coamings and elsewhere as required to reduce chafing of cargo hoists, etc. The deckhouse structures are of steel, welded. Support for the 'midship house is obtained by a system of pillars and girders integrated with certain subdivision bulkheads of structural steel. The majority of partitions in the accommodations are of the joiner type, and are not considered to add strength or stiffness to the structure. All accommodations are built of incombustible materials. Johns-Manville "Marinite" panels are used for joiner bulkheads throughout, except that enclosures where watertightness is essential are of steel. Inside doors in the accommodations are hollow steel, insulated. Outside doors on or above the upper deck are of hardwood, other outside doors are of steel. The vessels, including machinery and equipment, are built to meet classification requirements of the American Bureau of Shipping. Possibly the most interesting and unusual features of the hull structure are the rudder and the rudder supporting members. Unlike the conventional single-screw arrangement, the "Mariner Class" vessels each have a semi-spade type rudder, supported a little below the middle of its height by a faired, cantilever-type, cast-steel post. There is no bearing at the bottom of the rudder. The lower end of the rudder stock is tapered and keyed; it projects through a matching opening in the top member of the rudder frame, and is held firmly seated in this opening by a screw thread at the bottom of the stock and a locked nut. The upper bearing is on the rudder stock, and is carried in a second steel casting which forms the trunk around the stock. These two castings are bolted securely and welded to each other, and are integrated by welding with the flat at the 32-foot level, the shell plating, and all other adjacent structure. Another bearing for the rudder stock and the bearing which carries the weight of the rudder and stock are worked in at the steering gear flat. Above the rudder support castings, the stern frame is built of shaped steel plates; below, it is formed by three additional cast-steel members welded together. These castings are shaped carefully and faired to provide the best possible flow of water to the propeller. This rudder and stern-frame design was adopted in order to provide much greater clearance around the propeller than usual. For this installation, designed to deliver about 20,000 horsepower on a single propeller, unusually large clearance was considered necessary in order to avoid excessive vibration. With the conventional type of single-screw stern frame, which includes a rudder bottom bearing and shoe-piece, it would have been difficult, if not impossible, to provide the clearance desired; the resulting increase in the length of the shoe-piece, combined with large forces on the rudder, due to speed, would have required a massive structure of great strength. Elimination of the shoe-piece appeared to be the only feasible way of obtaining the necessary propeller clearance. With the shoe-piece gone, it was possible to move the propeller downward nearly two feet. This gain was divided between increasing the clearance above the propeller and improving the shape of the hull. Elsewhere in the hull, special consideration has been given to the high power and necessity for avoiding vibration. Among these are the location of the thrust bearing abaft the reduction gear case (unusual in American merchant designs) for the purpose of strengthening its foundations and tying them in more securely with longitudinal hull members, including the forward ends of the shaft alley bulkheads. The absence of objectionable vibration, the excellent steering qualities, and the good propulsive characteristics which have been noted on Mariner class ships already in service demonstrate the wisdom of these features of the design.

Accommodations

On the main deck within the house amidships there are 22 rooms, for 39 of the ship's crew, arranged along the periphery of the house to make each an "outside" room with at least one airport. Most of these rooms are designed for occupancy by two men, none by more than two. Single rooms are provided here for the chief cook, the second cook, the boatswain, and the carpenter. Each stateroom is furnished with built-in berths (upper and lower in double rooms), wardrobes, settee, desk, and chair, lavatory, toilet accessory case, and mirror. Six double rooms, for 12 passengers, are located on the upper deck (next above the main deck) in the house, also the passengers' lounge and ten single rooms for the purser, the chief steward, six engineering officers and two cadets. A bulkhead at one end of the machinery casing separates passenger spaces from the officers' accommodations. On the next higher level, named the cabin deck, are staterooms and offices for the captain and the chief engineer, six single rooms for four deck officers and two assistant engineers, and a dining room for officers and passengers, together with a suitable pantry. The bridge deck, highest in the house, is used for navigating spaces, radio, radar, and gyro-compass equipment, radio operator's room, and ventilating machinery. The main galley, pantry, and two mess rooms for the crew are located on the second deck, below the deckhouse; a motor-operated dumbwaiter with pushbutton control connects the main galley with the pantry for the officers' and passengers' dining room. On the second deck, also, are the laundry, large linen lockers, and the crew's hospital, a single large room, with private washing and toilet facilities, fitted with five beds on the earliest vessels delivered, three beds on later ships. Each of the six staterooms for passengers is arranged for occupancy by two persons. Equipment and furnishings include two single beds, each 36 inches by 81 inches, bedside tables with lockers below, two full length lockers for clothing, a dresser, an arm chair, and a side chair. Each of these rooms has a private shower and toilet, and each is an "outside" room. These staterooms for passengers are grouped about, and entered from, the passengers' lounge, an attractive and comfortably furnished room about 14 feet by 24 feet in size. Outside the house, on this deck, an open deck space provides a promenade and deck chair area of ample size for the passengers. The officers' and passengers' dining room is a bright and cheerful room measuring about 21 feet by 29 1/2 feet. It is arranged to seat 32 at eight tables for four persons. Furniture, both built-in and portable, throughout the ship is generally of steel. Upholstery is generally Naugh-ahyde, a plastic material closely resembling leather in appearance. Table tops, dresser tops, and the like are Formica. Lighting in the accommodations is flourescent. Deck covering in accommodations is generally mag-nesite; carpets are fitted in passenger staterooms and lounge, linoleum in the officers' and passengers' dining room, ceramic tile in shower and toilet spaces, and non-slip tile in the galley and pantries. Hot and cold fresh water is supplied to all showers and to the lavatories for each stateroom. One fresh-water supply and system provides water of drinking quality at all outlets. A circulating ice-water system supplies chilled water to drinking fountains. Some features of the accommodations are unusual, and may be entirely new for cargo ships. Most noteworthy are the following: Built-in berths, of the type commonly used for lower ranking officers, have replaced pipe berths throughout the crew's quarters. All, or nearly all, of the living and working spaces and passageways in the accommodations have ceilings which, by concealing overhead ducts, pipes, and wiring, improve cleanliness, neatness, and light. Ceilings are made up in screwed panels which can be removed for purposes of maintenance or repair. While commonly used on modern passenger ships, ceilings of this kind are a bit unusual in the crew's quarters of cargo vessels. Throughout the crew's quarters, private and semi-private toilet and shower spaces are provided, eliminating all large washrooms and toilet spaces. Single rooms generally have private shower and toilet spaces; double rooms, and a few single rooms below officer level, have connecting shower and toilet spaces so arranged that the occupants of two adjacent rooms share in the use of one toilet and shower space. Separate lavatories are fitted in each room. It is believed that this is the first time, on any cargo ship, such an arrangement has been used. The general use of fluorescent lighting in accommodations is new to cargo ships; it follows, however, the general trend, on passenger ships and ashore, toward better and more efficient illumination, in spite of a somewhat higher cost of installation.

Hull Fittings and Equipment - Safety Features

There is one hinged, watertight side port, 42 inches by 78 inches, on each side of the second deck amidships for access to the galley and storerooms when the vessel is in port. With all accommodations on or above the bulkhead deck and a combined boiler and engine room, only one watertight door in a main bulkhead is required. This one is a horizontal sliding door which provides access to the shaft tunnel from the machinery space. It is operable hydraulically by hand pump from either side of the door, locally, and can be closed by a pump in a main deck passageway. Exterior doors on the main deck are hinged, watertight. All entrances to accommodations from exterior decks are fitted with screen doors. Insect screens are supplied for airports in the accommodations. Hinged airports are used in the accommodations, vertical sliding windows in the wheelhouse. Each stateroom is provided with an Ilg Portvente motor-driven fan mounted on a swivel arm which permits the fan to be swung into an open airport, if desired. These fans are also fitted in mess rooms, offices, and the passengers' and officers' dining room. All accommodations have mechanical ventilation. The arrangement is planned to supply fresh air to living and working spaces, and to exhaust vitiated air from the galley, pantries, passageways, and toilets, the total amount exhausted mechanically from the quarters being approximately equal to the amount supplied. Air intakes are fitted with filters and with steam preheaters to temper the supply air in cool weather. Supply outlets are provided in each stateroom, office, mess room, lounge, and in other working spaces generally. Galleys, pantries, the laundry, and the hospital have mechanical supply and mechanical exhaust. Mechanical exhaust only is provided for all toilet and shower spaces and for passageways generally. Doors in accommodations are either provided with louvers or given sufficient clearance at the bottom to permit circulation of air. Steam convection-type radiators are fitted in all spaces in the accommodations which are subject to heat loss from exposure. All dry cargo holds are provided with forced supply ventilation and dehumidification. There are seven mechanical supply systems, five rated at 6,000 cubic feet per minute each and two at 4,000 cubic feet per minute each. Pneumatically controlled dampers regulate the fresh and dry air supplies, the recirculation and the natural exhaust. A dehumidification unit, rated at 7,000 cubic feet per minute, supplies dry air through ducts which connect with the hold supply and recirculating systems. This unit is of the continuous-cycle type which employs a recirculated, unexpended liquid desiccant. A panel in the chart room provides remote control of all dampers and the dehumidification unit, and includes a strip chart recorder to indicate dry bulb and dew point temperatures of the hold exhausts, the dry air supply, and the atmosphere. Mechanical fresh air supply and natural exhaust is provided for the refrigerated cargo spaces. These spaces are cooled by recirculated air which passes over the cooling coils of a Freon-12 direct expansion refrigerating system. A separate Freon-12 direct expansion system is provided for the refrigerated stores compartments. Both of these systems are arranged for automatic operation. The machinery space is ventilated by four mechanical supply systems of 30,000 cubic feet per minute each. Branch distribution ducts carry air to working areas; these are fitted with easily adjusted combination blast-difTusion terminals which are intended to provide comfort without undue reduction of air supply in cold weather Three exhaust fans, 30,000' cubic feet per minute each, discharge air from the machinery space, while the forced-draft blowers take air from the warm portions of the machinery space on the upper levels.

Safety

In 1948, an International Convention for Safety of Life at Sea proposed new regulations, to provide increased safety, which affected the design, construction, and equipment of seagoing vessels. By November of 1951, these proposals had been accepted by a sufficient number of maritime nations, as agreed upon, to make them effective, as of November 19, 1952, for the construction of new vessels. During this interval, the United States Coast Guard undertook the revision of its regulations to include the recommendations of the 1948 Convention. The Mariners were designed during the summer of 1950; thus it was possible, though not legally required at that time, to follow the principal recommendations of the Convention in their design, and to anticipate the more important revisions to the regulations of the Coast Guard. Later modifications to equipment bring full compliance with those portions of the Coast Guard regulations which enforce the recommendations of the 1948 Convention. Thus, there are built into the vessels of the Mariner class certain provisions for safety that have not been required previously on any general cargo vessel. The quarters are constructed of incombustible materials, equaling the most modern of passenger ships and bulk oil carriers in this respect. Each ship has an emergency generator, Diesel-driven, located in a separate compartment above the bulkhead deck, here again equaling modern passenger ship requirements. Complete flooding of the propelling machinery space by carbon dioxide, as a fire-extinguishing agent, is provided, together with means of closing ventilators and other openings to prevent escape of carbon dioxide; both of these provisions are in excess of any previous requirement for a cargo vessel. Lifeboat arrangements include the fitting of lifelines, suspended from guys between the davit heads, and the provision of embarkation ladders and floodlights, previously requirements for passenger ships only. Provisions for safety which are customary on American general cargo ships are, of course, also included. The combined smoke detecting and carbon dioxide extinguishing system, covering all cargo holds, the Diesel generator room, storerooms, shops and similar spaces, registers both visually and audibly in the wheelhouse the presence of smoke in air drawn from each of those spaces and permits carbon dioxide to be discharged where needed. Firemains, hydrants, hoses, spray nozzles, and the like are installed in the usual manner. Portable fire extinguishers of suitable types are installed in many locations.

Cargo - Handling Gear and Deck Machinery

The Mariners are the first Americal general cargo ships to be equipped throughout, except for four small lower deck hatches, where local conditions preclude their use, with quick-acting, folding steel hatch covers assembled with hinged sections. When opened, the hatch cover sections fold compactly and lock in vertical position at the ends of their respective hatches. All hatch covers on the forecastle, main, and second decks close watertight without the use of tarpaulins; weather deck hatches have 30-inch coamings. Pontoon-type hatch covers are used in each of two 35-foot by 10-foot hatches in the lowest deck of No. 5 (refrigerated cargo) hold. Hinged oil-tight covers are fitted in the two small hatches in the lowest deck of No. 6 hold, for access to spaces which may be used for either dry cargo or fuel oil. The folding, hinged hatch covers on all ships of this type were designed by the Seaboard Machinery Corporation, except that for one complete hatchway on a ship building at San Francisco folding hatch covers developed by the Alvin R. Campbell Company will be fitted. Cargo handling arrangements of the Mariners, though not revolutionary in design, make use of the latest types of proven equipment and ideas for facility and safety in handling cargo through vertical hatchways. There are seven pairs of kingposts. Two pairs of stayed kingposts are connected transversely by trusses which carry the two topmasts and support the hoisting and topping forces of the 60-ton booms. There are two 60-ton booms, each 70 feet long, mounted on pedestals at the centerline of the ship in positions to serve Holds 4 and 6. There preten 10-ton booms and fourteen 5-ton booms mounted in pairs, port and starboard, on the kingposts. The arrangement of these makes it possible for each of five hatches to be worked by two 10-ton booms and two 5-ton booms simultaneously. Holds 1 and 7 are each served by one pair of 5-ton booms. All topping lifts for 5-ton and 10-ton booms are secured permanently on topping winches which are mounted on the kingposts. There are 24 of these winches, each driven through worm gearing by a 440-volt, 3-phase alternating-current, squirrel-cage induction-type motor. There are twenty-four single-drum type cargo winches each driven through double-reduction gearing by a 50-horsepower, 230-volt, direct-current motor. Each winch has solenoid brakes, drum disconnect jaws, and a pedal-operated drum brake. Many of the winches are fitted with gypsy heads. Four winches have auxiliary low-speed drums and gearing, with clutches and brakes arranged to permit independent operation of either drum. These auxiliary drums are used with the 60-ton booms. For each of the 60-ton booms, the cargo hoist is a 12-part purchase and the topping lift a 14-part purchase. Each is permanently secured on the auxiliary low-speed drum of one of the four winches so fitted, an arrangement which provides convenience and greatest possible safety for personnel when use of the 60-ton booms is required. Each 60-ton boom is swung by means of one single-vang and one double-vang, each of which is powered by the gypsy head of a winch. Two winches are located on the main deck, four on the forecastle deck, all others on the tops of houses, at the upper deck level. Cargo winch and topping lift motor controls are grouped at operating stations so that each operator has a clear view into the hatch and over the side. Specified cargo hook hoisting speeds vary from 287 feet per minute with 1 1/2-ton loads, single purchase, to 118 feet per minute with 5-ton loads, double purchase, and 58 feet per minute with 10-ton loads and 4-part purchase. An improvement in anchor handling and stowage was made by increasing the span between the chains on deck, and consequently between the wildcats on the windlass, over that normally used. This led to a revision in windlass design, in which trie wildcat shafts were made inde-nendent of each other and a driving gear was fitted to each wildcat. With this arrangement, each wildcat shaft is carried in two easily reached bearings, and these shafts are smaller than usual because they carry no torsional stress. Sliding pinions are used to couple the main gears to the intermediate shafts, and these are shifted by mechanical screw gear and links. Resulting operation is believed to be easier and is certainly much safer to personnel than with the conventional locking heads. The windlass drive is electro-hydraulic, with Water-bury reversible, variable-speed transmission and a squirrel-cage, induction-type, 440-volt, 3-phase, alternating-current motor located below the forecastle deck. The windlass is fitted with warping heads which may be operated without turning the wildcats. Two capstans on the main deck aft are driven from below, through vertical shafts and reduction gears, by two-speed reversible squirrel-cage induction-type 440-volt, 3-phase alternating-current 35-horsepower motors. Two sets of boat davits of the gravity type, built of steel, are provided, each designed to handle a 30-foot by 10-foot lifeboat, of 70-person capacity, of either aluminum or steel. Aluminum boats are being furnished for most, if not all, of the Mariner class ships. Two boat winches provide power for hoisting boats, and speed control, by means of automatic braking devices, when boats are lowered by gravity. Boat winch motors are non-reversing, single-speed, squirrel-cage induction-type, and operate on 440-volt, 3-phase alternating current. A motor-operated winch is provided for the hoisting and lowering of each accommodation ladder. The steering gear is electro-hydraulic; four cylinders, opposed in pairs, work a crosshead on the rudder stock through Rapson slides. Duplicate variable-stroke hydraulic pumping units are provided either one of which operates the steering gear, the other standing by. Pump motors are each 50-horsepower, 440-volt, 3-phase, 60-cycle squirrel-cage, induction type. Most vessels of the Mariner class are fitted with the recently designed American Engineering Company rotary telemotor. A rotary hydraulic pump is driven, through gearing, by the steering wheel to transmit fluid to a ram-type receiver in the steering gear room. Advantages claimed for this type of telemotor include reduction in wheel-turning effort, due to the elimination of centering springs and equalizing valves; low hydraulic pressure; elimination of the lost motion which is usual at amidships position with plunger-wire telemotors; and independence between wheel position and helm position, which is reported accurately to the wheelhouse by an electric indicator operated from the telemotor receiver. Hand and automatic electrical steering control is provided by a Speery gyro-pilot of the latest model which employs a magnetic amplifier, a rate generator, and electro-hydraulic equipment.

Propulsion Machinery and Auxiliaries

The propelling machinery of the vessels of the Mariner class is designed and built to provide for each ship a reliable and efficient installation, with sufficient reserve to assure that maximum ratings will be easily attained. A single-screw installation was desired, due to its greater efficiency, its simplicity of operation, and its smaller number of working parts in comparison with a twin-screw installation. In order to assure a sea speed,' for the loaded ship, of 20 knots, it appeared that about 20,000 shaft horsepower would be required. While there are many installations, in multiple-screw ships, that develop 20,000 horsepower and more on each shaft, the application of this power in a single-screw, geared-turbine installation for the Mariners. Careful consideration indicated, however, that the contemplated installation would be feasible, provided that propulsion units were of a well proven type, and provided that possible vibration troubles could be avoided successfully. Hence, the decision was made to use a single-screw, geared-turbine installation for the Mariners, and to pay particular attention to the design of the stern frame, rudder, and propeller and to all other factors whose influence upon vibration could be estimated in advance.

Turbines and Gears

The main propulsion unit of each Mariner class ship consists of a two-cylinder, cross-compound turbine, which drives a four-bladed, solid, manganese bronze propeller of 22 feet diameter and 22 feet 10 inches pitch through double-reduction gearing. The turbines have a normal rating of 17,500 shaft horsepower at 102 revolutions per minute, and a maximum rating for continuous operation of 19,250 shaft horsepower. The turbines of Bethlehem design and manufacture, used on the ten vessels built at Bethlehem's Quincy and Sparrows Point Yards, each have a high-pressure turbine with one stage of impulse blading followed by seven expansions of reaction blading, totaling twenty moving rows. Bleeder connections are provided on the high-pressure turbine at the entrance to the fourth expansion and at the cross-over between the high and low-pressure turbines. The Bethlehem low-pressure turbine is a single-flow type with twenty moving rows of reaction blading. A bleeder connection is provided at the entrance to the fourteenth expansion of this turbine. Also incorporated in the low-pressure turbine casing are the two stages of impulse blading of the astern turbine, which is capable of operating astern continuously at approximately 6,100 shaft horsepower with a condenser vacuum of 27.5 inches of mercury. The main reduction gears are of the double-reduction, double-helical type. The reduction ratios are 4,233 to 102 for the high-pressure turbines and 2,201 to 102 for the low-pressure turbine. The propeller thrust bearing is a Kingsbury 45-inch, 8-shoe, self-alining, equalizing type, located just aft of the reduction gear casing.

Steam Generators

Steam is supplied by two two-drum, bent-tube type marine watertube boilers fitted with superheaters, desuperheaters, waterwalled furnaces (except front walls), economizers, steam soot blowers, automatic combustion control, superheat control, automatic two-element feed regulators and Todd Hex-Press type mechanical atomizing fuel-oil burners. The boilers are designed to maintain a pressure of 600 pounds per square inch at the superheater outlet, with a temperature not in excess of 875 degrees F at normal and maximum power ratings. Each boiler evaporates 64,000 pounds per hour at normal power. Steam normally reaches the turbine throttle valves at 585 pounds per square inch and 855 degrees F. Each boiler has a generating and waterwall surface of 8,040 square feet, a superheater surface of 1,565 square feet, and an economizer surface of 4,190 square feet. The furnace volume is 1,315 cubic feet. The superheater is two-pass, integral, convection type, located in the boiler bank. Superheater tubes are rolled into the headers and are fitted with forged return bends. An aluminum fin-tube economizer is placed in the gas uptake of each boiler. Two submerged-type desuperheaters are located below the water level in the steam drum. One is to furnish auxiliary steam at reduced temperature; the other is for use with the superheater temperature limiting control. This limiting control provides a manually controllable by-pass between the two passes of the superheater, thus furnishing a means for controlling the amount of superheat. Feed System. Exhaust steam from the main turbines is condensed in a horizontal, single-pass reheating-type condenser with 16,000 square feet of cooling surface which maintains a vacuum of 28.50 inches of mercury when supplied by scoop injection with 33,000 gallons per minute of sea water at 75 degrees F. For port use, astern operation, and low speeds ahead, a motor-driven, 18,000 gallon per minute, propeller-type circulating pump is provided. Two stages of feed heating are employed in conjunction with steam-type air heaters, producing a simple and highly effective regenerative feed system. There are two main condensate pumps, each having sufficient capacity to handle the condensate when the vessel is running at maximum power. They are vertical, two-stage, centrifugal-type pumps, driven by 25-horsepower motors* and each can deliver 325 gallons per minute against a total discharge head of 135 feet when turning at 1,800 revolutions per minute. The discharge from the main condensate pumps passes through the inter and after condensers of the main air ejectors into the low-pressure feed heater. This is a horizontal, straight-tube unit having feed heating, gland leak-off condensing and drain cooling sections combined within a single shell. The feed heater section will heat 109,000 pounds of condensate per hour from 110 degrees F to 175 degrees F when supplied with 7,500 pounds per hour of steam at a pressure of 9 pounds per square inch absolute. The gland leak-off section will handle up to 1,000 pounds per hour of steam leakage from the main propulsion and generator turbine glands, the deaerator vent and flash vapor from the drain collecting tank. A motor-driven gland exhauster fan is provided. The drain cooling section cools the feed heater drains to 110 degrees F. From the low-pressure feed heater, the condensate enters a direct-contact, deaerating feedwater heater. This heater raises the feedwater temperature to 250 degrees F. It has a storage capacity of 2,500 gallons and, under normal conditions, utilizes steam at a pressure of 15 pounds per square inch from the auxiliary exhaust system. The condensate pump which serves the auxiliary condenser discharges through the auxiliary air ejector inter and after condenser into the main condensate line just before the low-pressure feed heater. The two main feed pumps are turbine-driven, using desuperheated steam from the main boiler and exhausting at a back pressure of 15 pounds per square inch into the auxiliary exhaust system. They are 5-stage, horizontal, centrifugal-type pumps, each designed to deliver 450 gallons per minute against a total head of 2,000 feet at 4,650 revolutions per minute. One turbine-driven, single-stage, centrifugal-type feed pump, of 150 gallons per minute capacity against a 1,770 foot head, is installed for use while the ship is in port. The feed pumps take suction from the deaerating feed heater and discharge directly into the economizers.

Bleeders and Exhaust Steam Systems

For feed heating and for operation of various heat exchangers, three bleeder connections are provided on the main turbines. The high-pressure bleeder (4th expansion) supplies steam to the contaminated water evaporator. The intermediate bleeder (crossover) supplies steam to the boiler air heaters, and to the auxiliary exhaust system through a 15 pounds per square inch reducing valve. The low-pressure bleeder supplies steam to the distilling units and to the first-stage feed heater. The auxiliary exhaust system's primary service is feed heating in the deaerating feed tank. Feed pump exhaust steam, augmented by bleeder steam through a reducing valve set at 15 pounds per square inch, heats the incoming feedwater to a temperature of 250 degrees F. Excess auxiliary exhaust steam will automatically unload to the auxiliary condenser at 201 pounds per square inch. At low powers, when the normal bleeder supply pressure drops below the exhaust main pressure, make-up steam is supplied, at 7 pounds per square inch, to the auxiliary exhaust main through a reducing valve from the 600-pound desu-perheated steam line.

Contaminated Water Evaporator

A contaminated water evaporator is provided to supply steam for those services which might otherwise cause contamination of the boiler feedwater. This evaporator supplies saturated steam for tank heating coils and fuel-oil heaters, the steam heating system, the cargo conditioning system, for galley and pantry requirements, and for the hot fresh-water supply. It is designed to provide 4,000 pounds per hour of saturated steam at 88 pounds per square inch gage pressure when supplied with bleeder steam at 120 pounds per square inch gage and 550 degrees F, and with fresh water at 180 degrees F. When bleeder steam is not available, it will produce 7,500 pounds per hour of saturated steam at 140 pounds per square inch when supplied, through a regulating valve, with steam from the auxiliary desuper-heated line at 300 pounds per square inch and 450 degrees F.

Distilling Plant

The ship has two double-effect low-pressure distilling units, each complete with distillate pump, brine pump, air ejector, and air ejector condenser, salinity indicator, and weir-type level controller. The distilling plants are of the horizontal, submerged-tube type, and include within a single shell the evaporator tube nests, the distilling condenser and the vapor feed heater. The air ejector condenser and cooler are external. Each unit is rated to produce 12,000 gallons per day of fresh water, salt content not exceeding 0.25 grain per gallon, when supplied with steam from the auxiliary exhaust system at 5 pounds per square inch gage and with sea water at 85 degrees F. The clean tube capacity under these conditions is 15,600 gallons per day. During normal operation at sea, taking steam bled from the low-pressure turbine at about 11 inches of mercury vacuum, each unit will produce about 6,800 gallons of fresh water of the same purity per day.

Boiler Air Heaters

Boiler air heaters consist of four heavy duty fin-tube heating coils assembled to form a single-pass air heater. In normal operation, each heater will raise 18,500 cubic feet of air from 100 degrees F to 261 degrees F with an air pressure drop of 1.3 inches of water when supplied with bleeder steam at 35 pounds per square inch and 375 degrees F. When bleeder steam is not available, the boiler air heaters take steam from the auxiliary exhaust system through a 7-pound per square inch reducing valve.

Lubricating System

A combination lubricating-oil system using either gravity or pressure flow is provided for the main propulsion unit. Either of two lubricating-oil service pumps, 500 gallons per minute capacity each, draws oil from the sump tank in the reduction gear casing through a magnetic type, duplex strainer. The discharge from these pumps passes through another duplex strainer into either of two lubricating-oil coolers, which discharge to the main lubricating-oil header, with the gravity tank on the line. From the main header, branch lines supply oil to bearings and to gear sprays. When operating by gravity flow, the gravity tank is full to the overflow pipe and maintains a constant head on the system. When operating by pressure flow, the gravity tank is isolated and drained to the reduction-gear sump, the excess oil being transferred to the settling tank. A back-pressure valve then maintains a constant head of 12 pounds per square inch on the lubricating-oil header by discharging excess oil to the sump.

Smokestack and Uptakes

The design of the smokestack and uptakes is based upon results of Bethlehem's recent studies of the smoke nuisance problem, and follows closely the pattern used successfully for the liners Independence and Constitution. The two uptakes are relatively small, to produce high velocity in the gases. They are combined in a centrally divided trunk measuring 4 feet by 5 feet as it approaches the top of the stack, and emerge from the stack as far aft as possible. An adjustable damper is fitted in each uptake to control flue gas exit velocities. The outer casing is slightly tapered and is well rounded at the top to reduce the formation of air pockets and eddies; and the stack is tall enough to discharge gases well above the probable limit of disturbed air flowing over the house top.

Electrical Installation

Each of the Mariner class ships has two 600-kilowatt, 450-volt, 3-phase, 60-cycle turbine-driven generators, either one of which will supply all normal electrical requirements. Power distribution from the main switchboard in the engine room is generally through 3-phase, 3-wire, 450-volt lines, and most of the electrically driven auxiliary and deck machinery (except cargo winches) operates on this current. 450/230-volt transformers supply current for the electric ranges and ovens in the galley. Lighting circuits and outlets for portable appliances are supplied from 450/117-volt transformers with 117-volt, 3-phase, 3-wire feeders to distribution panels and 115-volt, 2-wire branch circuits. A 75-kilowatt, 450-volt, 3-phase, Diesel-driven generator and an emergency switchboard are located on the main deck amidships. This installation is arranged to provide automatic starting of the emergency generator, and automatic transfer to this generator of circuits powering certain vital electrically-driven auxiliaries, upon loss of power from the ship's main generators. Emergency lighting and communication circuits are powered, from the Diesel generator, through an independent group of 430/117-volt transformers in the Diesel generator room. Nickel-cadmium storage batteries furnish current to start the Diesel generator and for emergency use with radio equipment and the general alarm. Electric cables, except those in staterooms, are insulated by asbestos and varnished cambric, and have impervious sheaths and aluminum armor. This type of cable is used customarily on naval vessels, due to its light weight and resistance to heat; regulations have permitted its use on merchant vessels only recently. Controllers for motor-driven engine-room auxiliaries are arranged generally in groups. Duplicate auxiliaries are^connected in different groups, to prevent the loss of an important function due to power failure in one group. Cargo winches operate on direct current, which is produced by motor-generator sets, one set powering two winches. Each motor-generator set consists of a squirrel-cage induction-type 440-volt, 60-cycle, alternating-current motor which drives two 240 nominal volt direct-current generators, of the variable-voltage type, and the necessary exciters. These motor-generators and their controls produce a speed-current curve with a drooping effect in both hoisting and lowering directions of the winches. On the Mariners built at the Quincy Yard and on others which have General Electric Company winch-operating equipment, the drooping effect is obtained by the use of "cross-flux'' exciters whose voltage output is inversely proportional to the load. These are connected to weaken the generator field and strengthen the motor field with heavy loads. This is the first application of this type of winch control on large general cargo ships. Westinghouse and Reliance controllers used on some ships of this class have adjustable-speed motor-generator sets with selenium rectifiers which block the current through the winch motor series field winding under certain conditions.