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458 MARINE REVIEW FIG. 4—MARINE TYPE BRAKE FOR CARGO WINCH MOTOR winchman being able to land it accur- ately. The loaded sling is replaced on the hook by an empty one ‘which is raised by the whip, caught by the whip runner, and thrown to the pier. The cycle is again repeated. The single whip method of cargo handling is slow, also there is danger of damaging some of the freight by dragging it over the skids, swinging of booms, etc. Burtoning Method By the use of two booms and two falls, the handling of cargo can _ be speeded up considerably, also there is no need of dragging the cargo on skids. The central boom has its end block through which the up and down fall passes, over the hatch, and the second boom has its end block through which the Burton fall passes, over the pier. The ends of both falls are fastened to the load, which when loading the ship, is lifted from the pier on the Burton fall, moved over the deck by means of both falls, and finally transferred to the up-and-down fall by which it is lowered to the hold or platform under the hatch. Two winches, one for each fall, are needed to care for this so-called Burton- ing method of handling cargo. It is seen that this method is _ not dependent upon the swinging of booms, the motions of which must be carefully gaged. Since nothing moves but the lines and the hook, the action is very positive, for when one line is carrying, the hook is directly in position over the hatch, and when the other line is carrying, the hook is directly over the door in the pier shed. There are some who consider the Bur- toning system a poor method of handling cargo, because the load is lowered to a precise spot. If this depositing point is blocked, the system is put out of action until the place is ‘clear. The quay crane used -extensively abroad is free from this disadvantage on account of action. However, this ap- parent advantage is offset by the neces- sity of swinging the cargo instead of moving it in direct lines. | The half-hour rating for winch mo- tors corresponds to that used for crane or general hoist work. Knowing the average weight of each draft, the effi- ciency of the winch, and the hoisting speed required at rated load, we use for the horsepower rating of the winch mo- tor the following formula: Half hour rating of motor in horsepower equals weight of draft in pounds multiplied by the rope speed in feet per minute divided by 33,000 multiplied by efficiency of winch, The rated speed of the motor to com- ply with these conditions is that for which the gear ratio of the “winch is best suited, or that upon which the man- ufacturer has standardized as a result of his knowledge of the trade requirements. The speed load curve of the motor is re- ferred to for speeds other than normal. The power necessary for the different operations (Burtoning, lowering loaded hook, hoisting empty hook, etc.) is known as a result of the study of graphic current curves or direct read- ing meter tests taken from similar winches handling cargo, or a series of test loads. When the frame its radial size of the motor December, 1924 of the half- hoisting, a is selected on the basis hour rating required for check is made to determine whether the frame size is sufficiently large to care for the heating over certain cycles operation carried on loading or unloading or periods of throughout the processes. Allowance for Heating Since the heating varies as the square of the current, and the time during which the current flows, the cycle can be divided into well defined sections for special operations (hook load, hoist load, rest, lower empty hook, etc.), each hay- ing the value of the current squared multiplied by the actual time in seconds required for the operation. When the motor is running at normal speed or faster, the actual time values are re- corded under “equivalent” time. How- ever, when the motor is at rest, or during periods of acceleration, heat is dissipated less rapidly, therefore under “equivalent” time, there are recorded figures less than: the actual time values (50 per cent in the case of an en- closed motor). The summation of the A°’T values divided by the total equivalent time values, gives the mean square value of the current. Extracting the square root of this, gives the root mean square (R.M.S.) value. This R.M.S. value of current, both for the armature and the fields, is known for the various sizes FIG, 5—WATERTIGHT CAM ER FOR DECK SERVICE CONTROL-