Static bollard pull is a measurement of the amount of force a tug is capable of applying to a tow under certain conditions. It may be approximated by multiplying the brake horsepower by 1.3 and dividing by 100, with the answer in tons, as in the formula below:
T = 0.013 x BHP where T is the static bollard pull
This is an approximate formula only; estimates may also be made as follows:
Standard hull: Approximately 4,400 pounds plus 23.5 pounds per bhp for open-blade propellers
Hydroconic tugs of double chine construction: Approximately 36 pounds per bhp
Kort-nozzle tugs: Approximately 39 pounds per bhp
Voith-Schneidertugs: Approximately 25.5 pounds per bhp, which is somewhat less than for conventional propellers
3 x 14 Standard Warping Tug Operations Platform
Propulsion power for the warping tug is provided by two harbormaster marine tractors installed on the sterns of the two outboard rows of pontoons. Although many different types and sizes of these outboard propulsion units are available in Navy stock, it would appear from drawings and data furnished that the units shown are Model 0-A62, rated at 180 horsepower, each. Propellers are 5-foot-diameter by 4-foot pitch turning at 308 rpm at maximum available engine power and at about 250 rpm at rated power. Each propulsion unit can develop a dead pull thrust of up to 5,000 pounds if the propeller is adequately submerged. Each propeller can rotate about its vertical shaft through 360 degrees and can be elevated to a horizontal position by a hydraulic system powered by the engine; hydraulic reverse gears are also provided, a 32-volt electric starting system is installed in each engine. Steering, elevating, and engine operating controls are installed directly on the after side of the engine allowing the operator a clear forward view for maneuvering. Each unit is fitted with a heat exchanger for cooling and each unit weighs about 16,700 pounds. A 275-gallon fuel tank is installed on the centerline of the warping tug just forward of the two propulsion units.
The primary mission of the warping tug is to handle the pontoon causeways used in making up an LST to the beach. It tows the pontoons into position, secures them together, plants any required anchors, and then maintains tension on the system out from the beach until the LST is in position for make up. The outfit furnished to sup port this mission capability comprises a sheave mounted in an A-frame overhanging the bow, a double drum winch amidships, and a 2,500-pound anchor housed in a readily releasable stowage position at the stern. Four pairs of double bitts are installed for alongside towing, a deckhouse is installed for stowing equipment, and a small bridge structure is erected from which operations can be directed. The anchor cable passes through tunnels in these two structures along the deck centerline. All deck equipment over 4 inches in height between the launching angle and the centerline of the tug must be removed when preparing for side loading on an LST. The outboard propulsion units are used primarily for positioning and towing.
Warping tugs designed by the Naval Facilities Engineering Command are configured from the NL Equipment P-Series pontoons. They employ 37 of the NL P-l rectangular pontoons and 6 of the N.L. P-2 trapezoidal pontoons used as bow and stern rake ends. The NL P-l pontoons are 5 by 5 by 7 feet; three of these units are fitted the long dimension athwartships giving a total beam for the tug of 21.25 feet including connecting hardware. The two outboard pontoon assemblies each comprise 12 P-l pontoons, with a P-2 pontoon at the bow and at the stern, for a total length, including hardware, of 84.25 feet. The centerline assembly has 13 P-l pontoons with a P-2 pontoon fore and aft for a total length of 89.96 feet. This is the overall length of the basic hull, excluding fenders. Each pontoon, including its connection hardware, weighs approximately one long ton; the P-l pontoons, with their 35 ft2 waterplane area, draw about 1 foot of water. Thus, the mean draft of the assembled warping tug, before the addition of deck house, bridge, A-frame, propulsion units, and winch is very close to 1.00 foot. In this condition, the tug has a metacentric height of 46.60 feet.
Each P-l pontoon is constructed of 3/16-inch steel plate with 3- by 3- by 3/16-inch vertical angle stiffeners spaced 1.75 feet along the 7-foot length and 1.67-foot angle along the 5-foot dimension. These stiffeners and all joints are completely welded throughout and gussets and are provided at the corners both for securing side and deck framing and for preventing racking of the assembled unit. The P-2 pontoons are similarly constructed except that the sloping plates, used for bow and stern fairing, are 3/8 inch thick. At the four corners of the deck and at the four corners of the bottom, recessed weldments are fitted in to provide for bolts and nuts used in securing contiguous pontoons to the connecting hardware. This hardware, or "jewelry" comprises 6- by 6- by 1/2-inch steel angles and 8- by 8- by 1/2-inch steel angles, bolted to the pontoon's top and bottom, and to each other by 3/4-inch steel bolts and nuts. The entire assembled structure of the warping tug has adequate strength to withstand launching from the side of an LST and to withstand many years of exposure to the marine environment. Although this pontoon series has been discontinued, the units are still available in many military stock centers.
Was this article helpful?