Towing vessel meaning6/6/2023 ![]() ![]() The calculated figures must be taken as rough estimates and may vary based on the tugboat’s building specifications. There are some formulas we can use for this: Tug equipped with fixed pitch propeller: (freewheeling) :īHP x 0,9 x 1,10 / 100 = (t) Tug equipped with fixed pitch propeller and kort-nozzle:īHP x 0,9 x 1,20 / 100 = (t) Tug equipped with controllable pitch propeller: (freewheeling)īHP x 0,9 x 1,25 / 100 = (t) Tug equipped with controllable pitch propeller and kort-nozzle : From the horsepower (BHP) of the tug's machine, the approximate bollard pull value of the tug in question can be calculated. There must be a water depth of at least 20 meters at the measurement site and the length of the rope must be long enough not to allow the water returning from the dock to reach the tugboat. It is essential to ensure that the bollard pull test protocols are followed appropriately since this value is crucial to the marketing of the tug: As the tug makes way, the towing force decreases due to the underwater resistance of the tugboat.We can say that there is an inverse proportion between the speed of the tug and its towing capability.īollard pull tests are done under the supervision of class Institutions. Pulling force or bollard pull value describes the towing ability of a tugboat when its position is stationary, that is, when it is not making way. For an accurate measurement, the dynamometer must be calibrated before the test. Mechanical or load cell powered electronic dynamometers are generally used in the bollard pull test.However, a stern trim of 1/100th of the length of the tug may be permitted. In an ideal bollard pull test, the tug should have almost no trim.This is also important for newly built tugs. Another issue that significantly affects the bollard pull test result is that the propeller blades are clean and smooth.If there is a wind of more than 15 knots at the bollard pull test location, a healthy measurement value cannot be obtained.If the current in the region is above 1 knot, it will not be possible to obtain a healthy measurement value. There should be no significant current at the location where the bollard pull test will be performed.An engine room with a higher than normal ambient temperature adversely affects the performance of the engines. The temperature of the engine room is also a factor affecting the performance of the machine.Sea water temperature at the measurement location, as machine performance is affected by the temperature of the cooling water.How rough the sea is at the place where the measurement is made, so whether the tugboat makes a port or starboard roll (rolling) or fore and aft movement (pitching).Whether the submerged part of the tug, and especially the hull, is clean.Underwater area of the tug and its shape.Whether the propellers are housed in specially designed shrouds (Kort Nozzle ).However, other factors affecting this measurement value are listed below. The first factor affecting the bollard pull is the total horse power (BHP) value of the tug's machinery. The Bollard Pull value, which can be interpreted as the maximum thrust that is developed for a specific amount of time by the propulsion systems of any vessel to the fullest, when it has zero speed in the forward direction, is the criterion that allows us to understand how suitable a tugboat is for a port maneuver or a towing operation.Īlthough the Bollard Pull value can be calculated in a simulation environment with some accuracy, the most realistic method is to use the standart procedures, which involve connecting a pier bollard with a towing line & mechanism on the tug and calculating the force or tension developed in the connection using a dynamometer either with load cell type or mechanic type. ![]()
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