Various Aspects of Bollard Pull Tests and Analysis of Test Results

Abstract

The static force exerted on a hawser at zero ship speed by a vessel, otherwise known as the bollard pull, is one of the key performance indicators of Tugs, Anchor Handling Tugs (AHTs) and Anchor Handling Tug Supply Vessels (AHTSVs). The value of bollard pull is considered critical as it defines the functionality and performance of the vessel. When a company decides on chartering a vessel, a definite prerequisite considered is the value of the bollard pull. The value may be obtained via three ways: calculations, model-testing, and full-scale trials. The latter is often used officially to certify the vessel's bollard pull rating, with the presence of the vessel's owners, surveyors, and any other third parties. The tests and trials follow a set of guidelines provided by classification societies but do not have a standardized set of rules. Therefore, disagreements often arise over the results of such tests and trials. Tests are often carried without any load cells measuring the shaft power to ascertain the brake horsepower (BHP). Simply, engine rpm/ rating is used to fix the 100% maximum continuous rating (MCR) which often in the range of 105–108% MCR. Some of the parties involved in certifying the correct bollard pull tests (BPTs) do not even understand what is all about the bollard pull. Everybody is looking for a higher figure for the bollard pull on the certificate when the reality is different. The author examines and discusses the broad spectrum of factors that affects the "true" value of the bollard pull and explains why such a standardized set of mandatory BPT and the trial code is deemed necessary. The author also presents some of the interesting BPTs data to show the differences in various ways of conducting BPTs. 1. Introduction The bollard pull (BP) is the zero speed pulling/pushing capability of a vessel, i.e., Tugs, Anchor Handling Tug (AHTs), Anchor Handling Tug/ Towing Supply Vessel (AHTSVs), trawlers, etc. It is considered as one of the key practical performance indicators of the above-mentioned vessels, measuring the usefulness of the vessel in a stranding scenario or in holding large vessels such as tankers or towing a rig.