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Thursday, April 19, 2018

EXPLANATION OF OCIMF MOORING GUIDELINES

Due to a number of concerns raised by members regarding mooring equipment and the subsequent scrutiny during vetting inspections, INTERTANKO has received the following clarification from OCIMF regarding the specifics and reasoning of the primary brake being set at 60% the mooring lines’ MBL (Minimum Break Load).

It is recommended that the primary winch break should be set at 60% MBL of the mooring line which is 5% above the nominal SWL (Standard Working Load) of the mooring line (SWL = 55% MBL). In order to design a ship's mooring system, the environmental loads likely to act upon the ship must first be determined. As these can be highly variable from terminal to terminal, and to ensure that a minimum standard is met for mooring equipment on ships engaged in world-wide trades, OCIMF recommends that, for design purposes, Standard Environmental Criteria be assumed as detailed in the OCIMF Publication "Mooring Equipment Guidelines - Second Edition 1997" (Para 2.2). These are broadly as follows: -

60 knots wind from any direction simultaneously with either:

3 knots current at 0 deg. or 180 deg.

or

2 knots current at 10 deg. or 170 deg.

or

0.75 knots current from the direction of maximum current loading.

The mooring restraint available on board as permanent equipment should therefore be sufficient to hold the ship safely alongside under those conditions. Once the maximum longitudinal and transverse forces under the standard environmental criteria are known, the number and size (MBL) of lines needed to resist those forces can be derived (OCIMF Mooring Equipment Guidelines Section 3.2.1). Working on the premise that there must be a weakest point in the system, and that the "giving" of the weakest point must not put any seafarers at risk, the winch brake is that weakest point.

It follows that if the winch starts to render (and assuming that the brake is correctly set at 60% MBL) then the design conditions for the ship are being exceeded. It is the OCIMF view that if that point is reached then the ship should either vacate the berth, have tug assistance to maintain it alongside or supplement its own mooring restraint with appropriate shore-based equipment.

For further information or clarification then please contact either robert.bishop@intertanko.com or tim.wilkins@intertanko.com

(Thanks to OCIMF for supplying the clarification on this matter)