fokidelta.blogg.se - Determine the anchoring force required

The OCIMF document on anchoring refers to MEG Edition 3 however, MEG has been updated to Edition 4, and the same shall be referred to in this article. The environmental loads of wind and current are estimated from the non-dimensional coefficient curves provided in the OCIMF document, which in turn are taken from OCIMF Mooring Equipment Guidelines (MEG). Step 1: Calculating the environmental loads the catenary effect of the anchor chain is not considered.

wave drift forces have been estimated using a Pierson-Moskowitz sea spectrum.As a result, only the longitudinal components of the wind, waves and current forces need be considered. the vessel lies at anchor such that the lead of the anchor chain is parallel to the centreline of the vessel.the anchored vessel is in a steady position, having swung at anchor in the direction of the dominant environmental force or has reached an equilibrium position.the vessel is lying to a single anchor.Interaction effects between the forces are not considered.

the environmental forces are considered as individual components that are summed to provide a total force.

yawing, pitching) can result in forces in the anchor system being 2 or 3 times higher than the estimated static forces. It should be noted that dynamic effects (e.g.

the data presented refers to the static condition.

environmental forces acting on the vessel comprise:.

the vessel is an oil tanker or an LNG carrier (spherical or prismatic) with accommodation aft.

However, there are some important assumptions which the method relies upon. Catenary effects of the mooring chain are ignored. Thus, all the three forces of wind, current and wave need to be considered only in the longitudinal direction of the vessel. The method also ignores the interaction among the three forces, and assumes that the vessel is lying to a single anchor and longitudinally aligned with the anchor chain. It is to be noted that dynamic effects can have a multiplier effect on the forces obtained from the static condition. The vessel is considered as static while the environmental forces of wind, wave and current act on it. This means that the effects of the vessel’s own motion (pitching, heaving etc.) have been ignored. Further, only a static condition has been considered for calculation of forces. The method can be used for tankers down to a DWT of 16000 MT. However, the method is NOT universally applicable to all types of vessels, and is limited only to Oil Tankers or Gas Carriers with accommodation located aft. The simple outline of the method is to find out what these loads are, sum them up and check if the anchor has enough holding power to overcome the combined environmental loads. Step 2: Selecting the right anchor with holding power sufficient to take the total environmental loadĪn anchoring system is subjected to the three primary environmental loads – Wind, Wave and Current. Step 1 : Calculating the wind, current and wave load on the vessel to give the total environmental load

The method is based on OCIMF’s publication ‘ Estimating The Environmental Loads On Anchoring Systems‘. In this article we will present a simple method based to estimate the holding power required for an anchor operating in a given environmental condition. While vessel masters have reliable experience in knowing the holding power of their vessels and decide based on their invaluable practical knowledge, an estimate of the forces which the vessel is experiencing in a particular weather is always useful in knowing whether the anchor can hold or not, helping in critical decision making on whether to remain at anchor or let go – thus saving the vessel from a potential damage of anchoring systems. Thus, it is critical to know if the anchor has enough holding power when the weather goes inclement. The anchor is supposed to hold the vessel in varying environmental conditions depending on where the vessel is being anchored. When a vessel is at anchor, it swings to align itself along the direction of the dominant environment. Anchoring is a fundamental and sensitive operation for a vessel.