The holding power of an anchor determined through the calculation of Equipment Number or EN. The requirements of the various Classification Societies that are members of IACS have been unified within ‘Unified Requirement A1’ (UR A1).
UR A1 provides a method of calculating the weight and size of the anchoring equipment required to be installed on-board through the calculation of the Equipment Number (EN):
EN = Δ²/³ + 2.0 hB + ( A/10 )
Δ = moulded displacement, in tonnes, to the Summer Load Waterline
B = moulded breadth in meters
h= freeboard in meters, plus the sum of the heights at the centreline of each tier of houses having a breadth greater than B/4
A = area in square meters, in profile view of the hull, superstructures and houses above the Summer Load waterline with a breadth greater than B/4
Once the EN has been calculated, the number and minimum weight of the anchor, together with the total length and diameter of the chain can be determined.