Calculating the Size of the Ship Anchor as per Classification Society

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The equipment number, EN, on which the requirements of equipment ship anchor are based is to be calculated as follows :-
EN = K * ENc

where,
ENc = Δ^2/3 + 2BH + 0.1A

where,
Δ = moulded displacement, [t], to the summer load water line.
H = effective height, [m], from the summer load waterline to the top of the uppermost deck-house, to be measured as follows:
H = a + Σhi
a = distance [m] from summer load waterline amidships to the upper deck at side.
hi = height [m] on the centreline of each tier of houses having a breadth greater than B/4. For lowest tier, hi is to be measured at centre line from the upper deck, or from the notional deck line where there is a local discontinuity in the uppers deck.
A = area [m2] in profile view of the hull, superstructures and houses above the summer load waterline, which is within the Rule length of the vessel. Houses of breadth less than B/4 are to be disregarded.
In the calculation of H and A, sheer and trim are to be ignored.
Parts of windscreens or bulwarks which are more than 1.5[m] in height are to be regarded as parts of houses when determining H and A. The height of the hatch coamings and that of any deck cargo, such as containers, may be disregarded.

‘K’ is a factor depending upon the type of vessel and service notation as given below: For fishing vessels,
K = 1.00
For other vessels,
K = 1.00 for vessels of Unrestricted Service.
K = 0.85 for vessels of Coastal Service

Having  found  the  equipment  numeral  the  details  regarding  sizes  and  quality   may  be  obtained  from  the  rigging  tables  provided  in  these  regulations. The  equipment  numeral  is  also  given  in  the  class certificate  and  hence  there  is  no  need  to  refer  to  this  formula  to  find  the  equipment  numeral   whenever  there  is a need as  in  the  case  of  ordering  new  chain  lengths  when  old  chain  lengths  have  been  worn  beyond  the  rule  requirement. For  information  and  guidance  a specimen  of  the  Rigging  table  is  reproduced  in next blog.

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