Section 7 Equipment Number (2024)

Parent topic: Chapter 1 General

7.1 Calculation of Equipment Number

7.1.1The equipment of anchors and chain cables specified in Pt 3, Ch 13, 7 Equipment is based on an `Equipment Number' which is to be calculated as follows:

where

A	=	area, in m², in profile view of the hull, within the Rule length of the vessel, and of superstructures and houses and funnels above the summer load waterline, which are within the Rule length of the vessel, and also having a breadth greater than . The side projected area of the funnel is considered in A when A_FS is greater than zero. In this case, the side projected area of the funnel should be calculated between the upper deck, or notional deck line where there is local discontinuity in the upper deck, and the effective height h_F. See also Pt 3, Ch 1, 7.1 Calculation of Equipment Number 7.1.3, Pt 3, Ch 1, 7.1 Calculation of Equipment Number 7.1.4 and Pt 3, Ch 1, 7.1 Calculation of Equipment Number 7.1.5.
B	=	greatest moulded breadth, in metres.
H	=	effective height, in m, from the summer load waterline to the top of the uppermost house.
a	=	vertical distance at hull side, in m, from the summer load waterline amidships to the upper deck.
h_i	=	height, in m, on the centreline of each tier of houses having a breadth greater than ; for the lowest tier, h₁ is to be measured at centreline from the upper deck or from a notional deck line where there is local discontinuity in the upper deck, see Figure 1.7.1 Computation of ‘H’ for an example. See also Pt 3, Ch 1, 7.1 Calculation of Equipment Number 7.1.2, Pt 3, Ch 1, 7.1 Calculation of Equipment Number 7.1.3 and Pt 3, Ch 1, 7.1 Calculation of Equipment Number 7.1.4
Δ	=	moulded displacement, in tonnes, to the summer load waterline.
S_fun	=	effective front projected area of the funnel, in m², defined as: S_fun = A_FS- S_shield See also Pt 3, Ch 1, 7.1 Calculation of Equipment Number 7.1.4.
A_FS	=	front projected area of the funnel, in m², calculated between the upper deck at centreline, or notional deck line where there is local discontinuity in the upper deck, and the effective height h_F. A_FS is taken equal to zero if the funnel breadth is less than or equal to at all elevations along the funnel height.
h_F	=	effective height of the funnel, in m, measured from the upper deck at centreline, or notional deck line where there is local discontinuity in the upper deck, and the top of the funnel. The top of the funnel may be taken at the level where the funnel breadth reaches .

S_shield

the section of front projected area A_FS, in m², which is shielded by all deck houses having breadth greater than

. If there is more than one shielded section, then the individual shielded sections i.e. S_shield1, S_shield2 etc as shown in Figure 1.7.2 Computation of Sshield to be added together. To determine S_shield, the deckhouse breadth is assumed B for all deck houses having breadth greater than

as shown for S_shield1, S_shield2 in Figure 1.7.2 Computation of Sshield.

Figure 1.7.1 Computation of ‘H’

Figure 1.7.2 Computation of S_shield

Figure 1.7.3 Computation of h_F and A_FS in the case of multiple funnels

7.1.2In the calculation of H, sheer and trim are to be ignored. Where there is a local discontinuity in the upper deck, H is to be measured from a notional deckline.

7.1.3If a house having a breadth greater than is above a house with a breadth of or less, then the wide house is to be included, but the narrow house ignored.

7.1.4Screens and bulwarks more than 1,5 m in height are to be regarded as parts of houses when determining H and A. Where a screen or bulwark is of varying height, the portion to be included is to be that length the height of which exceeds 1,5 m. The height of the hatch coamings and that of any deck cargo, such as containers, may be disregarded when determining H and A.

7.1.5When several funnels are fitted on the ship, the parameters mentioned in Pt 3, Ch 1, 7.1 Calculation of Equipment Number 7.1.1 are to be taken as follows:

h_F: effective height of the funnel, in m, measured from the upper deck, or notional deck line where there is local discontinuity in the upper deck, and the top of the highest funnel. The top of the highest funnel may be taken at the level where the sum of each funnel breadth reaches as shown in the Figure 1.7.3 Computation of hF and AFS in the case of multiple funnels. When one funnel is fully or partially shielded by another funnel, the shielded area shall be omitted in calculating the sum total breadth of the funnels.

A_FS: sum of the front projected area of each funnel, in m², calculated between the upper deck, or notional deck line where there is local discontinuity in the upper deck, and the effective height h_F. A_FS is to be taken equal to zero if the sum of each funnel breadth is less than or equal to at all elevations along the funnel’s height. When one funnel is fully or partially shielded by another funnel, the shielded area shall be omitted.

A: Side projected area, in m², of the hull, superstructures, houses and funnels above the summer load waterline which are within the Rule length of the ship. The total side projected area of the funnels is to be considered in the side projected area of the ship, A, when A_FS is greater than zero. The shielding effect of funnels in the transverse direction may be considered in the total side projected area, i.e. when the side projected areas of two or more funnels fully or partially overlap, the overlapped area needs only to be counted once.

7.1.6The Equipment Number for tugs is to be calculated as follows:

where

Δ, B and A	=	are defined in Pt 3, Ch 1, 7.1 Calculation of Equipment Number 7.1.1
b	=	breadth, in metres, of the widest superstructure or deckhouse on each tier having a breadth greater than
f	=	freeboard amidships, in metres, from the summer load waterline
h	=	the height, in metres, of each tier of superstructure or deckhouse at side having a breadth of or greater. In the calculation of h, sheer and trim are to be ignored.

7.1.7In the case of dredgers having normal ship shape underwater hull, bucket ladders and gallows are not to be included in the Equipment Number calculations. If the dredger has an unusual underwater hull design or has a limited service area, the anchoring equipment needs to be specially considered.

7.1.8The Equipment Number formulae for anchoring equipment as given in this Section are based on an assumed maximum current speed of 2,5 m/s, maximum wind speed of 25 m/s and a minimum scope of chain cable of 6, the scope being the ratio between length of chain paid out and water depth. For ships with a Rule length, L, greater than 135 m, the required anchoring equipment is also considered adequate for a maximum current speed of 1,54 m/s, a maximum wind speed of 11 m/s and waves with maximum significant height of 2 m.

7.1.9For sailing passenger ships, the equipment requirement is to be in accordance with the letter and numeral two grades higher than that corresponding to the calculated Equipment Numeral.