2 Anchoring Windlass and Chain Stopper

2.1 General

2.1.1

The windlass is to be efficiently bedded and secured to the deck.

2.1.2

The builder and the windlass manufacturer are to ensured that the foundation is suitable for the safe operation and maintenance of the windlass equipment.

2.1.3

The supporting structure is to be dimensioned to ensure that for each of the load scenarios specified in [2.1.5] and [2.1.6], the stresses do not exceed the permissible values given in [2.1.12] to [2.1.15].

2.1.4

These requirements are to be assessed based on net scantlings.

2.1.5

where:

BS : Minimum breaking strength of the chain cable.

2.1.6

The following forces are to be applied in the independent load cases that are to be examined for the design loads due to green sea over the forward 0.25 L, see Figure 1:

P_x = 200 A_x, in kN, acting normal to the shaft axis.

P_y = 150 A_y f, in kN, acting parallel to the shaft axis (inboard and outboard directions to be examined separately).

where:

A_x : Projected frontal area, in m².

A_y : Projected side area, in m².

B_W: Breadth of windlass measured parallel to the shaft axis, in m, see Figure 1.

H : Overall height of windlass, in m, see Figure 1.

Figure 1 : Directions of forces and weight

2.1.7

Forces resulting from green sea design loads in the bolts, chocks and stoppers securing the windlass to the deck are to be calculated. The windlass is supported by a number of bolt groups, N, each containing one or more bolts. See Figure 2.

Figure 2 : Bolting arrangements and sign conventions

2.1.8 The axial forces, R_xi and R_yi, in bolt group (or bolt) i, positive in tension, are given by:

R_xi = P_x h x_i A_i ⁄ I_x

R_yi = P_y h y_i A_i ⁄ I_y

R_i = R_xi + R_yi – R_si

where:

P_x : Force acting normal to the shaft axis, in kN.

P_y : Force acting parallel to the shaft axis, either inboard or outboard, whichever gives the greater force in bolt group i, in kN.

h : Shaft centre height above the windlass mounting, in cm, see Figure 1.

x_i, y : x and y coordinates of bolt group i from the centroid of all N bolt groups, in cm. Positive in the direction opposite to that of the applied force.

A_i : Cross sectional area of all bolts in group i, in cm².

R_si : Static reaction at bolt group i, due to the weight of windlass, in kN.

2.1.9

The shear forces, F_xi and F_yi, applied to the bolt group i, and the resultant combined force F_i, are given by:

where:

C₁ : Coefficient of friction, taken equal to 0.5.

m : Mass of windlass, in t.

g : Acceleration due to gravity, taken equal to 9.81 m/s².

N : Number of bolt groups.

2.1.10

The resultant forces from the application of the loads specified in [2.1.5] and [2.1.6] are to be considered in the design of the supporting structure.

2.1.11

Where a separate foundation is provided for the windlass brake, the distribution of resultant forces is to be calculated on the assumption that the brake is applied for load cases (a) and (b) defined in [2.1.5].

2.1.12

2.1.13

The tensile axial stresses resulting from green sea design loads in the individual bolts in each bolt group i are not to exceed 50% of the bolt proof strength. The load is to be applied in the direction of the chain cable. Where fitted bolts are designed to support shear forces in one or both directions, the von Mises equivalent stresses are not to exceed 50% of the bolt proof strength.

2.1.14

The horizontal forces resulting from the green sea design loads, F_xi and F_yi may be supported by shear chocks. Where pourable resins are incorporated in the holding down arrangements, due account is to be taken in the calculation.

2.1.15