Analysis of Holding Force Limit and Provision against Dragging Anchor
Publication: Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 148, Issue 1
Abstract
Analyses of the equilibrium conditions of an anchor and a cable of a ship at anchoring are presented. Three conditions are considered: (1) a part of the cable lies on the seafloor; (2) no part of the cable lies on the seafloor and rises from the seafloor with a zero gradient of the slope; and (3) a nonzero gradient of the slope. In the third condition, a coefficient is introduced to represent the effects of the vertical component of the cable tension on the holding force of an anchor while considering the decrease in the apparent anchor weight. Formulas of the holding force limit in each condition are presented by analyzing the parameters representing the three cable conditions. Numerical examples demonstrate the effects of extended cable length, water depth, soil properties of the seafloor, and the coefficient of upward cable tension on the holding force limit and parameters characterizing the three cable conditions. Measuring the safety of anchoring in terms of the extended cable length and the current cable conditions associated with the risk allowance for dragging anchors is discussed.
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Data Availability Statement
All data, models, and code generated or used during the study appear in the published article.
Notation
The following symbols are used in this paper:
Greek Symbols
- α
- upward tension coefficient;
- ρa
- density of air;
- θA and θH
- cable slopes at A and H; and
- , , b*, , d*
- θA, θH, b, s1, and d when Th is equal to .
Roman Symbols
- A, Ai
- anchor point, anchor point in Conditions 1 (i = 1), 2 (i = 2), and 3 (i = 3);
- Af
- longitudinal projected area above water;
- a
- Th divided by wc;
- b
- horizontal distance between H and F;
- CX0
- longitudinal wind load coefficient in head wind;
- D
- water depth;
- d
- horizontal distance from A to H;
- e
- vertical distance between H and F;
- F
- intersection of the cable and the calm sea surface;
- H
- hawse point;
- h
- height of hawse from the seafloor;
- k
- extended cable length;
- kc
- k in Condition 2;
- l
- length of holding part of cable;
- ra
- holding force coefficient of anchor when applied with wa;
- holding force coefficients of anchor when applied with ;
- rc
- holding force coefficient of cable when applied with wc;
- holding force coefficients of cable used when applied with ;
- s
- cable length of catenary part;
- s1
- cable length between H and F;
- Th
- holding force, horizontal component of cable tension at H and A;
- holding force limit;
- ThA
- horizontal component of cable tension at A;
- ThH
- horizontal component of cable tension at H;
- Th[n]
- nominal holding force;
- Th[n]A
- anchor nominal holding force;
- Th[n]C
- cable nominal holding force;
- TvA
- vertical components of cable tension at A;
- TvH
- vertical components of cable tension at H;
- Ua
- apparent wind speed;
- wa
- anchor weight in water;
- wa value in the air;
- wc
- weight per unit length of cable in water;
- wc value in the air;
- Xw0
- longitudinal wind load in head wind;
- (xA, yA)
- coordinates of A;
- (xF, yF)
- coordinates of F; and
- (xH, yH)
- coordinates of H.
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Published In
Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 148 • Issue 1 • January 2022
Copyright
© 2021 American Society of Civil Engineers.
History
Received: Jan 6, 2021
Accepted: Aug 27, 2021
Published online: Nov 1, 2021
Published in print: Jan 1, 2022
Discussion open until: Apr 1, 2022
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