A ship's anchor does more than place a heavy object on the seabed. For the fluked anchors discussed here, holding involves the anchor engaging the ground and resisting the pull transmitted through the anchor chain. How the anchor enters the seabed, the ground it encounters and the direction of that pull all matter. Weight alone does not describe the result.[1–3]
Our guide to commercial ship anchor types explains names such as Hall, Spek and AC-14. This article takes the next step: understanding how a hold develops and why an anchor's mass is not a complete measure of its performance. The focus is commercial ship anchoring, not small-boat sizing or permanent offshore mooring design.
From Touching Bottom to Developing a Hold
The flukes are the parts of an anchor intended to engage the seabed. Touching bottom is only the starting point. As the chain pulls, the anchor can change its orientation and its flukes can enter the ground. The ground resists that movement: developing a hold involves engaging the seabed, not merely placing steel on top of it.[1]
The process can be seen in controlled tests of an AC-14 model anchor in loose sand. Starting flat on the surface, the model was pulled with its flukes free to open. The tests tracked how its orientation and penetration changed alongside the force needed to pull it.[1]
The useful distinction is between reaching the bottom and developing resistance in it. The model tests illustrate that distinction; their measured depths and forces are not universal values for anchors in service.
Why Equal Weight Does Not Mean Equal Holding Power
Weight remains an important specification. The mistake is treating it as the whole explanation.
Anchor size, fluke dimensions, opening geometry and soil properties all affect penetration. Mass is one relevant factor, not a substitute for understanding those other features.[1]
The distinction also appears in ship classification requirements. IACS UR A1 compares high holding power anchors with ordinary stockless anchors of the same mass and requires holding-power tests on different types of bottom.[2] The useful point here is not a reduction in specified weight: anchors of equal mass need not have equal holding performance.
That does not mean a particular design is better in every situation, or that an anchor can be substituted merely because its advertised holding power is higher. Performance evidence and the vessel's applicable requirements still matter.
Why the Seabed Changes the Result
An anchor does not work independently of the material around it. A holding-power claim therefore needs context: which anchor, in which ground, under which test conditions?
IACS UR A1 explicitly bases its anchoring-equipment requirements on good holding ground and states that holding power is significantly reduced in poor holding ground.[2] Its HHP holding-power tests cover different bottom types rather than relying on one seabed condition.
Even a label such as “sand” does not describe every relevant property: sand density can affect an anchor's penetration.[1] A result from one test cannot simply be treated as the result for every anchorage with the same broad seabed label.
For a buyer comparing anchors, the practical question is therefore not just “How much does it weigh?” but also “What conditions support the performance being quoted?”
What the Anchor Chain Changes
The chain connects the vessel to the anchor, but the direction of pull at the anchor is also important. DNV's anchoring guidance identifies good holding ground and a chain arrangement that remains horizontal at the seabed as key conditions for achieving the necessary holding power.[3]
In a simplified arrangement, part of the chain hangs in a curve—the catenary—while another part contacts the seabed. That shape is not fixed. Japan P&I's explanation shows that, with the deployed chain length held constant, increasing external force increases the suspended length and reduces the length in contact with the bottom.[4]
The lesson is that a sketch showing a horizontal chain near the anchor represents a condition, not a guarantee. The chain configuration and the loads acting on the vessel must be considered together. The chain's weight does not ensure the same pull direction under every condition.
This is a reason to understand the complete anchoring arrangement, not a formula for deciding how much chain to deploy.
What to Look at Beyond Anchor Weight
The following questions help put an anchor specification or performance claim in context:
| Factor | Why it matters | Useful question |
|---|---|---|
| Anchor design and geometry | Shape affects penetration; equal mass does not establish equal holding performance. | Which design and drawing does the specification describe? |
| Seabed and test conditions | Holding depends on the ground, not just the anchor. | What bottom conditions were used to establish the quoted performance? |
| Chain arrangement | Its changing shape affects the conditions of pull near the seabed. | Has the anchor been considered as part of the vessel's chain arrangement? |
| External loads | Holding must be considered against the forces acting on the vessel. | What operating and environmental conditions form the equipment's design basis? |
The last point separates available holding from the demand placed on it. Japan P&I describes dragging as occurring when external forces exceed the holding power of the anchor and cable.[4] An anchor being on the bottom does not, by itself, establish that the vessel will remain in position.
The design basis also has limits. IACS UR A1 describes the equipment covered by its requirements as intended for temporary anchoring in a harbour or sheltered area; it is not designed to hold a ship off a fully exposed coast in rough weather.[2] A heavier anchor is not, on its own, evidence that those limits have changed.
From Understanding Holding Power to Comparing Products
Anchor weight tells you one part of the specification. Holding power describes performance in particular conditions. Understanding the difference means looking at the anchor, the seabed and the chain arrangement together—not searching for a single weight that answers every question.
To explore the designs, browse Andy Marine's marine anchor range. When asking about a specified anchor, include the design name, required mass, available drawing and project requirements. Those details identify the product being discussed; final suitability remains subject to the vessel's applicable design and approval requirements.
References
[1] Sharif, Y.U. et al. (2024), Comparison of the behaviour of a drag embedment anchor using 1-g and centrifuge scale model testing, Proceedings of the 5th European Conference on Physical Modelling in Geotechnics. Abstract, Section 2.2 and Sections 3–4. AC-14 model tests in loose sand; cited for qualitative explanation, not vessel-specific performance values.
[2] IACS, UR A1 — Anchoring Equipment, Rev.8, June 2023, A1.1.1–A1.1.3, A1.4.1.2 and A1.4.2. Cited for the design basis and holding-power comparison framework, not as a determination of the rules applicable to an individual vessel.
[3] DNV (8 November 2021), Anchor losses are on a negative trend — How to improve, “Key principles for safe anchoring.”
[4] The Japan Ship Owners' Mutual Protection & Indemnity Association (July 2013), Preventing an Anchor from Dragging, Loss Prevention Bulletin Vol.25, Sections i2 and i5. Cited for qualitative relationships only; operational formulas are not reproduced.
