A Technical Guide to Ship Anchor Types, Sizing Criteria, and Selection Requirements

Marine anchors are essential outfitting components for commercial vessels, including oil tankers, bulk carriers, container ships, LNG carriers, and offshore vessels. Unlike small craft anchors, ship anchors are designed as part of a complete anchoring system that includes anchors, stud link anchor chains, windlasses, chain stoppers, hawse pipes, and chain lockers.

For large vessels, anchor selection is not determined by anchor weight alone. The correct specification is based on vessel parameters, equipment number calculations, classification society requirements, anchor holding performance, and compatibility with the complete anchoring system.

A properly selected marine anchor must provide sufficient holding power under expected operating conditions while meeting the structural and installation requirements of the vessel.

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1. Types of Anchors Used on Large Commercial Ships

1.1 Stockless Anchor

The stockless anchor is the most widely used anchor type for modern commercial vessels.

It is commonly installed on:

· Oil tankers

· Bulk carriers

· Container ships

· LNG carriers

· Offshore support vessels

The main feature of a stockless anchor is the hinged fluke design, which allows the flukes to rotate relative to the shank. This structure enables efficient seabed penetration while allowing the anchor to be easily retrieved through the vessel's hawse pipe.

Common stockless anchor designs include:

· Hall Anchor

· Spek Anchor

· Pool Anchor

· AC-14 High Holding Power Anchor

Advantages of stockless anchors include:

· Compact structure for easy storage

· Reliable penetration performance

· Efficient recovery through hawse pipes

· Compatibility with modern anchor handling systems

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1.2 High Holding Power (HHP) Anchor

High Holding Power (HHP) anchors are designed to provide greater holding capacity compared with conventional anchors of the same weight.

Through optimized fluke geometry and improved seabed penetration capability, HHP anchors can achieve higher holding efficiency while reducing the required anchor weight for a given vessel application.

Typical applications include:

· Large crude oil tankers

· VLCCs

· Ultra-large container vessels

· Offshore vessels

Compared with conventional stockless anchors, HHP anchors offer:

· Higher holding force-to-weight ratio

· Reduced bow equipment load

· Improved anchoring performance in demanding conditions

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1.3 Super High Holding Power (SHHP) Anchor

SHHP anchors are designed for applications requiring higher holding performance than standard HHP anchors.

They are mainly used for:

· Large offshore vessels

· Specialized vessels

· Applications requiring enhanced anchoring capability

The selection between ordinary,HHP, and SHHP anchors depends on vessel design requirements and classification approval.

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2. How Is Ship Anchor Size Determined?

For commercial vessels, anchor size is determined according to classification society rules rather than vessel length alone.

The key parameter used for selecting anchoring equipment is the Equipment Number (EN).

The Equipment Number is calculated based on vessel principal dimensions and exposed areas above the waterline. The calculation typically considers:

· Length of vessel

· Breadth of vessel

· Depth of vessel

· Projected lateral windage area

· Other vessel design parameters specified by classification rules

Based on the Equipment Number, the required anchoring equipment is determined, including:

· Number of anchors

· Anchor weight

· Anchor chain diameter

· Anchor chain length

Classification societies providing relevant requirements include:

· International Association of Classification Societies (IACS)

· China Classification Society (CCS)

· American Bureau of Shipping (ABS)

· Det Norske Veritas (DNV)

· Lloyd's Register (LR)

The final anchor specification must comply with the approved vessel design and applicable classification requirements.

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3. General Reference Range of Ship Anchor Weight

The actual anchor weight varies depending on vessel design, anchor type, and classification requirements. The following table provides general reference ranges for commercial vessels.

Vessel Type	Typical Vessel Size	Approximate Anchor Weight Range
Small Commercial Vessel	5,000–10,000 DWT	1–3 tons
Handy Size Bulk Carrier	20,000–40,000 DWT	3–8 tons
Panamax Bulk Carrier	60,000–80,000 DWT	8–12 tons
Aframax Tanker	80,000–120,000 DWT	10–18 tons
VLCC Tanker	200,000+ DWT	15–25 tons
Ultra Large Container Vessel (ULCV)	15,000+ TEU	20 tons or above

These values are only general references. The final anchor specification is determined by the vessel's Equipment Number, approved design documentation, and classification society requirements.

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4. Anchor and Stud Link Chain Matching

A marine anchoring system is composed of multiple interconnected components:

· Marine anchor

· Stud link anchor chain

· Chain stopper

· Windlass

· Hawse pipe

· Chain locker

The anchor chain transfers the forces generated by wind, waves, and vessel movement between the ship and the anchor.

Large commercial vessels generally use stud link anchor chains because they provide:

· High tensile strength

· Improved chain stability

· Reduced deformation under heavy loads

· Long service life under marine conditions

Typical anchor chain diameter ranges:

Vessel Category	Approximate Chain Diameter
Small Commercial Vessel	40–60 mm
Medium Bulk Carrier	70–90 mm
Large Tanker	100–120 mm
VLCC	120 mm or above

The anchor, chain diameter, windlass capacity, and hawse pipe dimensions must be designed as a complete system. Increasing anchor size without considering other components may affect operational performance.

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5. Factors Affecting Anchor Holding Performance

The holding performance of a marine anchor depends on more than its weight. Key factors include:

Anchor Design

The geometry of the flukes, shank design, and penetration capability directly influence holding force.

High holding power anchors achieve improved performance through optimized structural design rather than simply increasing weight.

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Seabed Conditions

Different seabed types affect anchor performance:

· Sand: generally provides good penetration and holding performance

· Clay: holding capacity depends on penetration depth and soil strength

· Mud: requires suitable anchor geometry for effective grip

· Rock or hard seabed: may reduce penetration capability

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Anchor Chain Scope

The angle between the anchor chain and seabed affects the horizontal force applied to the anchor.

A longer scope generally reduces vertical loading on the anchor and improves holding performance.

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6. Anchor Selection for Different Ship Types

Oil Tankers

Oil tankers typically have large displacement and significant windage areas.

Common configurations include:

· Stockless HHP anchors

· Large diameter stud link anchor chains

· Heavy-duty windlass systems

The anchoring system must accommodate high environmental loads during waiting, offshore operations, or port approaches.

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Bulk Carriers

Bulk carriers generally feature wide hull dimensions and deep drafts.

Common anchor selections include:

· Hall type stockless anchors

· Spek anchors

· HHP anchors for larger vessels

The anchor system is designed according to vessel size, operating routes, and classification requirements.

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Container Ships

Modern container vessels have increased windage area due to stacked containers above deck.

Typical requirements include:

· High holding power anchors

· Large diameter anchor chains

· High-capacity anchor handling equipment

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7. Materials, Manufacturing Standards, and Certification

Ship anchors are manufactured using high-strength marine-grade steel materials to withstand impact loads and long-term exposure to seawater.

Important manufacturing considerations include:

· Material quality control

· Casting or forging process control

· Dimensional accuracy

· Mechanical property testing

· Surface protection requirements

For commercial vessels, anchors and related equipment may require approval or certification from recognized classification societies, including:

· CCS

· ABS

· DNV

· LR

· BV

Certification requirements depend on vessel type, flag administration, and project specifications.

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8. Example: Anchor System for a 100,000 DWT Tanker

A typical Aframax tanker may have the following anchoring arrangement:

· Vessel length: approximately 250 m

· Anchor type: HHP stockless anchor

· Anchor weight: approximately 15–20 tons per anchor

· Anchor chain diameter: approximately 100–120 mm

The final configuration is confirmed through equipment number calculation and classification approval.

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Conclusion

The selection of anchors for large commercial ships is a technical process involving vessel calculation, classification requirements, and system compatibility.

Modern commercial vessels mainly use stockless anchors and high holding power anchors because they provide efficient holding performance while meeting the installation requirements of large ship structures.

A complete anchoring solution requires proper matching of anchor type, anchor weight, stud link anchor chain, windlass capacity, and installation arrangement to ensure reliable anchoring performance throughout the vessel's service life.