Different Types of Anchors: Marine, Yacht & Aquaculture Guide

Anchors are not interchangeable — the right anchor depends entirely on vessel size, seabed type, environmental conditions, and application. The five most practical anchor categories are: marine ship anchors (stockless, admiralty), yacht anchors (plow, fluke, roll-bar), and aquaculture mooring anchors (deadweight, helical, drag embedment). Selecting the wrong type can result in dragging, structural damage, or total mooring failure. This guide breaks down each type with holding power data, ideal use cases, and direct comparisons so you can make an informed choice.

Why Anchor Type Matters More Than Anchor Weight

A common misconception is that a heavier anchor always holds better. In reality, anchor geometry and seabed compatibility are far more important than mass alone. A 15 kg modern plow anchor on sandy seabed can outperform a 40 kg traditional admiralty anchor in the same conditions because its design allows it to bury deeply and generate horizontal resistance far exceeding its own weight.

Holding power is typically expressed as a ratio of holding force to anchor weight. High-performance modern anchors achieve ratios of 20:1 to 50:1 in optimal seabed conditions, while traditional designs may only achieve 3:1 to 8:1. Seabed type — sand, mud, rock, gravel, or coral — determines which anchor geometry will dig in reliably and which will skip across the surface.

Marine Ship Anchors: Built for Commercial and Naval Vessels

Large commercial vessels, naval ships, and offshore platforms require anchors that can be deployed and retrieved rapidly through a hawse pipe and windlass system, and that hold reliably in varied deep-water seabeds. The two dominant types are stockless and admiralty anchors.

Stockless (Hall-Type) Anchor

The stockless anchor is the global standard for commercial shipping. Its defining feature is a pivoting crown with two flukes and no horizontal stock bar, allowing the entire anchor to retract flush into the hawse pipe. This makes stowage and deployment fully mechanized — critical for vessels weighing tens of thousands of tonnes.

• Typical weight range: 500 kg to 30,000 kg for large tankers and bulk carriers
• Holding power ratio: approximately 3:1 to 5:1 — lower than modern designs but acceptable given the massive absolute weight
• Best seabed: soft-to-medium mud and sand; poor performance on hard rock or coarse gravel
• Governed by classification society rules (Lloyd's, DNV, ABS) based on vessel Equipment Number (EN)

Admiralty (Stocked) Anchor

The admiralty anchor features a long horizontal stock perpendicular to the flukes, which forces one fluke to dig into the seabed when the anchor lands. It offers superior holding on rocky or irregular bottoms where stockless anchors fail to set. However, the protruding stock makes stowage difficult, limiting its use to smaller vessels, heritage ships, and specific naval applications.

• Holding power ratio: 8:1 to 12:1 in mixed or rocky seabeds
• Disadvantage: the exposed fluke can foul the anchor chain as the vessel swings with tide changes
• Still specified for some naval and coast guard applications where rocky bottom holding is paramount

High-Holding-Power (HHP) and Super-HHP Marine Anchors

Modern classification societies recognize HHP anchors (holding power ≥ 2× equivalent stockless anchor) and Super-HHP anchors (holding power ≥ 4×). Designs like the Spek, Pool, and AC-14 anchors fall into these categories and are increasingly specified for offshore support vessels and semi-submersible platforms. The AC-14 anchor, widely used in North Sea operations, achieves holding power ratios of up to 15:1 in soft clay seabeds — the predominant bottom type in that region.

Yacht Anchors: Performance and Convenience for Recreational Vessels

Yacht anchors must balance high holding power with easy manual or windlass-assisted handling, compact stowage on a bow roller, and reliable setting across the diverse seabeds encountered in cruising — sand bays, muddy estuaries, weedy patches, and mixed bottoms. Three types dominate the modern yacht market.

Plow (CQR and Delta) Anchors

The plow anchor, shaped like an agricultural plowshare, is one of the most widely used yacht anchor designs globally. The original CQR (Secure) features a hinged shank that allows the anchor to pivot and re-set if the vessel swings 180°. The Delta is a fixed-shank evolution offering faster setting and better holding in most conditions.

• Typical sizes: 10 kg (yachts up to 10 m) to 35 kg (yachts up to 18 m)
• Holding power ratio: 15:1 to 25:1 in sand; 8:1 to 15:1 in soft mud
• Fits standard bow rollers and self-stows cleanly on most production yachts
• Weakness: can struggle to set quickly in weed or hard sand; hinged CQR design is less efficient than Delta in independent tests

Fluke (Danforth and Fortress) Anchors

Fluke anchors have two large flat pivoting flukes that dig down into soft seabeds at a shallow angle. They deliver exceptional holding power-to-weight ratios in sand and soft mud — the Fortress FX-37 (4.5 kg aluminum) is rated to hold a 12-metre vessel in 30-knot winds — a remarkable performance for a sub-5 kg anchor.

• Holding power ratio: 25:1 to 50:1 in soft mud (among the highest of any anchor type)
• Aluminum Fortress models are 40–50% lighter than steel equivalents — ideal as a kedge or secondary anchor
• Critical limitation: performs poorly on rock, coral, gravel, or heavily weeded bottoms where flukes cannot penetrate
• Does not fit a bow roller well — typically stowed on deck brackets or in a locker

Roll-Bar (Rocna, Manson Supreme, SPADE) Anchors

Roll-bar anchors represent the current state of the art for cruising yachts. A concave scoop-shaped fluke is attached to a roll-bar that rotates the anchor into the correct orientation the moment it touches the seabed, ensuring fast, consistent setting. Independent comparative tests — including those conducted by Practical Sailor magazine — consistently rank roll-bar designs at the top for holding power, setting speed, and re-setting after a direction change.

• Rocna 15 kg (suitable for yachts 10–14 m): holding force up to 4,500 kg in sand — a 300:1 ratio relative to vessel displacement for a 10-tonne yacht
• Sets reliably in sand, mud, weed, and mixed bottoms; acceptable (not excellent) on rock
• Fits bow rollers designed for plow anchors; the roll-bar can occasionally snag on roller lips — check compatibility before purchasing
• Price premium: 20–50% more expensive than plow anchors of equivalent weight, but widely considered worth the cost for offshore cruisers

Anchor Comparison by Seabed Type and Application

No single anchor excels in every condition. The table below summarizes performance across the most common seabed types and applications to guide selection.

Aquaculture Mooring Anchors: Holding Fish Farms and Offshore Structures

Aquaculture mooring anchors serve a fundamentally different purpose from vessel anchors — they must hold cages, longlines, buoy systems, and net pens in position continuously, often for years at a time, under multi-directional currents and storm loading. Reliability over a multi-year deployment life takes priority over deployability or retrieval convenience. Three anchor types dominate aquaculture mooring systems.

Deadweight (Gravity) Anchors

Deadweight anchors resist mooring loads through sheer mass, relying on friction and the weight of the anchor against the seabed. They are typically cast concrete blocks, steel frames filled with concrete, or fabricated steel plates.

• Typical weight: 500 kg to 10,000 kg per anchor depending on load requirements
• Horizontal holding force: approximately 40–60% of submerged weight (due to friction coefficient of concrete or steel on seabed material)
• Advantages: simple fabrication, works on any bottom type including hard rock where embedded anchors fail, easy to inspect by diver or ROV
• Disadvantages: requires heavy lifting equipment (crane barge) for installation and removal; relatively low holding efficiency per tonne compared to embedded anchors
• Most cost-effective for inshore and sheltered water sites where transport of heavy equipment is practical

Helical Screw Anchors

Helical anchors consist of a central steel shaft with one or more helical bearing plates that are rotated into the seabed using a hydraulic torque motor, typically mounted on a diver-operated tool or a subsea ROV. The helix plates lock into the soil matrix, providing resistance to both vertical uplift and horizontal tension.

• Holding capacity: 50 kN to 500 kN depending on shaft diameter, helix size, number of plates, and soil conditions
• Installation does not require heavy surface crane equipment — a significant operational cost advantage in exposed offshore locations
• Can be removed and relocated by reversing rotation — valuable for aquaculture leases with limited tenure or for farms that rotate sites for environmental recovery
• Torque-to-capacity relationship allows installation quality to be verified in real time: measured installation torque correlates directly with achieved holding capacity, providing built-in quality assurance without additional load testing
• Limitation: requires sandy or cohesive soil; cannot install through cobble, gravel, or rock

Drag Embedment Anchors (DEA)

Drag embedment anchors — including designs like the Bruce, Stevpris, and Vryhof Stevmanta VLA (Vertically Loaded Anchor) — are dragged along the seabed until the fluke buries to a depth where soil resistance exceeds the applied load. At depth, holding power increases dramatically as the anchor plows deeper under load.

• Holding power ratios: 30:1 to 100:1 for modern VLA designs in soft clay — making them the most efficient anchor type by weight for offshore applications
• A Stevpris Mk5 anchor weighing 3,500 kg can develop holding forces exceeding 200 tonnes in medium-strength clay — the reason this design is used for FPSO and semi-submersible moorings
• VLA variants are designed to accept near-vertical load angles after deep burial, making them suitable for taut and semi-taut mooring configurations used in exposed offshore salmon farming in Norway and Scotland
• Disadvantage: requires significant drag distance (typically 5–10× anchor depth) to achieve full embedment, demanding large clear seabed areas; also difficult to retrieve without specialized anchor-handling vessels

Mooring System Design for Aquaculture: Single vs. Multi-Anchor Configurations

Individual anchor selection is only part of aquaculture mooring design. The configuration — how anchors are arranged and connected — determines whether the system can handle multi-directional storm loads, tidal current reversals, and the dynamic forces of large net pens moving in waves.

Spread Mooring

The most common configuration for salmon cages and mussel longlines. Four to eight anchors are deployed radially around the structure. Each anchor handles a portion of the total load. For a 50-metre diameter salmon cage in a site with design current of 1.5 m/s and 5-metre design wave height, total horizontal mooring force can reach 150–300 kN — requiring multiple anchors rated well above individual load share to provide safety factors of 3:1 to 5:1 per anchor.

Long-Line Mooring (Mussel and Oyster Culture)

Shellfish farms use weighted longlines suspended between end anchors. Deadweight or helical anchors at each end must resist both the downward weight of the crop and the horizontal drag of the line in current. As mussel crop weight can reach 15–25 kg per linear metre of line, a 200-metre longline may carry 3,000–5,000 kg of biomass — anchor sizing must account for this static load in addition to environmental loading.

Single Point Mooring (SPM) for Offshore Farms

Exposed offshore aquaculture systems — increasingly deployed in locations with water depths of 30–100 m — use single point moorings that allow the structure to weathervane into prevailing wind and current, minimizing transverse loads. A single large DEA or a cluster of helical anchors forms the seabed attachment point. These systems are designed to withstand 50-year or 100-year return period storm events per classification society guidelines such as those published by DNV (DNVGL-ST-0437).

How to Select the Right Anchor: A Practical Decision Framework

Anchor selection follows a logical sequence of questions. Work through the following steps to narrow your choice:

1. Define the application: Is this a vessel anchor (temporary holding) or a mooring anchor (permanent or semi-permanent installation)? Vessel anchors prioritize ease of deployment and retrieval. Mooring anchors prioritize long-term holding capacity and corrosion resistance.
2. Determine vessel or structure size: For yachts, consult the manufacturer's anchor sizing table (typically based on LOA and displacement). For commercial ships, anchor weight is governed by Equipment Number calculations per classification society rules. For aquaculture structures, commission a formal mooring analysis using site-specific environmental data.
3. Identify the seabed type: Request a seabed report or geological survey for critical permanent installations. For yacht anchoring, consult cruising guides and chart notations (e.g., "s" for sand, "m" for mud, "r" for rock).
4. Assess environmental conditions: Maximum expected wind speed, wave height, current velocity, and tidal range all affect required holding force. A yacht anchoring in a sheltered bay in 15-knot winds has a very different requirement from one anchored off an exposed headland in 40 knots.
5. Consider retrieval requirements: Permanent aquaculture installations may never need retrieval. Yacht anchors must be retrieved daily. Commercial ship anchors must be deployed and weighed in minutes. Each scenario favors a different anchor type.
6. Apply appropriate safety factors: For recreational vessels, a safety factor of 2:1 above calculated maximum load is typical. For offshore aquaculture and commercial mooring systems, DNV and ISO standards specify safety factors of 3:1 to 5:1 for permanent moorings in exposed locations.

Materials, Corrosion, and Long-Term Reliability

Material selection affects both structural integrity and maintenance costs over the anchor's service life, particularly for anchors in continuously submerged or intertidal environments.

Steel Anchors

The vast majority of marine and commercial anchors are fabricated from mild steel or high-tensile steel. Hot-dip galvanizing (minimum 85 µm coating thickness per ISO 1461) provides 10–20 years of corrosion protection in seawater for infrequently deployed yacht anchors. Continuously submerged mooring anchors require cathodic protection (sacrificial zinc or aluminum anodes) and periodic inspection. Unprotected steel in tropical seawater loses 0.1–0.3 mm of thickness per year — significant over a 10-year deployment.

Aluminum Anchors

Marine-grade aluminum alloy (5000 or 6000 series) anchors — primarily fluke designs like the Fortress — offer excellent corrosion resistance in seawater without coatings and are 60–65% lighter than equivalent steel anchors. The trade-off is lower strength: aluminum anchors are not appropriate for vessels above 15–18 metres or in high-energy offshore conditions where shock loading could cause fatigue cracking.

Stainless Steel

Grade 316L stainless steel is used for high-specification yacht anchors and mooring hardware. It is highly resistant to crevice and pitting corrosion in seawater, but should not be used in permanently buried or oxygen-depleted sediment environments, where crevice corrosion can proceed rapidly even on 316L — a known failure mode in mooring chain and anchor shackles buried in anoxic mud.

Anchor Sizing Quick Reference by Vessel and Structure Type

The following table provides general sizing guidance as a starting point. Always verify against manufacturer specifications and site conditions.