Different Types of Mooring Systems and How They Work

By Duracordix
November 4, 2025

Table of Contents

Introduction

Do you need to protect your boat or ship? A mooring structure is vital for safety. We will study several different types of mooring systems. You will understand their fundamental designs. We will also touch upon key system elements. This guide demonstrates how they function, so you can adopt the right approach.

What Is The Primary Function Of Mooring Systems?

A mooring system has one critical job, which is keeping the vessel secure. This engineered design secures the vessel and effectively prevents drifting from its position. Environmental forces of wind, waves, and currents will almost always act upon the vessel’s hull.

The main function of what is a mooring is to successfully counteract these strong forces. The system creates restoring forces to hold the vessel in a specific position. A certain level of safety and operational efficiency is always required for mooring a ship. This applies to securing a boat at a dock or holding an FPSO in deep waters.

Exploring The Main Types Of Mooring Systems!

Now, let us look at the principal types of mooring. Each mooring system is designed for a specific water depth, vessel type, and environment.

A. Single Point Mooring (SPM)

A Single Point Mooring (SPM) is a common type of mooring used for offshore assets. SPM uses one mooring point, like a turret or a buoy, to secure a vessel. This design is very important for Floating, Production, Storage, and Offloading (FPSO) units. The pivot, or the vessel anchor, is truly key to this specific design. It is not fixed and can therefore turn 360 degrees around the anchor point.

This movement is known as “weathervaning.” The vessel must use this feature to counter the wind and waves. This action greatly reduces the strains imposed on the vessel from the environment. This single point mooring system is crucial for deep-water cargo transfer.

A turret mooring system FPSO is a more elaborate SPM type. Here, the turret mooring system is incorporated directly into the vessel’s hull. The vessel’s rotation occurs around this internal turret. These systems are designed permanently and can last twenty years or more.

1. What Are Its Key Features?

360 Degree Weathervaning

This weathervaning FPSO movement greatly reduces environmental forces on the mooring structure. It allows the vessel to turn into the wind and waves.

Turret System

The turret mooring system merges the mooring system into the hull. The FPSO or FSO rotates around this fixed internal or external component.

Buoy Connection

Many SPMs use the CALM Bluewater buoy setup. A moored boat connects to the floating buoy, which is anchored by 4 to 8 catenary lines.

Fluid Swivels

These are sophisticated elements that permit the transfer of fluids and gases. They also transfer power from the seabed through the turret while the vessel rotates.

2. What Is the Core Technology?

CALM Buoy

CALM is an acronym for Catenary Anchor Leg Mooring. It is a simple, reliable floating water buoy anchored by chains, making a good connection point.

SALM Tower

A Single Anchor Leg Mooring supports a rigid tower. A hinged rigid tower is set at the base, which allows use in shallow water.

Yoke System

A yoke is a rigid A-frame. It creates a permanent and rigid boat mooring by connecting the vessel directly to the SPM buoy or tower.

Riser Tethers

These are flexible pipes. They move oil and gas from the seabed to the turret and bend as the vessel moves.

3. What Are the Primary Benefits?

Reduced Loads

Weathervaning minimizes the force from wind and waves. This reduces strain on the mooring lines and the vessel’s hull.

The Deep Water

Capable SPM SPM systems, especially with taut-leg designs, have proven effective in ultra-deep water. They can operate in depths greater than 2,000 meters.

Cargo Transfer

SPMs work well for ship-to-ship (STS) transfers. Tankers can moor boat to the buoy, enabling efficient loading or lightering operations at sea.

4. What Are the Top Applications?

FPSOs

These types of FPSO mooring systems allow floating units to produce for 20-30 years at one location.

FSOs

Floating Storage and Offloading units store oil. They do not have onboard production equipment like FPSOs.

Offshore Terminals

SPM buoys serve as offshore moorings for oil tankers. They relieve port congestion by providing offshore terminals.

B. Spread Mooring

A spread mooring system is a type of conventional mooring system. It differs from an SPM because it keeps a vessel on a fixed heading. It employs several mooring lines from the vessel’s bow and stern. These lines connect to seabed anchors in a set configuration.

This type of mooring lines system prevents a vessel from weathervaning. Spread mooring system designs are common for semi-submersibles and drilling rigs. A simple example is a 4 point mooring procedure. It uses four anchors, usually two at the bow and two at the stern.

More complex mooring systems utilize 8, 12, or more lines. The mooring lines arrangement is crucial. It offers stability but also greater exposure to environmental forces, like beam seas.

1. How Is It Designed?

Fixed heading

The vessel’s heading is fixed. It cannot turn to face the wind. This is the main aspect differentiating it from a single point mooring system.

Multi-Line

The system uses 4 to 16 lines on average. They extend from fairleads at the vessel’s corners to seabed anchors.

4×2 Pattern

This is a common 4 2 2 mooring arrangement. It means 4 groups of 2 lines each, for eight lines total, often used on semi-submersibles.

Symmetric Spread

Lines are evenly spread around the vessel. For example, 8 lines would be 45 degrees apart.

2. What Are the Performance Metrics?

High Stability

This provides excellent station-keeping. The fixed position is ideal for drilling or connecting to subsea equipment.

No Weathervaning

The vessel is fixed. It must withstand environmental forces from all sides, including beam seas.

Directional Control

This system is effective in slower winds. It is also useful where wind and waves are highly directional.

3. What Are Its Operational Limitations?

Calm Seas

Spread moorings are effective in predictable conditions. They are less suitable for open oceans with shifting weather.

Higher Loads

The vessel requires stronger lines than in weathervaning. This is especially true during a 100-year storm. I’ve seen firsthand how under-specced lines on a spread mooring system Wikipedia entry can part under severe beam seas.

Fixed Position

The fixed position is a limitation. This is true for shuttle tankers that need to connect and disconnect easily.

4. Who Is This Product Designed For?

Semisubmersibles

These drilling platforms depend on the high stability of spread mooring system designs.

Deep-draft Spar

Spar platforms, which are deep-draft floating cylinders, also use these fixed systems.

Non-Ship Shaped

This is the preferred design for non-ship-shaped floaters. Barges, rigs, and platforms use it, while ship-shaped vessels prefer SPMs.

C. Catenary Mooring (CMS)

The catenary mooring system is a classic design. It is one of the most common types of mooring systems, including gravity mooring systems. The lines are heavy and long, often made of chain or steel wire. The lines are set on the seabed in a ‘U’ shape or catenary.

When the vessel moves, it lifts a part of the heavy chain from the seabed. This lifted portion’s weight pulls the vessel back to position. It is a passive system where gravity does the work. This system requires a large seabed area because long lines are needed. The anchor catenary must be long enough so the anchor is only pulled horizontally.

1. What Is the Core Principle?

Weight of Line

The system’s mooring lines, usually all-chain, get their retaining force from their own submerged weight.

Catenary Curve

This refers to the shape the line forms. The mooring catenary calculation is an important component of the design.

Horizontal Force

The line must be long enough to ensure no vertical uplift on the anchor. The anchor is only designed to withstand horizontal pull.

2. What Are the Technical Specifications?

All-Chain

This is the most basic CMS type. It consists of only studlink chains and is ideal for shallow waters.

Chain-Wire-Chain

This is a common composite design. It uses heavy chain on top and bottom, with lighter wire rope in the middle.

Large Footprint

These systems need considerable area. The anchor radius (R) can range from 3 to 8 times the water depth (D).

3. How Does It Rate on Durability?

Heavy chain

This is one of the most superior forms of chain. It is highly durable and can withstand abrasion, cuts, and handling damage, ensuring long-term marine mooring.

Abrasion Resistant

The bottom chain section is designed to withstand the most abrasion.

Seabed Contact

This contact is relied upon in most designs. This is not ideal for sensitive environments like coral, a primary focus of mooring design handbook rules. The American Petroleum Institute’s API RP 2SK states that anchor uplift should be avoided in catenary systems.

4. What Are the Recommended Environments?

Shallow Water

This system is the most economical option among different types of mooring systems for boats in shallow water.

<500m Depth

Catenary mooring system designs are preferred for water depths less than 500 meters. Beyond that, the line weight becomes too heavy.

Large Offsets

These systems are “softer” than taut systems. They allow greater vessel offsets, which can be 5% or more of the water depth.

D. Taut Leg Mooring (TLM)

The taut leg mooring system is an innovative solution for deep water. It is a significant innovation in new mooring systems designs. Unlike catenary systems applying weight, TLM systems apply tension. The mooring lines are lightweight, high-modulus synthetic ropes, like polyester.

These lines are kept taut. They are anchored to the vessel and to vertical-load anchors on the seabed. As the vessel moves, it stretches the lines. The elastic tension then pulls the mooring lines taut. It is a stiff configuration, preferred for mooring system for floating structures in ultra-deep water.

1. What Makes the Design Unique?

Tensioned Lines

The lines are pre-tensioned. The restoring force comes from the line’s elastic stretch, not its weight.

Vertical Loads

The lines apply an upward force on the anchor. This requires special anchors like suction piles or helix mooring screws that handle vertical loads.

No Seabed Contact

Syntactic float buoys can keep these synthetic lines suspended. This protects them from abrasion and minimizes environmental impact.

2. What Is the Material Composition?

Polyester Rope

Polyester ropes provide low-stretch, high strength, and excellent fatigue life. Have you ever wondered why polyester is preferred over nylon for taut systems? It’s because polyester doesn’t creep significantly under load.

Synthetic Lines

Submerged weight is a concern in offshore mooring systems pdf documents. Lightweight synthetic lines are crucial for viability in 3,000 meters of water. A 2019 study in Ocean Engineering noted that polyester taut-leg systems significantly reduce vessel offset in deep water.

High Modulus

These ropes are stiff. The resulting stiffness gives a “hard” mooring with minimal offset of only 3-5% of water depth.

3. What Are the Primary Benefits?

Small Footprint

The nearly vertical lines are optimal in congested subsea fields with pipelines and risers.

Reduced Offset

Vessel movement is limited due to the system’s high stiffness. This is important for connecting to inflexible steel risers.

Cost-effective

In deep water (over 1,000 meters), TLM systems are economical. They require less line length and are easier to install.

4. What Are Its Operational Limitations?

High Pretension

The system’s high pretension (10-20% of MBL) must be controlled to avoid fatigue failure.

Creep <1%

Polyester ropes “creep” slowly under load. This is a design consideration, kept well under 1% over the service life.

Deployment 4-6%

New ropes have a one-time “bedding-in” stretch of 4-6%. This is managed by pre-stretching lines during installation.

E. Dockside Mooring

Dockside mooring is the most common method you will see in a harbor. It consists of securing the vessel parallel to a fixed structure like a quay, pier, or finger berth. The mooring vs docking difference is simple: docking is always to a structure, while mooring can be in open water.

The aim is easy access for crew, passengers, and cargo. A ship’s berthing and unberthing operation of a ship relies on a defined set of mooring lines. The UK’s Port Marine Safety Code emphasizes that ‘all berths should be fit for purpose,’ making line arrangement critical.

This set includes head lines (stopping backward movement), stern lines (stopping forward movement), and spring lines (controlling fore/aft surge). Fenders minimize the risk of the hull touching the dock.

1. What Are the Main Components?

Dock Cleats

These are the T-shaped fittings on the dock. The mooring lines on a ship attach to these using a cleat hitch knot.

Bollards

A mooring bollard is a large, sturdy post. It is a metal or wood post on a wharf for tying up the mooring lines of large ships at a commercial quay.

Fenders

Fenders are cushions. They absorb impact and stop the hull from rubbing against the dock, protecting both the ship is moored and the dock.

2. How Is It Configured?

Alongside

Positioning the vessel parallel to the dock or quay is the standard configuration for most quay mooring operations.

Parallel

In this configuration, the ship’s flat midship side provides maximum contact for stability and easy access.

4 Lines

It is common to moor a boat with at least four lines. A bow line, a stern line, and two spring lines are a typical example.

3. What Problems Does This Solve?

Easy Access

People may easily walk off the vessel via a gangway, which is the main benefit.

Cargo Loading

This type of mooring is helpful for stabilizing the vessel for cranes during cargo loading and unloading.

Passenger Boarding

Cruise ships and ferries rely on the alongside position for easy passenger boarding.

F. Pile Mooring

Mooring a boat to piles is common in busy harbors. This type of mooring does not use anchors. Instead, mooring posts are long, cylindrical poles driven vertically into the seabed, with their tops above water. A moored boat is secured between these piles, providing excellent stability and preventing uncontrolled swinging. Vessels tie lines to two, three, or four piles to lock themselves in position.

More effort is in the pile installation, but the boat is in a very secure position. This protects the boat from wakes and allows maneuvering in constricted spaces.

1. What Is the Core Technology?

Driven Poles

The base consists of 2 or 4 strong, heavy-duty poles. They are driven deep into the seabed for a rigid, permanent hold.

2 Piles

A 2-pile system is common for smaller boats. The bow is tied to one pile and the stern to the other.

4 Piles

A 4-pile system offers maximum stability. The boat is secured between four piles, one at each “corner,” eliminating all movement.

2. What Are the Primary Use Cases?

Crowded Waters

This is one of the top mooring systems for boats. It resolves the issue of boats swinging into one another in busy marinas.

Waterways

Best suited for rivers, it keeps the vessel secure and enables safe passing of other vessels.

Fixed Position

This is ideal for residential docks. It keeps the vessel aligned with a personal pier or lift.

3. How Does It Enhance Workplace Safety?

High Stability

The vessel is locked in place. This high stability is safer for boarding.

Minimal Swing

Unlike swing mooring, this method has a zero-swing radius. This allows maximized use of water in a marina.

Precise Install

While the install requires precision, it pays off with a dependable mooring site that needs little upkeep.

G. Swing Mooring

A swing mooring is a rudimentary yet popular type of mooring system. It is commonly used in open bays or harbors. A swing mooring consists of a single heavy anchor on the seabed. This anchor is linked to a mooring buoy on the water surface by a chain or rope. The vessel then ties to the buoy.

It gets its name because the boat “swings” in a circle. The boat will “weathervane,” meaning its bow faces the wind or current. This is the simplest and cheapest way to moor a vessel. The swing technique requires a large, unobstructed circle of water. This means it is not effective in densely populated or narrow regions.