SPM Design Basis
Single Point Mooring Design Basis covering CALM buoy systems, mooring and hawser engineering, anchors, pipelines, marine hoses, fluid-transfer systems, structural design, environmental criteria, stationkeeping, marine operations and safety requirements.
Single Point Mooring Design Basis
A Single Point Mooring (SPM) Design Basis establishes the engineering criteria, design assumptions, environmental conditions, operational requirements and applicable standards used to develop, analyse and verify an offshore SPM terminal.
The design basis provides the technical framework connecting the offshore environment, tanker characteristics, SPM buoy, mooring system, hawser arrangement, fluid-transfer system, submarine pipelines, marine hoses, loading operations, structural integrity and safety requirements into one controlled engineering basis.
For CALM-type SPM systems, the design basis should consider the complete load path and operational interface from the tanker through the hawser, buoy and swivel system to the subsea pipeline and shore or offshore receiving facility.
Purpose and Scope of the SPM Design Basis
Engineering Control
Establishes a common technical basis for naval architecture, offshore, structural, mechanical, pipeline, marine operations and electrical/control engineering.
Design Verification
Defines environmental and operational design cases against which the SPM system is analysed and verified.
Interface Management
Defines interfaces between tanker, hawser, buoy, swivel, hoses, pipelines, terminal facilities and control systems.
Lifecycle Integrity
Establishes requirements supporting fabrication, installation, commissioning, operation, inspection, maintenance and integrity management.
SPM System Configuration
The design basis should identify the SPM configuration and establish the design philosophy for all major components.
| System | Design Basis Considerations |
|---|---|
| SPM Buoy | Buoy dimensions, displacement, draft, reserve buoyancy, structural configuration, marine loads, equipment arrangement, access and maintenance philosophy. |
| Mooring System | Number and configuration of mooring legs, line properties, pretension, catenary behaviour, anchor loads, environmental loading and stationkeeping performance. |
| Hawser System | Hawser type, length, diameter, strength, stiffness, connection hardware, dynamic loads, fatigue and operational limitations. |
| Swivel System | Fluid passages, mechanical loads, pressure rating, rotational requirements, seals, bearings, emergency shutdown interfaces and maintenance requirements. |
| Marine Hoses | Floating and submarine hose configuration, pressure, temperature, cargo compatibility, flow rate, bend radius, dynamic behaviour and connection arrangements. |
| Subsea Pipeline | Pipeline route, design pressure, wall thickness, stability, seabed interaction, crossings, expansion, free spans, protection and integrity requirements. |
| Tanker Interface | Vessel dimensions, displacement, manifold arrangement, hawser connection, approach, mooring and departure requirements. |
Principal SPM Design Inputs
Site Data
- Geographical coordinates
- Water depth and bathymetry
- Tidal levels and tidal range
- Seabed characteristics
- Geotechnical investigation
- Existing subsea infrastructure
Metocean Data
- Wind speed and direction
- Wave height and period
- Wave directionality
- Current velocity and profile
- Storm conditions
- Extreme and operational criteria
Vessel Data
- Design tanker dimensions
- Deadweight and displacement
- Draft range
- Windage area
- Underwater projected area
- Manifold location and dimensions
Cargo Data
- Cargo type
- Density and viscosity
- Temperature
- Vapour characteristics
- Flow rate
- Transfer pressure
Environmental Design Criteria
Environmental conditions form the basis for calculating SPM motions, mooring loads, hawser loads, buoy loads, pipeline stability and operational limitations.
Wind
Wind criteria should define reference height, averaging period, extreme wind speed, operational wind speed, directionality and appropriate coefficients for the tanker and SPM structure.
Waves
Wave data should define significant wave height, maximum wave height, peak period, spectral characteristics, wave direction and environmental combinations used for operational, storm and survival conditions.
Current
Current criteria should consider surface and subsurface velocity, direction, depth variation and combinations with wind and waves.
Water Depth and Bathymetry
Water depth and seabed geometry affect mooring line configuration, anchor loads, pipeline stability, hose configuration and subsea clearances.
Seabed and Geotechnical Conditions
Geotechnical data should support anchor selection, anchor holding capacity, pipeline stability, seabed interaction and installation engineering.
SPM Mooring Design Basis
The mooring system is the primary stationkeeping system for a conventional CALM-type SPM. The design basis should establish the complete mooring philosophy before detailed mooring analysis.
Mooring Configuration
- Number of mooring legs
- Radial arrangement
- Fairlead locations
- Anchor locations
- Line length
- Water depth
Mooring Components
- Stud-link chain
- Wire rope where applicable
- Synthetic fibre rope where applicable
- Shackles
- Swivels and connectors
- Anchor points and foundations
Design Verification
- Static analysis
- Quasi-static analysis
- Dynamic analysis
- Offset response
- Line tension
- Anchor loads
Integrity
- Corrosion allowance
- Wear
- Fatigue
- Inspection
- Monitoring
- Replacement philosophy
Hawser Design Basis
The tanker-to-buoy hawser is a critical dynamic interface and should be treated as part of the complete SPM stationkeeping and tanker mooring system.
Hawser Parameters
- Hawser material and construction
- Diameter and length
- Minimum breaking strength
- Elastic and dynamic stiffness
- Weight and submerged weight
- End fittings and connection arrangements
- Environmental exposure
- Fatigue and cyclic loading
- Wear and abrasion
- Inspection and replacement criteria
SPM Buoy Structural Design Basis
The buoy structure should be designed for the combined environmental, mooring, hawser, swivel, fluid-transfer and operational loads applicable to the selected SPM configuration.
Structural Design Considerations
- Buoy hull geometry and structural arrangement
- Global strength
- Local structural strength
- Fatigue assessment
- Mooring attachment loads
- Hawser loads
- Swivel loads
- Pipe support loads
- Equipment foundations
- Corrosion protection
- Access and maintenance
- Inspection provisions
Swivel and Fluid Transfer Design Basis
The swivel system provides the rotating fluid-transfer interface between the SPM buoy and the tanker or subsea pipeline system. The design basis should establish mechanical, hydraulic and operational requirements.
| Parameter | Design Basis Requirement |
|---|---|
| Cargo | Product type, density, viscosity, temperature and compatibility. |
| Flow Rate | Normal, minimum, maximum and transient flow conditions. |
| Pressure | Operating pressure, design pressure, surge pressure and shutdown conditions. |
| Temperature | Normal, maximum, minimum and transient thermal conditions. |
| Rotation | Required rotational capability and operating envelope. |
| Sealing | Seal configuration, leakage monitoring and maintenance philosophy. |
| Emergency Shutdown | ESD philosophy, valve closure sequence and pressure surge considerations. |
Marine Floating and Submarine Hose Design Basis
Marine hoses form a critical part of the offshore fluid-transfer system. The design basis should establish the hose arrangement and performance requirements for the full operating envelope.
Floating Hoses
- Hose diameter
- Length and configuration
- Operating pressure
- Design pressure
- Flow rate
- Minimum bend radius
- Buoyancy configuration
- End connections
Submarine Hoses
- Subsea configuration
- Depth and seabed clearance
- Hydrodynamic loading
- External pressure
- Dynamic bending
- Support and buoyancy
- Protection against abrasion
- Inspection requirements
Hose design should also consider cargo compatibility, temperature, static and dynamic loads, cyclic service, electrical continuity where applicable, testing, inspection and replacement requirements.
For projects involving marine cargo hoses, the SPM Design Basis should be coordinated with the detailed hose specification and applicable manufacturer and classification requirements.
Subsea Pipeline Design Basis
The submarine pipeline connecting the SPM system to the offshore or shore-based terminal should be addressed as part of the overall fluid transfer system.
Pipeline Design Inputs
- Design pressure and temperature
- Operating pressure and temperature
- Fluid properties
- Design flow rate
- Pipeline diameter
- Wall thickness
- Material specification
- Corrosion allowance
- External pressure
- Seabed conditions
- Pipeline route
- Free-span requirements
- On-bottom stability
- Pipeline protection
- Installation methodology
Hydraulic and Fluid Transfer Design Basis
Hydraulic design should establish the operating envelope from the receiving or exporting facility through the subsea pipeline, swivel, hoses and tanker manifold.
Steady-State Conditions
- Normal flow
- Maximum flow
- Minimum flow
- Pressure losses
- Static head
- Fluid properties
Transient Conditions
- Pump start
- Pump stop
- Emergency shutdown
- Valve closure
- Pressure surge
- Flow interruption
Offtake Tanker Design Basis
The design basis should define the range of vessels that the SPM facility is intended to accommodate.
| Vessel Parameter | Design Consideration |
|---|---|
| Deadweight | Minimum and maximum design tanker range. |
| Length Overall | Influence on windage, hydrodynamic response and operating envelope. |
| Beam | Wind and current loading and tanker/SPM interaction. |
| Draft | Under-keel clearance, hydrodynamic response and hose geometry. |
| Manifold | Manifold location, flange dimensions, connection arrangement and transfer equipment. |
| Bow Fittings | Bow chain stopper, chocks, fairlead and hawser connection requirements. |
| Loading Operations | Approach, connection, transfer, disconnection and departure criteria. |
Stationkeeping and Dynamic Analysis
Stationkeeping analysis should establish SPM and tanker responses under the defined environmental and operational conditions.
Typical Analysis Cases
- Normal operating condition
- Maximum operational environmental condition
- Extreme environmental condition
- Survival condition
- One-line failure where applicable
- Hawser failure condition
- Thruster-assisted condition where applicable
- Environmental direction combinations
- Different tanker loading conditions
- Different water depths and tidal conditions
Key Outputs
- SPM offsets
- Tanker offsets
- Hawser tensions
- Mooring line tensions
- Anchor loads
- Buoy motions
- Relative motions
- Line utilization
- Component loads
- Operational limitations
Fatigue, Reliability and Integrity Design Basis
Fatigue and lifecycle integrity should be addressed for components subject to cyclic loading, environmental exposure and repeated tanker operations.
- Mooring chains and connectors
- Hawsers and terminations
- Buoy structural members
- Hawser padeyes and structural attachments
- Swivel components
- Pipeline components
- Flexible hose systems
- Buoyancy modules
- Subsea structures
Materials and Corrosion Protection
The SPM Design Basis should define the materials philosophy and corrosion protection requirements for marine and subsea equipment.
- Carbon and low-alloy steels
- Stainless and corrosion-resistant alloys
- Coating systems
- Cathodic protection
- Corrosion allowance
- Marine atmospheric exposure
- Submerged exposure
- Internal corrosion
- Galvanic compatibility
- Inspection and corrosion monitoring
Electrical, Instrumentation and Control Systems
Depending on the SPM configuration, the design basis should define the philosophy for monitoring, instrumentation, communications and emergency systems.
Monitoring
- Mooring loads
- Pressure
- Temperature
- Flow
- Leak detection
- Equipment condition
Control and Safety
- Emergency shutdown
- ESD valves
- Alarm systems
- Fire and gas where applicable
- Communication systems
- Emergency procedures
Marine Safety and Operational Design Basis
SPM design should integrate marine operational safety from the engineering stage rather than treating it solely as an operational procedure.
- Tanker approach and departure
- Weather limitations
- Current limitations
- Maximum allowable tanker offset
- Hawser connection and disconnection
- Marine hose connection
- Emergency release
- Emergency shutdown
- Loss of propulsion
- Loss of steering
- Loss of communication
- Hawser failure
- Mooring line failure
- Pollution prevention
- Personnel safety
Risk, HAZID and Design Safety
The SPM Design Basis should provide suitable technical inputs to the project's risk assessment process.
Hazard Identification
- Collision
- Hawser failure
- Mooring failure
- Hose failure
- Pipeline failure
- Loss of containment
Consequence Considerations
- Oil spill
- Fire
- Explosion
- Environmental damage
- Loss of production
- Personnel exposure
Applicable SPM Design Standards and Guidelines
The governing standards should be established in the project Design Basis and confirmed against applicable contractual, classification, regulatory, operator and site-specific requirements. The latest applicable editions should be verified at project commencement.
Typical SPM Engineering Deliverables
Design Basis Documents
- SPM Design Basis
- Metocean Design Criteria
- Environmental Design Criteria
- Design Philosophy
- Operational Philosophy
Mooring Engineering
- Mooring Arrangement
- Mooring Analysis
- Hawser Analysis
- Anchor Load Assessment
- Stationkeeping Assessment
Structural Engineering
- Buoy Structural Design
- Padeye Assessment
- Foundation Assessment
- Fatigue Assessment
- Corrosion Philosophy
Fluid Transfer
- Pipeline Design Basis
- Hose Specification
- Hydraulic Analysis
- Pressure Surge Assessment
- ESD Philosophy
SPM Inspection, Verification and Integrity Support
The engineering design basis should establish requirements that can be carried forward into inspection, verification and lifecycle integrity activities after installation and commissioning.
Structural Inspection
- Buoy structural condition
- Padeyes and attachments
- Corrosion and coating condition
- Welded structural areas
- Equipment foundations
Mooring Inspection
- Mooring chains
- Connectors and shackles
- Anchor interfaces
- Wear and corrosion
- Line condition and monitoring
Hawser and Hose Inspection
- Hawser condition
- End terminations
- Marine hose condition
- Connections
- Leakage and damage indicators
Technical Verification
- Design documentation review
- Inspection records
- Testing documentation
- Certification review
- Integrity recommendations
SPM Equipment Procurement and Technical Specification
The SPM Design Basis can be used as a controlled technical reference for procurement specifications and vendor technical evaluation. Procurement requirements should remain consistent with the approved engineering design basis and project operating envelope.
| Procurement Area | Typical Technical Requirements |
|---|---|
| SPM Buoy | Structural requirements, materials, buoyancy, foundations, equipment interfaces, corrosion protection and certification. |
| Mooring Equipment | Chain, connectors, shackles, anchors, design loads, breaking strength, fatigue requirements and testing. |
| Hawsers | Construction, dimensions, minimum breaking strength, stiffness, terminations, testing and inspection criteria. |
| Marine Hoses | Diameter, pressure rating, cargo compatibility, temperature range, bend radius, configuration, connections and testing. |
| Swivel Equipment | Pressure, flow, rotation, sealing, materials, maintenance, testing and emergency shutdown interfaces. |
| Instrumentation | Measurement range, accuracy, environmental rating, communications, alarms and monitoring requirements. |
Engineering Evidence and Technical Resources
An effective SPM Design Basis should be supported by controlled technical evidence. The evidence should demonstrate that the design inputs, assumptions, calculations, equipment selections and operating limitations are traceable.
Site and Metocean Evidence
Bathymetry, water depth, geotechnical information, wind, wave, current, tide and environmental studies.
Vessel Information
Tanker particulars, loading conditions, manifold arrangements, bow fittings, windage data and vessel operating limitations.
Engineering Analysis
Mooring analysis, stationkeeping assessment, structural calculations, hydraulic analysis, pipeline assessment and fatigue evaluation.
Equipment Documentation
Vendor data sheets, material certificates, testing records, inspection documentation, certification and equipment manuals.
Operational Evidence
Operating limits, tanker approach criteria, transfer procedures, emergency procedures, ESD philosophy and weather limitations.
Standards and Regulatory References
Applicable class rules, regulatory requirements, international standards, OCIMF guidance, API practices and project specifications.
Independent SPM Design Basis Review
An independent technical review can determine whether an existing SPM Design Basis is complete, internally consistent and appropriate for the intended offshore application.
Review Scope
- Design assumptions
- Environmental criteria
- Vessel design envelope
- Mooring philosophy
- Hawser requirements
- Buoy structural criteria
- Swivel requirements
- Pipeline design inputs
- Marine hose requirements
- Hydraulic criteria
- Operational limits
- Failure cases
- Fatigue requirements
- Inspection and integrity philosophy
- Standards and classification requirements
- Engineering interfaces
PAMS SPM Technical Consultancy
PAMS Pacific Admiralty Maritime Services provides independent marine and offshore technical consultancy for SPM, FPSO, FSO and offshore fluid-transfer engineering projects.
Technical support can cover SPM design-basis development, independent engineering review, marine surveying, offshore equipment assessment, marine hose and fluid-transfer systems, project technical documentation and verification of engineering interfaces.
The consultancy approach is focused on independent technical assessment and engineering support rather than acting as a ship agency or cargo-handling operator.
For broader SPM technical consultancy, see: Single Point Mooring (SPM) Technical Consultancy .
For marine cargo hose engineering, see: Marine Cargo Hoses for SPM, FPSO and Offshore Oil Transfer Systems .
SPM Design Basis Frequently Asked Questions
What is an SPM Design Basis?
An SPM Design Basis defines the technical, environmental, operational, structural, mechanical, marine and safety criteria used to develop and verify a Single Point Mooring system.
What SPM systems can be covered by a design basis?
The design basis can cover CALM buoy systems and other applicable single point mooring arrangements, including buoy structures, mooring lines, anchors, hawsers, swivel systems, pipelines, marine hoses and associated equipment.
What environmental data is required?
Typical inputs include wind, waves, current, water depth, bathymetry, seabed conditions, tides, storm conditions, environmental return periods and vessel operating conditions.
Does the design basis include hawser design?
Yes. Hawser configuration, materials, strength, stiffness, dynamic behaviour, connection arrangements, fatigue, inspection and operational limitations can be defined.
Does it include marine floating and submarine hoses?
Yes. Hose diameter, pressure, temperature, cargo compatibility, flow rate, configuration, bending behaviour, minimum bend radius, connections, testing and inspection requirements can form part of the design basis.
Which standards apply to SPM design?
The applicable standards depend on the project. They may include ISO offshore standards, API recommended practices, OCIMF guidance, classification society rules, regulatory requirements and project-specific specifications.
Can an existing SPM Design Basis be independently reviewed?
Yes. An independent review can assess environmental criteria, design assumptions, mooring philosophy, hawser requirements, fluid-transfer systems, engineering interfaces, standards compliance and technical completeness.
Can the SPM Design Basis support equipment procurement?
Yes. The approved design basis can provide technical inputs for equipment specifications, vendor data requirements, technical bid evaluation, inspection requirements, testing and certification, subject to the project's procurement process.
What evidence should support an SPM Design Basis?
Supporting evidence may include metocean and geotechnical data, vessel particulars, engineering calculations, mooring studies, hydraulic assessments, structural assessments, vendor documentation, certification, testing records and applicable standards.
Engineering Reference Notice
This page provides a technical engineering reference framework for SPM Design Basis development and review. It is not a substitute for project-specific engineering calculations, metocean studies, geotechnical investigations, class approval, regulatory approval, manufacturer certification or detailed engineering. The governing standards, editions, safety factors, environmental return periods and acceptance criteria shall be confirmed for each individual project.
Independent SPM Engineering Support
PAMS Pacific Admiralty Maritime Services provides independent technical consultancy for Single Point Mooring systems, offshore transfer systems, marine hoses, mooring arrangements, technical reviews and project engineering support.
SPM Technical Consultancy Marine Cargo Hoses