SPM Design Basis – Single Point Mooring Technical Engineering
Engineering design basis for Single Point Mooring systems covering metocean conditions, tanker compatibility, mooring loads, marine systems, cargo transfer, structural integrity, operability and technical design requirements.
What Is an SPM Design Basis?
A Single Point Mooring (SPM) system is a critical offshore marine infrastructure asset used to moor tankers and transfer liquid cargo between a vessel and an offshore or subsea pipeline system. The SPM arrangement must remain capable of safely accommodating environmental loads, tanker motions, mooring forces and cargo transfer requirements throughout its defined operating envelope.
The SPM Design Basis establishes the technical assumptions, design criteria, operating conditions, environmental parameters, vessel characteristics, applicable standards and engineering requirements governing the development and verification of the SPM system.
A properly developed design basis provides the engineering reference against which the buoy, mooring system, subsea pipeline connection, marine hoses, hawser arrangement, tanker interface and associated equipment can be designed, analysed and subsequently verified.
PAMS SPM Design Basis Methodology
Project Definition
Establishment of project objectives, operating philosophy, cargo characteristics, transfer rates, offshore location, tanker requirements and overall SPM configuration.
Environmental Design Conditions
Definition of metocean parameters including wind, waves, currents, water depth and relevant environmental design cases affecting the SPM and tanker.
Vessel Interface
Assessment of tanker dimensions, displacement, draft, freeboard, bow configuration, manifold arrangement and operational limitations relevant to the SPM interface.
Mooring & Structural Design
Definition of design requirements for hawser, chain, anchors, buoy structure, swivel arrangement and associated load-bearing components.
Cargo Transfer System
Establishment of technical requirements for marine hoses, piping, swivels, valves, emergency release arrangements and cargo transfer performance.
Verification & Operability
Definition of design verification requirements, operational limits, inspection requirements, maintenance philosophy and technical acceptance criteria.
SPM Design Basis – Principal Engineering Inputs
The SPM design depends on a controlled set of technical inputs. These inputs should be established at the beginning of the engineering process and maintained under project configuration control.
Offshore Location
- Geographic location and offshore coordinates.
- Water depth and seabed characteristics.
- Nearshore or offshore operating environment.
- Bathymetric information.
- Subsea pipeline route and connection requirements.
Metocean Conditions
- Wind speed and direction.
- Significant wave height and associated wave periods.
- Current speed and direction.
- Wave spectrum and directional conditions.
- Extreme and operating environmental conditions.
- Design return periods where applicable.
Tanker Design Envelope
- Minimum and maximum tanker dimensions.
- Deadweight and displacement.
- Length overall and beam.
- Draft and freeboard.
- Bow configuration and mooring arrangement.
- Cargo manifold location and dimensions.
- Loading and unloading operating conditions.
Cargo Characteristics
- Cargo type and product properties.
- Density and viscosity.
- Temperature range.
- Cargo transfer rate.
- Maximum operating pressure.
- Compatibility requirements for hoses and seals.
SPM System Configuration
The design basis should define the complete SPM arrangement and the interfaces between its principal components. The final configuration depends on the project location, environmental conditions, cargo transfer requirements, vessel envelope and applicable engineering criteria.
| SPM Component | Principal Design Considerations |
|---|---|
| SPM Buoy | Buoy dimensions, displacement, structural strength, stability, equipment arrangement, access and connection interfaces. |
| Mooring System | Chain configuration, anchors, hawser arrangement, pretension, environmental loads, fatigue and ultimate strength requirements. |
| Swivel System | Fluid transfer capacity, rotational movement, pressure rating, sealing arrangement, structural loads and maintenance requirements. |
| Marine Hoses | Hose type, diameter, length, pressure rating, bending behaviour, buoyancy, configuration, fatigue and compatibility with transferred cargo. |
| Hawser System | Hawser construction, breaking strength, fatigue, connection arrangement, tanker compatibility and environmental loading. |
| Subsea Pipeline | Pipeline route, design pressure, thermal and hydraulic requirements, free spans, stability and connection to the SPM system. |
| Cargo Transfer System | Flow rate, pressure, valves, emergency shutdown, isolation and operational control requirements. |
Environmental Design Criteria
Environmental loading is one of the principal inputs to SPM design. The design basis should establish both normal operating conditions and appropriate extreme environmental conditions for the relevant design cases.
Wind Loading
Wind speed, direction, exposure and projected areas of the tanker and SPM structure are considered when establishing environmental loads and vessel response.
Wave Loading
Wave height, period, direction, spectrum and associated environmental combinations are established for operating and design conditions.
Current Loading
Current velocity and direction influence tanker drift, hawser loading, mooring loads, hose behaviour and overall SPM response.
Combined Environmental Conditions
Wind, wave and current combinations are evaluated according to the applicable design criteria and environmental operating envelope.
Mooring System Design Basis
The mooring system provides the primary station-keeping function of the SPM and transfers environmental loads between the buoy, mooring components and seabed foundation system.
Catenary Configuration
Mooring geometry, line length, weight, seabed contact and pretension characteristics are established according to water depth and environmental loading.
Anchor System
Anchor capacity and seabed interaction are assessed against the design loads and geotechnical conditions applicable to the installation location.
Hawser Loads
Hawser loads are considered for the defined tanker envelope, environmental conditions, vessel motions and operating configuration.
Fatigue Assessment
Fatigue considerations are established for components exposed to repeated cyclic loading during the intended service life.
SPM Structural Design Considerations
Structural design of the SPM should address the principal load cases generated by environmental conditions, mooring loads, hose reactions, tanker interaction, cargo system loads and equipment arrangements.
- Global structural strength of the buoy.
- Local structural strength at equipment and connection points.
- Mooring and hawser attachment loads.
- Swivel and piping support loads.
- Marine hose connection and reaction loads.
- Access platforms and maintenance structures.
- Fatigue-sensitive structural details.
- Corrosion allowance and structural degradation considerations.
- Lifting and installation loads.
- Accidental and abnormal load cases where applicable.
Marine Cargo Hose Design Basis
Marine cargo hoses form a critical part of the SPM cargo transfer interface. Their design must account for pressure, flow, movement, bending, buoyancy, environmental exposure and repeated operational loading.
Hose Diameter & Flow
Internal diameter and hose configuration should support the specified cargo transfer rate while maintaining acceptable pressure loss and operational performance.
Pressure Rating
Hose pressure rating should be compatible with the cargo system design pressure, operating pressure and applicable pressure surge conditions.
Bending & Motion
Hose configuration should accommodate vessel and buoy movement while maintaining acceptable bending radius and mechanical integrity.
Cargo Compatibility
Materials, lining, reinforcement and sealing arrangements should be compatible with the transferred cargo and defined temperature range.
Swivel & Cargo Transfer System
The swivel and associated cargo piping provide the fluid transfer path between the offshore pipeline system and the tanker interface while allowing the SPM system to rotate relative to the mooring arrangement.
| Design Area | Engineering Considerations |
|---|---|
| Flow Capacity | Required cargo transfer rate, pressure loss and hydraulic operating envelope. |
| Pressure | Design pressure, operating pressure, transient conditions and pressure protection. |
| Rotation | Continuous or defined rotational movement according to the SPM configuration. |
| Sealing | Sealing performance, material compatibility and maintainability. |
| Piping | Structural support, flexibility, stress and connection requirements. |
| Emergency Isolation | Emergency shutdown, isolation and cargo containment requirements. |
Tanker Compatibility Assessment
The SPM Design Basis should define the tanker population or design envelope that the facility is intended to accommodate. Compatibility should consider both the physical interface and the environmental operating limitations of the tanker-SPM system.
Vessel Dimensions
Length, beam, draft, displacement and freeboard are considered when defining the tanker operating envelope.
Bow & Mooring Arrangement
Bow configuration, chain stopper or hawser connection arrangement and associated tanker interface requirements.
Cargo Manifold
Manifold position, flange arrangement, hose connection, transfer rate and safe operating configuration.
Vessel Motions
Vessel response and relative movement affecting hawser loads, hose movement, cargo transfer and operating limits.
SPM Design Load Cases
The design basis should establish the load cases required for structural, mooring, hose and system verification. Load cases are project-specific and should be developed from the approved environmental and operational assumptions.
| Load Case | Typical Engineering Purpose |
|---|---|
| Normal Operating Condition | Assessment of normal cargo transfer and routine tanker mooring conditions. |
| Maximum Operating Condition | Verification of the defined upper operating envelope. |
| Extreme Environmental Condition | Assessment of high environmental loading according to the applicable design criteria. |
| Combined Wind / Wave / Current | Assessment of combined environmental loading and vessel response. |
| Hose Load Case | Assessment of marine hose movement, bending and connection loads. |
| Mooring Failure Case | Assessment of relevant abnormal or damaged mooring configurations where required by the design criteria. |
SPM Operability & Operating Envelope
A technically sound SPM design basis should establish the relationship between environmental conditions and operational limitations. The system should have clearly defined criteria for safe tanker approach, connection, cargo transfer, disconnection and shutdown.
Approach & Connection
Environmental and vessel conditions applicable to tanker approach, hawser connection and cargo hose connection.
Cargo Transfer
Defined environmental and operational envelope for maintaining safe cargo transfer.
Disconnection
Technical requirements and environmental limitations associated with cargo hose and tanker disconnection.
Emergency Shutdown
Isolation, emergency shutdown and cargo containment principles applicable to abnormal operating conditions.
SPM Design Basis Documentation
The design basis should provide a controlled engineering reference for subsequent design calculations, specifications, drawings and verification activities.
Project Design Criteria
Overall project assumptions, design philosophy, operating envelope and applicable engineering requirements.
Metocean Design Basis
Environmental parameters, operating conditions, extreme events and relevant return-period data.
Vessel Design Envelope
Tanker characteristics, vessel operating conditions, mooring interface and cargo manifold requirements.
Cargo Transfer Basis
Cargo properties, flow rates, pressure requirements, hose configuration and transfer-system design criteria.
Mooring Design Basis
Mooring configuration, environmental loads, line properties, anchor requirements and design verification criteria.
Structural Design Basis
Structural load cases, material requirements, corrosion allowances, fatigue criteria and verification requirements.
Technical Verification & Engineering Review
Once the design basis is established, the engineering development should be verified against the approved technical assumptions. PAMS technical review can focus on consistency between design criteria, system configuration, calculations, equipment specifications and operational requirements.
Design Basis Verification
Review of technical assumptions, project criteria and environmental inputs for consistency and traceability.
Interface Review
Assessment of interfaces between buoy, mooring, swivel, hoses, tanker, pipeline and cargo systems.
Technical Specification Review
Review of equipment and component specifications against the established design basis.
Engineering Consistency
Cross-check of design assumptions against drawings, calculations, equipment data and operational requirements.
Technical Findings
Identification of inconsistencies, missing information, technical risks and areas requiring clarification or further engineering.
SPM Design Basis – Applicable Standards & References
The applicable standards and engineering references should be established according to the project configuration, jurisdiction, classification requirements, cargo type and contractual design criteria.
SPM Design Basis – Technical Deliverables
Design Basis Document
Structured technical document defining project assumptions, environmental criteria, vessel envelope, design philosophy and engineering requirements.
Technical Data Register
Controlled register identifying principal project inputs, technical data sources and outstanding information.
Design Criteria Matrix
Consolidated technical matrix identifying applicable design criteria, standards and verification requirements.
Interface Requirements
Definition of principal interfaces between tanker, buoy, mooring, swivel, hoses, pipeline and cargo transfer systems.
Independent SPM Technical Consultancy
Independent Engineering Review
PAMS provides independent technical consultancy for SPM, offshore loading systems and marine engineering projects, focusing on technical integrity and engineering consistency.
FPSO & Offshore Engineering
Technical experience covering FPSO, SPM, marine cargo transfer systems, floating hoses and offshore engineering interfaces.
Technical Risk Identification
Identification of technical inconsistencies, incomplete design assumptions, interface risks and areas requiring further engineering verification.
Decision-Ready Technical Reporting
Findings are presented in a structured technical format to support engineering decisions, project development and technical review.
About the Technical Author
Technical Content Review
Last Technical Review
July 2026
Review Frequency
Technical content is reviewed periodically to reflect relevant international maritime standards, offshore engineering practices and applicable technical guidance.
SPM Design Basis FAQ
What is an SPM Design Basis?
An SPM Design Basis is the controlled technical document that establishes the environmental conditions, tanker envelope, cargo requirements, mooring criteria, structural requirements and engineering assumptions used for development of a Single Point Mooring system.
Why is an SPM Design Basis important?
It provides a common engineering reference for detailed design, calculations, equipment specifications, verification and technical review. It also helps maintain consistency between the different systems forming the SPM installation.
What information is required for an SPM Design Basis?
Typical inputs include offshore location, water depth, metocean conditions, tanker characteristics, cargo properties, transfer rate, pressure requirements, mooring configuration, hose arrangement and applicable project standards.
Does the SPM Design Basis include metocean conditions?
Yes. Wind, waves, currents, water depth and relevant operating and extreme environmental conditions form important inputs to the SPM design and should be defined within the project engineering basis.
Are marine hoses included in the SPM Design Basis?
Yes. The design basis can establish requirements for hose diameter, flow rate, pressure rating, cargo compatibility, configuration, bending behaviour, buoyancy and operational movement.
Does the design basis cover tanker compatibility?
Yes. Tanker dimensions, displacement, draft, freeboard, bow configuration, mooring interface, cargo manifold arrangement and vessel operating conditions can form part of the defined tanker design envelope.
Can PAMS review an existing SPM Design Basis?
Yes. PAMS can provide independent technical review of an existing SPM Design Basis, including review of engineering assumptions, environmental inputs, vessel criteria, interfaces, cargo transfer requirements and technical consistency.
Does a design basis replace detailed engineering?
No. The Design Basis establishes the engineering criteria and assumptions used by detailed engineering. Detailed calculations, structural analysis, mooring analysis, hydraulic analysis and equipment design remain separate engineering activities as required by the project.
Engineering Reference Notice
This article provides general technical information concerning the development and review of an SPM Design Basis. Actual design criteria depend on the project location, metocean data, water depth, tanker envelope, cargo characteristics, operating philosophy, classification requirements, applicable standards and client specifications. Detailed engineering calculations and verification should be performed by appropriately qualified engineering specialists in accordance with the approved project design basis and applicable requirements.