Swivel Forerunner: Three vs. Five- Which to Choose?
In anchor chain systems, the Marine Swivel Forerunner (also known as a Swivel Group) is a crucial component connecting the anchor and anchor chain. At SMEOCEAN, we specialize in supplying high-quality swivel forerunners for marine and offshore applications. As discussed in our previous article, this design with special swivels effectively prevents excessive twisting of the anchor chain, improving operational smoothness.
Swivel Forerunners are composed of multiple chain links. Depending on the configuration, they are mainly divided into three-ring groups and five-ring groups. How should you choose between them for different application scenarios? Let's discuss that today.
I. Structure of Two Configurations
The structure of the five-ring assembly is: E + EL + SW + EL + C
- E (End Link): Connects to ES (End Shackle), which in turn connects to the anchor shackle, achieving a diameter transition from 1.2d to 1.4d.
- EL (Enlarged Link): Two links of different sizes. The end closer to the anchor chain matches C, and the end closer to the swivel matches SW.
- SW (Swivel): The core anti-torsion component.
- C (Standard Link): Connects to the subsequent anchor chain and is the starting point of the anchor chain.
The three-ring assembly has two common variations:
- Standard Type: E + SW + EL + C
- Simplified Type: E + SW + E + C (using the end link instead of the enlarged link)
In the three-ring assembly, E connects to JS or ES (depending on the configuration), and C also connects to the subsequent anchor chain.
II. Why does the five-ring configuration have one more EL than the three-ring configuration?
The five-ring configuration achieves two diameter transitions: E(1.2d) → EL(1.1d) → C(1.0d), resulting in smoother load transfer and more uniform stress distribution.
The three-ring configuration only has one transition (or a simplified version), resulting in a more compact structure and shorter overall length.
III. Comparison of the two configurations
IV. Where are they used?
Three-ring swivel forerunner are suitable for:
- Small to medium-sized vessels
- Yachts, sailboats
- Scenarios with limited space in the anchor chain canister
- Cost-sensitive projects
- Retrofitting of older vessels or replacement of spare parts (maintaining consistency with the original configuration)
Five-ring swivel forerunner are suitable for:
- Large merchant ships (bulk carriers, tankers, container ships)
- VLCCs, offshore platforms
- Designs requiring two smooth transitions
- Explicit requirements from shipowner specifications
It is important to note that five-ring swivel forerunner are not exclusive to large vessels. Smaller chain diameters (e.g., 22mm, 26mm) can also be fitted with five-ring swivel chains. Selection depends primarily on customer specifications and design requirements, not chain diameter.
V. Materials and Certifications
All components of the Swivel Forerunner are manufactured using high-strength forged alloy steel, with the same material grade as the anchor chain (Grade 2 / Grade 3 / R3 / R4, etc.).
The swivel itself requires separate inspection and the provision of classification society certificates (DNV, ABS, LR, CCS, etc.), along with material certification. Surface treatment options include black paint or hot-dip galvanizing.
VI. Procurement Confirmation Checklist
When providing Swivel Forerunners to customers, it is recommended to confirm the following information:
1. Anchor chain diameter (d): Determines the dimensions of all components.
2. Configuration options: Five-ring assembly / Three-ring assembly (standard/simplified)
3. Material grade: Grade 2 / Grade 3
4. Classification society certification: DNV, ABS, LR, CCS, etc.
5. Surface treatment: Original color, black paint, hot-dip galvanizing
Summary
The five-ring assembly (E+EL+SW+EL+C) has an extra EL, resulting in a smoother transition, suitable for large vessels or scenarios with strict regulations; the three-ring assembly has a compact structure and lower cost, suitable for small and medium-sized vessels and scenarios with limited space. Selection depends on customer specifications and design requirements, not chain diameter.
For any questions regarding other anchor chain accessories, please feel free to contact us!
SMEOCEAN – Marine & Aquaculture Mooring Solutions
More Links:
Anchor Chain Accessories: A Complete Guide
Why Swivel Forerunner is a Transformative Design？