The nozzle segment forms the inlet and outlet geometry of a bow or azimuth thruster tunnel, shaping the flow into and out of the propeller to keep thrust efficient and cavitation low. Moreover, Ningbo Ruican casts and machines these segments to print for thruster OEMs, newbuild yards and repair facilities. Casting the segment as a controlled-thickness body with an accurate internal profile solves the two problems yards see most: fabricated segments that distort during welding, and mismatched tunnel ends that generate cavitation, noise and lost bollard pull.
Specifications
| Item | Specification |
|---|---|
| Casting process | Silica sol lost wax investment casting; water glass process for large diameter tunnel segments |
| Material options | Nickel aluminium bronze C95800, aluminium bronze C95500, duplex 2205 (ASTM A995 4A), super duplex 2507, CF8M / 316L stainless |
| Dimensional tolerance (ISO 8062-3 CT grade) | CT6-CT7 as-cast; CT5 on machined tunnel bore, joint faces and bolting circle |
| Machining | 5-axis and horizontal boring: internal tunnel profile, joint faces, bolting circle, weld preparation bevels |
| Surface finish (Ra) | Ra 3.2-6.3 um on internal flow surface; Ra 1.6 um on joint faces; optional polish to Ra 0.8 um |
| Corrosion protection | As-cast bronze finish, or pickle and passivate to ASTM A967, or blast and epoxy scheme for sea chest duty |
| Weight range | 25-420 kg per segment |
| Typical lead time | 6-8 weeks including tooling and first-article approval; 4-5 weeks for repeat orders |
Scope and options
Key features
- Internal flow profile cast near net shape, then CNC verified against the tunnel diameter and radius layout.
- Machined joint faces and bolting circle, so segments align on the hull without shimming or reaming.
- Consistent wall thickness to control distortion during welding into the tunnel.
- Moreover, Weld preparation bevels machined to your WPS, ready for the yard to weld in.
- Nickel aluminium bronze for cavitation, erosion and biofouling resistance in the tunnel bore.
- Generally, Segments cast in matched sets with sequential identification for multi-piece tunnels.
Applications
- Bow thruster tunnels on ferry, ropax and passenger vessels.
- Azimuth thruster tunnels on offshore support and construction vessels.
- Dynamic positioning thruster arrangements on cable laying and survey ships.
- Thruster tunnel renewal and repair during dry-docking and class surveys.
- Additionally, Thruster OEM build packages and sub-assembly supply.
- Tunnel thruster installations on dredgers and heavy lift vessels.
Images
Quality & compliance
Every segment ships with EN 10204 3.1 material certification, mechanical test results and a dimensional report on the tunnel profile, joint faces and bolting circle. Dye penetrant inspection of the flow surface and machined faces is standard on request, with ultrasonic testing on thick sections and radiography on the joint areas. Also, weld preparation bevels are verified against your WPS, and weld maps plus heat treatment records are included where applicable. Ningbo Ruican also supplies supplementary test material for your weld procedure qualification. Classification-society type approval of the finished thruster installation remains the customer’s responsibility and that of their classification society; we supply the certified component, not the class certificate.
FAQ
How accurate is the internal flow profile after casting?
The internal profile is cast near net shape using simulation-verified rigging, then machined or ground and verified on a CMM or by 3D scanning against the tunnel model. We report deviation across the flow surface and confirm the bore diameter and radius layout on the dimensional report, so your fitting team knows the actual geometry before the segment reaches the hull.
Do you machine the weld preparation bevels?
Yes. Bevel angle, root face and root gap are machined to your weld procedure specification, and we verify them on the dimensional report. Machined bevels give the yard a consistent root and reduce weld volume, which in turn lowers distortion when the segment is welded into the tunnel.
Why is nickel aluminium bronze often specified for thruster tunnels?
Nickel aluminium bronze C95800 combines high strength with strong resistance to cavitation erosion, impingement attack and seawater corrosion, and its surface resists biofouling better than many steels. It is also galvanically compatible with common nickel aluminium bronze propeller and tunnel hardware, making it the standard choice in many tunnel designs.
Can you supply a single replacement segment for a repair?
Additionally, yes, and repair orders are common. Send the drawing, the tunnel diameter and the segment identification, plus a photograph of the removed unit if available. We match the original geometry and bevel preparation, and machine the joint faces so the new segment fits the remaining tunnel without modification.
How do you prevent distortion of the segment during casting?
Distortion is managed before the metal is poured. We run solidification and stress simulation on the rigging, set uniform wall thickness, and stress relieve the casting before machining. Rough machining is followed by a finishing pass, and joint faces are cut last so the finished geometry is not released by earlier material removal.
Can you support our weld procedure qualification?
Yes. Ningbo Ruican can supply material test reports compatible with your WPS, additional test coupons from the same heat where the order allows, and dimensional records for the bevel preparation. Your welding engineer and surveyor then complete the qualification; we provide the certified material and evidence, not the approval itself.
CTA
Send your thruster tunnel nozzle segment drawing, tunnel diameter and material specification to Wendy She at sales@cnsandcasting.com, or message her on WhatsApp at +86-13777124360, for a quotation from Ningbo Ruican within two working days.
