Industries / Marine and offshore
Large Part Machining for Marine and Offshore
Alignment over the length of a shaft line, and a lot of work that cannot leave the vessel.
The defining problem in marine machining is alignment over distance. A propeller shaft line runs through bearings that can be many metres apart, and the bores have to share an axis. That is not a tolerance a machine table can deliver, so the work is done with a supported bar passing through both bearings, aligned to the vessel rather than to a machine.
The second constraint is that the part often cannot come out. A stern tube is part of the hull. A rudder carrier is welded into the structure. This is why portable and in-situ machining is normal here rather than exceptional, and why a shop that only quotes table work is only quoting half the sector.
Parts that come through this route
Not an exhaustive list. It is here so you can tell whether your part behaves like these, which is what decides the machine and the sequence.
- Stern tubes and bearing housingsLine bored in the hull, coaxial by construction because one bar cuts both ends.
- Rudder stocks and carriersBore alignment to the shaft line, usually in situ.
- Winch and windlass drumsLarge diameter turning, grooving and end flange work on a vertical lathe.
- Thruster and tunnel housingsLarge bores and flange faces in welded structures.
- Deck structures and foundationsMachined mounting pads and bolt patterns on heavy weldments.
- Chain stoppers and fairleadsWear surfaces and pin bores in cast or fabricated bodies.
Where this work usually goes
Machine classes that suit the sector. Full typical envelopes and part weights are on the machine class reference.
Portable line boring
The core of the sector. A bar through both bearings, driven by a portable motor, aligned to the vessel.
Heavy horizontal lathe
Shafts and long cylindrical parts that come ashore to be machined between centres.
Vertical turning lathe
Drums, flanges and rings where diameter beats length.
Materials
EH36 and similar hull grades, S355 for structures, 316 and duplex stainless where corrosion rules, bronze bearing liners bored in place after the housing is finished, and forged carbon or alloy steel for shafting.
Paperwork this sector expects
- Class society surveyMany of these parts are surveyed by a classification society, so the inspection plan and the witness points have to be agreed before work starts.
- Welding qualificationStructural welding to a qualified procedure, with the inspection carried out before machining covers it.
- Material certificatesTraceability on hull grade and shafting material.
- Alignment recordsFor shaft lines, the as-found and as-left alignment, recorded with the method used.
What to put in the RFQ
On top of the envelope, finished weight, material and tolerance that every heavy part needs, this sector wants these as well.
- Whether the machining happens in the hull or ashore in a shop
- For in-hull work, access, working hours, power available and any permit requirements
- The bearing spacing and the alignment tolerance between bores
- Class society involvement and which witness points apply
- Whether bronze liners are supplied separately and bored in place
- The docking or outage window, because it usually governs everything else
Have a part like these?
Send the envelope, the finished weight and the sector. We match it with shops that already work to this paperwork. Reply within 24 business hours.