Marine

Marine

BTI builds balancing and measurement systems for marine propulsion and auxiliaries — propellers, propeller and intermediate shafts, pump impellers, and turbochargers. Marine work sits at both ends of BTI’s range: very large, slow rotors and small, fast ones on the same vessel.

What BTI Balances in Marine

BTI balancing machines are built on four platforms — VNR (vertical non-rotator), H (horizontal cradle), VR (vertical rotator) and P (platform suspension) — plus tool holder balancers, spinners and test stands. The platform follows the part geometry and how it has to be held; the correction method follows the material and where there is room to add or remove mass.

How a Machine Gets Sized

A BTI machine designation names a platform and a class. A P-5 is the platform suspension base, class 5. The number is a class, not a part weight limit — it describes the size and load envelope of the base.

Sizing works from the tooling and the part together, not the part alone. Tooling is not specified until the part prints are reviewed and the fixture is concepted, and the heavier the tooling-plus-part assembly is relative to the class, the less repeatable the measurement becomes. A shop that needs one machine to cover a wide range of parts, and does not need tight repeatability, can run a much broader weight range on a given class than a production program can.

Tell BTI the part weight and BTI will name a class the same day. See BTI machine platforms for the full platform and class architecture.

Balance Grade and Tolerance

Balance tolerances are set by ISO 21940-11, which superseded ISO 1940-1. The standard assigns a balance quality grade G, and the permissible residual specific unbalance follows from that grade and the service speed:

e_per = (G × 60) ÷ (2π × n)

where e_per is permissible residual specific unbalance in g·mm/kg, G is the balance quality grade in mm/s, and n is the service speed in rev/min. Permissible residual unbalance is then U = e_per × m, divided across the correction planes.

Large marine diesel crankshaft drives fall into considerably coarser grades, which the standard treats separately by engine type and mounting.

Work out a specific tolerance with the ISO balance tolerance calculator.

Moment Balancing for Propellers and Blades

A propeller blade is matched by moment, not only by mass. Two blades of identical weight still produce a couple if their mass is distributed differently along the radius, so blade sets are matched on the moment they produce about the hub axis before assembly. BTI builds moment balancers for propellers and rotor blades — the same equipment class used for helicopter blades.

Correction Methods

Standards

BTI certifies machines to ISO 21940, SAE International balancing specifications, and DIN specifications. Where a program carries a measurement system capability requirement, BTI evaluates the part and the process first, then confirms what is achievable and commits to it in the machine specification.

Frequently Asked Questions

What is moment balancing and when is it required?

Moment balancing matches components by the moment their mass produces about an axis, rather than by weight alone. It is used where several identical parts assemble into one rotor, propeller and rotor blade sets in particular.

Can BTI handle large-diameter marine rotors?

BTI has engineered solutions for parts from under a pound to well over 200,000 lb. Sizing follows the tooling-plus-part weight and the part print.

Does BTI rebuild or retrofit existing balancing machines?

Yes, including machines built by other manufacturers. See BTI rebuilds and retrofits, competitor rebuilds and retrofits, and PC upgrades.

How are BTI lead times quoted?

Lead times are quoted in weeks at the time of quotation. They move with current backlog, so BTI confirms the schedule for a specific machine as part of the quote rather than publishing a fixed figure.

What information does BTI need to quote?

The part print, the part weight, the service speed, the balance tolerance if one is specified, and the required production rate.

Related applications: turbines, jet engines, blades and propellers, pumps, fans, impellers and blowers, driveshafts, turbochargers and superchargers.

Browse BTI balancing machines or request a quote.