NMX‑MPS‑30 / Rev 00 / propulsion shafting / stern gear 2026 · Product Page

NMX-MPS-30 · ENGINEERED TO ORDER — MARINE PROPULSION SHAFTING & STERN GEAR

Turn the propeller. Push the ship.

Name: Marine Propulsion Shafting & Stern Gear System
Brand: Neometrix

The ship’s driveline. Between the gearbox and the propeller runs a machine that does two jobs at once: it carries torque out to the propeller, and it takes the propeller’s thrust back into the hull — because the propeller pushes the ship, not itself, and that push arrives through the thrust block. Along the way: line and tail shafts on plummer bearings, the stern tube where the shaft leaves the hull, and the seals that keep the sea out and the oil in. It all stands on alignment — bored, sighted and set to computed offsets on a hull that flexes, to the classification rules, before and after launch. We engineer, machine, assemble, install and align it; the propeller, castings, gearbox and thruster units are bought in. It drives the ship — the steering gear turns it. Engineered to order — no specific delivered ship is claimed.

Enquire — propulsion shafting Capability sheet (PDF)

Illustrative image, not a delivered installation — a ship's propulsion shaft line in a shaft tunnel: a long heavy horizontal steel shaft supported on plummer bearings bolted to steel foundations, with a large bolted flange coupling joining two shaft sections, no text, no insignia and no people

Fig · 01 A propulsion shaft line — heavy shafting on plummer bearings, joined by bolted flange couplings, running aft to the stern tube — illustrative, not a delivered installation

Transmits

torque + thrustengine to propeller, thrust to hull

Shaft line

line + tail shaftbearings + couplings

Stern gear

tube + sealswhere it leaves the hull

Alignment

to classbored, sighted, set

Delivered

to ordermachined + installed

ISO 9001 / 14001 Engineered to order Marine & naval machinery Heavy machining & alignment Noida · India

Overview

Torque out, thrust in.

It is easy to picture a propeller as the thing that moves a ship, and forget the machine that makes it possible. The propulsion shafting carries the engine’s torque the length of the vessel to the propeller — and then does the harder thing: it collects the thrust the propeller generates and feeds it into the hull, through the thrust block, so that the ship goes forward rather than the shaft. Everything else in the system exists to let that happen reliably: bearings to carry the weight, couplings to join the sections, a stern tube to take the shaft through the hull, and seals to hold back the sea.

Illustrative image, not a delivered installation — a stern tube assembly: a large heavy cylindrical steel housing with a bolted circular flange and seal housing, the polished shaft passing through it into thick hull structure, with oil piping to the bearing, no text and no people

Fig · 02 The stern tube — where the shaft leaves the hull, carrying the stern-tube bearing and the seals that keep the sea out and the oil in — illustrative, not a delivered installation

The shaft line. From the gearbox aft run one or more line shafts, joined by flanged or muff couplings and carried on plummer bearings bolted to seatings in the hull, ending in the tail (propeller) shaft that passes out through the stern tube. The sections are heavy forgings machined to size, with journals, tapers and keyways cut to fine tolerance, because everything downstream — bearing loads, vibration, seal life — follows from how truly the shafting is made and set.

Where the shaft leaves the hull. The stern tube is the most demanding part of the system: a bearing running under water, for years, that must not leak. It carries the aft and forward stern-tube bearings — either oil-lubricated white-metal or water-lubricated composite — and the seals at each end that keep the sea out and, in an oil system, the oil in. Outboard, the shaft is supported by the stern boss or A-bracket, and then the propeller goes on.

Alignment is the whole game. A ship’s hull is not rigid: it flexes between light and loaded, and sits differently afloat than on the blocks. So the bearings are not simply set in a straight line — they are set to computed offsets so the load shares correctly across them in service. That means boring and sighting the seatings, setting the shafting to the calculation, and verifying it with bearing-load and deflection checks — done to the classification rules, before and after launch, and proved on trials. Get it wrong and you get overloaded bearings, vibration and damage.

A shaft line looks like the simplest machine on the ship — a bar that turns. It is in fact one of the most unforgiving, because it must stay true inside a hull that changes shape, and stay dry at the one point where it goes through the bottom of the vessel.

Torque Out, Thrust In

Two jobs, one machine

The driveline carries torque from the gearbox to the propeller and returns the propeller’s thrust into the hull through the thrust block — which is what actually drives the vessel forward.

The Shaft Leaves the Hull

A bearing under water

The stern tube carries the shaft out through the hull on oil-lubricated white-metal or water-lubricated composite bearings, with seals at each end holding back the sea for years between refits.

Alignment To Class

Set for a hull that flexes

Bearings are set to computed offsets, not a straight line: bored, sighted and set to the classification rules pre- and post-launch, then proved by bearing-load and deflection checks on trials.

Architecture

Shafting, stern gear, alignment.

The schematic shows the driveline — gearbox to propeller, and the thrust coming back into the hull — and the machine that carries it: the shafting, the bearings and thrust block, the stern tube and its seals, and the alignment that ties them together. The detail panel covers the two jobs it must do, and how it differs from the steering gear.

FIG · 03MPS ARCHITECTURE · SHAFT LINE / BEARINGS & THRUST / STERN GEAR · BORED, SIGHTED, ALIGNED TO CLASS

Fig · 03 Carry the torque out to the propeller and the thrust back into the hull — on shafting that is machined, borne, sealed at the stern tube and aligned to the classification rules

Arc · 01

The Shaft Line

Line and tail shafts machined to size from heavy forgings, joined by flanged or muff couplings with journals, tapers and keyways cut to fine tolerance.

Arc · 02

Bearings & Thrust Block

Plummer bearings on hull seatings carry the shaft’s weight; the thrust block takes the propeller’s push and puts it into the hull structure — the point of the whole system.

Arc · 03

Stern Tube & Seals

The shaft’s exit through the hull: aft and forward stern-tube bearings, oil-lubricated white-metal or water-lubricated composite, and the seals that keep the sea out and the oil in.

Arc · 04

Alignment & Installation

Boring, sighting and setting to computed bearing offsets to the classification rules, pre- and post-launch, verified by bearing-load and deflection checks and proved on trials.

Have a propulsion-shafting, stern-tube, re-shafting or shaft-alignment requirement? Send the shaft power, the arrangement and the rules — a clause-by-clause compliance matrix within two working days · [email protected]

Send tender spec

Specifications

Reference shaft line, built to the vessel.

The parameters below describe a reference propulsion shafting and stern gear system. The shaft diameters, the number of bearings, the stern-tube type, the sealing arrangement and the alignment calculation all follow from the vessel — the shaft power it transmits, the length and arrangement of the shaft line, and the classification rules it is built to.

Illustrative image, not a delivered installation — a very long heavy marine propeller shaft being machined on a large horizontal lathe, held between centres with a steady rest supporting it and a tool post cutting a bright turned surface, steel swarf on the machine bed, no text and no people

Fig · 04 Machining a tail shaft — a long, heavy forging turned between centres on a steady rest: journals, tapers and finish cut to the tolerance the bearings need — illustrative, not a delivered installation

Where shaft lines go wrong

Almost always in the alignment and the sealing, not the shaft itself. Bearings set without computed offsets overload once the hull takes up its service condition; a badly bored seating puts the line out and shows up as vibration; a stern-tube seal that is wrong for the lubrication or poorly fitted leaks; and shafting machined out of tolerance spoils every fit downstream of it.

So the shafting is machined to fine tolerance, the seatings are bored and sighted, the bearings are set to the alignment calculation and re-checked after launch when the hull is waterborne, and the whole line is verified by bearing-load and deflection measurement and proved on trials to the classification rules. The measure of a shaft line is simple: it turns true, it stays dry, and it is still doing both at the next refit.

Full specification — expand

System	Marine propulsion shafting & stern gear system — the driveline of a surface vessel: shaft line, bearings and thrust block, stern tube and seals, engineered, machined, installed, aligned and commissioned
Function	Carries torque from the prime mover and gearbox to the propeller, and returns the propeller’s thrust into the hull structure through the thrust block
Shaft Line	Line shaft(s) and tail (propeller) shaft, machined from heavy forgings, with flanged or muff couplings, sleeves, journals, tapers and keyways
Bearings & Thrust	Plummer / line-shaft bearings on hull seatings; a thrust block transferring propeller thrust into the hull
Stern Gear	Stern tube with aft & forward stern-tube bearings — oil-lubricated white-metal or water-lubricated composite — plus the stern boss / A-bracket interface
Sealing	Stern-tube seals at each end — keep the sea out and, on an oil system, the oil in; monitored in service and renewed at refit
Alignment	Bored and sighted, set to computed bearing offsets to the classification rules, pre- and post-launch; verified by bearing-load & deflection checks and proved on trials
Manoeuvring	Bow thruster, waterjet and propulsion-unit installation, integration and support where fitted
Vessels	Surface naval vessels and ships — new-build, refit, re-shafting and indigenisation of shaft lines
Sourcing	The propeller, the stern boss & stern-tube castings, the main gearbox, propulsion motors, waterjet / thruster units, bearing shells and seal cartridges are bought-in specialist items; Neometrix engineers, machines, fabricates, assembles, installs, aligns & commissions the shaft line and stern gear
Status	Engineered to order · sized to the shaft power, the shafting arrangement & the classification rules · quoted across propulsion-shafting, stern-tube & shaft-alignment requirements · no specific delivered ship or class is claimed on this page

PDF · 1 page

Marine Propulsion Shafting & Stern Gear — Capability Sheet

Tender Response

Send your shaft power, arrangement & rules — compliance matrix in two working days

Variants

One driveline, the scope you need.

Tenders call it propulsion shafting, stern gear, a stern tube, gearing and shafting, or pre- and post-launch alignment and installation. The principle — torque out to the propeller, thrust in to the hull, on a line that is true and sealed — is common; the scope is set by the vessel and the yard.

Var · 01

Propulsion Shafting — Line & Tail Shaft

Machined shafting and couplings for the shaft line — line shafts, tail shaft, sleeves and keyways, cut to the tolerance the bearings need.

Var · 02

Stern Tube & Stern Gear Assembly

The stern tube, its bearings and seals, and the boss / A-bracket interface — assembled and fitted where the shaft leaves the hull.

Var · 03

Alignment, Installation & Commissioning

Boring, sighting and setting to computed offsets, pre- and post-launch, with bearing-load and deflection verification to class.

Var · 04

Thruster, Waterjet & Unit Installation

Installation, integration and support of bow thrusters, waterjet and propulsion units — seatings, alignment and fit-out around bought-in equipment.

Applications

Where it drives them.

Wherever a surface vessel has to turn a propeller — new-build, refit or re-shafting.

A · 01Surface-vessel propulsion shafting

A · 02Stern tube, bearings & seals

A · 03Shaft alignment, boring & sighting

A · 04Thrust block & bearing installation

A · 05Bow thruster & waterjet installation

A · 06Refit, re-shafting & indigenisation

FAQ

Common questions.

Plain-language answers from the engineering team.

Q · 01 What is propulsion shafting and stern gear?

It is the ship’s driveline — all the machinery between the gearbox and the propeller. It does two jobs at once. First it carries torque: the prime mover drives a gearbox, which drives one or more line shafts, which drive the tail (propeller) shaft that carries the propeller. Second, and less obvious, it carries thrust: the propeller pushes the ship, not itself, so the push it develops travels forward along the shaft and has to be put into the hull — which is the job of the thrust block. Around those two functions sit the parts that make it last: plummer bearings carrying the shaft’s weight, couplings joining the sections, the stern tube through which the shaft leaves the hull with its own bearings, the seals that keep the sea out, and the stern boss or A-bracket supporting the shaft outboard. Together they are what actually converts engine power into a moving ship.

Q · 02 Why is shaft alignment so critical?

Because the hull the shafting sits in is not rigid. A ship’s structure flexes: it sits one way on the blocks and another afloat, and changes again between light and loaded conditions. If the shaft bearings were simply set in a perfectly straight line, then as soon as the hull took up its service shape some bearings would carry far too much load and others almost none — which shows up as bearing overload and wiping, vibration, coupling distress and, at worst, damage to the stern tube. So alignment is a calculation, not a straight edge: each bearing is set to a computed vertical offset so the loads share correctly in the condition that matters. Practically, that means boring and sighting the bearing seatings, setting the shafting to the calculated offsets, and then re-checking after launch, when the hull is waterborne and has changed shape. It is verified by bearing-load measurement (jacking) and shaft deflection checks, to the classification society’s rules, and proved on trials. It is the single thing that most determines whether a shaft line has a quiet, long life.

Q · 03 How is this different from your steering gear and deck equipment?

Three different machines, three different jobs — and we build all three, which is why they are cross-linked here. This propulsion shafting and stern gear drives the vessel: it turns the propeller and puts the thrust into the hull. Our naval steering gear and rudder system steers it: an electro-hydraulic machine that moves the rudder to the helm order. They live in neighbouring compartments aft and are often quoted together on a refit, but one is a driveline and the other an actuator — different engineering, different scope. Our marine and naval hydraulic deck equipment is different again: the winches, capstans, windlasses and davits up on the deck, handling mooring and towing lines, the anchor and cable, boats and stores. Going, turning, and working the deck — three systems, one common competence in heavy marine machinery.

Q · 04 What do you build, and what is bought-in?

We are honest that this is a system where a good deal of the value is engineering, machining and installation rather than manufacture of every component. What Neometrix does is the shaft-line engineering (shafting design and the alignment calculation to class), the precision machining of line and tail shafts, sleeves, couplings and stern-tube assemblies, the fabrication of thrust-block seats, bearing seatings and foundations, the assembly of the stern gear with its bearings and seals, and — the demanding part — the boring, sighting, installation, alignment and commissioning on the slip and afloat, pre- and post-launch, plus shaft test rigs where they are needed. What is bought-in specialist is the propeller, the stern boss and stern-tube castings, the main gearbox, propulsion motors, waterjet and thruster units, the bearing shells and the seal cartridges, and the large shaft forgings — which we machine, assemble, install and align. It is the same heavy machining, fabrication and marine-machinery competence behind our deck equipment and steering gear. Engineered to order; no specific delivered ship or class is claimed on this page.

Q · 05 How is the sea kept out where the shaft leaves the hull?

By the stern tube and its seals — the hardest-worked interface on the driveline, because it is a rotating shaft passing through the bottom of the vessel with the sea on the other side. The stern tube houses the aft and forward stern-tube bearings that carry the tail shaft, and there are two broad arrangements. In an oil-lubricated white-metal system the tube is filled with lubricating oil, held at a controlled head, and seals at each end keep the sea out and the oil in — oil loss or water ingress is the warning sign. In a water-lubricated composite system the bearing runs on sea water itself, with a simpler sealing arrangement and no oil to lose. Which is right depends on the vessel, the service and the owner’s maintenance policy. Either way the seals are monitored in service — oil consumption, temperature, leakage — and renewed at refit, when the shaft is drawn and the bearings inspected and, if needed, re-metalled or replaced.

Q · 06 Is this for surface vessels — and can you re-shaft or indigenise an existing line?

Yes to both. This page is about propulsion shafting and stern gear for surface naval vessels and ships. And a large share of real demand is not new-build at all but refit and re-shafting: drawing the tail shaft, inspecting and renewing stern-tube bearings and seals, replacing or re-machining shafting, re-boring seatings and re-aligning the line, then re-commissioning it to class. The same applies to indigenisation — re-engineering and building here the shafting, stern-tube assemblies and associated equipment that a vessel currently depends on an overseas supplier for, so that spares and refits no longer wait on an import. That is squarely the work we do: engineer, machine, assemble, install, align and prove. Whether the requirement is a new shaft line, a stern-tube assembly, an alignment and installation package, or the indigenisation of an existing arrangement, it is engineered to order — and no specific delivered ship or class is claimed on this page.

↗

The marine-machinery line from Neometrix.

The machine that steers the ship, the machinery that works its deck, and the rig that fatigue-tests a shaft — engineered at our Noida facility.

↗ Steering

Naval Steering Gear & Rudder System

The electro-hydraulic machine that turns the ship — this one drives it.

↗ Deck Machinery

Marine & Naval Hydraulic Deck Equipment

The winches, capstans and windlasses that work the deck above.

↗ Shaft Testing

Shaft Torsion Fatigue Testing Machine

The rig that torsionally fatigue-tests a shaft — proving what a driveline must survive.

Browse all Neometrix product lines.

Get a quotation

Send the shaft power
and the arrangement.

The defence programmes desk replies within two working days with a clause-by-clause compliance matrix and a budgetary quotation. Write to [email protected] or use the form.

Enquire — propulsion shafting Capability sheet (PDF) +91 7777 876 876

ISO 9001 / 14001 ENGINEERED TO ORDER — MARINE PROPULSION SHAFTING & STERN GEAR SYSTEM LINE & TAIL SHAFT · BEARINGS & THRUST BLOCK · STERN TUBE & SEALS · BORED · SIGHTED · ALIGNED TO CLASS ENGINEERED IN NOIDA · INDIA

Turn the propeller. Push the ship.

Torque out, thrust in.

Two jobs, one machine

A bearing under water

Set for a hull that flexes

Shafting, stern gear, alignment.

The Shaft Line

Bearings & Thrust Block

Stern Tube & Seals

Alignment & Installation

Reference shaft line, built to the vessel.

Where shaft lines go wrong

One driveline, the scope you need.

Propulsion Shafting — Line & Tail Shaft

Stern Tube & Stern Gear Assembly

Alignment, Installation & Commissioning

Thruster, Waterjet & Unit Installation

Where it drives them.

Common questions.

The marine-machinery line from Neometrix.

Naval Steering Gear & Rudder System

Marine & Naval Hydraulic Deck Equipment

Shaft Torsion Fatigue Testing Machine

Send the shaft power
and the arrangement.

Similar Products

Share This Page

Turn the propeller. Push the ship.

Torque out, thrust in.

Two jobs, one machine

A bearing under water

Set for a hull that flexes

Shafting, stern gear, alignment.

The Shaft Line

Bearings & Thrust Block

Stern Tube & Seals

Alignment & Installation

Reference shaft line, built to the vessel.

Where shaft lines go wrong

One driveline, the scope you need.

Propulsion Shafting — Line & Tail Shaft

Stern Tube & Stern Gear Assembly

Alignment, Installation & Commissioning

Thruster, Waterjet & Unit Installation

Where it drives them.

Common questions.

The marine-machinery line from Neometrix.

Naval Steering Gear & Rudder System

Marine & Naval Hydraulic Deck Equipment

Shaft Torsion Fatigue Testing Machine

Send the shaft powerand the arrangement.

Similar Products

Share This Page

Send the shaft power
and the arrangement.