Stern Gear Assemblies

Stern gear is easy to shop for one part at a time. That is not usually how the work arrives. A repower, a new build or a serious refit needs the running gear complete, from the back of the gearbox to the trailing edge of the rudder, and every part of it has to agree with the parts either side.

DH Porter design, make and supply that package complete. It is the thing we are set up to do, and the reason a business that started in 1912 is still worth ringing.

What a complete package covers

The drawing above is a typical assembly. Working aft from the gearbox flange:

• Couplings: flexible, clamp or tapered, matched to the gearbox flange at one end and the shaft at the other. See couplings.
• Propeller shaft: 316, 2205, Marinox 22 or 431, single or double tapered, turned, keyed and finished to suit. See shafting.
• Shaft seal: a PSS dripless face seal, or a traditional packed or oil-sealed gland if that suits the boat better. See shaft sealing systems.
• Stern tube and housing: bronze or marine brass, made to length and bore, complete with its bearing.
• Propeller: cast from our own patterns, bored to the shaft taper it will actually run on, then brought into class and balanced. See propellers.
• Prop nut and hardware: bronze castellated nuts, keys and fastenings. See marine hardware.
• Rudder, stock and gland: stainless or bronze, with the gland assembly and tiller arm to match.

Not every job needs all of it. Plenty need one end or the other, and the point of designing the package as a whole is that the parts still line up when they are supplied separately.

Made here, not just supplied

Almost everything in that drawing is ours from the start. The bronze parts are cast from patterns we hold or make: prop nuts, tiller arms, glands, housings and propellers. The steel and stainless work is fabricated and machined here. Shafts are turned, tapered and keyed on our own machines, and rudders are built to the section and balance the boat needs rather than to whatever is on a shelf.

Where a proprietary part is genuinely the better answer, we say so and fit it. PSS dripless seals come from the manufacturer, and we are the NSW stocking distributor for them. Engine mounts, clamp and flexible couplings are Poly Flex, a line we have supplied long enough to trust. What we do not do is pass off a box-shifting exercise as engineering.

Trial assembled before it leaves

This is where a package earns its keep. A complete assembly is put together in the workshop before it goes anywhere near a boat: shaft into stern tube, bearing pressed and checked, coupling fitted to the shaft taper, propeller offered up to its own taper, gland and rudder assembled and turned by hand.

Tolerances that look fine on separate drawings have a way of disagreeing in the flesh. Finding that out on our bench costs an afternoon. Finding it out on a slipway, with a boat blocked up and a tide to make, costs considerably more. When the crate is opened the parts fit each other, because they already have.

One drawing, one supplier, one phone call

Buying stern gear piecemeal means multiple suppliers and as many sets of tolerances, and when something does not fit there is rarely agreement about whose millimetre it was. A package designed as a set removes that argument, because the taper on the shaft was cut to the propeller that is going on it and the stern tube was bored for the bearing that is going in it.

It also means one number to ring afterwards. We keep the drawings and the patterns, so a replacement shaft or a second propeller years later is made to the same figures rather than reverse-engineered from a worn part.

Typical work

• Repowers, where a new engine and gearbox change the flange, the shaft centreline or both
• New builds, from a naval architect’s drawings or developed with the builder from the hull aft
• Refits and survey work, replacing gear that has reached the end of its life
• Commercial and workboat fleets, where a spare assembly on the shelf is cheaper than downtime
• Older and classic vessels, where nothing is standard and patterns often have to be made

Send us a drawing, a parts list or the old gear itself and we will quote the package. Ring the workshop on (02) 9890 1766, or ask for a set of dimensions to check before you commit to anything.