Gearbox, propeller shaft and stern gland — inspection
Inspecting the gearbox, shaft alignment and cutless bearing, plus servicing conventional and dripless seals.
The drive train between the gearbox and the propeller carries the engine's full power and at the same time forms a hole in the hull below the waterline — mistakes here risk flooding the boat. A regular inspection covers the gearbox, the shaft, the cutless bearing, the gland and the alignment. Most problems show up as vibration, noise, a leaking gland or cloudy oil in the gearbox. It is worth doing the diagnosis ashore with access to the propeller and shaft.
Change the gearbox oil (ATF or the gear oil recommended) at the maker's interval. A milky colour means water, a metallic sheen means internal wear. Check the cable or the gear control mechanism, the play and the mountings. Check the clutch and its adjustment for correct engagement of the gears. A gearbox that grinds or jumps out needs attention before it leaves you without propulsion.
Aligning the shaft to the gearbox is the foundation of quiet, durable running. Misalignment causes vibration and accelerated wear of the gland, the cutless bearing and the engine mounts. Check the alignment with feeler gauges on the separated flanges (gearbox and shaft coupling) — the gap around the circumference should be even to within hundredths of a millimetre. Adjust it by raising and moving the engine feet. Do the alignment with the boat afloat and settled into its natural shape, because the hull works.
The cutless bearing is a rubber-and-brass sleeve, water lubricated, in which the shaft turns. When worn it gives play — grab the shaft at the transom and check for any perceptible sideways movement. Excessive play causes vibration and noise and eventually damage. Replacing it usually means withdrawing the shaft and pressing out the old sleeve. While you are there, assess the shaft itself (straightness, corrosion, pitting) and the propeller and shaft anode.
The gland seals the shaft where it passes through the hull. A classic packed gland should drip a few drops a minute while running, to cool itself — a completely dry one overheats and ruins the shaft. In time the packing is replaced with new material of the right section, wound on as successive rings with the joints staggered. The alternative is a dripless seal (such as the PSS bellows type), which needs periodic servicing of the bellows and rings and burping after launching.
A complete inspection also covers the gland hose and its clamps (a safety item — a burst means a leak below the waterline), the engine mounts (cracked rubber ruins the alignment), the anodes protecting the shaft and propeller, and the state of the propeller itself (balance, damage to the edges). After the service and launching, watch the gland and the bearing temperature during the first run. Vibration that appears suddenly is always a warning sign.
Safety: work on the shaft only with the engine off and secured against starting (earth disconnected, key removed), because a turning shaft is lethal. With the boat afloat, remember that loosening the gland or the hose can flood it — work prepared, with a pump and materials to hand. If you lack experience, it is better to have the cutless bearing replaced and the alignment done by a workshop. After any work, check for leaks before you leave the boat unattended.
Material prices — products and options
Indicative prices in EUR (incl. VAT), as of July 2026. Products widely available in Europe; prices depend on the shop, the pack size and consumption. The links lead to example shops that ship across the EU. Dollar amounts are converted at 1 EUR = 1.1622 USD (ECB, 7 September 2026) and rounded — treat them as a rough guide, not a price in a US shop. Imperial values in brackets are conversions of the metric figure.
Gearbox oil
- Volvo Penta / ZF — gearbox oil (ATF or to specification)
oil for the saildrive/reverse gearbox; as the maker recommends; 1 l (0.3 US gal)€12–25 (≈$14–29) - Volvo Penta — synthetic oil 75W-90
for saildrives; 1 l (0.3 US gal) pack€18–30 (≈$21–35) - ZF Marine — ATF gearbox oil
for ZF hydraulic gearboxes; 1 L (0.3 US gal)€12–22 (≈$14–26) approx.
Glands and shaft seals
- PSS (PYI) — maintenance-free mechanical shaft seal
shaft seal for 25–35 mm (0.98 in–1.38 in) shafts; complete with bellows€140–260 (≈$163–302) - PTFE/graphite gland packing
braided packing 5–10 mm (0.2 in–0.39 in); sold by the metre€10–30 (≈$12–35) - Vetus — stuffing box
traditional gland with bushes and a compression nut€60–130 (≈$70–151) - Volvo Penta — shaft seal 91254
original seal for a 25 mm (0.98 in) shaft€30–70 (≈$35–81) approx.
Shaft bearing and gland hose
- Cutless bearing — shaft bearing (rubber/brass)
plain shaft bearing to size; various diameters€25–70 (≈$29–81) - Reinforced gland hose + stainless clamps
hose joining the stern tube to the gland; complete with clamps€15–40 (≈$17–46) approx. - AISI 316 hose clamps (2 per joint)
stainless steel clamps for the gland hose€2–6 (≈$2–7) / piece
Anodes, mounts and accessories
- Shaft / propeller anode (zinc or aluminium)
cathodic protection of shaft and propeller; various diameters€10–35 (≈$12–41) - Engine mounts (feet)
flexible engine mounts — when worn; each€30–90 (≈$35–105) approx. - Feeler gauges + thread sealant
for aligning the coupling and for assembly; set€8–20 (≈$9–23) approx.