A one-page checklist of what to inspect on every slipping — plus the five things that are cheap now and ruinous later.

Why a checklist helps

Stern gear problems rarely announce themselves. A cutless bearing wears gradually; an anode disappears quietly; a shaft seal drips a little more each month. The engines-on-top-of-engines mentality that keeps outboards running doesn’t quite fit inboard shafts, so this is a short checklist for your next slipping or your workshop day.

Propeller — inspection points

• Blade edges — look for nicks, erosion, bent tips.
• Blade root — hairline cracks appear here first.
• Hub — fit on taper, keyway wear.
• Nut and split pin — torque to spec, new split pin.
• Zinc anode on hub — replace at <50% remaining.

Measure diameter and pitch of each blade. Variations of more than 1° blade-to-blade mean a trip to the propeller shop.

Cutless bearing — the wear test

With the propeller off, grab the shaft at the stern tube and try to lift it. A good cutless bearing lets the shaft lift roughly 0.5–1 mm. More than 1.5 mm, and the bearing is worn. Replace before the next trip — a worn bearing lets the shaft whip and will chew the shaft and the next bearing in minutes.

Shaft seal

• Face-type seal: Carbon face thickness > 3 mm. No weeping with the shaft turning.
• Stuffing box: Re-pack annually. The shaft under the packing should be smooth.

Shaft itself

Run a dial gauge against the shaft near the coupling. More than 0.1 mm total indicated run-out and the shaft is bent. On the taper, check for fretting — a sign the propeller nut has been loose.

Coupling and alignment

Check the engine-shaft coupling for a 0.05 mm feeler gap all round. More than that and the alignment is out — re-shim before leaving the slip.

Anodes

Shaft anode, rudder anode, hull anode. All three should show less than 50% consumption at every slipping. If one is going fast and another barely at all, there may be a bonding problem — investigate before the next haul.

The five cheap jobs

1. New propeller nut split pin — $0.50.
2. New shaft anode — $35.
3. Fresh grease in grease-type seal cup — $10.
4. New propeller key if any sign of wear — $25.
5. Fresh paint on bonding wires — $5.

Together: under $100. Skipping any of them has sunk boats.

Need advice on your boat’s stern gear or propeller? Call Brian directly on 0413 771 090 or use the contact form — we respond the same day.

The humble cutless is the most important part most owners never think about — until it fails.

What a cutless bearing does

A cutless marine bearing is a bronze or composite shell lined with grooved nitrile rubber. Water flowing through the grooves lubricates the shaft and carries away heat. Simple, reliable, and good for 5–10 years in most pleasure boats.

Why they fail

Three main reasons:

1. Blocked water flow — barnacles in the strut or stern tube.
2. Dry running — common when a boat is dry-sailed and started before the sea water reaches the shaft.
3. Shaft misalignment — the bearing wears unevenly and oval-locks.

The wear check

Grab the shaft near the bearing and lift. If the shaft rises more than 1.5mm, the bearing is at or beyond its wear limit. Replace before next season.

Clearances when fitting a new bearing

Standard shaft-to-bearing clearance is 0.004–0.006″ per inch of shaft diameter. Too tight and the bearing runs hot; too loose and the shaft whips.

Duramax vs. Tufnol — the long-running debate

Duramax rubber is the modern standard — tolerates small particulate, runs cool, lasts well. Tufnol (phenolic) is traditional, slightly more tolerant of brief dry-running, but less tolerant of grit. For most boats, Duramax wins.

Fitting

Press-fit with a mandrel; don’t hammer. Note the bearing orientation — grooves must align with water flow. We supply bearings with clear install sheets.

Need advice on your boat’s stern gear or propeller? Call Brian directly on 0413 771 090 or use the contact form — we respond the same day.