Aquamet, 316, bronze. The right choice depends on your use case — not the price list.

Introduction

Pick the wrong shaft material and you’ll know within three seasons — either from a corroded shaft, a bent one, or an unnecessarily expensive stern-gear bill. Here’s how to choose.

Aquamet 22 — the premium choice

A specifically marine-engineered precipitation-hardened stainless. 50% stronger than 316, with excellent seawater corrosion resistance. Expensive but worth it on commercial vessels and premium pleasure boats.

316 Stainless

The industry workhorse. Good corrosion resistance, moderate strength. Watch for crevice corrosion under cutless bearings and inside the shaft taper. Great value in the 25–50mm range.

Manganese bronze

Traditional sailboat material. Soft but immune to seawater corrosion. Easy to repair-weld. Softer than stainless so wears cutless bearings faster — a trade some sailors accept for the longer-term corrosion story.

Nickel-aluminium bronze

Harder and stronger than manganese bronze. Suits high-torque commercial applications. More expensive but longer-lasting under heavy duty.

Decision matrix

Pleasure boat, moderate budget: 316 stainless. Pleasure boat, premium: Aquamet 22. Commercial workboat: Aquamet 22. Classic sailboat or traditional restoration: manganese bronze.

A note on galvanic compatibility

Mixing dissimilar metals in a seawater drive train is a battery waiting to corrode something. Keep shaft, propeller, cutless bearing, and bronze fittings on a sensible galvanic series — and bond and anode everything properly.

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.