Vibration and noise: reading what the boat is telling you

Vibration is information. Boats broadcast exactly what's wrong — the skill is decoding whether it's the propeller, the driveline, or the installation. Getting this wrong buys the wrong fix.

The quick diagnostics

• Changes with engine RPM, present in neutral: engine mounts or engine itself — not the prop.
• Changes with shaft RPM, worse under load: propeller (damage, fouling, pitch mismatch) or shaft alignment.
• Appeared suddenly: strike damage or a lost blade edge — inspect now, not next haul-out.
• Always been there, worse at cruise: classic misalignment — the driveline fighting the mounts' flex.

Why alignment vibration never shims away

Flexible engine mounts deflect under thrust; the hull changes shape afloat. A driveline aligned on the hardstand runs misaligned at cruise — no amount of static shimming chases a dynamic problem. The engineering fix is a constant-velocity coupling: SigmaDrive absorbs up to 3° of working misalignment and takes the vibration out at the source.

When it is the propeller

A damaged, fouled or badly matched prop shakes the boat at shaft frequency. Over-pitched props lug and rumble; cavitating tips (too little clearance) drum on the hull overhead. This is why the Builder asks about vibration — and why 'vibration' enquiries get a driveline review alongside the prop sizing. Sometimes you need both; sometimes the prop was innocent all along. We'll tell you which.