Add a blade and you add thrust and smoothness — but lose a half-knot. Here’s the real trade-off.

The simple rule

Fewer blades = more efficient (higher top end). More blades = smoother, more thrust at a given diameter. That’s the whole trade-off, and the right answer depends on what you want your boat to do.

Three blades

Classic planing and semi-planing choice. Best fuel economy at WOT. Simplest and cheapest to repair. Can be rougher at idle, more cavitation-prone when heavily loaded. Good for sports fishers, runabouts, light cruisers.

Four blades

Smoother at low RPM. More thrust per diameter — useful when the hull aperture is restrictive. Slight loss of top-end efficiency. Good for cruisers, displacement sail under power, and semi-displacement workboats.

Five blades

Maximum thrust, smoothest running. Common on large commercial vessels, trawlers, and premium motor-yachts where quietness is prized. Most expensive to make and repair.

Workshop lore

If you can run 3 blades and still make rated RPM at WOT, do it. If you can’t — hull aperture too tight, too much vibration — add a blade. If still not enough thrust, go to five. Rarely do we recommend starting at five without a reason.

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.