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BRUNTONSAustralia

Symptom diagnosis

Boat slower than identical sisterships — propeller causes

Sisterships are the best benchmark in boating — same hull, same rig, same engine. When yours is consistently slower, the difference is bolted on somewhere, and the shaft end is the first place to look.

  1. 1. Fixed-blade drag under sail

    most likely

    A fixed three-blade drags like a towed bucket — roughly 20× a folded prop, worth up to a knot in light air. If the quick sisterships run folders or featherers, that's the gap.

    Do thisSee the drag comparison, then check what your sisterships actually fitted.

    The drag comparison →

  2. 2. Wrong pitch under power

    common

    Over-pitched props can't reach rated RPM; under-pitched ones rev without pushing. Either way the boat is slow for its fuel burn.

    Do thisThe WOT test tells you in sixty seconds.

    Run the WOT test →

  3. 3. Fouling and finish

    common

    A season's slime is measurable; barnacles are decisive. Race crews polish props for a reason.

    Do thisClean everything below the waterline, then benchmark again.

Before you spend money

Check what the fast boats run before assuming — your model's page in our database lists the documented fitments, engines and sizes across the fleet. Sistership envy is a data problem first.

Other symptoms

Engine won't reach max RPMBlack smoke under loadVibration at cruising revs

Want the numbers checked properly?

Tell the Builder about this symptom — it screens for it, and an engineer reviews every recommendation before anything is supplied.

Build my prop spec0418 327 403