Propellerheads
Fixed props are still the most efficient when you’re under power alone, but as sailors, we’re more interested in using wind power. With the sails up in a good breeze, a fixed prop can generate 30-40kg of drag on a 40-footer – costing you up to a knot in boat speed. But a folding or feathering prop can eliminate 95 per cent of that unwanted friction.
If you are repowering your boat, it is a golden opportunity to upgrade a propeller that may well need to be changed in any case. But it’s worthwhile on its own merits. Club racing without a folding prop is no fun at all, while the prospect of 10 per cent faster passage times has obvious appeal to cruisers.
What you want in a prop
A good propeller must always be designed to suit your boat’s engine and gearbox, otherwise it cannot perform efficiently. Too small and the prop won’t get the boat up to hull speed or perform in heavier conditions (when you might need it most); too large and it can stop the engine from reaching optimum power.
“The main misunderstandings are the big differences between engines, even when their power ratings may be similar,” explains Glen Print, MD of Sillette. “Yes, I say to the boat owner, but your new engine rpm is 3200 and your old engine was 3800 and therefore the propeller requirement is vastly different. Same applies to different gearbox reduction
