How much tip clearance is required?
To obtain clean water away from the water that is dragged forward along with the hull and impacts on propeller performance all propellers require clearance from the tips to the hull. Having low tip clearances can also cause vibration to be transmitted through the hull from the disturbance caused by the propeller blades displacing the incompressible water as they sweep past the hull. Some rules of thumb use 10 % of the diameter – but higher clearances generally lead to higher shaft angles which reduces propeller performance. Due to the low boat speeds typically involved with low powered displacement yachts – clearance is not as critical as on many applications. With thin tips, unlike folding propellers which use the mass in the tips to provide reverse thrust from the centrifugal force generated, our empirical experience is that clearance can be lower with virtually no impact on performance or vibration. We would suggest no less than ” or 12 mm in a tight situation – obviously more is be
