No more whine, please

Q

I have a Sadler 26 fitted with a Beta 16, a conventional shaft and stuffing box and a conventional three-bladed prop. A little beyond tickover speed in terms of revs, there is an annoying and fairly high-pitched whine that needs quite a bit of throttle to get through. The stuffing box is re-greased every hour or so on passage by a convenient large greaser. I read somewhere that such a noise could be to do with the very tips of the blades that need filing in one direction only: could you kindly shed some light on the problem? pAT MAnleY replies:

You may be able to reduce the prop whine by re-contouring your blade tips, but it may be a little more profound than this. The original 26 had a 10hp engine, I think, and upgrading to a 16hp engine may have resulted in the prop diameter being on the large side. The normal clearance required between the prop tip and hull is around 15%, but you can often get away with about 10% diameter. If the tip clearance is too small, you could possibly reduce the whine by fitting a smaller-diameter prop with a greater pitch to maintain the engine thrust, or just reduce the diameter if you are getting sufficient performance anyway. It’s always tempting when re-engining a boat to put a bigger one in, but this often has other consequences. It may be useful to look at the Sadler owners’ club forum to see who has done what in this respect. The Beta is higher revving than the Bukh, I think, but that should have been taken care of with the gearbox ratio selection on installation.