Propeller Dressing

[seaesta]

I have fitted a new engine and now have a low rumbling noise from the prop/shaft/sterngland area above 2000 revs.

I have two conflicting peices of advice both from very trustworthy sources and would like opinions / experiences from other forum members

1. Trusted source 1 says the problem may be over sharpness on the "attacking edge" of the prop and to round the outer 1/3rd of the attacking edge of the prop to stop the noise which is from a kind of cavitation. The attacking edge is that which bites ino the water when in forward gear.

2. Trusted source number 2 (prop suplier) says to file the outer half of the trailing edge of the prop (the end of the prop near the shaft nut on the edge which is hidden from view when looking stern on at the prop)

I could do both of these things but would appreciate coments before applying the file and emery.

Prop is 12x9 two blade on a Beta 13.5 h.p

Martin

 

[Stemar]

From my (rather limited) experience, depending on the gearbox ratio and the size of you r boat, that prop seems on the small side for a 13.5hp engine. My old 7Hp engine had a 13x8 3-blader in a 24 footer. If your new engine revs freely and doen't seem to be trying very hard, or you can get peak revs whilst (strongly!) tied up to a pontoon, you may well need something a bit bigger rather than worrying about dressing the old prop.

You can download a program that will give you an idea from Castle Marine

It only works for 3-blade props, but I also have a spreadsheet that does the sums for 2 & 4 blade props which I downloaded from the net, I think via one of the forums. PM me if interested.

 

[seaesta]

Steve,

Thanks but the prop is the right size

Martin

 

[Medskipper]

This sounds much more like an allignment problem to me! or is it possible the shaft is not totally straight? or perhaps worn in an area?

I would make a thorough check of allignment before messing about with your props!

Regards Barry

 

[reeac]

A worn cutless bearing makes a low rumble at those rpm. Any chance that that could be the problem?