Trimming propeller blades

[Bert Large]

Has anyone had any experience of trimming down propeller blades & if so could they explain how to do it & how easy is it please ?

The reason I ask is that I recently bought my boat & it had two propellers with it. One was in better condition than the other so I fitted that. It is 15" x 12" but when I calculated what prop my boat should have it worked out to 12" x 9".

My other prop is a bit dog eared around the edges but is 15" x 10" so if I could cut the blades down it shouldn't be too far off what I need.
The boat isn't in the water yet so I can't have any practical tests yet.

 

[Tranona]

Forget it. If they are that far out (and I have difficulty in that!) you need to get the correct prop. There is no way the props you have will work IF you need a 12*9.

 

[William_H]

Prop size

How do you calculate the diameter of the prop you need. Surely for best power you need the biggest diameter that will fit the aperture?
Perhaps a smaller prop will give better sailing performance.
The pitch AFAIK is what matters. The 10 inch pitch prop will give you lower speed at higher engine revs but more push into wind and better reverse /stopping power. The 12inch pitch will give lower revs for given hull speed. But will suit a higher hull speed with less punch into wind and waves. It is a bit like gearing a car or bicycle.
So just clean up the 10 inch and refit IMHO see how you go. Can you reach hull speed without over revving the engine? If you can't then 12inch would be better. good luck olewill

 

[Bert Large]

Thanks for the replies. Tried the boat today. Too much pitch on the prop but goes quite well. She needs more ballast too so difficult to tell exactly until that is sorted out.