Propeller question

[josip_voyager]

1) Does anybody know what can I expect (I mean rpm and max. speed) if I increase prop pitch from 9 to 11? I have Honda BF20 outboard installed on inflatable with prop 9-1/4x9 and want to buy 9-1/4x11. I've only found on this forum that one inch bigger prop diameter means approximately 200 rpm less. <br />2) Is it better to buy prop with three or four blades on smaller outboards (20 PS)? I've red that four blades prop means higher trust compared with three blades prop. Is that correct?<br />

 

[cobra 3.0]

Re: Propeller question

Usually the available four blade props on a smaller motor is for thrust...like for a pontoon boat. <br /><br />Finding the correct prop for your boat is dependant on knowing your present rpms at WOT. You may find a slight increase in speed at the cost of less acceleration/sluggishness. Inflatables are generally quite light and if you don't have much weight in the boat, it might just work out.<br /><br />A tiny tach would help you determine present rpms.<br /><br /> http://www.tinytach.com/tinytach.html

 

[Hooty]

Re: Propeller question

As a rule of thumb, it's one inch of pitch that makes the 200rpm difference, depending on the prop. <br /><br />c/6<br />Hooty