What kind of prop?

[mmawonder]

I have a 3 blade prop on my 1978 johnson 25, that looks like it came out of a fan or used for weedwhacking purposes in the past. It is 10 inches in diameter, i dont its pitch. I want to replace it, and my goal is to get the highest speed out of my RIB without exceeding manufac. recommended max rpm. What are my options?

 

[tashasdaddy]

Re: What kind of prop?

these are what BRP offers.

0388883 PROPELLER, 9-1/4 x 11 std.

0389067 PROPELLER, 9-1/4 x 7

0389068 PROPELLER, 9 x 9

0389069 PROPELLER, 9 x 10

0389070 PROPELLER, 9 x 10 weedless

 

[Silvertip]

Re: What kind of prop?

Read the sticky titled "READ THIS FIRST" at the very top of this forum. Without a base line and not knowing what prop pitch you have now, there is no way for us to offer any reasonable suggestions. Maximum speed will be with whatever prop you end up with that allows the engine to run at its maximum recommended RPM range. More pitch than that will lug the engine and you lose speed. Less pitch than that will cause the engine to over rev.

 

[mmawonder]

Re: What kind of prop?

Ok, can you guys tell me the difference between a 4 blade prop and a 3 blade prop?

 

[Silvertip]

Re: What kind of prop?

Go to the same link I posted above and you will fiind thorough descriptions of propeller theory. Other than one blade difference, the reason(s) to use one over the other are rather complex and depend on what performance characteristics you are trying to improve. Many folks feel that just because a prop has four blades it's faster than a three blade. In some cases that's true. Most cases it's not. In most cases the four blade gets you out of the hole quicker than a three blade at the expense of top end. Then through the aluminum vs stainless steel variable in the mix and I think you get the idea why prop selection is a crap shoot.