4 blade?

[dabalone]

Great forums and info, thanks. Have a stock alum 3 blade on my 17 alum v, get up to 5200 rpm trimmed up and have to back off because of porpoising, motor rated to 5750. Dont have gps to check speed and just going faster is not my priority, what would going to a 4 blade 17 pitch trophy plus possibly do as opposed to my stock alum? New 115 opti. Or other suggestions appreciated. Raised the motor up couple holes and it helped with the porpoising but now the prop blows out in any kind of tight turn on plane.

 

[WillyBWright]

Re: 4 blade?

If your goal is to keep the prop from blowing out, it should work. Trim tabs should cure that porpoising problem.

 

[dabalone]

Re: 4 blade?

Thanks Willy, I have 60# smart tabs but they may be too heavy. Get a lot of spray coming off them, I actually (carefully) reached down and pulled them up while on plane and they were digging into the water by slightly and took some pressure to pull them up out of water. Need to talk to the man at Nauticus about going to the 40# actuators I think.

Wot and full trim is 5200, 5300 rpm depending on conditions. Missing 400 to 600 rpm to hit motors recommended top rpm. Just wondered what going down to 17 pitch in a 4 blade might do with my rpm's. Setting the motor back down two holes the porpoising starts at 4600 rpm and gets bad, so need to keep the motor raised which helped a lot with that problem but now have prop blowout.

Cheers

 

[Silvertip]

Re: 4 blade?

Do you have the lower end of the actuator moved fully forward in the slot (least pressure)??

 

[dabalone]

Re: 4 blade?

Yes, had the acuator's set a least resistance. Called Nauticus and gave them the info and explained what was happening, they are shipping new actuator's. Nauticus is a class act, helpful and set on satisfying their customers. My tabs may have been a little heavy for my application but they have done everything as advertised, highly recommend them.

Back to prop question, have decided the four blade ss is what I want. Have a 13 x 19 pitch stock alum., if I went to a 4 blade 19 pitch trophy plus what would that likely do to my rpm's, same, up or down? They come in odd pitches so going down would put me at a 17 pitch.

Thanks

 

[MikDee]

Re: 4 blade?

Common sense will tell you if your only doing 5200rpm with a 3blade 17" pitch, you will lose rpm with a 17" 4blade, then lose more rpm because it's a stainless steel prop. Maybe a 15" 3blade aluminum would put you where you need to be. You said your motors new, Is your motor fully broken in yet? If not give it some hours to get loose. By the way, tabs that are too restrictive can cause your prop to blow out also. Get the right actuators, then see how it runs.

 

[Crownie2]

Re: 4 blade?

I agree 100% with the above...

Bob

 

[dabalone]

Re: 4 blade?

Should have been more specific in my original post. Have a 13 X 19 pitch stock alum 3 blade mercury prop on the motor now. If I understand, going to a ss 4 blade with the same 19 pitch will decrease my rpm. I need to pick up some rpm trimmed out at wot to get me closer to the max 5750 the motor is rated for. A increase of 400 rpm would put me around 5600 ... 5650.

Since the motor is rated for 5750 rpm, should you try and hit that mark at full trim and wot, or something under that. Where should I try to be with rpms at wot, I don't want to lug the motor nor do I want to overstress it.

 

[MikDee]

Re: 4 blade?

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Since the motor is rated for 5750 rpm, should you try and hit that mark at full trim and wot, or something under that. Where should I try to be with rpms at wot, I don't want to lug the motor nor do I want to overstress it.

Yes, shoot for that rpm, or very close to it with a light load at WOT , & full trim, that's the motors best efficiency, then if, or when, you load the boat down, you usually have about a 500rpm lower range that it can fall to, and handle safely. a 15"pitch 3 blade aluminum prop will give you about 400rpm more, then you are now.