Prop Selection

[lape0019]

Hey Guys,

I messed up a 17p aluminum prop last year to the point where it is just not cost effective to fix it. There were only a few nicks in it, but the hub had started slipping as well. I have been using my 19p (spare) which I assume originally came with the motor and the whole shot sucks and I cannot get it into the max RPM range so I know this is too much for my setup.

With the 17p on my 2006 Mercury Fourstroke 75HP, I was able to hit 6000rpm without blowing out but I usually run it around 5500rpm (RPM operating range in the book is 5500-6000). Top speed is about 39mph

With the 19p, The max rpm I was able to get without blowing out was 5100. My top end was faster, but I was not hitting the operating rpm's and it was really touchy when I got to 5100. If I trim it too much, the rpm would sky rocket, if I trimmed it to run at 500rpm, I could not easily steer the boat. Top speed with this is 40mph but it is touchy.

I am going to be buying a new 17p this weekend and am thinking about going Stainless. From what I have read, most people state to drop another pitch (17 to 15 in my case I guess) but is this necessary or true?

Any information you can provide me with at this point would be greatly appreciated. There is a lot of info on the internet, but I haven't really found a definitive answer to my questions.

Thanks!

Adam

Do any of you guys have any experience trying to use the same pitch size stainless as your aluminum prop?
If so, how did it affect your rpm's?

Will staying with the same pitch allow me to trim the motor up more if I do go stainless.

[CNs]

Adam

Aluminum props flex quite a bit, most find that 2" less pitch with stainless keeps the RPMs the same. The same pitch may be too much due to the cup on a stainless prop. SS usually provides more cup, allowing you to trim out more and provide more efficiency. Since the blades are thinner, have less drag. There will be a perfomance increase given you choose the correct prop.

Each engine mfg. has a series of props for hp. ranges.e.g. Mercury : Laser, Mirage,Tempest,Trophy,Vengence,Revolution,High 5 and Bravo. Props are like cam shafts for V8 car motors. It depends on where you want the performance of your boat to be ( hole shot, mid rang, top end, carry the bow, more stability in turns etc. ) Remember once you pick a prop you can fine tune it with a knowledgeable prop shop. He could add some variable cup and pitch, ventilation holes to help the prop spool up to a desirable RPM etc..

You could call aim outboard in Carp. They mmay be able to steer you in the right direction.

[StarTzar]

Adam

Aluminum props flex quite a bit, most find that 2" less pitch with stainless keeps the RPMs the same. The same pitch may be too much due to the cup on a stainless prop. SS usually provides more cup, allowing you to trim out more and provide more efficiency. Since the blades are thinner, have less drag. There will be a perfomance increase given you choose the correct prop.

Each engine mfg. has a series of props for hp. ranges.e.g. Mercury : Laser, Mirage,Tempest,Trophy,Vengence,Revolution,High 5 and Bravo. Props are like cam shafts for V8 car motors. It depends on where you want the performance of your boat to be ( hole shot, mid rang, top end, carry the bow, more stability in turns etc. ) Remember once you pick a prop you can fine tune it with a knowledgeable prop shop. He could add some variable cup and pitch, ventilation holes to help the prop spool up to a desirable RPM etc..

You could call aim outboard in Carp. They mmay be able to steer you in the right direction.

Adam,

You need not look any further than what CN posted.

[lape0019]

Thanks Norm and Frank,

I didn't end up buying a prop this weekend because I still have not decided on if I want to go stainless or not. I have someone offering me a good deal in a 17p powertech SS that would work. He says that it will run almost identical (100-150 rpm different) to an aluminum because the blade surface is smaller but I am hesitating just because reducing the rpms that much could drop the rpms out of the wot rpm range.

I think I just answered my own question but with going with what Norm stated, I will probably just replace the old aluminum with another aluminum. If I do go stainless, I will drop down to a 15p.

Thanks again!

Adam

[CNs]

Thanks Norm and Frank,

I didn't end up buying a prop this weekend because I still have not decided on if I want to go stainless or not. I have someone offering me a good deal in a 17p powertech SS that would work. He says that it will run almost identical (100-150 rpm different) to an aluminum because the blade surface is smaller but I am hesitating just because reducing the rpms that much could drop the rpms out of the wot rpm range.

I think I just answered my own question but with going with what Norm stated, I will probably just replace the old aluminum with another aluminum. If I do go stainless, I will drop down to a 15p.

Thanks again!

Adam

Adam will he let you try it first? Then you would know if it works or not.

[lape0019]

Honestly Norm,

I didn't even bother asking. The guy who offered it to me, did so on Bass Boat Central and is a dealer in Illanois. If I could find something similar out here, I would most definitely ask but I don't feel like taking the risk on having to ship something out here without knowing for sure.

[bostonwhaler]

My local boat shop will let me try the prop before I buy it. If I damage it, then its mine, if it doesnt work to the desired outcome then they ship it back

[lape0019]

Hey BostonWahler.

I was hoping to hear that was comon around here but ended up just buying a 17P Mercuray Black Max prop. It was the same pitch as the Michigan Wheel that gave me great all around performce so I am hoping to get the same if not better performace out of an OEM prop.

The one difference is that the Michigan wheel had some vent holes almost in line with the blades. This probably helped a bit with holeshot but would have done nothing for top end so I am not worried.

My main concern with going stainless was I don't have the money to replace a lower end if I hit something with stainless and I really don't need an extra 1MPH. I figure the next boat will need a stainless prop but for now, aluminum will be fine.

[Pepe]

Hi Adam

Try this link as well - it may help you narrow down selections - http://www.mercurymarine.com/propellers/prop-selector/#

[lape0019]

Hey Pepe,

I have checked out the prop selector a few hundred time. I love how my manual states to stay within 5500-6000 rpm yet the prop selector always tells me to go with a prop with an estimated wot rpm of 5100...

I took the boat out for the first time today and the merc prop made a pretty big handling difference over the 17p michigan wheel as well at the 19p black max prop. Rpms at wot were at 5800 and I no longer felt like the prop/hub was slipping.

With my wife and kids and all of my gear in the boat, I still managed 38mph which is good considering my top speed with the 19p was 40mph.

Just want to say thanks again to all who have replied.