4 Blade to 3 Blade?

Ruggybuggy · Oct 27, 2009

I have a 1998 Evinrude 25hp 3 cylinder that is mounted on a 1998 Princecraft Pro 142 (14' with a beam of 73"). The boat is running a OMC 10.5 X 12 four blade prop and achieve 25 mph. I want better top end performance and considering a 3 blade 10 X 13. Will the 13 pitch result in the same RPM's or should I go to a 15? I have a very good holeshot so I'm thinking it won't be a problem with the 3 blade.

trendsetter240 · Oct 27, 2009

Re: 4 Blade to 2 Blade?

Re: 4 Blade to 2 Blade?

Going from 4 blade to 3 blade and adding 1 inch of pitch should give you roughly the same RPM. (Drop 200RPM for the 1 inch pitch increase and add 200RPM for the drop from 4 to 3 blades). You may be able to get another 5mph from that change.

You can also look at raising the motor up on the transom. If the anti-cavitation plate is currently inline with the bottom of your boat, try raising it up 1/2" and see if that helps.

If the anti-cavitation plate is below the bottom of your boat then definitely raise it to at least even with the bottom.

jdsgrog · Oct 27, 2009

Re: 4 Blade to 2 Blade?

Re: 4 Blade to 2 Blade?

The number of blades does not matter for rpm. Whether a 4 blade or 3 blade, if the pitch is the same, the rpm should be the same. A 13 inch pitch will be about 200 less rpm than a 12 pitch. The reason you have a good hole shot with the four blade is that you reach your rpm's faster (lower pitch) and you have more surface area to "bite" the water (4 blade). I would think that a higher pitch prop may help marginally in top speed at best, but may also decrease top speed if it's pitched too high (especially with heavier loads).

Ruggybuggy · Oct 27, 2009

Re: 4 Blade to 2 Blade?

Re: 4 Blade to 2 Blade?

trendsetter240 said:
Going from 4 blade to 3 blade and adding 1 inch of pitch should give you roughly the same RPM. (Drop 200RPM for the 1 inch pitch increase and add 200RPM for the drop from 4 to 3 blades). You may be able to get another 5mph from that change.

You can also look at raising the motor up on the transom. If the anti-cavitation plate is currently inline with the bottom of your boat, try raising it up 1/2" and see if that helps.

If the anti-cavitation plate is below the bottom of your boat then definitely raise it to at least even with the bottom.

The motor is already about 1/2 inch about the bottom of the boat I'm good there. If I could get an extra 5 mph I would be a happy camper. The local prop shop said that OMC is not making a 3 blade for the 25-35 any more and the only thing available would be the 4 blade. He seemed to think that 28 mph would be doable with the right pitch 3 blade so if I achieved better it would be icing on the cake. I manage to find someone that has a new 3 blade in 10 X 13 for $60 so I'll probably buy it.

Ruggybuggy · Oct 27, 2009

Re: 4 Blade to 2 Blade?

Re: 4 Blade to 2 Blade?

jdsgrog said:
The number of blades does not matter for rpm. Whether a 4 blade or 3 blade, if the pitch is the same, the rpm should be the same. A 13 inch pitch will be about 200 less rpm than a 12 pitch. The reason you have a good hole shot with the four blade is that you reach your rpm's faster (lower pitch) and you have more surface area to "bite" the water (4 blade). I would think that a higher pitch prop may help marginally in top speed at best, but may also decrease top speed if it's pitched too high (especially with heavier loads).

From everything I've read going from 3 blade to 4 blade decrease pitch 1" and visa versa to maintain the same RPM. Some were even saying 2" that why I wasn't if I should go to a 13" or 15".

trendsetter240 · Oct 27, 2009

Re: 4 Blade to 3 Blade?

Ruggybuggy said:
The local prop shop said that OMC is not making a 3 blade for the 25-35 any more and the only thing available would be the 4 blade.

You don't have to get an OMC prop, there are lots of aftermarket props available.

They sell them right here on iboats, try the link below:

http://boatpropellers.iboats.com/Ev...00-Pitch_Amita_2211-101-13_Propeller/37/6166/

I used that one on my 1997 evinrude 25hp and it would push my 14" runabout at 30mph.

http://www.youtube.com/watch?v=yaO8mmagZvg

walleyehed · Oct 27, 2009

Re: 4 Blade to 3 Blade?

I don't see a single post about rpm....the deciding factor on where to go...
4 to 3??? yes, you will gain rpm in the same blade design, but you will not gain 5mph with any other prop on that engine.
figure about 16-17hp more required per mph to gain with all other factors the same....yea, you should optimize the set-up and get the most height out of the prop you have first without venting, then look into higher tech wheels or more HP.
You can throw props at it all day long and you might find 1, maybe 1-1/2mph but you'll be at the lowest rpm of the range if still in it at all.

Ruggybuggy · Oct 28, 2009

Re: 4 Blade to 3 Blade?

trendsetter240 said:
You don't have to get an OMC prop, there are lots of aftermarket props available.

They sell them right here on iboats, try the link below:

http://boatpropellers.iboats.com/Ev...00-Pitch_Amita_2211-101-13_Propeller/37/6166/

I used that one on my 1997 evinrude 25hp and it would push my 14" runabout at 30mph.

http://www.youtube.com/watch?v=yaO8mmagZvg

Thanks for the link to the prop. I was trying to get the OMC prop because the local prop rebuild guy had told me there was a lot of junk out there and to stay with the manufactures prop. Your boat looks to be fiberglass so the weight may be similar to my aluminum. If I could get that kind of speed from mine I would be very please. I'll go ahead and order the Solas 10 X13 prop you linked me.

Thanks for your help.

trendsetter240 · Oct 28, 2009

Re: 4 Blade to 3 Blade?

Ruggybuggy said:
I was trying to get the OMC prop because the local prop rebuild guy had told me there was a lot of junk out there and to stay with the manufactures prop.

Yep, there probably is a lot of junk out there. I've had a few Solas props and haven't been let down yet.

Good luck with your new prop and post back with your results!

Ruggybuggy · Nov 8, 2009

Re: 4 Blade to 3 Blade?

I got a chance to put on a 15 pitch prop that the local prop shop let me try out. The boat ran 27 mph but the RPM's were down compared to the 4 blade that I had on. I'll have the Solas 13P tomorrow and hopefully the weather will hold out to try it. It should put me exactly in the right RPM's and hope to get another 1 or 2 mph.

This might all be in vain because I'm looking at buying a 2004 Merc 50hp for a very good price, $1500.

trendsetter240 · Nov 8, 2009

Re: 4 Blade to 3 Blade?

Nice! Sounds like you are right on track. You can expect another 400-500RPM with the 13p prop,

Is your boat rated for a 50hp? $1500 sounds like a very good deal if the motor is in good condition.

Ruggybuggy · Nov 8, 2009

Re: 4 Blade to 3 Blade?

trendsetter240 said:
Nice! Sounds like you are right on track. You can expect another 400-500RPM with the 13p prop,

Is your boat rated for a 50hp? $1500 sounds like a very good deal if the motor is in good condition.

Nope, boat is only rated for a 35 tiller or 40 console. If I use the Coast Guards formula it works out to 47hp so it should be OK. The boat has a beam of 73" and transom of 70" and 20" deep so it should be a problem. In Canada we have insurance problems with overpowering. The guy is bringing the motor around tomorrow for me to check out. If it doesn't work on the boat I'll sell it in the spring and make a few bucks.

trendsetter240 · Nov 8, 2009

Re: 4 Blade to 3 Blade?

Well I would never recommend going over the maximum HP rating for any boat. I'm in Canada too and insurance aside, it's a safety issue for you and other boaters.

As for buying a motor for a good deal and selling it in the spring, go for it! I do that all the time. Just be sure of what you're buying. i.e. why is this guy selling it? Is there something wrong with it? Is it stolen?

Lots to think about. Also if he is willing to bring it out to you to test it I'm sure he is a motivated seller. Offer him less than he is asking; limit your risk factor as there may be something you need to repair/replace on the motor before selling it.

Good luck with that and be safe!

junior1113 · Nov 9, 2009

Re: 4 Blade to 2 Blade?

Re: 4 Blade to 2 Blade?

Ruggybuggy said:
From everything I've read going from 3 blade to 4 blade decrease pitch 1" and visa versa to maintain the same RPM. Some were even saying 2" that why I wasn't if I should go to a 13" or 15".

3 to 4 go down 1 inch in pitch and 4 to 3 go up 1 inch pitch. # of blades of same pitch is is definatly going to change rpm. why go to 3. 4 blades are all around better performers (all i run). i think youll lose mph with a 3. hope your within recomended upper wot rpm range. wot rpms mean more than wot mph (for the life of engine)

Ruggybuggy · Nov 15, 2009

Re: 4 Blade to 3 Blade?

trendsetter240 said:
Well I would never recommend going over the maximum HP rating for any boat. I'm in Canada too and insurance aside, it's a safety issue for you and other boaters.

As for buying a motor for a good deal and selling it in the spring, go for it! I do that all the time. Just be sure of what you're buying. i.e. why is this guy selling it? Is there something wrong with it? Is it stolen?

Lots to think about. Also if he is willing to bring it out to you to test it I'm sure he is a motivated seller. Offer him less than he is asking; limit your risk factor as there may be something you need to repair/replace on the motor before selling it.

Good luck with that and be safe!

I tried the 50 on the boat today and I'm disappointed. With the 50 on the boat becomes a handful. I have to trim it all the way down to keep it from porpoising and slowly trim up as I increase speed. Wide open I would do around 34-35 mph but it's not an enjoyable ride. With the 3 blade on the 25 Evinrude I could run 28-29mph so for the extra 6 mph it's not a good trade off. For me to run the 50 Merc comfortably my speed was down to were the Evinrude runs at WOT. The 25 is going back on and I'll sell the Merc in the spring and make some cash.

I'm now a true believer that smaller outboards (under 30hp) should all be two stroke. The two stroke are lighter and less weight on a small boat is a good thing.

Ruggybuggy · Nov 22, 2009

Re: 4 Blade to 3 Blade?

I put back the Evinrude 25hp and used the 3 blade 13 pitch and achieved 28mph so that's a 3mph increase over the 4 blade 12 pitch prop. I'm pretty happy with the result so my next step is to remove the hydrofoil and see if I can squeak another 1-2 mph out of her.

trendsetter240 · Nov 22, 2009

Re: 4 Blade to 3 Blade?

Ruggybuggy said:
I put back the Evinrude 25hp and used the 3 blade 13 pitch and achieved 28mph so that's a 3mph increase over the 4 blade 12 pitch prop. I'm pretty happy with the result so my next step is to remove the hydrofoil and see if I can squeak another 1-2 mph out of her.

Hey was this with the Solas prop? 3mph increase is pretty good, I know 5 would've been better

, does it spin at the same RPM as your 4 blade 12p did?

Ruggybuggy · Nov 23, 2009

Re: 4 Blade to 3 Blade?

trendsetter240 said:
Hey was this with the Solas prop? 3mph increase is pretty good, I know 5 would've been better , does it spin at the same RPM as your 4 blade 12p did?

Yep, was the same one you are running on your boat. The RPM's seem to be about the same as the 12p but I didn't put a tach on it, by ear. The boat I have it on weights around 600lbs which is probably a little heavier then yours. When I remove the hydofoil I think I can get pretty close to 30mph but it might have to wait till spring, the lakes are freezing up here.

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