Which would be better for my performance? A 3 or 4 blade prop?

[Jquest]

I have a 20ft'r. I usually just run with 2 to 3 people on board and that is it. Right now I'm swinging a 14 1/4x19 prop. Fully trimmed I'm getting 5200rpm. I know I'm lugging the engine and I'm trying to get those 300 rpms that the engine would love. Could I go to a 4 blade 14 3/8 by 18 pitch or should I try a 15 x17- standard for my engine? I know I should be making it with the prop I have now ,but I have a Dusky and my haul is heavier than most boats. On top of that...I added a t-top last year so that is more resistance when it comes to the wind.

The reason why I'm asking about the 4 is....I've heard it brings the stern out of the water more and I'm hoping that will be less friction when it comes to my haul and the water when it comes to speed. I've also heard that having a 4 blade might take a little of my top end. My top speed with my current prop is about 41-42 (according to my gps).

 

[walleyehed]

Re: Which would be better for my performance? A 3 or 4 blade prop?

I'm gonna leave this to Dhadley...I believe he knows the Dusky quite well.
I will say, however, that 15X17P OMC is a very good design in the aluminum market, But I think I see a Good, quality SS in your future.

 

[Jquest]

Re: Which would be better for my performance? A 3 or 4 blade prop?

I was thinking about the apollo 15 1/2 x 17. I know I might have to shave the anode a bit. About the only thing I'm concerned about is the diameter of the blade. 15 1/2 is rather large for a 150.
I also like the apollo blade cause of the hub design. No slippage and easy to replace.

BTW....thank your reply my friend.d

 

[Dhadley]

Re: Which would be better for my performance? A 3 or 4 blade prop?

When we ran the 60* 150 on our 20' Dusky we ran a 14 1/4 x 19 Turbo I. It topped out at about 5700-5800 depending on load. Obviously we're at sea level. You're right, if mine is anything like yours -- it's a tank.

We ran a 10" Bob's hydraulic plate. It got the motor weight further back to help lift the nose in rough water and cleared the transom which we had built up some. It's amazing how high we could run that prop. Don't be afraid to play witrh that.

 

[Jquest]

Re: Which would be better for my performance? A 3 or 4 blade prop?

First of all...thx for the reply Dhadley. I have pretty much put the prop on top of the water. My top rpm was 5300 at 42mph (gps) rooster tailing it and I could only do it for a bit cause I was venting the lower unit and the engine started to heat up. My boat has the dusky drive extension, but I don't have a jack plate. I think one of my problems is the t-top I put on it. More resistance , but with the summer sun down in S. Fla...I really do need it or I'm gonna bake.
Have you tried the new Apollo prop (15 1/2 x 17)? My only concern is the 15 1/2 width. The prop that I have now is only 14 1/4 so I might loose 100 rpms, but I think I will gain 500 on the pitch ( coming back to 17). I really love the prop I have now I just can't hit the sweet spot.

 

[Dhadley]

Re: Which would be better for my performance? A 3 or 4 blade prop?

Ah -- you have a wing.....er...T-Top. Yes, that can make a huge difference. The Dusky drive should help the balance even more than the 10" Bob's we had.

To be honest I never tried any other prop than the Turbo brand. One of my best friends had the boat for about 10 years before I bought it from him. We've had about every conceivable V4 or V6 OMC on it you can think of except a DI or an E-Tec. Yes, we had a Ficht on it. The 60* was the best overall.

You should pop over here (Fl west coast) tomorrow. We're having a prop shootout. We got all kinds of props you could try.

My son has the Dusky now with a crossflow 150 and he uses the OMC / BRP 15 x 17 prop. Works real good on the crossflow.

 

[Jquest]

Re: Which would be better for my performance? A 3 or 4 blade prop?

:'( you're killing me. I'd love to show up just to see all the hardware. Unfortunately I'm in Miami and Port Charlotte is a couple hours away. Not to mention all the family stuff I have to do tomorrow. But I thank you kindly for the info you have given me and the invite.
d

 

[walleyehed]

Re: Which would be better for my performance? A 3 or 4 blade prop?

For what it's worth here, I've ran the large apollo and don't let that diameter scare ya...The apollo does not have the same cupping as a higher tech Turbo and I don't think it'll cost ya any RPM...
As a wise man once told me; "If you need an excuse to get on the water, start testing every prop you can get your hands on"........(The Port Charlotte Prop Master)8)

 

[Jquest]

Re: Which would be better for my performance? A 3 or 4 blade prop?

Thank you for suggestion. I'm gonna have to test out that 15 1/2 from Michigan. I really like their props and love the replacement hub setup. Thx for the input buddy. I really appreciate you and DH chiming in.

 

[walleyehed]

Re: Which would be better for my performance? A 3 or 4 blade prop?

Keep us posted!

 

[Jquest]

Re: Which would be better for my performance? A 3 or 4 blade prop?

My son has the Dusky now with a crossflow 150 and he uses the OMC / BRP 15 x 17 prop. Works real good on the crossflow.

If It's not too much trouble. Could you ask your son if he has the old 391290 (true 15x17) or the new 176615 (14 3/4 x 17)SST that superceded it.
THX!

 

[Jquest]

Re: Which would be better for my performance? A 3 or 4 blade prop?

Well...I have a winner. Searched all up and down the net looking for hints and articles on prop performance when it came to OMC and props. Found a couple of guys who did a test on a Whaler with an OMC engine. IT convinced me to look for a 15 x 17 omc prop. The old number got superseded with this number "176615" (off shore SST model ). IT's a 14 3/4 x 17 pitched and cupped prop. I found one on ebay(N.I.B) for half the price of the dealer and ordered it. I took my boat out today and I was able to pop 5600 (could of gone to 5800) at 41.2 mph (gps). I'm sure I could of made it to 42 tweaking it ,but didn't feel like venting the lower unit like I did last time. Anyway....I'm happy as a clam.
Using the prop calc....it looks like my slip is around 14%. I guess that is decent.d

 

[walleyehed]

Re: Which would be better for my performance? A 3 or 4 blade prop?

Good deal..
If you ever get the chance, the original alum 15X17 OMC was a 391200 zillions of them around..this is the prop I am convinced is one of the best alum designs ever.