4 blade prop change pitch question

[lrazer]

im looking to change from a 3 blade to 4 blade for better performance for wakeboarding and tubing and im not sure what pitch to go with. i was told that my motor should be between 4200-4800 at wot is this correct?

1) Performance issue you are trying to correct. - better holeshot, maintain plane better at lower speeds
2) Current prop manufacturer, model, aluminum or stainless as a minimum. - aluminum
3) Current prop diameter and pitch (required). - 14.25 x 21
4) Wide open throttle RPM and speed with an average load (very helpful) - 5000 to 5200rpm at 48 to 50 mph
5) Engine/drive make, model, year, and HP - 01 glastron 195sx volvo 5.0l 220 hp
6) Boat make model, year, length and weight

 

[craze1cars]

Re: 4 blade prop change pitch question

Your motor's correct range is 4,400 to 4,800. If you are currently at 5,000 to 5,200 and are expecting an improvement in holeshot, you will be challenged to be satisfied...

You have a whole lot of slip right now for a boat like yours...22%. This assumes you have a 1.60 drive ratio which I believe is correct original...do you have any reason to believe your outdrive has been changed to a different ratio during its lifetime? Is your prop nicked up and/or damaged in some way? Are you trimming out for full speed? Have your speed and RPM numbers been verified with another source like GPS or another tach?

Anyway, if all of your provided data is accurate, and my 1.60 ratio assumption is accurate, I believe if you were to change to a more efficient/aggressively designed 4 blade of the same 21 pitch, it will bring your rpms down close to about 4,600 to 4,800 while maintaining and/or slightly improving your current overall performance....including holeshot AND top speed. This would happen due to a reduction in propeller slip. For some reason your current prop seems to be quite inefficient for your boat's size/weight/motor.

 

[albs]

Re: 4 blade prop change pitch question

I have the exact setup as you except on a 21' with a WOT of about 4500 at 48 mph. I just switched my prop to a 4 blade 14.25x19 and it holds much better at low speeds for wakeboarding. I would think keeping your same pitch and just switching to a four blade would help alot for your set-up.

 

[lrazer]

Re: 4 blade prop change pitch question

the speed was with gps and the rpm was the tach on the boat, the prop has small nicks nothing bad just the edges are roughed up a bit
would a 19 pitch 4 blade keep the rpms the same or make them higher? im on a small lake so im usually never wide open (only about 20 seconds and you're across the lake). im mainly interested for watersports but i dont want the rpms even higher than they already are

 

[Tail_Gunner]

Re: 4 blade prop change pitch question

the speed was with gps and the rpm was the tach on the boat, the prop has small nicks nothing bad just the edges are roughed up a bit
would a 19 pitch 4 blade keep the rpms the same or make them higher? im on a small lake so im usually never wide open (only about 20 seconds and you're across the lake). im mainly interested for watersports but i dont want the rpms even higher than they already are

Yes a 19 pitch 4 blade in a solas would suit you well. You may gain rpm but 20 seconds is not going to hurt a thing..You will be happy...better to much money in the account than to little...

 

[lrazer]

Re: 4 blade prop change pitch question

well i have a 19pitch 4 blade on now it is much better low end. high end didnt change still around 5100-5200 at wot

 

[lrazer]

Re: 4 blade prop change pitch question

so i actually am hitting around 5400 rpm at wot with the 4 blade 19 pitch. if my motor is over reving this much then am i correct to assume that it has enough power that a 21 pitch 4 blade wont hurt my low end much?

 

[craze1cars]

Re: 4 blade prop change pitch question

5400 is too much IMO. You're a full 600 rpms beyond the peak power output of your engine. I am surprised your RPMS went up that high, but my gut did tell me right up front that a 19 would be too low a pitch, as you were over-revving already when you started this post. Thus my initial recommendation that you buy a 4 blade 21.

And I still suggest the same.

Curious what brand/model of 4 blade 19 did you actually buy? It still seems to be slipping a lot. I'm guessing it is not actually a Solas brand that Tail Gunner mentioned?? They usually bite better than yours is (I am assuming you are now running 49 mph at 5400 rpm with this 19.

No matter how much power your boat has, going up to a 21 will indeed hurt your holeshot a little bit...but not much. It probably will also increase your top speed a bit.

So your other alternative is to leave this 19 on the boat, almost never use top speed, and be disciplined enough to keep it below 5,000 rpms for any extended run.

 

[lrazer]

Re: 4 blade prop change pitch question

its a solas amita 4 blade, its about 51-52 at 5400 that was with the boat speedo i didnt have the gps this time. the holeshot is great and i dont have a problem with keeping it at 4800. im just one of those guys that cant leave stuff alone, i wanted to see if i could get alittle more top end out of it as long as i dont hurt the low end too much. 5400 just seems like alot of wasted rpm

 

[craze1cars]

Re: 4 blade prop change pitch question

I'm surprised the Solas is spinning that fast, as they're generally quite efficient, but the Amita is the aluminum model, and I don't have much experience with those. I always prefer stainless in most applications. They cost more because they simply grab the water better, and I feel the money is worth the added performance, with few exceptions.

If I were you, I'd replace it with a 21. Whether you choose aluminum or stainless. I'm a fan of propping for slight over-revving, especially for watersports usage, but 5400 is just too much on a boat that's rated for 4,800 max.

The only way to answer your question as to how much more you can get and/or lose with prop changes is to spend money and experiment. Or find a local shop that will allow exchanges and testing.

 

[lrazer]

Re: 4 blade prop change pitch question

i would agree, i figured i would experiment with aluminum and find what works best before dropping the money on stainless