Three vs four blade vs pitch change

[Rmc]

Hi
I know three vs four blade prop performance had been discussed forever but here it is again.
I have an 18.5 Stingray with a 130 hp four cylinder Merc. inboard. Normal pleasure riding the boat performs fine. Top speed in the mid forties. The prop is an alum. three blade 14.5 X 19" pitch.
( A chacteristic of the boat is that you have to run it with the trim all the was down all the time no matter how it is loaded. I don't know if this is normal for this boat or not. If anyone has one and knows please post. )
My question is this.
I want to improve the hole shot, when trying to pull a slyier out of the water Currently the boat does not perform well. The engine appears to ramp up ok but the boat takes a long time getting up to speed. Should I go to a 17 " three blade, a 17" four blade or would a 19" four blade increase the pulling power while keeping the top end speed.
If the 19" would perform well I would not have to change props for pleasure cruising.
Thanks RMC

 

[John_S]

Re: Three vs four blade vs pitch change

What happens if it is not trimmed all the way in? cavitation? even once you planed out?

Current WOT RPMS and GPS speed?
Gear ratio?

 

[craze1cars]

Re: Three vs four blade vs pitch change

Stingrays are notorious for needing trim to be all the way down at most speeds below 35-ish mph. It is characteristic of their high-speed designed hull. If you trim out too early, I will suspect your complaint is that porpoising becomes severe? If yes, it's because you purchased a Stingray.

Many fix it with Smart Tabs. And many just leave the trim down at all speeds below 35.

As for your prop question, we need RPM information in order to make any recommendation. When you are going WOT/full speed/trimmed out with your current 19 pitch prop, what is your RPM?

Also, what is the recommended RPM range for your particular engine?

Your ideal target, for watersports purposes, is to be right at or slightly above the max number of this RPM range. This will maximize holeshot. Tell us where it is at now, and we can tell you what kind of pitch/blade change would be best to get you to that target.

 

[Rmc]

Re: Three vs four blade vs pitch change

No it dosen't cavitate,you just can't keep the bow down.
It's my daughter's boat so I am not sure of the gear ratio,but the rpms are around 4500 at 45 mph.
Rmc

 

[Rmc]

Re: Three vs four blade vs pitch change

craze1cars
I will have to check this out the next time we put the boat in the water to be sure. I will post again when I get the info. It may be a week or so.
Rmc

 

[90stingray]

Re: Three vs four blade vs pitch change

I would go with a 4 blade 17 pitch. Should suit you well for pulling. Just watch the rpms on the top if you are running light load. I have a turning point hustler 4 blade on my Stingray. I also have a whale tail. It does what its supposed to but after finding out how Stingray hulls operate... i should have went with trim tabs. And my stingray operates the same as you state... needs full trim down until 35 mph. Hope this helps.

 

[craze1cars]

Re: Three vs four blade vs pitch change

No it dosen't cavitate,you just can't keep the bow down.
It's my daughter's boat so I am not sure of the gear ratio,but the rpms are around 4500 at 45 mph.
Rmc

What year is this 3.0? Some of the older ones had a max RPM rating of 4,600. Newer ones have max RPM rating of 4,800. Whichever it is, that is your target for propping for watersports with a 3.0 powered boat, and exceeding it a little bit (100 or 200 rpms) is harmless...and better than being below it.

If your current speed/RPM is accurate, then I tend to agree with previous post. I also suspect that a 4 blade 17 pitch will probably serve you well and be a notable improvement over your current 19 pitch 3 blade. You might lose 1-2 mph top speed is all, but the planing improvement will be dramatic.

Definitely don't get a 19 pitch in a 4 blade, it'll drag your RPMS too low.

 

[John_S]

Re: Three vs four blade vs pitch change

Stingrays are notorious for needing trim to be all the way down at most speeds below 35-ish mph. It is characteristic of their high-speed designed hull. If you trim out too early, I will suspect your complaint is that porpoising becomes severe? If yes, it's because you purchased a Stingray.

Thanks for the explaination. It sounded like there was a problem with the boat. Would you want to put a 4 blade with more stearn lift on this type of hull?

 

[craze1cars]

Re: Three vs four blade vs pitch change

Going to 4 blade Solas HR Titan (advertised as a stern lifting prop) improved the porpoising on my Stingray a tiny little bit...but not a whole lot. I'm not a fan of how Smart Tabs slop-up a wakeboarding wake, and that is my primary usage, so I skipped the tabs and just leave the trim down...and it doesn't porpoise with trim down.

I even went so far as to relocate my battery from stern to up under the dash, and engine compartment storage is for life-vests ONLY (nearly weightless)...everything else gets stored in the bow, etc. That all provided very minimal improvement. Heck, it'll even porpoise with 3 people sitting in the bow (exciting for them!!)

Porpoising is the #1 complaint of Stingray owners....almost across the board. It's a combination of their hull design and their higher outdrive placement. They are pretty much set up more like bass boats than runabouts, and they often need to be treated as such.

Frankly I find ignoring the trim button rather simplifies driving for most everyone...it's one less button to worry about at normal watersports speeds, and it drives very normal and clean if left down. So I just trim it out only if exceeding 35-ish...which is generally rare with the exception of barefooting or the occasional high speed fun-run or boat race, and that stuff only happens if I'm the driver, and I understand how it needs to be handled.

The other thing to remember on my Stingray is that I NEED to trim it down AS I decelerate from 40+ towards 30. Trim it down too early and it starts to violently bow steer (dangerous). Trim down too late and the porpoising hits HIGH and HARD...there's a fine line on these boats that only is learned with experience. Then again, it's designed as a high-speed runabout, and mine can pretty much tickle 60 mph on a GPS....and once trimmed out at 55+ it is stable as a ROCK, even in heavy chop! Not many 20 foot 5.0L runabouts can claim that type of top speed or handling....it's what they're designed to do, but they drive much different than other brands at "normal" cruising speeds.

 

[John_S]

Re: Three vs four blade vs pitch change

Thanks for the detailed explaination. I was not familiar with how Stingray hulls handled. All the porposing issues I've experienced, have been at higher speeds when trimming out. Smart tabs eliminated the issue on my i/o.

I do have a heavy stearn with 5.7L. I just received an Amita 4 blade to try this coming weekend. I am generally happy with the performance of the current Black Max 14.25" X 21", but wanted to try a 4 blade for a little better water toy and mid cruising improvement. Went with a 19" pitch. Bayliner originally provided a 15" diameter prop on this boat, but its had only 14" diameter props on it since I owned it. I do plan to post a seperate thread on the results.

PS: My apoligies to original poster for getting a bit off topic.

Note: That is interesting. Stingray appears twice in the posted version, but there is only one in the text???

 

[Rmc]

Re: Three vs four blade vs pitch change

90stingray and crazeicars
Your advice sounds good. I believe we will go with the four blade 17" pitch prop.
Thanks Rmc