New gear ratio, need prop advice

[SC_Regal]

I replaced my outdrive with a new SEI drive and changed gear ratio in anticipation of a repower in (hopefully) near future.

1. 2000 Regal 2500 LSR
2. 25' LOA, 8'6" beam, 4200 dry (not sure if that is accurate) max HP 380(?)
3. 2-10 people, 30-70 gal of fuel
4. normal use is recreational, cruising and water sports
5. deep V, 24 degrees dead rise
6. engine - 2000 Merc 5.0 EFI Alpha I Gen II
7. HP - 240, new outdrive 1.47 (replaced 1.62)
8. max RPM 4800
9. N/A
10. N/A
11. Trim tabs
12. Mercury Enertia 18p, Quicksilver Black Diamond alum 16 x 16
13. WOT RPM Enertia 4100 rpm, 41.4 mph (GPS) Black Diamond 4600 39.8mph
14. sea level
15. tuned, good compression
16. New gear ratio
17. no damage to either prop
18. I'm trying to reach optimum WOT rpm. Prior to changing outdrives I was able to reach 4600 with the 18p Enertia. I would also like to improve holeshot.
19. testing today with 1 person and 1/4 tank, little wind and very little current:

18P Enertia:
3000 27.7
3400 33.0
4100 41.4 (WOT)

16P QS Black Diamond:
3000 25
3400 29.5
4600 39.8

I will be verifying the accuracy of my tachometer tomorrow (but I feel its accurate). Any advice would be appreciated.

Mike

 

[SC_Regal]

Re: New gear ratio, need prop advice

I was thinking about 15P Rev 4 or 15 Mirage

any thoughts?

 

[craze1cars]

Re: New gear ratio, need prop advice

I'm wondering if a 15 is small enough...here's my thinkin'...

I think you should throw out the results from the Black Diamond...aluminum, non-aggressive design. Has NOTHING similar to what you are shopping for. The Enertia results, being stainless, IMO provides you a better base run to work from.

So if you're turning 4,100 with the Enertia, and you want to target 4,800 (assumption based on your "optimum RPM" and "holeshot" comments), then you are trying to gain 700 rpms from your current.

Moving from Enertia to Mirage adds more cupping & rake...it appears to me a more aggressive prop. That sort of is like adding 1" of pitch in itself.

Moving form Enertia to Rev 4 adds cupping/rake AND a 4th blade...IMO that might be kinda like adding 1.5" of pitch.

So you propose a drop from an 18 to a 15 (but you must remember these are 15's which will act like a 16 or 16.5 for calculation purposes) so you've only effectively dropped 1.5" to 2" of pitch from where you started. I suspect your RPMS will therefore increase by maybe 300-400ish from your 4,100 starting point....bringing you up to about 4,400 or maybe 4,500. So I think they'd bring you to the bottom half of your RPM range...

Is that good enough for you to be at the bare minimum? Not sure...depends in your usage. And are my guestimates even accurate? Again I'm not sure.

I have no personal experience with ANY of these props. I'm goin' on theory alone, which is sometimes out-of-range in the field. But, that is why I'm still guessing maybe a 14 pitch prop might be in order for you, if available? Maybe even a 13?

And maybe those would over-rev a hair....

As always, test drives are worth 1,000 on-line calculations...if you have a local shop that will let you test/swap until you find a good one, that's an awesome place to buy a prop...

So howsabout an Enertia in a 14 pitch? It's available, and probably the easiest prop to predict of all since you already own one. I usually say 175 rpms per inch of pitch is a general solid guideline. So going from an 18 to 14 will drop you 4" of pitch x 175 rpm = 700 rpm....and that gives you your magic number...4,800....

Then again the 4th blade WILL help your holeshot even more...Enertia doesn't have this...but Rev 4 can only be had as a 15 pitch...and I think it might underrev for ya...

 

[SC_Regal]

Re: New gear ratio, need prop advice

Thanks for the reply

you (craze1)were very close

had a chance to take out a 15 Mirage. Added my wife and 2 dogs

WOT 4200-4300 38.8; 3400 30.3; 3000 26

best holeshot of the bunch however - if I could squeeze out some rpm

any other options in a 14 or less aggressive (maybe less diameter) 15?

 

[craze1cars]

Re: New gear ratio, need prop advice

I'm still thinking an Enertia in a 14 might be your best choice. Or save a few buck and just get an aluminum version from someplace, and call it good enough until you repower....

To be maybe painfully honest...I think you've handicapped yourself with this regear, and I believe you'll be challenged to match the performance you had prior to the regear. Short pitch props on big gearcases are rather inefficient....that's why very few manufacturers offer anything smaller than a 15 to fit the Alpha...they simply work rather poorly when compared to the more conventional 17 to 25 pitch range that most people run on I/O's. When you get outside of that general range, conventional wisdom says you should regear.

So I see a few options:

1. Run a stainless prop with too big a pitch and the motor will under-rev and be doggy...as you have now with that 15 Mirage....

2. Run a prop with a nice small pitch (find a 13 or 14 in stainless...or maybe a 15 in aluminum) and the motor will spin up to proper RPMS, but it will be a less efficient spin, with a bit of extra slip, and therefore your boat will not be much quicker out of the hole or faster on top end...but at least your motor will be happy and won't know the difference. Stainless 3 blade options to consider in 13 pitch: Solas New Saturn, Stiletto Advantage. Both should get your RPMs up nicely into range, I'd guess probably dang close to 4,800.
The Solas HR Titan in a 14 pitch is available as well and might work well for you, a bit more aggressive design than the Enertia and others above, therefore might rev less...maybe 4,500 or 4,600?: http://boatpropellers.iboats.com/Me...-150-14_Propeller/765/9594/?*******=955386690

Here's a Popular aluminum choice if you really want a 4 blade, and relatively cheap: Solas Amita. Smallest you'll find is 15...I'll speculate that it MIGHT run 4,600 max?? And probably will pull out of hole better than your current Quicksilver with similar top speed: http://boatpropellers.iboats.com/Me...65/9591/?prod_opt_id=405774&*******=955386690

3. Regear properly and go back to your original 18 pitch prop.

4. Add the horsepower necessary to push this big gear...in other words repower NOW rather than wait...then test with your 18 to get some baseline data and reprop accordingly from there.

5. If you're already stuck owning that 15 Mirage, maybe you can hand it over to a local prop shop, and pay him to take an inch or two of pitch out of it. It will help your holeshot, and rpms would come up, but it would introduce some inefficiencies and likely leave you with about the same top speed or maybe a bit less.

6. Don't spend a dime and run that Quicksilver you already have that runs at 4,600 rpm...and save up for repower ASAP.