Crazy Prop Performance - need suggestions

[drivehard]

Boat:
1997 Bryant 212 Limited (bowrider)

Engine:
7.4L Mercury Bravo I with 1.50:1 ratio

Goal:
60mph

Prop #1:
lightly damaged Mirage Plus 23"
55 mph (GPS) at ~4200 rpm
NOTES: less than 1/4 tank fuel, only 2 adults on board. RPM too low for engine, vibration due to damage

Prop #2:
Stiletto Advantage II 23" (this is for the alpha outdrives, has one vent hole per blade)
55 mph (GPS) at ~4050 rpm
NOTES: Half tank fuel, two adults on board. RPM WAY too low for engine, VERY efficient, bites hard, can trim all the way up.

Prop #3:
Stiletto Advatage III 21" (this is for the bravo outdrives, larger diameter over II by 0.25" and larger blades, no vent hole)
Greater than 5000 rpm, 55mph, and still climbing
cruised at 2900 rpm and 31 mph (18% SLIP!!!!!!!!!)
NOTES: Full tank of fuel, two adults and 2 children on board. Very quick out of the hole...prop can't hold the engine, way too much slip. Good bow lift.

Questions:
Why on Earth did I gain 1000+ Rpm by dropping the pitch only 2" on the Stiletto? Am I maybe slipping the hub? I will mark and re-run Prop #3 to be sure.

What prop to try next? My wife is NOT a fan of me dropping this kind of coin on props...when obviously to her they all "work".

 

[642mx]

Re: Crazy Prop Performance - need suggestions

Take prop #1 and send it to bblades for repair/lab finishing. Tell them your max rpm (4200) and they will modify the blades to raise your rpm. Speed normally follows rpm, so that should get you close to your goal. This should run you no more than $400-500 (depending on the damage) and you'll be set.

 

[TilliamWe]

Re: Crazy Prop Performance - need suggestions

Boat:
1997 Bryant 212 Limited (bowrider)

Engine:
7.4L Mercury Bravo I with 1.50:1 ratio

Goal:
60mph
...

Not gonna happen. Maybe on the "Wish-O-Meter" in the dash, but not in real life (GPS). Not with a stock motor, anyhow.

Something not right with the 3rd prop you tried. I know 642 recommended having the 1st prop reworked to give it "less" pitch (and thus raise your rpms), but I have been advised against that in the past, by a prop shop in Titusville, FL that modifies racing props for a living. It's better to add "cup" to a lesser pitch prop, thus raising its "effective" pitch in the process.

 

[QC]

Re: Crazy Prop Performance - need suggestions

I agree with Tilliam on this one. Local Prop guru, Ron Hill, and some posters here have said the same; taking out pitch is innefficient.

Greater than 5000 rpm, 55mph, and still climbing

Were both still climbing? I don't think anything is slipping and also making 55 MPH. And although I generally agree with Tilliam, if speed was still climbing this prop may hold some potential with some tweaking.

 

[642mx]

Re: Crazy Prop Performance - need suggestions

Not gonna happen. Maybe on the "Wish-O-Meter" in the dash, but not in real life (GPS). Not with a stock motor, anyhow.

If he had 12% slip with a 23p and could turn it 4600 rpm (with the lab work) he would be right at 59. If the slip was 10% he would see 60. I think its possible.

Something not right with the 3rd prop you tried. I know 642 recommended having the 1st prop reworked to give it "less" pitch (and thus raise your rpms), but I have been advised against that in the past, by a prop shop in Titusville, FL that modifies racing props for a living. It's better to add "cup" to a lesser pitch prop, thus raising its "effective" pitch in the process.

I've read many times how good prop shops can raise the rpm's and get the speed and good cruising speeds by working the magic on a prop that maybe a little big for the boat. I would put bblades's work up against anybody elses. He's pretty much "the man" on the performance boating sites. I've had him do a couple of them with excellent results.

 

[Tail_Gunner]

Re: Crazy Prop Performance - need suggestions

Your slip is consisentant...with the 21..thats good. Actually i would check the tach for accuracy all the way up and down the rpm band. Ive seen a lot of tach issues lately..a lot. 1000 rpm drop is a bit much coming from a 23 to 21..

Going from 55 to 60 is quite a reach for a prop change..How sure are you of the engine current state of tune...Is the hull clean and true...I am kinda agreeing with you in a sense...22' boat high torque 300 hp 7.4 what does the boat weigh...3500...4000lbs

again id take a close look at the power train and tach and fuel filter..before doing much more opps and the hull...can you run a straight edge down the hull and its it smooth...no waves or deformation

As to labbing..That could be fun..if he was a 59mph and 44-4600 rpm and desperately needed that last litte push,,To many unknowns at this point i believe..That 1000 point drop needs to be looked at a little closer

 

[QC]

Re: Crazy Prop Performance - need suggestions

If he had 12% slip with a 23p and could turn it 4600 rpm (with the lab work) he would be right at 59. If the slip was 10% he would see 60. I think its possible.

But where does the 400 RPM come from?

 

[Tail_Gunner]

Re: Crazy Prop Performance - need suggestions

But where does the 400 RPM come from?

Nooo how do you get from 18% slip to 12..Thats the question..

 

[QC]

Re: Crazy Prop Performance - need suggestions

I will agree that he could get 60 without people, seats, no more than one gallon of fuel, no gear, no anchors, no soaked anything, no towels, and I think he would need to ditch even the sunscreen and probably chapstick. Add in lab finish and lab fuel and I think we're there.

Don't mean to beat you up 642, but it feels farther off than that. I have a boat that runs very well, test data shows 62 MPH wioth a lab finished 24" Bravo 1. I've messed with it a lot and the best I've seen is 57. 53ish with a moderate load. 60 is a big jump from 55 unless the engine is struggling and the boat has a lot of extra weight to get rid of.

 

[Tail_Gunner]

Re: Crazy Prop Performance - need suggestions

Ok dropping the chapstik really isnt called for....But i am with you on the sunscreen.

 

[TilliamWe]

Re: Crazy Prop Performance - need suggestions

Once again QC, I appreciate your excellent attempts to educate. I know my posts can sound short, but I didn't feel the need to be elaborate in my explanation. I knew someone else would do it for me!

 

[642mx]

Re: Crazy Prop Performance - need suggestions

But where does the 400 RPM come from?

By changing the rake and pitch I would think... I'm in the ORV business, not props.

 

[642mx]

Re: Crazy Prop Performance - need suggestions

I will agree that he could get 60 without people, seats, no more than one gallon of fuel, no gear, no anchors, no soaked anything, no towels, and I think he would need to ditch even the sunscreen and probably chapstick. Add in lab finish and lab fuel and I think we're there.

Don't mean to beat you up 642, but it feels farther off than that. I have a boat that runs very well, test data shows 62 MPH wioth a lab finished 24" Bravo 1. I've messed with it a lot and the best I've seen is 57. 53ish with a moderate load. 60 is a big jump from 55 unless the engine is struggling and the boat has a lot of extra weight to get rid of.

Your boat is slow!...lol. Its all good fun, I've got thick skin and I've also got a light wallet from playing with different wheels. What I can tell you is; Mercury Mirage, Rev 4 and B1's are all fast props. The Rev 4 is hard to beat out of the box and the B1 & M+ work the best with lab finishing. I also know that nothing compares to a proper lab job. I won't run a stock prop after having some "worked" wheels. They corner, cruise, and are quicker than a box stock wheel. And I also know its better to not be able to hit the rev limiter on a prop that you intend to have labbed.... its best to be at the low end of the rpm range and let the experts bring your rpm back.

BTW, my last boat had just under 10% slip on the ole calculator...

 

[QC]

Re: Crazy Prop Performance - need suggestions

ok dropping the chapstik really isnt called for...

OK, I'll back off on the chapstick

 

[45Auto]

Re: Crazy Prop Performance - need suggestions

BTW, my last boat had just under 10% slip on the ole calculator

Why so much slip? Does the labbing cause more slip?

Mine shows 9% slip where I usually cruise (40 MPH, 3000 RPM) and 1% at WOT.

 

[drivehard]

Re: Crazy Prop Performance - need suggestions

Thanks for the advice folks, and the friendly banter!!!

I have an email off to bblades with my situation, and will let you guys know what kind of reply I get.

I am also investigating the Tempest Plus 23" as a possible next candidate. From what I have read, it will spin a couple hundred RPM higher than the same pitch Mirage Plus, and gain me a couple MPH.

True, 60 mph is a stretch goal...I know this, and I won't be heartbroken if it doesn't happen...its just good to have a goal. I have to admit I have a freind with a 21' Ebbtide that is heavier, and deeper, and he can run 59.7mph (GPS) with a 260 hp sbc 350...so I was thinking I could at least get in that ballpark. He is swinging a 21" Stiletto Advantage II with a Volvo outdive.

I disagree that there is promise with Prop#3 I tried. It was just not efficient at all...yes the speed and RPM were still climbing, but obviously I feared for my engine, as I know those stock big blocks (non-mag) don't like to be oversped. I do enjoy cruising between 25 and 30 mph, and I don't see why I have to be all the way up to 3000 rpm to get that done with such a torquey motor.

What prop is a "B1"?

"Lab fuel" will have NO impact on a carb motor like this...just a gimick. I will say my first two runs were with non-ethonal fuel, and my third run was WITH ethonal fuel...but that only helps to make the comparison even "fishier" as the ethonal should have slightly LESS horsepower, not more.

The hull is indeed clean and true...I just bought the boat, and had a 5' straight edge all over the hull when I was inspecting it. The glass looks brand new with no wear, build up, etc...it was garage kept, and looks like new.

The engine purrs like a kitty, and appears as brand new. Compression checks out, and it feels to run good and strong...no issues at all.

I do need to double check the tach. but I can say that the engine felt like it was over revving with prop #3...it for SURE did not feel "right". I would say that perhaps the tach was reading low with prop #1 and #2 on it. What is the easiest way to check (cheapest)?

 

[642mx]

Re: Crazy Prop Performance - need suggestions

I have an email off to bblades with my situation, and will let you guys know what kind of reply I get.

Brett takes forever returning an email, its best to call. Brett or Brad are who you want to talk to.

What prop is a "B1"?

A B1 is short for Bravo 1. Its a performance 4 blade from Mercury. Lots of prop shops recommend them for heavy hulls because they have a lot of lift and they take well to labbing.

Have fun with the prop testing! And when you talk to Brett, ask him about trying out some props. They have a try before you buy program...

 

[Tail_Gunner]

Re: Crazy Prop Performance - need suggestions

Thanks for the advice folks, and the friendly banter!!!

I have an email off to bblades with my situation, and will let you guys know what kind of reply I get.

I am also investigating the Tempest Plus 23" as a possible next candidate. From what I have read, it will spin a couple hundred RPM higher than the same pitch Mirage Plus, and gain me a couple MPH.

True, 60 mph is a stretch goal...I know this, and I won't be heartbroken if it doesn't happen...its just good to have a goal. I have to admit I have a freind with a 21' Ebbtide that is heavier, and deeper, and he can run 59.7mph (GPS) with a 260 hp sbc 350...so I was thinking I could at least get in that ballpark. He is swinging a 21" Stiletto Advantage II with a Volvo outdive.

I disagree that there is promise with Prop#3 I tried. It was just not efficient at all...yes the speed and RPM were still climbing, but obviously I feared for my engine, as I know those stock big blocks (non-mag) don't like to be oversped. I do enjoy cruising between 25 and 30 mph, and I don't see why I have to be all the way up to 3000 rpm to get that done with such a torquey motor.

What prop is a "B1"?

"Lab fuel" will have NO impact on a carb motor like this...just a gimick. I will say my first two runs were with non-ethonal fuel, and my third run was WITH ethonal fuel...but that only helps to make the comparison even "fishier" as the ethonal should have slightly LESS horsepower, not more.

The hull is indeed clean and true...I just bought the boat, and had a 5' straight edge all over the hull when I was inspecting it. The glass looks brand new with no wear, build up, etc...it was garage kept, and looks like new.

The engine purrs like a kitty, and appears as brand new. Compression checks out, and it feels to run good and strong...no issues at all.

I do need to double check the tach. but I can say that the engine felt like it was over revving with prop #3...it for SURE did not feel "right". I would say that perhaps the tach was reading low with prop #1 and #2 on it. What is the easiest way to check (cheapest)?

You would be far better of getting a stilletto baypro 11 in a 22 pitch and then having it labbed or a rev 4. 4 blades have more surface and it seems that is what you need....17% slip is way off for that boat and that is how you get down slip ratio's..along with tabs..Does the boat have tabs?

 

[QC]

Re: Crazy Prop Performance - need suggestions

"Lab fuel" will have NO impact on a carb motor like this...just a gimick

In my best Foghorn Leghorn, "that was a joke son" . . . I kind of sell fuel for a living, but more like sell engines, more precisely fuel systems. Mouse Milk and I are old friends, and we have agreed to disagree

the ethonal should have slightly LESS horsepower

And this tells me you get it!! Good on ya mate

 

[drivehard]

Re: Crazy Prop Performance - need suggestions

You would be far better of getting a stilletto baypro 11 in a 22 pitch and then having it labbed or a rev 4. 4 blades have more surface and it seems that is what you need....17% slip is way off for that boat and that is how you get down slip ratio's..along with tabs..Does the boat have tabs?

No, I don't have tabs. I have enough trouble getting the bow UP as it is...I don't know why I would want tabs. Its a very bow-heavy boat. The fuel tank is up there, the cooler is up there, the anchor is up there, and the kids are always up there. That poor slip was only with the 21" prop...not with the smaller 23" prop. The Advantage III is supposed to have bigger blades, and 0.25" larger diameter than the 23"...but the 23" hooked up waaaaaay better.

I think I need a 23" that is know to spin a bit faster than the others, and have great bow lift...at least that is where logic and research are taking me now. Right now the Tempest Plus seems to be the next logical choice...but I am open to suggestions!