Update - New prop seems to slip a lot

[250Gimp]

I just installed a new 21p High Five prop on the weekend.

My concern is that the prop seems to slip a lot on holeshot. wack the throttle and it jumps up to 4000rpm right quick, almost like the vent holes were open.

I changed the prop blind under water.

Could I have put something together improperly, or missed a part that could cause this?

Thanks for your help!

Cheers

 

[daman4469]

Re: New prop seems tpo slip a lot

Re: New prop seems tpo slip a lot

Are you trimmed down the whole way? Watch behind you, is it pushing a lot of water? If its cavitating a lot, you'll have pits on that prop in no time. Are your RPMs coming back down slowly? Thats a pretty steep prop, hard to believe you would be getting a lot of slip.

I had this issue on my old boat, an 88HP with a 17" prop on it. Turned out it was just something with the prop cupping and a hydrofoil helped a lot. My guess is that if youre slipping on the holeshot, its slipping at speed too. There are some good calculators out on the web..just need your RPMs, top speed, prop pitch, and gear ratio. Should ideally be under 12%%, but the lower the better, and under 17% to me is acceptable. Get er up to speed and write down this info, then throw it in one of those online calculators...that will tell you a lot.

If you changed it under water blindly, I'm willing to be something might not be right....Double check it!

-In my experience, prop slip and cavitation hangs around a while, it doesnt rev up then drop right back down...it takes a while. Hard to say whether its prop slip or cavitation without more info.....

 

[250Gimp]

Re: New prop seems tpo slip a lot

Re: New prop seems tpo slip a lot

Thanks for the reply Daman4469

I am trimmed down all the way, and it seems to push more water than the old prop, I think.

I will look into the slip calculators.

She revs up to arond 4000rpm and stays there until on plane, and then the speed rises unless I back off the throttle.

I read a note that if the thrust washer isn't right it could let exhaust gasses out and cause slip. Is this accurate?

Boat specs:

2006 Maxum 1800 SR3
Mercruiser 4.3l MPI, 220hp
Alpha 1 Gen II, 1:81 gear ratio
Mercury High Five 21 pitch 5 blade stainless

I don't know exact max rpm because the buzzer goes off, but I am above the rpm limit doing about 46-48mph at 5200rpm (Only went that high once briefly so speed may be off)

Thanks

 

[Texasmark]

Re: New prop seems tpo slip a lot

Re: New prop seems tpo slip a lot

Sounds like you nailed it. I ran/am running a ported prop and that's what the ports are designed to do. By getting the exhaust gasses across the prop you unload it allowing the engine to develop it's rpm's which is developing it's hp and away you go.....fast hole shots.

Mark

 

[steelespike]

Re: New prop seems tpo slip a lot

Re: New prop seems tpo slip a lot

Keep in mind prop calculations are only as accurate as the input and imo hull specs are the stumbling point.The prop needs to fit snugly with the gear case. What is the diameter of the prop? Being a 5 blade it would seem to me that with the vents plugged it would load the motor pretty good.But might still get up quick.Check the fit at the gearcase.

 

[250Gimp]

Re: New prop seems tpo slip a lot

Re: New prop seems tpo slip a lot

Thanks Texas Mark, I have the vents closed right now. If they were open I would feel better, or are you talking about me possibly having the thrust washer backwards?

Steelespike, I will check the fit at the gearcase. How tight should it be? The prop is 13-1/4" (going from memory)

Cheers

 

[craze1cars]

Re: New prop seems tpo slip a lot

Re: New prop seems tpo slip a lot

I guess I'm wondering why you think this is a problem? Frankly it sounds rather desirable...with that much slip and RPM on take-off it aughta be ripping out of the hole like a bandit I would assume? That's the whole point of the High 5, isn't it? As long as it bites strong after it gets goin', and is not over-revving out of the hole...I think I'd really like that for watersports...

Or maybe it's not biting after getting under way? Sounds kinda like it's acting like a 2 speed or CVT gearbox...or a shifting prop...which is a product that seems rather elusive, but would benefit boats greatly...it still kills me that in today's technology age we are all driving around in boats that have ONE gear that is supposed to take you from zero to full speed. Talk about a completely inefficient power transfer method....Land N Sea tried to correct it, but it didn't seeem to take off....but that's all a topic for another topic...don't wanna hijack this one.

All that said, I've never personally used a High 5, so take my comments with a grain of salt...I do not pretend to know what is "normal" for that prop.

 

[daman4469]

Re: New prop seems tpo slip a lot

Re: New prop seems tpo slip a lot

By the sounds of what you have said and what others have said, it sounds like what you have is OK. If youre accelerating fine out of the hole, its not cavitation (bad stuff if it is!), and like craze1 said, sounds rather desireable...if i could have my engine run at that rpm all the time, from start to full speed, it would be great (mine starts around 2200 and climbs)...
But if she accelerates fine, gets on plane fine, and runs well, dont worry about it..I think if you were having cavitation you would have a hard time getting up and going...just keep an eye on your prop for pits in case it is cavitating.
With a mid pitch like that (21 on the steeper end I would say)...your RPMs should be lower, but hey....maybe adjust your throttle cable/throttle stop. However, there is the possibility that the prop slip we're talking about is causing a few extra RPMs at the top end (Less load).
BTW, I ran your numbers based on the worst case scenario (46 mph at 5200 rpm) and got 19 % slip....which is high, but not too high that its unusable. with 48mph at 5200 RPM, youre right around 16 %, so it sounds like once on plane your prop slip is OK. If youre happy with how it gets up and accelerates, I wouldn't worry much bud.

 

[LiFeStArTs@FoRtY]

Re: New prop seems tpo slip a lot

Re: New prop seems tpo slip a lot

I ran a 23 mirage in my 18 foot glasstron and it was perfect for that boat. Strong hole shot and 4900 rpm doing 56-59 mph GPS. I'd go up one more pitch number.

 

[Texasmark]

Re: New prop seems tpo slip a lot

Re: New prop seems tpo slip a lot

Thanks Texas Mark, I have the vents closed right now. If they were open I would feel better, or are you talking about me possibly having the thrust washer backwards?
Cheers

Thrust washer is tapered as is the pop shaft, one way the taper of the washer fits the taper of the prop shaft....wider at the front and narrower at the prop end....matters and it installed incorrectly, you might not be able to get your prop nut on adequately to get the nylon locking mechanism on the shaft. Don't know what you are talking about when you say your vents are closed....do you have a vented prop and epoxyed them shut?

Mark

 

[craze1cars]

Re: New prop seems to slip a lot

Re: New prop seems to slip a lot

He's referring to the PVS adustable vent plug system that comess on the High Five and several other Merc props. He currently has the solid plugs in place:
http://www.mercurymarine.com/media/mercury/documents/PVS.pdf

 

[250Gimp]

Re: New prop seems to slip a lot

Re: New prop seems to slip a lot

Thanks for the feedback guys.

I am starting to wonder if I am under propped a bit now.

I lost at least 5 mph cruise speed at 3000rpm, but I do like the hole shot.

If I can I will try a 23p high five, or a 22p 4 blade and see how they run.

As for the vents, craze1 is right in that I have the PVS system, and the plugs are solid.

Cheers

 

[Tail_Gunner]

Re: New prop seems to slip a lot

Re: New prop seems to slip a lot

Thanks for the feedback guys.

I am starting to wonder if I am under propped a bit now.

I lost at least 5 mph cruise speed at 3000rpm, but I do like the hole shot.

If I can I will try a 23p high five, or a 22p 4 blade and see how they run.

As for the vents, craze1 is right in that I have the PVS system, and the plugs are solid.

Cheers

I dont think so...a small diameter prop will slip badly just as you have desribed...Is it really a 13.25 that spec is a outboard prop..Not a i/o

 

[250Gimp]

Re: New prop seems to slip a lot

Re: New prop seems to slip a lot

Thanks Gunner

It is 13.25", and that is the diameter for my alpha. The ones for outboards are even smaller.

I now have a 23 p to try when it stops raining here.

Well. See how it goes!

Cheers

 

[250Gimp]

Re: New prop seems to slip a lot

Re: New prop seems to slip a lot

Ok, update!

I tried the 23p high five, and I am still over revving!

I am hitting the alarm at 5200 rpm doing almost 52 mph by speedo.

I am thinking of going to a 25p to try, but that will be an expensive experiment.

The old prop I had is 15-1/4" diameter Bravo 1, 24p, and the Highfive is 13-1/4" diameter.

Anyone have any thoughts on this?

I am a bit baffled, as I am only running a 4.3l MPI, and my boat is fairly heavy!

I calculated the prop slip at abround 17% for this set up. Is that good for a V hull?

Thanks

 

[craze1cars]

Re: New prop seems to slip a lot

Re: New prop seems to slip a lot

The old prop I had is 15-1/4" diameter Bravo 1, 24p, and the Highfive is 13-1/4" diameter.

Anyone have any thoughts on this?

Well, my first thought is that you need a 25. But if you share your WOT top speed and RPM performance specs with that Bravo 1, I might just be able to be more accurate....

But I do now know that initially you dropped from a very aggressive 24P prop to a 21P, and for some reason were surprised by over-revving. I'm not sure why this would surprise you after dropping 3 inches of pitch.....I would fully expect a gain of 600-ish rpms. But again I don't know your "before" performance specs....maybe the Bravo 1 ran only 4,000 and you were trying to get your RPMS up?? I'm totally guessing here...

The Bravo 1 4 blade is a great all-around prop. What exactly were/are you trying to accomplish in changing to a High 5? Especially with such a large drop in pitch initially?

Your comment that you're "only" running a 4.3 MPI...and you're "fairly heavy"....I find that to be a very interesting take on your ride....exact opposite of my interepretation. You have 220 hp on a 18 ft boat. My last 18 footer I/O had "only" 115 hp, and it performed quite admirably. I believe the 4.3 MPI to be the largest motor avaialble on that boat. And you have a 1.81 gear ratio outdrive, which is quite a low raio for that much HP on what I feel is a rather light-weight boat. So with that combo, I think you're simply gonna need to turn a pretty big prop to keep your RPMS in check...

 

[250Gimp]

Re: New prop seems to slip a lot

Re: New prop seems to slip a lot

Hi craze1

With Bravo1 52 mph @ 4400 rpm ( by speedo )

I expected to gain 600 rpm with the pitch drop, but seem to have gained a lot more. I would have been happy maxing out at 5000 rpm but even with the 23p I am hitting the limit at 5200rpm.

The main reason for going to the high five is for better holeshot. The more I look into it I think the Bravo1 is too big a diameter prop for my little 4.3l MPI. The merc web site says it is a high performance prop made to run 60+ mph, with 300 - 600 hp.

Cheers & thanks for the help!

 

[craze1cars]

Re: New prop seems to slip a lot

Re: New prop seems to slip a lot

Well....again I have little to no experience with a High 5. However I did a quick search and found this comment on a Stingray website (a lot of them use High 5's)

"If I go from a 3 blade Laser II to a 5 blade High Five would the pitch remain the same?
When comparing the High Five with the Laser II of the same pitch, the rpm of the High 5 will usually be 150 to 300 RPM higher at WOT. Blade design and diameter are two of the indicators that will tell how one propeller will perform vs. another."

This is interesting to dissect, if it is true. You are starting with an aggressive 4 blade. Traditionally a 4 blade prop will turn a solid 200 rpms slower than a 3 blade. So if a High 5 will in turn spin 150 to 300 rpms FASTER than a quality stainless 3 blade like a Laser....that means you have to add these together for your purposes...and apparently the High 5 compared to a 4 blade stainless prop is fully expected to turn between 350 and 500 rpms faster IN THE SAME PITCH. So without even knowing your current High Five stats, that tells me you had the theoretical potential to spin right up to 4,900 rpms with a High 5 in a 24 pitch, if such a pitch exists. So it sort of makes sense that you're near or at an over-rev with your current 23 High Five.

So apparently (based on Stingray website) the "SUBTRACT a pitch for an extra blade" gets thrown right out the window when you go with a High 5....and it acts the opposite of what I would have expected...

About all I can say now, is that if you're absolutely wanting to get a High Five, and you're red-lining, you obvioustly simply need more pitch. 25 is probably next in line. I don't believe there is any other problem revealing itself here....

As for your slip question, at higher RPMS the High 5 will have a fair amount of slip. They are not speed props and get pretty inefficient at highier speeds. So I tend to think that 17% slip with a High 5 is pretty much expected on the top end.

And I'm first to admit, AGAIN, that I am not experienced with High 5's. So take my advice with a grain of salt...

 

[steelespike]

Re: New prop seems to slip a lot

Re: New prop seems to slip a lot

Craze,I think you meant "subtract" a pitch for an added blade.
Not nitpicking just didn't want anyone to be confused.

 

[craze1cars]

Re: New prop seems to slip a lot

Re: New prop seems to slip a lot

Craze,I think you meant "subtract" a pitch for an added blade.
Not nitpicking just didn't want anyone to be confused.

YES! My bad. I have edited and corrected the word above...

Thank you!