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Prop Slip - What are good numbers?

blue wonder

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Best we ever saw was 7% with the 2.5 Merced. The 300x is not dialed at all and it’s about 11%. 20%? Maybe the hub is slipping?
True story there, I had a 21’ Daytona w/300x on it, ran a 32p cleaver on it and got it to 7200 rpm, ran 112mph...comes in at 17%...too bad I couldn’t get the 3% my DCB Mach 22 w-twins does, holy shit that would have been fast!!!...has to do with the size of the gearcase for sure, I only had access to a 14.5 diameter 32p prop, would have loved to try a 15in diameter before I sold it
 

ONE-A-DAY

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True story there, I had a 21’ Daytona w/300x on it, ran a 32p cleaver on it and got it to 7200 rpm, ran 112mph...comes in at 17%...too bad I couldn’t get the 3% my DCB Mach 22 w-twins does, holy shit that would have been fast!!!...has to do with the size of the gearcase for sure, I only had access to a 14.5 diameter 32p prop, would have loved to try a 15in diameter before I sold it

Thats quick, I had a 21 classic deck with a 300 promax, 106 was the best, fun boats, after 50 mph you were basically committed to going straight :)
 

blue wonder

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Thats quick, I had a 21 classic deck with a 300 promax, 106 was the best, fun boats, after 50 mph you were basically committed to going straight :)
Yeah it was a beast, the 300x is a bad ass motor...it actually was on the rev limiter @ 7200 so long it shut the motor off @ 112mph, that was fun!!!
 

RiverDave

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Its a family deck boat joe, your kids won't notice the 2 mph your chasing buying props.

If those slip numbers are right he’s looking at waaaayyy more than 2 mph. More like 10+
 

pwerwagn

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Actually was researching that today (hub slipping)

Sent from my SM-N960U using Tapatalk

I had a hub slip on one of my Merc props. It only lasted about 2 minutes before the boat wouldn't move anymore.
 

RiverDave

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If you have 30% slip and you can smoke by your Buddy's boat that has 0% slip so badly you blow the paint off his boat you have the "perfect slip".

Focusing on Slip is like focusing on how "bad ass your boat looks on the trailer".... the only thing anyone cares about is how fast it goes. It helps for a "fuel mileage test" and we all know how many people track that metric as it is "critical" to all performance boaters.

Quite literally the dumbest thing you have said on here.. and that’s saying something because you routinely say dumb shit.
 

pwerwagn

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I was at 15-17% and as of last night I have it now at 6%. Went from four blade bravos and humpback cleavers to the new Hill 5 blade cleavers and changed from spinning out to spinning in. The prop change alone took me to 10%, engine height up and down in 1/4 inch increments and out to in got me to 6%. I think I can get it slightly lower but at the expense of water pressure dropping below 10 psi, with all this 6% is plenty good in my book. The numbers below work out to 6% with a 1.62 ratio.

Walt,
How did the bravos compare to the humpbacks to the Hill's? I have 14.25x32 humpbacks on my twin 300 carrera now worked by bbldes (had 15x34's on it before), and I'm kinda looking at picking up a set of ~28 or so bravos for normal use. The humpbacks work ok to pull my wife up on slalom, and ok to pull the kids on tubes and stuff, but I don't need to go 100mph very often. I'd sacrifice 10mph on top end if 90% of my use was better. I'm also spinning in vs out currently, my boat seems to like it better.

Are the Hill's the best of both worlds? I think I have ~$3K tied up in these humpbacks with as many times as I've had them worked, and I still feel they are a huge compromise (as are all props in one way or another). I guess I cant complain too much, they do everything I want. BUT...are the Hill props the real answer?
 

ONE-A-DAY

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Walt,
How did the bravos compare to the humpbacks to the Hill's? I have 14.25x32 humpbacks on my twin 300 carrera now worked by bbldes (had 15x34's on it before), and I'm kinda looking at picking up a set of ~28 or so bravos for normal use. The humpbacks work ok to pull my wife up on slalom, and ok to pull the kids on tubes and stuff, but I don't need to go 100mph very often. I'd sacrifice 10mph on top end if 90% of my use was better. I'm also spinning in vs out currently, my boat seems to like it better.

Are the Hill's the best of both worlds? I think I have ~$3K tied up in these humpbacks with as many times as I've had them worked, and I still feel they are a huge compromise (as are all props in one way or another). I guess I cant complain too much, they do everything I want. BUT...are the Hill props the real answer?

Bravos are the best all round, humbacks good for speed with light load and were best out of the hole, the Hills 5's are the best top end and stability wise but I dont think I can spin them now that the heat is up and they are slower out of the hole. They are going to be my winter time optimal top end props when its just me in the boat. I have 34 bravos, 34 humbacks and 32 hill 5 blades if you want to test any.
 

twocents

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I apologize but this thread has given me a headache. Granted, there are a bunch of so-called “formulas’ floating around out there to help you calculate propeller “slip’ or propulsion efficiency. Some seem to work okay, others are a train-wreck. If you have a minute, I’ll run through how I’ve been doing this for sixty years (on over 2000 different boats) – that’s right, really ‘old school’, I don’t need no stink’n computer.

First, you need four good data points to calculate ‘slip’ – your accurate speed (mph), accurate rpm, propeller pitch and gear ratio. That’s it – forget about weight, hull type, horsepower, altitude, wind, temperature, etc. These don’t matter when you’re trying to determine what your theoretical (100% efficient) speed could be with a certain pitch propeller. Okay, here we go – and if you doze-off I won’t hold it against you.

Let’s start with the three data points you need to calculate maximum theoretical top speed for any propeller -- for this example: max WOT rpm is 5200 – your gear ratio is 1.5 to 1 and you’re spinning a 26-pitch prop. Now the math – start by finding how many revolutions your propeller makes per minute (divide the gear ratio 1.5:1 into your rpm 5200 which = 3,467 revolutions per minute). Next, multiply 3,467 times propeller pitch (26 inches) = 90,134 inches which is how far your propeller would propel you at 100% efficiency (zero slip). Next convert inches into feet by dividing 90,134 by 12 (inches) = 7,511 feet. Next divide the 7,511 feet by 5,280 which is the number of feet in a mile = 1.423. And now multiply 1.423 times 60 (mph) = 85.35 mph. This is the maximum speed a 26 pitch propeller is capable of producing at 100% efficiency on any boat regardless of size, weight, hull type, horsepower, etc.

Okay, now we’ve got the theoretical max speed (85.35 mph) a 26 pitch prop can deliver given the rpm and gear ratio of this example. But, the actual top speed of your boat is 74.8 mph thanks to your GPS. To find ‘slip’ subtract 74.8 mph from 85.35 mph = 10.55 mph. Next divide 10.55 mph by 85.35 mph = 12.36%. And that’s it, your ‘slip’ factor or efficiency factor is 12.36% which is pretty good for most boats.

A couple of qualifiers to remember: if you had your prop modified (labbed, added cup, reduced the diameter, or just re-worked/repaired in general), it might not still be the pitch that is stamped on the hub. It could be more or maybe less. Or maybe when it left the original factory, the pitch was not totally correct to start with. It does happen.

If anyone took the time to read this entire dissertation, congrats but it might be a sign you have too much time on your hands.
 

Gone_Flat

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mercury racing has a prop calculator , u punch on your data , pitch , gear ratio , rpm slip and it will calculate a speed . Or put in a speed and it will calculate slip . Something is off with your #s
 

twocents

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The Mercury Racing prop calculator is one of the best around and most accurate. You might want to try to input my example data numbers again -- Mercury is calling out for a 12% 'slip' (they don't carry it out passed the decimal point -- 12.36% is actually more precise for slip in this case - and the 85.35 mph theoretical comes up as 0% slip or 100% efficient using the Merc formula).
 

New to boating

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Quite literally the dumbest thing you have said on here.. and that’s saying something because you routinely say dumb shit.

Dave... its replies like this from you that year after year reinforce why this Blog has ZERO credibility...... it's because of YOU and your lack of ability to keep your yap shut...... and everybody knows it... including you.

My post is 100% accurate..... you are simply not realistic or smart enough to digest it.....

Your comment about you "dialing in" boats... its laughable..... and so are you
 

RiverDave

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Dave... its replies like this from you that year after year reinforce why this Blog has ZERO credibility...... it's because of YOU and your lack of ability to keep your yap shut...... and everybody knows it... including you.

My post is 100% accurate..... you are simply not realistic or smart enough to digest it.....

Your comment about you "dialing in" boats... its laughable..... and so are you

Do you know literally every time you post on this website I get about ten phone calls from people in the industry that ask “who the f is that guy?” And they aren’t saying it because of your informed opinions. Lol.

You say this website has no credibility, yet right above ya is a post from a guy that has tested more boats for more publications than anyone on planet earth. Weird..
Don’t you ever get tired of being so right that you are wrong every single time? Lol
 

Dirtbag

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You have what, Shockwave 28 with the 600 SCI? What prop are you running?
ive been through a few...i have a 5 blade on there now but for the life of me cant remember the pitch...29 maybe? i wont be out till next week
 

Instigator

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Here is a good formula
Engine RPM x Prop Pitch / Gear Ratio / 1056= Theoretical MPH
Take Actual MPH / Theoretical MPH = Prop Slip
This is as close as anything you will find.
 

Dirtbag

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You need to run a smaller pitch prop for your increase in weight. Boat should be pitched to where u are right at ur rev limit or peak power curve. If u rev out too small of pitch for the most part.
i get to 5200 which i think is right for a 600
 

LC925

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ive been through a few...i have a 5 blade on there now but for the life of me cant remember the pitch...29 maybe? i wont be out till next week
Yeah keep me posted if you don’t mind. I have a Hill 30P 4 blade on my 26 with 600SCI but feel like it has a LOT left in her, mid range puts you in the seat. Was thinking maybe a 5 blade. But have to wait to not have the baby in the boat to see what I’m actually seeing RPM/Speed wise.
 

pwerwagn

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Bravos are the best all round, humbacks good for speed with light load and were best out of the hole, the Hills 5's are the best top end and stability wise but I dont think I can spin them now that the heat is up and they are slower out of the hole. They are going to be my winter time optimal top end props when its just me in the boat. I have 34 bravos, 34 humbacks and 32 hill 5 blades if you want to test any.

Good to know! I was hoping the Bravos would be better out of the hole than my humpbacks. Are yours vented? Still 15.25" and full diffuser length?
I'm running right at 101mph with the 14.25x32's, at ~61-6150 rpm. With the 15x34 humpbacks it would run ~113ish in havasu, but it wouldn't swing them past 5400rpm/94mph or so up here at my altitude (4400). I'm thinking maybe bumping down 4" in pitch on some vented bravos might get me a great holeshot, and more midrange acceleration. Any thoughts?
 

ONE-A-DAY

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Good to know! I was hoping the Bravos would be better out of the hole than my humpbacks. Are yours vented? Still 15.25" and full diffuser length?
I'm running right at 101mph with the 14.25x32's, at ~61-6150 rpm. With the 15x34 humpbacks it would run ~113ish in havasu, but it wouldn't swing them past 5400rpm/94mph or so up here at my altitude (4400). I'm thinking maybe bumping down 4" in pitch on some vented bravos might get me a great holeshot, and more midrange acceleration. Any thoughts?

yeah the bravos are worked, vented, diffusers cut off, lots of tweaks. 4400 feet changes everything,
 

OldSchoolBoats

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So a little update on this. We ran the boat to Springs for breakfast on Sunday. Just me and my three boys (all under 10). Tanks were about half full on each side and we had one cooler.

I found a good spot with trim and jackplate and we were able to do 63 at 4900 RPM which is 6% slip. Plenty of more speed in it for sure but not pushing it with the kids in tow.

Sent from my SM-N960U using Tapatalk
 

Flatsix66

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So a little update on this. We ran the boat to Springs for breakfast on Sunday. Just me and my three boys (all under 10). Tanks were about half full on each side and we had one cooler.

I found a good spot with trim and jackplate and we were able to do 63 at 4900 RPM which is 6% slip. Plenty of more speed in it for sure but not pushing it with the kids in tow.

Sent from my SM-N960U using Tapatalk
Saw you guys, we were just north of BlackMeadows... Boat looks good running fast. What prop?
 

BDMar

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Once you get everything else correct, prop slip is the final piece of the puzzle to fine tune. That's where i'm at right now. I'm 6 mph from a "goal number" this boat shouldn't be able to run with my hull & engine combo. But it absolutely will run the number with different props.
Anyone that says prop slip isn't important, doesn't know the fine details of boat setup.
 

New to boating

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Do you know literally every time you post on this website I get about ten phone calls from people in the industry that ask “who the f is that guy?” And they aren’t saying it because of your informed opinions. Lol.

You say this website has no credibility, yet right above ya is a post from a guy that has tested more boats for more publications than anyone on planet earth. Weird..
Don’t you ever get tired of being so right that you are wrong every single time? Lol

Dave:

You make the re-occuring mistake of thinking that just because you are not smart enough, or experienced enough to understand what someone else is saying it is automatically WRONG - and you do it with a lot of people, not just me. That's why you have NEVER had any credibility, and never will.

There are people that post here that know what they are talking about, I have no idea about the "industry experts" you refer to and I don't care (I would put my actual racing resume up against most (not all) of the people in this town and feel good about it - people whohave actually accomplished something - NOT LIKE YOU) - the subject matter of this post was PROP SLIP and the importance of it according to a lot of the people who commented. Reality is here at Lake Havasu if your Boat is fast enough to "blow the paint off the boat" of anyone who Fuc_s with you your boats Slip % dosen't mean SHIT. That's the reality of this lake..... and many other lakes... as i have said times in many other posts over the years, no one considers weight, power, hull designs or anything else.........

Case in Point - DESERT STORM year after year.... what was the only thing that anyone talked about..... come on GENIUS, what was it?..... "who will be first to the first card stop"..... NOT A SINGLE WORD EVER about how much "prop slip" the "winning" boat had......no one cared, no one cares now.

It's fun to test and improve and "chase the slip" to see if the changes matter and how the boat responds - but in reality if all you are seeing is the rooster tail of the guy that is spanking you if you have a "superior slip" number no one cares.....

And I also have had people talk to me about you.... not your loyal minions, credible people in town who are well know and highly visable and succesful.. they think you are a joke, the last time your name came up I was told "you live in your Daddy's house on the river"... Don't know if that is true, don't care.

I do know that you want your little world here to the world to believe that you have the inside tract on all land deals that go down, and are a trusted confidant of all successful local people in town (especially boating related businesses) and you hat think you are a boat setup expert (with ZERO actual resume) who defends Nordic, DCB and other brands even when it is clear that they are a complete mess - which at times they clearly have been, and obvious to everyone else, except you - with your blinders on all the time.

But whatever - I don't expect you to change and I am glad you don't - it keeps the entertainment at a higher level for me....
 

hallett21

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Dave:

You make the re-occuring mistake of thinking that just because you are not smart enough, or experienced enough to understand what someone else is saying it is automatically WRONG - and you do it with a lot of people, not just me. That's why you have NEVER had any credibility, and never will.

There are people that post here that know what they are talking about, I have no idea about the "industry experts" you refer to and I don't care (I would put my actual racing resume up against most (not all) of the people in this town and feel good about it - people whohave actually accomplished something - NOT LIKE YOU) - the subject matter of this post was PROP SLIP and the importance of it according to a lot of the people who commented. Reality is here at Lake Havasu if your Boat is fast enough to "blow the paint off the boat" of anyone who Fuc_s with you your boats Slip % dosen't mean SHIT. That's the reality of this lake..... and many other lakes... as i have said times in many other posts over the years, no one considers weight, power, hull designs or anything else.........

Case in Point - DESERT STORM year after year.... what was the only thing that anyone talked about..... come on GENIUS, what was it?..... "who will be first to the first card stop"..... NOT A SINGLE WORD EVER about how much "prop slip" the "winning" boat had......no one cared, no one cares now.

It's fun to test and improve and "chase the slip" to see if the changes matter and how the boat responds - but in reality if all you are seeing is the rooster tail of the guy that is spanking you if you have a "superior slip" number no one cares.....

And I also have had people talk to me about you.... not your loyal minions, credible people in town who are well know and highly visable and succesful.. they think you are a joke, the last time your name came up I was told "you live in your Daddy's house on the river"... Don't know if that is true, don't care.

I do know that you want your little world here to the world to believe that you have the inside tract on all land deals that go down, and are a trusted confidant of all successful local people in town (especially boating related businesses) and you hat think you are a boat setup expert (with ZERO actual resume) who defends Nordic, DCB and other brands even when it is clear that they are a complete mess - which at times they clearly have been, and obvious to everyone else, except you - with your blinders on all the time.

But whatever - I don't expect you to change and I am glad you don't - it keeps the entertainment at a higher level for me....

Lol but really who are you


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