Prop Lab Work
12-09-2022 | 07:59 PM
#11
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Joined: Mar 2020
Posts: 372
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From: East Tennesseee
It sounds like you already have the perfect prop on there. On the rev limiter at WOT if what everyone is always looking for. What are your goals? Are your slip numbers high? Do you struggle getting on plane? I would buy another prop and have them work it for what you’re looking for. Prop work isn’t an exact science and I would hate for you to screw up a good working prop if the changes don’t work out
As far as the RPM goes I've got a 23 Mirage that will go 65@5000rpm in light chop. I had a 24 Bravo that ran 68@4600rpm in light chop. Now I've got a 26 Bravo that runs 67@4350rpm on glass water. Have to wait till spring to see how it does in chop which should pick it up a couple. The 26 is about 4mph faster than the 24 @3500rpm. As far getting on plane their all pretty equal. The 26 carries the boat better at lower speeds than the other two. All of those are box stock props. I have a borrowed Billy Eaves Labbed 26 Trophy that runs 72@4600. That prop was labbed for use on an Allison with a 2.4 Merc. While it's the fastest thing I've had on it, it's hard to get on plane and falls off plane about 26-2800rpm. My BBC IO just doesn't like the smaller diameter at lower speeds. Eventually the 26 Bravo is heading down to Billy for a tune up.
12-09-2022 | 08:30 PM
#12
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Joined: Jun 2021
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From: SW Ohio
Being on the rev limiter is not the fastest. It's also not good for the motor to be hung on the rev limiter for more than just an instant. It causes bearing failure and accelerates cylinder wall/ring wear if it's there often. Rev limiters should only be used to prevent accidental over revs.
As far as the RPM goes I've got a 23 Mirage that will go 65@5000rpm in light chop. I had a 24 Bravo that ran 68@4600rpm in light chop. Now I've got a 26 Bravo that runs 67@4350rpm on glass water. Have to wait till spring to see how it does in chop which should pick it up a couple. The 26 is about 4mph faster than the 24 @3500rpm. As far getting on plane they’re all pretty equal. The 26 carries the boat better at lower speeds than the other two. All of those are box stock props. I have a borrowed Billy Eaves Labbed 26 Trophy that runs 72@4600. That prop was labbed for use on an Allison with a 2.4 Merc. While it's the fastest thing I've had on it, it's hard to get on plane and falls off plane about 26-2800rpm. My BBC IO just doesn't like the smaller diameter at lower speeds. Eventually the 26 Bravo is heading down to Billy for a tune up.
As far as the RPM goes I've got a 23 Mirage that will go 65@5000rpm in light chop. I had a 24 Bravo that ran 68@4600rpm in light chop. Now I've got a 26 Bravo that runs 67@4350rpm on glass water. Have to wait till spring to see how it does in chop which should pick it up a couple. The 26 is about 4mph faster than the 24 @3500rpm. As far getting on plane they’re all pretty equal. The 26 carries the boat better at lower speeds than the other two. All of those are box stock props. I have a borrowed Billy Eaves Labbed 26 Trophy that runs 72@4600. That prop was labbed for use on an Allison with a 2.4 Merc. While it's the fastest thing I've had on it, it's hard to get on plane and falls off plane about 26-2800rpm. My BBC IO just doesn't like the smaller diameter at lower speeds. Eventually the 26 Bravo is heading down to Billy for a tune up.
We aren’t on the rev limiter. We max out at about 5K RPM, running about 76MPH GPS. My hope is to keep it at that RPM, but with the lab work allowing for a little more pitch, rendering another couple MPH.
Thanks. Brad.
(947)545-8991
12-10-2022 | 07:16 AM
#13
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Joined: Nov 2005
Posts: 1,225
Likes: 769
From: Wichita, Kansas
Wally,
Yup. I've sharpened and balanced at least a hundred props for my model boats. I've got a jeweled balancing tool that will make you pull your hair out, trying to get a prop balanced. It is so precise and friction free, any out-of-balance at all shows up. I've also noticed, being cast and hand finished, these props will almost always have variance in the blades, not only in pitch, but in shape. It has always been my process to get the shape symmetrical, then the pitch, then balance. Something pretty cool that some of us do, in an effort to take advantage of the once-per-revolution power pulse that is inherent to single cylinder two strokes, is to actually pitch one blade a bit higher than the other, then clock the prop so that the heavier pitched blade is entering the water as that power pulse is set off. The trick is to determine the amount of twist in our flexible prop shafts (speedometer cable) to get this clocking at its most beneficial.
Pitch progression is also a major factor in engine load that doesn't translate into final product speed. In our model boats, it's pretty easy to get too much progression, so that the trailing edge pitch will actually push the back side, or non-working face, of the prop blade against the oncoming water. This results in the higher pitch at the trailing edge only serving to load the engine, and not actually increasing speed at all. I'm very sure our full-sized boats are WAY too heavy for the prop slip to be so minimal as to allow this to happen, but I'm also very sure there is an optimum pitch progression, based on HP, weight and effective pitch of the prop. And that's where Brett's expertise and experience/wisdom comes into play. He's undoubtedly got acres of notes and records for the various configurations he works props up for. I've emailed Brett on this very topic. While I await his reply, I thought I'd toss it out here for us laymen to discuss.
Thanks. Brad.
(937545-8991
Yup. I've sharpened and balanced at least a hundred props for my model boats. I've got a jeweled balancing tool that will make you pull your hair out, trying to get a prop balanced. It is so precise and friction free, any out-of-balance at all shows up. I've also noticed, being cast and hand finished, these props will almost always have variance in the blades, not only in pitch, but in shape. It has always been my process to get the shape symmetrical, then the pitch, then balance. Something pretty cool that some of us do, in an effort to take advantage of the once-per-revolution power pulse that is inherent to single cylinder two strokes, is to actually pitch one blade a bit higher than the other, then clock the prop so that the heavier pitched blade is entering the water as that power pulse is set off. The trick is to determine the amount of twist in our flexible prop shafts (speedometer cable) to get this clocking at its most beneficial.
Pitch progression is also a major factor in engine load that doesn't translate into final product speed. In our model boats, it's pretty easy to get too much progression, so that the trailing edge pitch will actually push the back side, or non-working face, of the prop blade against the oncoming water. This results in the higher pitch at the trailing edge only serving to load the engine, and not actually increasing speed at all. I'm very sure our full-sized boats are WAY too heavy for the prop slip to be so minimal as to allow this to happen, but I'm also very sure there is an optimum pitch progression, based on HP, weight and effective pitch of the prop. And that's where Brett's expertise and experience/wisdom comes into play. He's undoubtedly got acres of notes and records for the various configurations he works props up for. I've emailed Brett on this very topic. While I await his reply, I thought I'd toss it out here for us laymen to discuss.
Thanks. Brad.
(937545-8991
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Baja 252 Islander
Baja 252 Islander
12-11-2022 | 09:30 AM
#14
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Joined: Mar 2020
Posts: 372
Likes: 182
From: East Tennesseee
I'm fortunate to live close to Billy Eaves. He's top of the list for prop guys. Especially when it comes to the high performance/racing end of things.
12-17-2022 | 10:21 AM
#15
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Joined: Jan 2003
Posts: 6,019
Likes: 1,521
From: Grand Rapids, MI
It sounds like you already have the perfect prop on there. On the rev limiter at WOT if what everyone is always looking for. What are your goals? Are your slip numbers high? Do you struggle getting on plane? I would buy another prop and have them work it for what you’re looking for. Prop work isn’t an exact science and I would hate for you to screw up a good working prop if the changes don’t work out
Last edited by Rookie; 12-17-2022 at 08:07 PM.
12-26-2022 | 01:56 PM
#16
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Joined: Jun 2021
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From: SW Ohio
According to BBlades calculator, if I spin a 29P the same RPM as a 28P, with about the same slip, I should gain ~2.5MPH at WOT, and I'd assume proportional gains throughout the RPM range. I can't, for the life of me, find a disadvantage to a more efficient prop, assuming that's what I'd get.
Care to clarify "wash out your cruise speed"...? Just want to understand, as I definitely don't want to go backwards in total package performance.
Thanks. Brad.
(937)545-8991
12-26-2022 | 07:14 PM
#18
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Joined: Jan 2003
Posts: 6,019
Likes: 1,521
From: Grand Rapids, MI
Rookie,
According to BBlades calculator, if I spin a 29P the same RPM as a 28P, with about the same slip, I should gain ~2.5MPH at WOT, and I'd assume proportional gains throughout the RPM range. I can't, for the life of me, find a disadvantage to a more efficient prop, assuming that's what I'd get.
Care to clarify "wash out your cruise speed"...? Just want to understand, as I definitely don't want to go backwards in total package performance.
According to BBlades calculator, if I spin a 29P the same RPM as a 28P, with about the same slip, I should gain ~2.5MPH at WOT, and I'd assume proportional gains throughout the RPM range. I can't, for the life of me, find a disadvantage to a more efficient prop, assuming that's what I'd get.
Care to clarify "wash out your cruise speed"...? Just want to understand, as I definitely don't want to go backwards in total package performance.
I have a friend that sent off a set of 26" and a set 28" Bravo 1's to be labbed and tuned for his boat. They just never performed as the best overall prop. Would have been good money saved using each as a stock prop for what the lake conditions were that day. He was trying to build the best overall prop for his boat.
I have sets of stock Bravo 26", 28", 30" and Mercury labbed 28" for my boat. The stock 28's are probably the best overall and the Merc labbed 28's are the fastest, but they are loose and don't bite as hard under acceleration or throttling in bigger water.
I'm not saying don't send a prop out to get labbed, Just don't expect linear results.
Just my experience over the years.
01-21-2023 | 09:56 PM
#19
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Joined: Jun 2009
Posts: 9,974
Likes: 6,468
From: Chicago
If you lab the prop (making blades thinner) but add cup (I didn`t know this was possible) The end result would be the same in my opinion.
Would a car analogy work, if you go down in gear ration but get bigger tires you`ll still be at the same rpm so nothing changes at the end of the day ? Obviously you can run bigger tires so that the only change lol
Would a car analogy work, if you go down in gear ration but get bigger tires you`ll still be at the same rpm so nothing changes at the end of the day ? Obviously you can run bigger tires so that the only change lol
01-21-2023 | 11:49 PM
#20
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Joined: Oct 2007
Posts: 69
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Perhaps I am just unlucky. I have tried at least 3 labbed props on 3 different boats and not 1 of them was faster than the stock prop. Well one of them did run 1 mph faster but it had more slip, harder to come on the plane, didn't drive as well and certainly not worth the 1 mph at WOT. The other two ran the same speed as the unlabbed props but one of those drove as well and carried the bow higher but not increase in top speed. The last one was a Mercury labbed prop, the other two were done by "known prop experts". I tried these due to many good results that were posted by different individuals, but every boat is different and you never know until you try.
