Trying to prop the 27ZX non-stepped..

[The Hedgehog]

I went with a 26" Bravo I and was only able to pull it to 5,000 RPM at 67 mph. I had to trim it to the moon to get the bow up. It never blew out or porposed but I think that I was working against myself. My top end was running a little rough. I think that was is still running too rich. It was kind of hard to get a real accurate run since I was dealing with 2+3 foot chop.

In order to gain some bow lift I went back to a Mirage Plus 25" The boat is rock steady and does not blow out. It did not plane quite as well but really carried the bow better. It did not plane poorly either. At full throttle I was only able to get 65 and was starting to bang the rev limiter. That is not good on a blown engine since it can cause lean out problems so i backed off. At just shy of full throttle It seemed to go right around 64 at 5,100 pretty any way I went. That comes up to about 21% slip which is way high (vs the 15% slip on the Bravo I.) Maybe I should try the 27 Mirage. I heard that it is a totally different prop.

Does anyone have any ideas about what might work? I will say the boat seems to be running better than when I ran the Bravo I. After talking to Jamie at Lakeside, I made some adjustments to the fuel pressure regulator and it seemed to smooth out the top end. Maybe I should go back to the Bravo I and have another go at it.

I am working with Throttle-up in their prob testing program and was wondering what else I might want to try.

By the way all speeds are gps. I am running a Pro-Charged 502 with the M-3 supercharger and the 504 intercooler. I am thinking that I should have enough smash to clear 70 mph.

[Last Real Texan]

Bill try a Hydromotive Quad IV X it has a lot of bow lift and was faster then the Bravo I .

Coppied from my testing earlier in the summer.
Test conditions
1997 Donzi 27 ZX twin step
Merc 500 EFI Blue motor
Bravo I drive
Temp 98 degrees
Humidity 85 %
wind calm
water smooth , no chop at all but not glass
Boat 1/3 tank of 100 gallon load
me 220 lbs




MIxed at this point. I went to my little local lake today and gave it a try. Blistering top end compared to my Bravo I .
Bravo I 24 pitch = 5400 @ 67.1

Hdromotive 26 pitch = 5050 @ 72.2

Cruise was much better
Bravo = 4000 @ 48-50 consistant
Hydro = 4000 @ 58-59 consistant

out of the hole good with the Bravo I
with the Hydro better but not great.

Bravo blow out at will.3-4000

Hydromotive worse with the blow out at the same revs.


The hydomotive seems to be a great prop out of the box....But it needs a longer more subtle diffuser ring to get hooked up better under 4000 revs... a real pain in the ass....Also it tends to porpoise more than the Bravo I , actually a lot worse, in all fairness it seems that my test conditions were not that great, no boats on the water , small local lake 6 miles end to end, and smooth water, not glass but smooth, no chop at all just a slight breeze. I am guessing that with a little chop maybe a foot or so and I will pick up a little on the top end and the porpose will subside, all this acording to Tom from Hydromotive.


Am I happy? maybe , I will have to test it in better conditions over the weekend if I get a chance, just wish it would hook up better between 3-4000 for testing , it makes it kind of a pain because you have to get to the other side of 4-4500 and then come back on the throttle.... but I want to test in chop to verify the porpoise problem gets better.

On a side note the Bravo likes to chine wald at WOT and really sucks... I have been able to setlle bot the chine walk and the porpoise with the K- planes but until I get indicaters for them I don't like to mess with them too much, don't like not knowing where they are.....

I am thinking if I can get it not to porpoise in the chop it may be the prop for me, once the prop is swapped out for one with a longer diffuser ring, then Lab it pick up another 200 revs puts me at about 74-75 MPH in the chop......Not to bad for a hull that is 28' and weighs over 7000 lbs and is running a single bone stock Merc 500 EFI....

Thanks for your attention.


Bryan

[fasttrucker]

My 1998 28zx stepped-hull is running a 26 pitch lab bravo-1 4-blade from "throttle-up".Iam hitting 5400 rpm.I have no rev-limiter.my speedo has hit 80mph(but normally hits 75mph) and Ive checked-it with a hand held gps.Its 2-3 mph slower but iam unsure really.This year Iam buying my own gps unit and also having bottom work,blueprinting,taking out the hook.Does your boat have a hook or rocker?

[The Hedgehog]

Bill try a Hydromotive Quad IV X it has a lot of bow lift and was faster then the Bravo I .
Coppied from my testing earlier in the summer.
Test conditions
1997 Donzi 27 ZX twin step
Merc 500 EFI Blue motor
Bravo I drive
Temp 98 degrees
Humidity 85 %
wind calm
water smooth , no chop at all but not glass
Boat 1/3 tank of 100 gallon load
me 220 lbs
MIxed at this point. I went to my little local lake today and gave it a try. Blistering top end compared to my Bravo I .
Bravo I 24 pitch = 5400 @ 67.1
Hdromotive 26 pitch = 5050 @ 72.2
Cruise was much better
Bravo = 4000 @ 48-50 consistant
Hydro = 4000 @ 58-59 consistant
out of the hole good with the Bravo I
with the Hydro better but not great.
Bravo blow out at will.3-4000
Hydromotive worse with the blow out at the same revs.
The hydomotive seems to be a great prop out of the box....But it needs a longer more subtle diffuser ring to get hooked up better under 4000 revs... a real pain in the ass....Also it tends to porpoise more than the Bravo I , actually a lot worse, in all fairness it seems that my test conditions were not that great, no boats on the water , small local lake 6 miles end to end, and smooth water, not glass but smooth, no chop at all just a slight breeze. I am guessing that with a little chop maybe a foot or so and I will pick up a little on the top end and the porpose will subside, all this acording to Tom from Hydromotive.
Am I happy? maybe , I will have to test it in better conditions over the weekend if I get a chance, just wish it would hook up better between 3-4000 for testing , it makes it kind of a pain because you have to get to the other side of 4-4500 and then come back on the throttle.... but I want to test in chop to verify the porpoise problem gets better.
On a side note the Bravo likes to chine wald at WOT and really sucks... I have been able to setlle bot the chine walk and the porpoise with the K- planes but until I get indicaters for them I don't like to mess with them too much, don't like not knowing where they are.....
I am thinking if I can get it not to porpoise in the chop it may be the prop for me, once the prop is swapped out for one with a longer diffuser ring, then Lab it pick up another 200 revs puts me at about 74-75 MPH in the chop......Not to bad for a hull that is 28' and weighs over 7000 lbs and is running a single bone stock Merc 500 EFI....
Thanks for your attention.
Bryan


I thought the Hydro had more stern lift. I could definately be wrong since I am at the beginning of my education process. I will definately give it a try. I have no blow-out at any part of my power band. No chine walk either.

That is moving pretty good for your boat.

[The Hedgehog]

My 1998 28zx stepped-hull is running a 26 pitch lab bravo-1 4-blade from "throttle-up".Iam hitting 5400 rpm.I have no rev-limiter.my speedo has hit 80mph(but normally hits 75mph) and Ive checked-it with a hand held gps.Its 2-3 mph slower but iam unsure really.This year Iam buying my own gps unit and also having bottom work,blueprinting,taking out the hook.Does your boat have a hook or rocker?

My bottom is flat.

All speeds are GPS with 1/3 tank of fuel. Sometimes with an extra person.

Did you lab the prop or buy it that way. I am thinking that a labbed 26 might be the way to go. Maybe if they could add a little cup to help carry the bow.

I am also considering having Mark Boos at Precision Marine reprogram the ECU and raise the rev limiter to 5,400 in the process. He told me that although sometimes you don't need to reprogram on the M-3 with 5lbs of boost, it is often a good idea. I would tend to agree since I am constantly in cold start mode as I have yet to break 110 degrees. My transom soot is pretty heavy. It can't be good running that rich all of the time. It sounds like it will wash the cylinder walls and dump some good raw gas into the oil. Hmmm! lots of wear. Throttle-up also told me that I need more revs to be into my power band. They told that it would also be better on my lower unit since I would be getting past the strongest part of the torque curve. It makes sense to me.

If I can swing a 26" Bravo to 5,300 that should bump me to 71 or 72 at 5,400 and that would be okay for this summer.

[The Hedgehog]

Bill try a Hydromotive Quad IV X it has a lot of bow lift and was faster then the Bravo I .
Coppied from my testing earlier in the summer.
Test conditions
1997 Donzi 27 ZX twin step
Merc 500 EFI Blue motor
Bravo I drive
Temp 98 degrees
Humidity 85 %
wind calm
water smooth , no chop at all but not glass
Boat 1/3 tank of 100 gallon load
me 220 lbs
MIxed at this point. I went to my little local lake today and gave it a try. Blistering top end compared to my Bravo I .
Bravo I 24 pitch = 5400 @ 67.1
Hdromotive 26 pitch = 5050 @ 72.2
Cruise was much better
Bravo = 4000 @ 48-50 consistant
Hydro = 4000 @ 58-59 consistant
out of the hole good with the Bravo I
with the Hydro better but not great.
Bravo blow out at will.3-4000
Hydromotive worse with the blow out at the same revs.
The hydomotive seems to be a great prop out of the box....But it needs a longer more subtle diffuser ring to get hooked up better under 4000 revs... a real pain in the ass....Also it tends to porpoise more than the Bravo I , actually a lot worse, in all fairness it seems that my test conditions were not that great, no boats on the water , small local lake 6 miles end to end, and smooth water, not glass but smooth, no chop at all just a slight breeze. I am guessing that with a little chop maybe a foot or so and I will pick up a little on the top end and the porpose will subside, all this acording to Tom from Hydromotive.
Am I happy? maybe , I will have to test it in better conditions over the weekend if I get a chance, just wish it would hook up better between 3-4000 for testing , it makes it kind of a pain because you have to get to the other side of 4-4500 and then come back on the throttle.... but I want to test in chop to verify the porpoise problem gets better.
On a side note the Bravo likes to chine wald at WOT and really sucks... I have been able to setlle bot the chine walk and the porpoise with the K- planes but until I get indicaters for them I don't like to mess with them too much, don't like not knowing where they are.....
I am thinking if I can get it not to porpoise in the chop it may be the prop for me, once the prop is swapped out for one with a longer diffuser ring, then Lab it pick up another 200 revs puts me at about 74-75 MPH in the chop......Not to bad for a hull that is 28' and weighs over 7000 lbs and is running a single bone stock Merc 500 EFI....
Thanks for your attention.
Bryan

Whoops. I did not see the X after the Quad IV. I do hear that the X has bow lift. I would like to know how it compares to the Bravo I in that department. That will probably be next on the list of props to try.

[fasttrucker]

I bought the prop from bryan tuvell used.I would get those rpm,s up or go to a size 30 pitch.

[The Hedgehog]

They are sending the 26 Bravo I back. I will try to get some better readings without 2-3 foot white caps bouncing me around. Although the Mirage Plus carried the bow well, the 3 blade does not like heavy V-hulls with lots of torque. My slip at cruise (just shy of peak torque) was 24%. It was around 22% on top. Way too high. My slip on the Bravo I was 15%. Much better but not where I need to be for a 4 blade.

I sent the ECU off to get reprogrammed by Precision. I plan to raise the rev limiter to 5,400 in the process. Hopefully that will clean up the top end and I might be able to get up into the top of the power band. If I am not able to spin the 26 well this time, then I will drop down the the 24. Then the higher rev limit allow me to spin it higher without the dangerous top end lean-out concern. I don't plan to operate at that level often. If I need to drop down to a 24 then I will have readings on both sides and the prop can be pitched accordingly. They can then add some cup to carry the bow better and hopefully voila.

This whole thing about where you need to be on the HP curve vs the torque curve in order to achieve maximum efficiency has been quite interesting. This has been much more fun than a turn key solution. However, I am glad to not be doing this in the summer.