31' Profile Offshore - Prop Questions???
04-20-2005, 09:28 PM
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31' Profile Offshore - Prop Questions???
I have a 97 31' Profile Offshore, No steps in the hull, 6600lbs, Twin 502-502hp, Bravo ones with 1.50s. With 24 Hydromotives it does 75 gps at 5400 rpm and hitting the rev limiters. My next test was a set of 27 Hydromotives but I could only get 4700 rpm and I didn't have a gps then, I also tried a set of 28 bravo ones which was a little worse, about 4500 rpm. With the bravos my steering at top end was all over the place, is that because the props are way to big or is it just a bad combination of hull and prop designs?? I haven't tried a 3 blade prop but I'm curious if it would generate more top end? and how much mid-range acceleration would I loose? At this time I have to some-what ease into the throttles from a start with the 24s or I blow a hole in the water but the 27s it felt good from a start. My steering at top end felt most stable with the 24s. Is labbed 26 hydros the way to go?? My best Guess is 8% slip factor running the 24 hydros, is that correct. Thanks for any help - JShoup
04-21-2005, 06:51 AM
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Re: 31' Profile Offshore - Prop Questions???
Welcome to OSO.
The boat must like the characteristics of the Quad IV props. The Quad IV tends to carry the stern more than the Bravo 1.
What motors do you have? Are they modified 502's? If so what have you done to them? We need to know at what rpm to run the motors for max horsepower.
You are close on pitch. Depending on what rpm your motor should run at you are only an inch or two away from your optimum pitch.
If your props do not have diffuser rings those can be added and may take care of the problem you are having getting on plane. It's possible the 27's had diffuser rings and the 24's did not. That would explain the difference when getting on plane.
I don't think 3 blade props will give you any additional performance. Your slip numbers are good with the quad IV's. If the handling is good with those props I would suggest working with them and getting the rpm right.
Matt
The boat must like the characteristics of the Quad IV props. The Quad IV tends to carry the stern more than the Bravo 1.
What motors do you have? Are they modified 502's? If so what have you done to them? We need to know at what rpm to run the motors for max horsepower.
You are close on pitch. Depending on what rpm your motor should run at you are only an inch or two away from your optimum pitch.
If your props do not have diffuser rings those can be added and may take care of the problem you are having getting on plane. It's possible the 27's had diffuser rings and the 24's did not. That would explain the difference when getting on plane.
I don't think 3 blade props will give you any additional performance. Your slip numbers are good with the quad IV's. If the handling is good with those props I would suggest working with them and getting the rpm right.
Matt
04-21-2005, 08:49 AM
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Re: 31' Profile Offshore - Prop Questions???
Hello,
You may be overpowering the 24's out of the hole.
Do you have through hull exhaust? If so, diffusers may not be an issue.
Testing with too much pitch isn't a fair comparison. Therefore the 28 Bravo 1's were not showing their potential.
A 3bl propeller will most likely help top end but the cruise speed will suffer somewhat.
As Matt said, your not far off with the 24's. Consider testing with some more 4bl's in the 25P and 26P range.
Good luck.
You may be overpowering the 24's out of the hole.
Do you have through hull exhaust? If so, diffusers may not be an issue.
Testing with too much pitch isn't a fair comparison. Therefore the 28 Bravo 1's were not showing their potential.
A 3bl propeller will most likely help top end but the cruise speed will suffer somewhat.
As Matt said, your not far off with the 24's. Consider testing with some more 4bl's in the 25P and 26P range.
Good luck.
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Brett Anderson / BBLADES Professional Propellers
920-295-4435 http://www.bblades.com/
[email protected]
Brett Anderson / BBLADES Professional Propellers
920-295-4435 http://www.bblades.com/
[email protected]
04-21-2005, 10:03 AM
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Re: 31' Profile Offshore - Prop Questions???
A friend of mine had a 96' 31 profile
with HP450's.
He ended up running 28 Bravo's.
He also had a set of 27p Mirages
( old style)
He could spin those up to 5400.
The 3 blades were a tick faster,( high 70's)
but the 4 blades worked better overall.
Your steering problems sould like his,
it was tough to keep the thing going straight.
He had external, but it wasn't full hydraulic
to the helm.
I attributed most of the steering issues to
the slop in the cable and the p/s valve.
He also was running outside rotation.
Being the way it handle with outward rotation,
there was no way we were going to try inside
rotation.
with HP450's.
He ended up running 28 Bravo's.
He also had a set of 27p Mirages
( old style)
He could spin those up to 5400.
The 3 blades were a tick faster,( high 70's)
but the 4 blades worked better overall.
Your steering problems sould like his,
it was tough to keep the thing going straight.
He had external, but it wasn't full hydraulic
to the helm.
I attributed most of the steering issues to
the slop in the cable and the p/s valve.
He also was running outside rotation.
Being the way it handle with outward rotation,
there was no way we were going to try inside
rotation.
04-21-2005, 10:21 PM
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Re: 31' Profile Offshore - Prop Questions???
Thank you all for the responses.
Here is a little more information.
The motors came from Derebery Performance Marine. Leon said to run them up to 5400 rpm. They are 502hp/565 ft lbs torque. I don't have the specs as far as cam duration but they have Aluminum Edelbrock Performer Heads and Intakes, a mild cam by the sound of them, 850cfm carbs, MSD ignition,dist & rev limiters with thru hull exhaust and my props are spinning outside rotation.
I replaced the old motors which were 454s 310hp and it ran 61 gps at 4500 rpm with 24 hydros on bravo 1s with 1.5. When I bought the new motors I was told to go up probably 3 pitches??
Will a labbed 26 turn like a stock 24 ?
As far as diffuser rings, what do they do and what do they look like? Both sets of 24s and 27s that I have look the same.
I am also curious about the slip factors which went from 9% to 8% by changing motors, does that make any sense?
jts friend was able to turn 28 Bravos with HP450s in the same boat, I wonder what I have wrong?
I'm headed to Lake Powell tomorrow, I wish I had more props to test, do either of you have a prop loan test program???
Again, thankyou for the information.
JShoup
Here is a little more information.
The motors came from Derebery Performance Marine. Leon said to run them up to 5400 rpm. They are 502hp/565 ft lbs torque. I don't have the specs as far as cam duration but they have Aluminum Edelbrock Performer Heads and Intakes, a mild cam by the sound of them, 850cfm carbs, MSD ignition,dist & rev limiters with thru hull exhaust and my props are spinning outside rotation.
I replaced the old motors which were 454s 310hp and it ran 61 gps at 4500 rpm with 24 hydros on bravo 1s with 1.5. When I bought the new motors I was told to go up probably 3 pitches??
Will a labbed 26 turn like a stock 24 ?
As far as diffuser rings, what do they do and what do they look like? Both sets of 24s and 27s that I have look the same.
I am also curious about the slip factors which went from 9% to 8% by changing motors, does that make any sense?
jts friend was able to turn 28 Bravos with HP450s in the same boat, I wonder what I have wrong?
I'm headed to Lake Powell tomorrow, I wish I had more props to test, do either of you have a prop loan test program???
Again, thankyou for the information.
JShoup
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