Bravo1 prop pitch VS speed
10-28-2013, 07:42 PM
#1
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Thread Starter
Bravo1 prop pitch VS speed
My 29' Fountain with twin 6.2s will tach 5300 rpms with about 80 gallons of fuel and just me aboard. It has 26 pitch Bravo 1 props . Motors and props are untouched.
"Assuming" I could pull the same rpms with 28 pitch props, what would the speed increase be? Let's say for the sake of bench racing that the boat currently hits 70 mph.
Would "labbed" props increase efficiency enough to move up 2" in pitch with no increase in horsepower?
"Assuming" I could pull the same rpms with 28 pitch props, what would the speed increase be? Let's say for the sake of bench racing that the boat currently hits 70 mph.
Would "labbed" props increase efficiency enough to move up 2" in pitch with no increase in horsepower?
10-28-2013, 08:31 PM
#2
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iTrader: (1)
i'm in the same boat, no pun intended, i'm turning a stock 26 bravo at 5100 and am looking into a labbed 28. the way I understand it a merc lab will increase rpm 300, and every inch of pitch will decrease rpm 200, so, you should spin them at 5200 as I would spin it at 5000, again this is just my understanding, hopefully others will chime in and back this or bash this statement
10-28-2013, 09:16 PM
#3
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My 29' Fountain with twin 6.2s will tach 5300 rpms with about 80 gallons of fuel and just me aboard. It has 26 pitch Bravo 1 props . Motors and props are untouched.
"Assuming" I could pull the same rpms with 28 pitch props, what would the speed increase be? Let's say for the sake of bench racing that the boat currently hits 70 mph.
Would "labbed" props increase efficiency enough to move up 2" in pitch with no increase in horsepower?
"Assuming" I could pull the same rpms with 28 pitch props, what would the speed increase be? Let's say for the sake of bench racing that the boat currently hits 70 mph.
Would "labbed" props increase efficiency enough to move up 2" in pitch with no increase in horsepower?
10-28-2013, 09:24 PM
#4
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iTrader: (2)
in my experience a "labbed" 28 will give you the same speed as a stock 26, the 28 will just slip more. If you or somebody else knows exactly what your boat needs in a prop then one "labbed" specifically for you might get you an extra bit of speed. Best thing to do is try lots of different props and see what the boat likes and what you like and then have one custom made from your favorite of what you tested if needed. Remember that basic physics comes into play here also a certain amount of HP is required to move your boat at 70mph and no prop is magically going to get you some free speed, the ideal prop for your boat will just use that power most efficiently.
For example in my case I tried the following props:
24 maximus stock and 1/4 cut off the diffuser ring
24 Bravo stock
26 Bravo stock
28 Bravo stock
27 mirage plus stock
30 bravo labbed
26 P5x
28 P5x
29 P5 labbed
Surprisingly all these props that ran well on the boat got me to 53mph even the 29 pitch 5 blade, but what I found from all this testing is that I didn't like the load the 5 blades placed on the motors and drives even though they gave good cruise numbers my MPG was less at the same speeds as other props turning more RPM at the same speed. The 3 blade mirages gave a lot of vibration and were all around worse than the Bravos, the P5X diameter was to small and the boat just ran terribly with them (which was a shock because on my last boat a 28 Daytona they were fantastic), but what I learned from all this testing is that my boat needed bow lift to perform well and give me good MPG and cruise speed. So I ended up with 26 Bravos, with a big diffuser ring like a maximus and lots of cup in the blades to give them the ability to carry the bow at lower speeds and not start slipping like the stock 26 Bravo did. So at the end my "labbed" Bravos run 55mph get me 2.4 mpg at 40 and are easy on the engines and drives. I can get to 57 with stock 28 Bravos but the MPG is worse at cruise because the motors have to work a little harder to turn them. If I had listened to the advice I was given by people who are supposed to know better than me what prop is best for my boat I would be missing out. Try a bunch of different props and the person who will know what your boat needs will be you.
Sorry to answer your question if you can pull stock 28s to the same RPM you should pick up 3 MPH.
For example in my case I tried the following props:
24 maximus stock and 1/4 cut off the diffuser ring
24 Bravo stock
26 Bravo stock
28 Bravo stock
27 mirage plus stock
30 bravo labbed
26 P5x
28 P5x
29 P5 labbed
Surprisingly all these props that ran well on the boat got me to 53mph even the 29 pitch 5 blade, but what I found from all this testing is that I didn't like the load the 5 blades placed on the motors and drives even though they gave good cruise numbers my MPG was less at the same speeds as other props turning more RPM at the same speed. The 3 blade mirages gave a lot of vibration and were all around worse than the Bravos, the P5X diameter was to small and the boat just ran terribly with them (which was a shock because on my last boat a 28 Daytona they were fantastic), but what I learned from all this testing is that my boat needed bow lift to perform well and give me good MPG and cruise speed. So I ended up with 26 Bravos, with a big diffuser ring like a maximus and lots of cup in the blades to give them the ability to carry the bow at lower speeds and not start slipping like the stock 26 Bravo did. So at the end my "labbed" Bravos run 55mph get me 2.4 mpg at 40 and are easy on the engines and drives. I can get to 57 with stock 28 Bravos but the MPG is worse at cruise because the motors have to work a little harder to turn them. If I had listened to the advice I was given by people who are supposed to know better than me what prop is best for my boat I would be missing out. Try a bunch of different props and the person who will know what your boat needs will be you.
Sorry to answer your question if you can pull stock 28s to the same RPM you should pick up 3 MPH.
Last edited by pstorti; 10-28-2013 at 09:37 PM.
10-29-2013, 12:12 AM
#5
Registered
I turn mirage +25's with a little cup added to them and get 74-75.... Under 30ft twin engine boats like 3 blade props I would try a set of 25+'s befor I bought anything
10-29-2013, 02:10 AM
#6
Charter Member # 55
Charter Member
No way you will spin the exact same prop with 2" more pitch to the same rpm unless you're on the rev limiter.
Theoretically, spinning the same rpm going from a 26-28 is a 7mph increase without figuring in slip%.
When you figure in slip% its closer to 5 mph, then figure in rpm loss and you might gain 1-2mph and maybe 3mph with the perfect labbed props.
Theoretically, spinning the same rpm going from a 26-28 is a 7mph increase without figuring in slip%.
When you figure in slip% its closer to 5 mph, then figure in rpm loss and you might gain 1-2mph and maybe 3mph with the perfect labbed props.
10-29-2013, 02:58 AM
#7
Registered
Learned that the hard way also.
My first custom 35 pitch 5 blade was built because my Bravo 32p 4 blade would blow out down low, and I wanted more top end. First day out I snagged a piece of cable and trashed the 35, but I had a 37Px5 blade on the way, so tossed the 35 in a box and sent it back for repair. This 37 ran about 5mph faster than a stock 32, has a higher slip number, but also knocked off 400 RPM's up top. Sounds great?
When the 35 came back less 1/2" dia shaved to repair it, I was told it would only be a good spare. Radar and GPS testing showed it was still capable of running within 1mph of the 37, while only spinning 200 RPM's higher.. Slip is actually less, 1% better on the cut down prop. I can also monitor engine load, and that's where the difference is. The higher pitch equals considerably higher engine loads, but not necessarily higher speeds...
Just some food for thought
My first custom 35 pitch 5 blade was built because my Bravo 32p 4 blade would blow out down low, and I wanted more top end. First day out I snagged a piece of cable and trashed the 35, but I had a 37Px5 blade on the way, so tossed the 35 in a box and sent it back for repair. This 37 ran about 5mph faster than a stock 32, has a higher slip number, but also knocked off 400 RPM's up top. Sounds great?
When the 35 came back less 1/2" dia shaved to repair it, I was told it would only be a good spare. Radar and GPS testing showed it was still capable of running within 1mph of the 37, while only spinning 200 RPM's higher.. Slip is actually less, 1% better on the cut down prop. I can also monitor engine load, and that's where the difference is. The higher pitch equals considerably higher engine loads, but not necessarily higher speeds...
Just some food for thought
