RPM difference lab and cup

[VetteLT193]

I have 26" Bravo 1's that I spin to 4800 RPM. If I add cup and lab the props would I net the same RPM at a higher speed? I'm thinking the boat wants more bow lift.

 

[imco offshore]

I have 26" Bravo 1's that I spin to 4800 RPM. If I add cup and lab the props would I net the same RPM at a higher speed? I'm thinking the boat wants more bow lift.

do your self a favor don.t touch it calll julie and mat talk to them FIRST youl save a lot of time and money 727 531 2255 good luck

 

[VetteLT193]

before calling anyone I wanted to see if anyone had done something like this and what the results were.

 

[ThrottleUp Props]

Labbing will increase your RPM about 250. You can increase cup and reduce about 180, theoretically. BUT the whole point to labbing a propeller is gain top end from the taller pitch or by the greatest utilization of RPM. With the peak HP being your target. If your target rpm is 4800 then you should lab a 28P Bravo I, you are getting the increased speed thru the taller pitch. Labbing a 26P and then putting a tremendous aount of cup back into it will most likely net negligable top end.

Julie

 

[VetteLT193]

My target RPM is actually more like 5000-5200. The range Merc puts out is 4800-5200 so I'm at the bottom end of the RPM range.

The reason why I asked about cup and lab is I definitely don't want to lose RPM on top.

If I just lab the 26's and don't add cup would the cruise speed be affected any? Based on the math I could pick up 3-4 MPH from a straight lab job on the top end but I don't want to lose cruise speed in doing so.

 

[MarylandMark]

and that is why Juile ROCKS!

 

[ThrottleUp Props]

Thank you M&M!

General Prop Theory:
Lab Finishing increases RPM about 250.
Increasing Cup reduces RPM
Max top end is found at peak HP
Max cruise speed is found at low end of power band of motor. So top end and cruise speed DO NOT go hand in hand, in general

Julie

 

[VetteLT193]

Thank you M&M!

General Prop Theory:
Lab Finishing increases RPM about 250.
Increasing Cup reduces RPM
Max top end is found at peak HP
Max cruise speed is found at low end of power band of motor. So top end and cruise speed DO NOT go hand in hand, in general

Julie

I hear you for sure. My Max HP is at 5000 RPM.

In theory if I just lab the props and forget all about the cup: I should gain a couple MPH on top. But what happens to cruise? same or different? if different what happens?

What does a lab job cost, getting full polished labbed props back?

 

[bbladesprops]

Give us a call at your convenience, and I'll explain it in detail. Each application and Labbing formula is different depending on the desired outcome.

Brett

 

[Griff]

I hear you for sure. My Max HP is at 5000 RPM.

In theory if I just lab the props and forget all about the cup: I should gain a couple MPH on top. But what happens to cruise? same or different? if different what happens?

What does a lab job cost, getting full polished labbed props back?

If merc says 4800-5200 then run closer to 5200rpms...and even 5300 is just fine.

BBlades did my props. Custom labbed per my application. I did not lose any cruise speed and picked up 2-3mph on the top end.

 

[fastscarab22]

buy a 28 and have it repitched to a 27, and add some cup, say you lab your 26 prop and your running 5200 then you add 300 rpms then your at 5500, on the rev limiter , you go to a 28 you loose 300 rpms because off the prop change, it so your down to 4900 then you lab it then your up to 5300 , get it pitched to a 27 add the cup for bow lift and then your at 5000 to 5200 . i had the same problem and this worked for me bblades

 

[Griff]

buy a 28 and have it repitched to a 27, and add some cup, say you lab your 26 prop and your running 5200 then you add 300 rpms then your at 5500, on the rev limiter , you go to a 28 you loose 300 rpms because off the prop change, it so your down to 4900 then you lab it then your up to 5300 , get it pitched to a 27 add the cup for bow lift and then your at 5000 to 5200 . i had the same problem and this worked for me bblades

Not necessarily the only way.

I was at 4900-5000rpms with my 24 Bravo 1's and 502 mpi's with the rev limiter around 5150.

BBlades reworked them and I'm at 5000-5100 with labbing and added cup to increase pitch.

The original poster needs to gain about 300-400rpms. Labbing his current prop and adding some cupping for bow lift would most likely be the best and least expensive way to achieve the best results.

 

[VetteLT193]

I'm thinking I'll just lab them and call it a day. My biggest concern still is if I just lab do I lose anything. (cruise?, planing?)


I think If I lab I'll get the RPM's up to 5100-ish. Maybe even more because I'll finally get into peak power. So, it should gain 3 solid MPH on top.

I know I can go to a labbed 3 blade and get 10 MPH but I don't want a PITA planing boat.

 

[bbladesprops]

Standard template Labbing (as created at Mercury Racing in my earlier days) is a 300 rpm gain on a Bravo 1 propeller.

I would customize the recipe to gain about 200-250 rpm and create more bow lift. There is a possibility, although slight, that the HP could pull more R's due to the local we put you into. However, I doubt it will happen in this situation.

Adding and subtracting cup is art work. It can't be generalized with statements like "cupping reduces rpm 180". There are many variables with this type of rpm and boat attitude adjustments. Height, location and boat bottom/CG make a difference.

We could discuss the options in detail if you'd like to give us a call.

Thanks,
Brett

 

[bbladesprops]

Standard template Labbing (as created at Mercury Racing in my earlier days) is a 300 rpm gain on a Bravo 1 propeller.

I would customize the recipe to gain about 200-250 rpm and create more bow lift. There is a possibility, although slight, that the HP could pull more R's due to the local we put you into. However, I doubt it will happen in this situation.

Adding and subtracting cup is art work. It can't be generalized with statements like "cupping reduces rpm 180". There are many variables with this type of rpm and boat attitude adjustments. Height, location and boat bottom/CG make a difference.

We could discuss the options in detail if you'd like to give us a call.

Thanks,
Brett

 

[fastscarab22]

Brett, I bought the blade you did for mark c it was a 26 bravo 1 that you repitched to a 27 and add some cup , just for you know