Bravo28 - Under-pitched...?
 

Guys,

This is, in no way, intended as to throw shade of any kind on the seller I got the prop from. Just sayin'....

So, I picked up a Bravo28 to be used as a backup. Truthfully, my intention was to use the "new" prop as the main use prop, and the slightly dinged one I've had for awhile as the backup, but the "new" one is considerably slower than the one I've had for a while, across the RPM range.

While I didn't document any of this, nor did I even do an ad hoc study of any kind, I can tell you there is a considerable difference between to seemingly identical props, aside from the minor dings in the one. For example, the primary prop runs about 40-42 GPS at 3500RPM, where the "new" one runs 32-34 GPS. I could also reach my conscious rev limit of 5K WAY easier with the "new" prop than I can with the older one. As in, like, 75% throttle and no stretched out trim, where I need it on the firewall and trimmed out/up about as far as I'm comfortable with the older prop. While I know that every prop is different, being cast and hand finished, I wouldn't have expected THAT much of a difference. Is there that much difference between props of same part numbers?

Moving forward, there are a number of guys that do prop work. If I were to decide to send these out for repair/rework/labbing, who do I send it to? I'm familiar with BBlades, but I've heard/read of a handful of others. Just want some options. Also, can any of them just CHECK and compare these two props, just for the understanding of the empirical difference in output results?

Thanks. Brad.

Damn dude! Sorry it's not working out! As you can see it's a box stock never been touched bravo....wondering if the old prop maybe has thinner blades? You mentioned it has a couple dings on it wondering if some of the blade thickness or overall diameter is different?

BBYSTWY,

All good. Aside from the fact that the paint drip did not "just wipe off". Dang. That was some serious gnarly paint......

I did not do a side-by-side comparison, as I did the prop swap on the water. I should probably do that, now that I have the boat on the trailer in my shop. I saw nothing that might indicate I should expect anything out of place. In fact, I was hoping to recover any prop thrust lost from the dings in my other prop. I'll let you know what I find.

At this point, I'm just scratching my head, as I would have never thought there would be that much of a difference between seemingly identical props.

Thanks. Brad.

Guys,

For the record, I eliminated any errors in RPM reading that some may be aware of from another thread I have asking about a tach acting funny. I had my TechMate connected, both verifying the tach (It is off a little bit. Don't know why), and verifying same RPM between runs with the two props.

Thanks. Brad.

Is it possible that your original prop may have been labbed or modified at some point prior to you owning it??

From what I have been told, Merc quality control on new Bravo props is pretty bad with lots of variance

33 at 3500 with 28 pitch sounds way low. Something is off.

Griff,

I don't think so. There are no outward signs of any work done to it. Still a perfect mirror finish, and not-so-sharp of a leading edge we all know them for. Plus, the speed seems reasonable for the hull/HP involved, and for the prop pitch. I will be getting up in the boat and pulling the prop in question out of the pocket it's in and getting the older one off the drive in the next day or two to visually compare. I don't have any means of accurately measuring pitch without the excessive cost of a full cmm inspection, and I won't be sending either of them off till the boating season is over.

Thanks. Brad.

Liberator,

Ed Zachery.

Hell.... According to the BBlades prop slip calculator, 42GPS@3500 is 38% slip, which seems pretty high. But 33GPS is 47%, which is just nutz.

Thanks. Brad.

I ran 42 @3500 with 27 pitch(Bravo pitch is over stated) in Mercury calculator and it came in at 30% which is still crazy. When ever i checked slip on my 270 Laser it is always high also. Dont know if its a Powerquest norm or what.

It can be really hard to tell if prop has had work done and it should be if the prop was done right. It could have just been balanced, trued up the pitch and polished.
I'd wait for BBlades winter special.

Deduct 1" of pitch for Bravo props for calculating slip. They are stamped heavy compared to actual pitch. Prop slip still way high. What are your WOT speeds/rpms??