Bravo III XR prop-set

[Clay Washington]

As a blade from the forward prop crosses the top, the rear blade should be installed so that a blade from it crosses the bottom.

Like this...

[Knot 4 Me]

Yup, that is the correct timing. Merc really never stated in the owner's manuals to time the Bravo III props in this manner but they did indicate to time the old Blackhawk props in this manner. Same timing should apply. Jim knows how to time the props so that is not the reason for the prop burn.

[SeaRay Jim]

Knot's got my back. LOL

I was actualy able to prove that timing therory out when I first splashed it in the spring with the new motor. I was getting a definate "splat, splat" sound when trimmed out running at or newar WOT and I could feel it was loosing bite.

I checked and found the props one spline off from being at the clover leaf pattern like Clay posted. I reinstalled and it eliminated the "splat splat" and made a difference I could feel. That was within the first few hours and it's got about 45 on it now.

There are 2-3 others that I know with applications (they are bone stock, but big blocks) that are turning 28-30p props at 4800-5200 engine RPM wiht 2:1 gears, so turning the props in the 2500 RPM range and approaching the 60 MPH range, that have the same burns. One has labbed props.

I think it obviously has to do with the hydrodynamics once the props get past 2000 RPM, speeds are raching the 60 MPH range and maybe more pronounced with the higher pitches.

I've seen Clay's props which are also 30's, but his were labbed with significant cup and I don't believe he ever had any problem and he was definetly spinning them up there and at speeds in the range of 10 MPH higher.

One difference besides being labbed/cupped and having 1.81:1 gears was a nosecone.

I think the hydrodynamics of the BIII just fall apart once you start getting closer to 2300-2400 RPM and reach certain speeds (60 + MPH??) which is why the nosecone works.

Just a therory, but based one the few common threads between similar applications.

(pssst. are you listening Merc.? I'm an ideal candidate for a BIII XR (with the new props) case study. )

In the mean time, I have a cav. burned prop with a small stress crack I'm almost certain I'll need to give a proper burial to, so I'm looking for Plan B.

[ROY N MORIOKA]

Here's the reply from Mercury Marine re: application of new XR props on older Bravo IIIs..

Yes the Bravo 3 XR props will fit a standard Bravo 3 sterndrive. As a general rule the odd pitched numbered Bravo 3 XR props run similar engine rpm to the next higher pitch even numbered Bravo 3 props. For example the Bravo 3 XR 27 pitch matches rpm of a Bravo 3 28 pitch.

To find out the size of the original props that were placed on your boat / engine package you will need to contact the boat manufacture. I do not know how well the Bravo 3 XR props will perform on your product vs. the regular Bravo 3 props.


Best regards,

Jo-Ann Lawson
Consumer Service Specialist
MerCruiser Customer Service

[bbladesprops]

I used to work in the service capacity in 1993 at main line Mercury. Answers can be semi canned.

Let me know if you have any specific questions.

B

[SeaRay Jim]

For what it's worth, I'm digging up this old thread again.

I just discovered that the standard BIII props have finally been redesigned and are shipping from Merc now.

As far as I can tell, the new standard BIII prop is of course, a 4 blade front and 3 blade rear as the XR's are, but no cup and are the standard matte finish. Pitch should closely match old style BIII pitch unlike the XR which in addition to the extra blade, is cupped. i.e. current 28 pitch would be replaced with a new style standard BIII of the same 28 pitch or with 27 pitch XR's. In my case I don't have any choice but go from the 3/3 30's to a 4/3 28. I've been messing with this for a few years now but now, I'm now armed with dyno results to pin down max RPM better.

With my assortment of burned, cracked, stock, and now dinged 30 pitch BIII's, I'm either to pick out the 2 best out of mine and have them worked and hope for the best, or try the new style, or better yet, XR's. The new style standard 28 pitch BIII's are popping up for sale pretty cheap $500-$800 where the XR's are rare. I'm taking it down to Full Throttle Marine outside Austin this weekend for a little TLC including to address my now skegless BIII. I always imagined meant something different!

I really want to get this done and right this year which means I'll probably end up selling. Seems that's the way things go, get a boat tuned and running perfect just in time to sell.

The $64k question is, has anyone at this point done any testing or have any experience with replacing their old style with the new standard or the XR props?

[bbladesprops]

When going to XR's go down 1" of pitch if you are in the bottom half of the recomended rpm range for your engine.

4X3 sets have a touch better mid range. Personally I like the performance of the 3X3 with cup added to suit the boat. Thet tend to have the better top end and the cruise increases.

Brett

[SeaRay Jim]

Thanks Brett. I've really been wanting to try the XR's without buying a set for full pop but they just aren't very common. The new standard 4/3 is surprisingly easy to find for pretty cheap. I'm just afraid the extra blade just won't make enough difference over a 3/3 set like I've been running. The only comparison I have is running a box stock cupped 30 on the rear with a labbed front and the difference was pretty significant. I didn't need to go full trim to carry the boat higher and it just felt like it bit harder.

We'll see. The boat is with FTM right now so once I get it back, if I haven't found something else to try I may give you a call again, and have you work a set of 3/3 30's over for me.

[bbladesprops]

Let me know, we have done a ton of adjustments and Labs on the 3x3.

Brett

[SeaRay Jim]

Originally Posted by bbladesprops

Let me know, we have done a ton of adjustments and Labs on the 3x3.

Brett

Brett, I'll likely be calling you within the next week. Between your comments and the discussion you and I had a couple years ago and comments from others who have switched to either XR or the new 4/3 BIII's, I think having a set of mine worked is the best bet.

I just got off the phone with Bob and I didn't realize he was using you now too. I know others that sing your praises but to hear Bob's comments and what some of his customers has said is pretty impressive. As soon as I find a good time to head down to pick it up, my boat will be ready so I have work to do!