Bravo III Propellers

[Centaur]

Earlier this summer I purchased a Regal 2250 Cuddy that is fitted with a Mercruiser 5.7L 350MAG 300hp motor and Bravo III twin-prop sterndrive unit (the highest spec motor and drive combination available for this model).

The boat is 22' long, with a beam of 8'-6" and weighs 4,400lbs (actual weight on a weighbridge). The performance with the standard 26" Mercury 3x3 Bravo III propellers is pretty good all round, with a 0-30mph time of around 7 seconds and a top speed of around 53mph (GPS) at 5,100rpm WOT (WOT range 4,800-5,200rpm).

I started looking around for a spare propeller set simply to keep on board in case of emergency. From my test results, I took it that the current 26" pitch is about right for my boat and thought that I would therefore get a similar 26? 3x3 set. However, I have found that Mercury now do a 4x3 Bravo III propeller set (in matte or high-gloss) and a 4x3 Bravo III XR ? i.e. a 4-blade front propeller and a 3-blade rear. I use my boat primarily for water sports and so the 4x3 setup may be beneficial, although I wouldn?t want to take too much out of the top end.

It appears that the XR may be designed more for bigger boats with big-block V8?s, so I take it that the standard Mercury Bravo III 4x3 propeller would be the most suitable for my boat. Does anyone have any experience with going from a 3x3 to a 4x3 prop and have any information on the relative performance differences between the two?

I have also found an independent propeller supplier, Hill Marine, who manufacture Signature 4x4 propellers for the Bravo III drive ? i.e. a 4-blade propeller front and rear. Again, I would be interested to hear from anyone who has experience of these propellers. Additionally, I would be interested to know whether they are as robust as the Mercury items? My 3x3 Mercury propellers are constructed of a fairly thick stainless steel and seem to withstand occasionally churning up sediment in shallow water. Some propellers I have owned in the past were made of far thinner stainless and would not take that kind of abuse ? how do the Hill Marine propellers compare?

Thank you in advance!

 

[tpenfield]

Re: Bravo III Propellers

It sounds like your current 26p set is a good match for your boat. A spare Bravo 3 set will be pricey, ($1300+/-) so you won't want to make any light-hearted moves on this.

You *might* be OK the a 24p 4 blade set . . . It seems that the 4-blade Bravo 3 sets are somewhat new, so maybe not a lot of experience out there.

All too often I see boaters trying to optimize their props trying different things and then find out that they had a good prop to begin with.

 

[PJ Tad]

Re: Bravo III Propellers

I would like to get in on this conversation re recommendations for B3 props. My boat is a Ebbtide 2300 Sport Cuddy, also with the 300 HP 350 Mag MPI engine and a 26P prop set. My water ready weight is about 4350 lbs, plus 50+ gals of gas. My WOT speed is also 53 MPH (speedo) at 4700 RPM. I'm OK with a 50+ top end, as I seldom run over 40 - 45, but I am thinking my engine should be turning higher RPM at WOT. Per dash speedo and tach - my trimmed out cruise speed is 32 MPH at 3000 RPM, which is fine for the way I boat.
The guy I bought the boat from claims he could turn 5100 RPM at 58 MPH - with the same set-up. But I cannot get that, even with one person on board. I was thinking of trying 24P 3x3 props, or maybe even a 22 to see if the RPM would come up where I think it should be, then having one or the other for the spare set. I would also like to hear what others experience with the newer 4x3 or 4x4 prop sets for the Bravo 3.
Comments?

 

[Centaur]

Re: Bravo III Propellers

Hi PJ Tad,

It sounds like you have a very similar setup to my boat. However, the drive ratio on my boat is 2.2:1 - is this the same on yours? Also, do you have any accurate GPS speed data, as the speedo is usually off by 3-5mph?

I'm not sure what speed is showing on my speedo at 4,700rpm but at 5,100rpm it is reading about 58mph - I did once get it to hit 60 on the speedo with 55mph showing on the GPS but that was very lightly loaded, with only 2 persons on board and a following wind! I take it from these figures that you are probably running the same drive ratio but IF you speedo was spot on accurate (unlikely!) you could be running a 2.0:1 drive ratio.

Assuming that you have the same drive ratio and that everything else is broadly equal, the guy you bought the boat from may well have got 5,100rpm and an indicated 58mph. In this case, you should first eliminate the possibility of other issues before experimenting with new props. It would seem unlikely that Ebbtide would fit props of too high a pitch at the factory and, equally, why would a previous owner change the props for a higher pitch unnecessarily?

Firstly, if you haven't done so already, give the existing props a visual inspection to ensure that there are no defects that could account for the loss of rpm's. Secondly, get a Mercruiser engineer to test the motor and drive for problems - it will only need a very minor problem to knock off 300-400rpm and so might not be apparent when just cruising about. The engineer should also be able to tell you whether or not the rev-counter is reading correctly.

If no issues are found, and it's still running the same revs after a service and tune-up, then you could experiment with a different prop set. Each 1" of pitch is likely to vary your revs by 150-200rpm, so going down to a 24" prop set is likely to take you WOT revs to around 5,000-5,100rpm. This would be ideal and therefore going to 22" props would almost certainly be a step too far.

Of course, if you need to go down this route, then you will have the same dilemma as me with regard to the 3x3's, 4x3's or 4x4's!

 

[Mischief Managed]

Re: Bravo III Propellers

Talk to some prop experts and they'll tell you the B3 3 blade props are pretty hard to improve upon (there's a reason they have remained the same forever). 4 blade props of the same pitch are not going to help holeshot or top speed on such light boats with small block engines. Your standard 3 blade props are not really slipping much at all. If you can get into the recommended WOT RPM range with what you have now, rest assured you have a very efficient setup and leave it alone.

FWIW, I tried cupped props and polished props and such on my B3/7.4MPI and was able to alter the WOT RPM a bit, but the top speed never changed much and holeshot never improved. I'm still running the original satin 3 blade props.

 

[Centaur]

Re: Bravo III Propellers

Wow, that's very helpful!

I didn't think that there was much scope to improve top speed but did wonder whether the 4x3's might give even more out-of-the-hole performance without loss of top end. Looks like it's not worth the cost for a brand new set of props and, for a spare set, I would be better off to search around a certain well-known auction site...

Thanks again!