I was wondering if anyone here on the board has tried the new Mercury "cupped" Bravo 3 props.

Seabuddy, I remember you asking about the cupped props one on an earlier post. It was before I was able to research what my boat came from the factory with.

In my case, A Cobalt 220/496 Mag/1.81 ratio. It seems to be able to turn 28 inch Props to at least 5000 RPM in the limited amount of time I am willing to run hard with the new engine.

I am wondering if 28 inch cupped props might be just the ticket. I was thinking about looking for a spare set "just in case". If I have them, I probably will not need them.

Matt

Couple thoughts.

1. Merc and Volvo put a rev limiter on their 8.1 375 Hp engine that should come in the general range of 4,700-4,800 rpm (Volvo) and 4,850-4,900 rpms (Merc) This is in place to keep the engine from going to your 5,000 rpm tach reading. Is it possible that your tach reads high? Or conditions were such that a good tach reading could not be achieved?

2. Both marine brands of this engine develope power such that it falls off at above 4,650-4,700 rpm. Best performance is uaully achieved at 4,200-4,400 rpm for fuel ecomony and 4,600 rpms for top speed (this can vary boat to boat somewhat) with this engine. It would be unusual to gain speed by propping to a WOT of 4,900 rpm with this engine in most boats.

3. Merc does not automatically show a rpm difference for the cupped versas not-cupped prop sets of the same pitch.

4. Most cupped props show a 100-150 rpm drop compared to a not-cupped prop.

5. Cupping also helps the prop from slipping in a hard, powerful, high speed turn.

6. If there is any extra slip or "bite" problems when you slam the pedal to the metal on hard accelration, cupping will help with this.

7. Yours is a new boat model ( I hope you love it) and the cupping props for bravo IIIs is a new design. So you are going to pioneer on this.

8. Give me some feedback on what I have said here and fill in the numbers with speedo reading, full tank of gas, or empty, 1, 3, or 5 aboard. Lots or little gear aboard, etc. Lets get started on this.

Thanks for the response Seabuddy,

First to the most important things, We Love our new boat. It seems to do everything great!

As I get a few more hours on it, I will be able to get some more hard information as to loading/Speed/Engine RPM.

The boat was delivered from Cobalt with the 28 pitch props. I was expecting to see 26 inch props based on the test reports that I had read. Althought some of them made absoulutly now sense at all based on their description of prop size and drive ratio's.

I have not run much or for very long at WOT. From what I have seen, the factory tach. shows about 5000 RPM. This is with about four adults and a half+ tank of gas. I have not experienced anything that gives me a indication that we are "hitting" the factory Rev limiter. I talked to a Merc rep an half hour ago and he said that the 5000 rpm should not be a problem. Based on the HP/RPM curves for this engine, it should be loosing power by spinning this high.

The "holeshot" is fantastic, no complaints here. It seems like it could actually use 29 or 30 inch props for top speed. I agree that this might be uncharted waters here. I will have the boat out with a group of relatives ths Saturday. I might be able to get some additional hard data then.

I appreciate you help,
Matt

Ok, let's see what the next spin in the boat brings.

By the way, some engines run harder after about 30 hours of total time is on the clock. Yes, that is more than the break in time usually listed in the owner's manual. But, we are talking two different things. One is max. power, the other is a way to insure long, smooth at all rpms engine life.

Just wondering if there've been any more developments on the prop front. I too am curious about how a cupped prop will act vs. a non-cupped prop.

I guess I just want to tinker around a bit. I picked up a used 28" polished set for spares, but haven't tried them yet. My boat came with 26" props (and 2:1 gear ratio) but I got a pretty good deal on the 28"er's, so I got them as spares, for the time being.

I did get out last weekend, but the passenger conditions were not good for testing. My next oppertunity will be in a couple of weeks. We will be on a houseboat for 10 days!

In my case, I am wondering if a set of 30inch props might be the best choice, but this is just thinking ahead. I did read in Powerboat Mag that the 496's like to be "overpropped" more that "underpropped". This is probably more so for the 496 MAG vs the H.0. The HP of the 496 Mag is dropping fast at higher RPM.

Hopefully, we can keep this thread going as more information get available.

Does anybody have a set of the cupped props on their boat?

Matt

I believe that subject to production variances, a 375 Hp 8.1 is within 10 Hp over the range of 4,400 to 4,800 rpm and then drops off in power quite rapidly over 4,800 rpms. With this broader range this engine does not need to be perfectly propped to give a very good level of performance. It feels like a smooth building of power as you go up the rpm range, no gettting on the "cam" power surges at a given rpm. I liken it to a turbine/electric motor feel.

I also believe a Mag HO 420/425 Hp is (again, subject to production variances) within 5 Hp from 4,900 rpm to 5,300 rpms. As this engine ramps up to this peak on a fairly steep curve, its short about 20 Hp at 4,500 rpms, but is still less than 10 Hp short at 5,400 rpms, a rather slow tapering off for such overspeeding of the engine. This engine first comes alive above 4,000-4,200 rpms and really "wakes up" as it hits peak engine speed, as a good performance engine should. I would be very fussy about getting a verified on one or more shop tachs a full 5,000-5,150 rpm at WOT on a boat powered with a HO 420/425 Hp engine.

This may or may not apply to other boat mfgs. I visited the SeaRay dealer yesterday and had a look at the '04 sales guide. Some B-III equipped boats now come with cupped props as standard equipment. For example, if I'm remember correctly, the '04 200 Sundeck is so equipped, while the 240 BR is not. The 260 Sundancer is also equipped with cupped props while other similar models are not.

Wonder why??? Have they simply not tested all of their models with cupped props or do some models perform better without the cupped props?

In most cases, but not all, the B-III offered a slightly higher top speed the its single prop counterpart with the same engine.