Paul311

Has anyone an idea in which direction I need to look for the right props on a 311-SR1 1989 with bravo's and hp500's?
I have been speaking to Brett @ Bblades. He recommended to run the engines with the standard props (mirage plus 23p) and observe the amount of throttle at the moment the engine just hits the rev limiter. That would be a good starting point to advise on new props. As he is the specialist I believe this is the best way to go, but due to the fact I am not living in the US this route is time consuming. I will perform such a test anyway, but maybe there are people on this forum who have the same or similar boat/power as I have.
In another thread I read that a bravo 1 28p would be close with this combination.
Does anyone have a suggestion or experience?

Thanks in advance...Paul

billeickmann

I just sold my Formula 336 with HP 500s plus a little. I tried 24 hydromotive 4 blades, 25 Stilletos 3 blades, 25 Mirage, and 25 Mirage plus. The 25 plus were the fastest by a half mph. The 24s were smoothest, but lost 2 or 3 mph. The stilletos and mirages were about the same. Best speed was 72.2 at about 5150 rpm. Bill

billeickmann

I just remembered we tried 26 bravos and 27 mirage. Both were about 70 mph. Bill

Paul311

Thanks for your input Bill,

The 336 seems to me a little faster than the older 311, but from your experience I can conclude that a bravo 28p is way to much prop. You were about right with a 26p bravo.
I never though about the mirage plus, browsing this formum I don't read so much about 3-blade props. The cupped mirage series are in any case performing well with the heavy 311 hull.
What is your drive's gear ratio?

I expected more input on this topic, I thought that I either asked a very stupid question or a difficicult one.

Ted G

iTrader: (1)

Paul I'm sorry I haven't gotten back to you, but I have not been able to try the 28's yet. The one's I borrowed were for XRs ad I haven't been able to find a set of hubs yet. And now one of my brand new Mercruiser starters has decided to go to crap so I need to replace that. Last week on a poker run I had 6 on the boat and with the 26's and could only get 4900 on flat water, so I am leaning toward staying with the 26's in order to be able to handle loads, etc. Although if my cruise improved well with the 28's I might deal with the times when it's loaded. (I rarely run with more than 4)

Paul311

Thanks Ted,

What speed did you get at 4900rpm and 6?
From my experience with the stock 454 MAG's 365hp there was only a little difference between loaded or not. With a full tank, 5 people and gear I was also at 5000-5100.

Ted G

iTrader: (1)

69-70

billeickmann

My drives were 1.50s. I was under the impression the three blades worked best on the older, unventilated hulls, and with my tests, they did. Good luck. Bill

tylerjustinhunt

I have a 93 303 with 500hp's and run 27p mirage plus and If im real light on people fuel and beer can barely geet on the limiters.

Paul311

Thanks for the info.

If I give an estimated calculation of your speed at that point, it should look like follows:

(RPM x Pitch) x gear ratio) / 1056) x (100% - slip) = Speed [mph]
If the engines are spinning 5200 , gear ratio = 1/1,5 and I estimate your slip at 15%, you would go 75.3 mph right?

I assume that the 311 with 2 x 500hp would go around 69-70mph, maybe even faster.
With 2 x 365hp and mirage plus 23p I calculated my slip at 15%

If I calculate the speed with 25p, the 311 with 2x 500hp would go 69,7 mph. I guess that it can be a little faster, with 25p three blade I would also hit the rev limiter.
26p three blade at 5200 rpm will give 72,5 mph. Might be too much prop.

I can't figue out how Bill got this numbers with his 336 and 2 x 500hp+ . Only reason could be that with this set-up the slip is a lot less than 15%.