Bravo I Or Iii ??

[jaxnjil]

Re: Bravo I Or Iii ??

thanks for the link rick.
i have to work on this more but the advice i have got so far was to gear down to the 2.2 and go with the higher pitch props because they grab the water better. as you stated i dont want to go to low and then not be able to a pitch high enough back down. i will double check but i think my wot range is 4200 to 4800. to gear to 24 pitch would be right in the middle of the range and would give me the most options for sure.
i'm trying to get hold of a dealership in denver or salt lake to get an idea of what they start at. the only 2 i talked are stuck on the "88" 7.4. they are used to dealing with the fuel injected late models.

 

[180shabah]

Re: Bravo I Or Iii ??

I heard Force OBs were carp . . .

...hit'em with a little startron though, and they run like a raped ape.

 

[HT32BSX115]

Re: Bravo I Or Iii ??

What sort of performance did you get with the current drive and engine? (pitch, ratio & RPM?)

 

[QC]

Re: Bravo I Or Iii ??

...hit'em with a little startron though, and they run like a raped ape.

In my business we do something like that on purpose and call it Dual-Fuel We even charge $40K for it sometimes . . .

Sorry for the hijack jax.

To get back on topic . . . I am now thinking twin turbos, a Continously Variable Transmission (eliminates the ratio and pitch discussions), and a new Yanmar ZT350 (it's lighter)

 

[180shabah]

Re: Bravo I Or Iii ??

sounds cool, but my wife would completely freak out, if we had that clear transom and she could see how "high" the water is.

 

[jaxnjil]

Re: Bravo I Or Iii ??

What sort of performance did you get with the current drive and engine? (pitch, ratio & RPM?)

except for steam boat lake and here i always got 43 mph gps. . i think this tells me that is max for my hull and hp. the biggest difference was the higher elevations take less pitch and longer to get to plane and max rpm. i think this means while slower to spool up motor is making the max torque at all elevations and must be fair shape.
down at mead i was running 21 pitch 4 blade and 4900 rpm. i didnt push it past 49.
powell was 21 pitch and 4600 rpm
flaming gorge 19 pitch and 4300

when i checked at mead i was dissapointed because i thought at that elevation i would get 50 mph, i might have if i would have pitched up, but was realy surprised that the speed was the same as i got at powell with the same prop but yet the rpm was higher.

i do know i had a 17 pitch on that i run here and forgot to change it at powell. put the power to it down there and we were realy slow and it just boiled the water. the more i have tryed to figure all this out, the more i find i dont know.

 

[HT32BSX115]

Re: Bravo I Or Iii ??

That is a fairly heavy boat then

You might be ok with a 2.00:1 drive and start with a 24p prop.

4000 RPM would give you about 40 mph. (2.20:1 would give you about 38mph so it's almost a "wash"......5000 RPM and 30p props give you 60 MPH if you have the power to turn that fast!!)

http://www.go-fast.com/Prop_Slip_Calculator.htm

(use 7-8% slip for a Bravo III at planing speeds with medium loads)

I almost never run mine at WOT. I do like the way it literally JUMPS up on a plane with very little throttle. Before with the single prop the bow would rise really high and it took quite a while to get up on a plane.

By the way, Lake Mead elevation is a little over 1000ft MSL, Powell is around 3500 MSL.

And Tahoe is a little over 6000ft MSL.

I don't think you'd have a problem with Powell or Mead. Tahoe would be a problem though with tall gears and a tall prop!





Good luck finding what you want!


Rick

 

[TilliamWe]

Re: Bravo I Or Iii ??

Jax, with your engine and boat, i would go with the 2.2 drive. You will NOT have any problem propping up, if you ever go to a lower elevation.

 

[jaxnjil]

Re: Bravo I Or Iii ??

flaming gorge and tahoe are close to the same elevation then.
thats where we summer the boat and spend the most time on the water with it. thats where i want to prop it for and if it dosnt work well for the high mountain lakes around here we'll leave it at the gorge. we'll do powell in the fall and spring and winter it there in dry storage but realy dont get enough hours there that we couldnt work around being under proped there.
unless the elevation at mead gets up over 1112 and stays ther or higher we'er not in a hurry to get back there. that + it 700 miles one way make it quite a trek.

i agree on the 2.2 the 6000+ at flaming gorge showes up a lot more than the 1000 ft or so at mead to the 3600 or so at powell.

the dealer i'm working with is going to get with mercruiser and get there recommendation for the ratio and prop at 6000 ft. he tells me they have wed sight you can plug your hp boat weight and hull type and it will give you a starting point but i cant find it

rick thanks for slippage on the 2props. when i pluged my numbers in to the calculator link you gave it came up with 19%. is that possible or am i way off on my numbers?

 

[HT32BSX115]

Re: Bravo I Or Iii ??

A single prop will usually be 12-15% slip in a runabout type boat. Cruisers will be higher........ My Liberator came in at 12% (1.41:1, 5000 RPM, 60 mph radar speed TABS all the way-UP)

If you're higher it can be many things including in-accurate tach, speedo and a particularly heavy boat or a big cruiser.

You MUST use GPS for speed (Pitot Speedos are not always right on!) and a known (tested) tach to get realistic numbers and you must know know the prop pitch and ratio.

The calculator is a pretty good tool.. Mercury uses basically the same calculation to decide which prop to suggest.

The calculator assumes that your engine will produce enough HP to turn the RPM and is tuned correctly too.

Also, loading the boat will change the slip. (A light boat will exhibit a lower slip than a heavily loaded boat)


It sounds like you're on the right track....

I think you'll be really happy with the Bravo III once you get the right ratio/props on it!

Just make sure that you can get the dealer to let you try the suggested props and change them if they don't perform the way you like....

 

[jaxnjil]

Re: Bravo I Or Iii ??

ok; dealer got some numbers from merc. this morning.
we'er looking at the 2.2 ratio with 24 pitch prop set for my weight power and elevation.