bravo 3 ratio questions

[scutly]

hey guys, long time no post. well my donzi needs a drive. corroded beyond repair. heres my situation. 1995 29 foot 6500 lbs cruiser. single merc 7.4 with a bravo 3. 2.00 ratio and 24p props. i dont really have performance numbers but i know she planed out quick and cruised nice around 25 mph at 3 grand if i remember right. i'm not really a top speed kinda guy but i know she did 40 no problem. now i found a good deal on a 2.20 ratio drive. will this drive work with my setup? and would i have to change prop pitch to get proper performance?

 

[HT32BSX115]

Re: bravo 3 ratio questions

Howdy,


You can use a prop slip calculator to get ball-park numbers......

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

Using your previous numbers (25mph, 2.00:1, 3000 RPM) AND 8% slip,

You would need 26p props to get similar performance with a 2.20:1 drive. (this is approximate and you cannot go very far in either direction) Even using the 24's you're not going to see a HUGE reduction in performance.......and it should hole-shot better too!

I have 24p props for mine and I bought 26p props right after I installed the entire mess......I get a few MPH higher top speed with the 26's. (57MPH 4600RPM 1.81:1 lightly loaded) 54-55 MPH (GPS) with the 24's.


If it's a GOOD one at a good price, I would get it!!

I'll also add that I AM a top-speed kinda guy!! My plan is the tricked high HP engine from USENGINE up the road and 30p props for mine!! Using the propslip calculator, 5000 RPM, 1.81:1, 30p props, 8% slip..........well.......you get the idea!!


Cheers,


Rick

 

[TilliamWe]

Re: bravo 3 ratio questions

... 2.20 ratio drive... will this drive work with my setup? and would i have to change prop pitch to get proper performance?

Yes and probably. But you would certainly try your 24s first. If it doesn't over-rev at WOT, then you're good to go.

 

[Mischief Managed]

Re: bravo 3 ratio questions

The serious corrosion is usually limited to the lower half. The gear ratio is determined by the upper half. You can swap the lower half in very little time. Just a thought.

 

[HT32BSX115]

Re: bravo 3 ratio questions

Once he gets it back together, he'll need to have the Mercathode setup and verified as working properly or it'll happen all over again.......

I wouldn't park ANY stern drive in salt water for extended periods of time......

 

[scutly]

Re: bravo 3 ratio questions

Once he gets it back together, he'll need to have the Mercathode setup and verified as working properly or it'll happen all over again.......
I wouldn't park ANY stern drive in salt water for extended periods of time......

well the salt water parking is hard to avoid with a 6500 lb 30 footer if i want to boat at all on long island. shes no trailer queen that's for sure. now about my mercathode. how do i know its setup and workin proper?

 

[HT32BSX115]

Re: bravo 3 ratio questions

well the salt water parking is hard to avoid with a 6500 lb 30 footer if i want to boat at all on long island. shes no trailer queen that's for sure. now about my mercathode. how do i know its setup and workin proper?

Yeah, I know. ....You're just NOT going to have a choice sometimes where you park the boat!

Mercury has procedures for properly setting up a Mercathode that includes installing a second Mercathode if necessary and there's no shortage of info out there on Bravo III corrosion. (Those huge stainless steel props are part of the problem!)