What is the proper gear ratio?

[Markrhoyt]

I have a Bayliner 2859 classic, I have a 4.2 litre CMD diesel rated at 220 hp that i want to
put in it and i want to put a Bravo III on it.
My question is what would be the right gear ratio for it?
The boat weighs around 8500 lbs fully loaded.
Is it better to leave it as a Bravo II, or will I gain anything with
The III ? If I stay with the II, what ratio do I need for it?

 

[Volphin]

Re: What is the proper gear ratio?

If you want a Bravo III, add one.
I'd stick with a 2.0:1 or 2.20:1

But if the BII is able to fit the bill, and you already have it, why do you ask? What are you trying to achieve?

V

 

[Markrhoyt]

Re: What is the proper gear ratio?

Ok, here's the thing.
In my experience with the volvo penta drives, I switched from a single prop 290 to a duoprop 290 and the difference was phenominal.
Almost twice the speed, got on step in about one tenth the time as the sinle prop, fuel consumption went down by around 25%, and overall performance with a full load was great.
Do you think i will realize similar benefits with the III as opposed to the II?

 

[oops!]

Re: What is the proper gear ratio?

the twin blade around the dock will be very noticable as compaired to one large wheel.....i would go b3 if you can get it cheap enough.....new they are 7k

 

[Don S]

Re: What is the proper gear ratio?

Almost twice the speed, got on step in about one tenth the time as the sinle prop, fuel consumption went down by around 25%, and overall performance with a full load was great.
Do you think i will realize similar benefits with the III as opposed to the II?

Nope, it will be a little better, but not near what the Volvo drives were, and I have had the chance to run both.

You wouldn't by any chance live in KTN and used to have a shop out by Lighthouse?

 

[Volphin]

Re: What is the proper gear ratio?

B3 would help the on plane. The diesel powerplant is going to use less fuel than any gasser and have a higher torque curve. BTW, the 4.2L is rated at 3800RPM, working RPM is 2700.

V

 

[TilliamWe]

Re: What is the proper gear ratio?

mark, obviously you can try to stay with your same ratio, but I *believe* that Mercruiser would put a 2.43 ratio drive on that engine. But you can use whatever ratio you want, as long as your prop (or propset if you go to a B3) allows the engine to operate at its max WOT RPM. B3 propsets get expensive new (less expensive used) so experimenting with props is not real cost effective.

 

[Markrhoyt]

Re: What is the proper gear ratio?

Thanks for all the help. I can get a B3 bottom half pretty cheap so I think I will try it.
I can always put the 2 back on and sell the 3 if i don't like it.
Yes Don, that's me. Who are you?

 

[Don S]

Re: What is the proper gear ratio?

I used to work at Lighthouse marine up till I moved in 07.

 

[Markrhoyt]

Re: What is the proper gear ratio?

Ok, I remember, love your saying about time.