Mercruiser Stern Drive Ratio

[Darryl V]

I have a 35 foot Bayliner which weighs 6 tons. I have repowered it with a single Yanmar 315 diesel engine and Mercruiser Bravo 2X stern drive.
The agent supplied the package with a 1.81 to 1 ratio. However the engine installer (a different company) said that because of the weight of the boat, I should have a 2 to 1 ratio which will enable me to swing a bigger prop (21 inch).
I have discussed this with the agent, who have said that they will not change the ratios.
Would I get better performance by changing to a 2 to 1 ratio? (I have not yet purchased a propellor).
Thanks
Darryl

[martylee]

I bought a d219 190hp turbo diesel with a bravo 2 and 2.2 to 1 ratio, it came out of a 28ft bayliner that weighed about 6t it had a 17 3/4 x 21 prop.

[Jango]

According to "PropCalc" software, prop shaft speed is not ideal with EITHER the 1.81 or the 2.0 gear. With either gear (1.81 or 2.0 ) a 21 D prop with min. 63% D.A.R. is recommended.
Pitch :
1.81 gear, 14 P
2.00 gear, 16 P

Ideal gear is 2.5 ratio with a 24 x 19 Prop, 55% D.A.R.

[powerabout]

You need 2 of those engines in that boat
The guy that sold it knows a lower ratio will probably blow up but the guy installing knows it will struggle with the higher ratio.
Sorry that's probably not helpful

[powerabout]

Originally Posted by Jango

According to "PropCalc" software, prop shaft speed is not ideal with EITHER the 1.81 or the 2.0 gear. With either gear (1.81 or 2.0 ) a 21 D prop with min. 63% D.A.R. is recommended.
Pitch :
1.81 gear, 14 P
2.00 gear, 16 P

Ideal gear is 2.5 ratio with a 24 x 19 Prop, 55% D.A.R.

So you worked out it shouldn't be a stern drive