Prop vs drive ratio

[eskimo2k]

I have a Chaparral 180SSe with a 3.0 Volvo 4 cyl, 135 hp.

Currently the boat has the 2.18 ratio VP SX-m drive spinning a 23 pitch 3 blade stainless wheel. The boat will still over rev by about 400 rpm (max is 4600, it will spin to 5000 with a light load).

Long story short, the drive is completely shot. Obviously I can replace it with another 2.18 but I'm considering going to the next ratio down of 1.97. Anyone know how much that ratio change will effect my prop selection? I'm wondering if it will put my 23 around 4600 rpm or if I'm going to need to step down to a 21 or even 19.

 

[steelespike]

Re: Prop vs drive ratio

How did you end up with a 2.18 All I found was 1.97.
I can tell you that a typical Mercruiser 135 has a 2.00 ratio
and runs a 21-23" prop for abiut a 17' to 19ft boat.Depending on the boat these would typically be for speed with smaller pitches for skiing or heavy loads.
I woulds think a 1.97 would be close.

 

[eskimo2k]

Re: Prop vs drive ratio

http://www.marinepartsexpress.com/vp_outdrives.htm

A 2.18 is a version of the SX Volvo sells. IMHO it was never properly matched to the 180SSe hull by Chaparral, considering I'm running a 23 and still over-revving. Sounds like stepping down to the 1.97 would be perfect.

-Jason

 

[extreme76]

Re: Prop vs drive ratio

Using a prop calculator and then changing your ratio. If you are getting 5k with 2.18 you can expect 4522 with 1.97 and the same prop.

 

[eskimo2k]

Re: Prop vs drive ratio

That's the same number the guy at the marina I ended up talking to came up with (must be using the same calc). 50 rpm short of the 4600 redline sounds better than 500 over.