Prop pitch help for 1.5 gear ratio ,

[orona777]

I have recently purchased a 95 sea ray 180 signature with a 4.3L mercruiser and an alpha one drive and the gear ratio is 1.5 my elevation is about 5000ft, im not to sure how gear ratio works but I’m not hitting my WOT I currently have a14.25x 19 P the boat came with but it’s in rough shape and my wot is about 3100 rpm at 25-30 mph according to my speedometer not gps. I only have put the boat out in the lake once and would like to have correct prop. I’m not to worried about top speed I mainly just use it for tubes and wake-boarding any info would be helpful. Thanks

 

[jimmbo]

If you have 1.5:1 as an Altitude drive, somebody swapped in the wrong direction. For Altitude you should have gotten something like a 1.9:1 ratio. With a 1.5:1 you are going to be needing props in the 12" - 13" range.

The 1.5:1 ratios were for the V8s, I have a 1.51:1 behind my VP 5.7, non altitude model

 

[orona777]

Thanks I’ll start with a 13p

 

[jimmbo]

You're certain about the drive being a 1.5:1? Props in the 13" pitch range are designed more for Barges and Tugboats, not for runabouts

 

[porscheguy]

I would assume the original drive was pulled from service previously for whatever reason and whoever put that drive on either didn’t know about different ratios, didn’t care, or just threw on whatever was cheap that they could easily get their hands on.

You can a 13P prop. I can’t speculate on the performance you’ll see from it. But I can say that used drives are on Craigslist all the time in varying condition and price point. It may behoove you to keep your eyes open in case a deal comes your way.

 

[orona777]

The drive has a 1.50 stamped on it, and thanks I’m going to keep my eye out for a used drive. What would be the correct ratio for my boat?

 

[porscheguy]

1.82 was the standard ratio for the 4.3. Skip the 1.6X. They may have used 1.94/2.00 for high elevation. But you should be able get decent performance with a 1.82 and the correct prop.

 

[jimmbo]

At 5000 ft, I would go for the higher numerical gear ratio.