V drive gear ratio help

[Bb588]

I’m new to v-drive boats I have always run sterndrives. Ok here’s what I have.
boat is 27 foot 5800lbs v bottom
588 ci 700ftlbs 700 hp 5200
No clue what gear I need and advise on a gear to start with would be very helpful. I have a casale box with a 1.33 gear now. The box is new to me so if the 1.33 is way off I will change it. Thanks.

 

[obnoxious001]

If it pulls 5200 with that gear and big heavy boat, you are golden.

Sounds over geared if you have not tried it.

 

[Bb588]

I don’t know if it will pull that gear or not. Do you think that gear is even close? Or better to start with something different.

 

[Bb588]

When you say over geared like 1:1 would be better?

 

[beaverfab]

Need more information what prop diameter and pitch, what do you want it to do with the boat?
I would think 1.09 to 1.15% over would work.

 

[Bb588]

It’s a offshore fishing boat no prop yet. Mostly be long part throttle runs. Wot will likely not be often. I would definitely trade topend for dock side manners and acceleration.

 

[obnoxious001]

I don’t know if it will pull that gear or not. Do you think that gear is even close? Or better to start with something different.

You didn't say if you have a transmission, or just velvet drive. I don't think it can pull it with the big boat. Do you have any idea what was in it before and what it ran? Are you sure the ratio is 1.33? I would have to guess like JJ, a bunch of steps lower.

As an example that won't directly cross over, I built a 548 for a 24' Spectra. With whatever prop he has on there, and I think he said it was a 1.06 gear, he turns the engine 4500 rpm to cruise in the 40's I would guess. While the engine is well built and stood up to it all last season, I told him he would get longer life out of it if he would put a different prop, and/or gear to get it to go that speed under 4000 rpm.

 

[Bb588]

Yes it has a velvet drive 72c and I have a casale box on the way. The boat previously had a yanmar diesel in it. 310hp 580ftlbs. I was told the boat would top out at 26 cruse at 21. No clue what prop he had. I am just looking for a starting point. Should I just get a set of 1:1 to start and go from there? Do the make underdriven gears? Thanks for the schooling on this stuff.

 

[beaverfab]

Yes there 1to 1 gears you can also underdrive by installing the large gear in the bottom and small on top. Casale split case v drives have a 10 and 12 degree angle you will need to know which one you have for gear replacement. You can give me a call if you want . JJ shop 254-854-2083

 

[BamBam]

If you're looking for a 1.15 (15%) set of gears for a 10* Casale split case, I have a set for sale.

Gearing the boat for proper performance is a balance of prop and gearing to get the boat to act as you want in all aspects. It should dock well, plane well, mid throttle at a reasonable RPM and top out where you want it for performance. What I mean by that is you can correct for a little extra gear by adjusting the prop. If the prop works well and carries the boat well you can adjust the gear up or down. It sounds to me like you want to turn a bigger prop for the weight of that boat which would mean less gear.

 

[Bb588]

When you say bigger prop do you mean diameter , pitch or both.

 

[BamBam]

Possibly both diameter and pitch. Thinking more about what was in the boat and what you are going to set it up with are complete opposites. The Yanmar probably topped out at 2500 RPM on the Governor and made all of it's power down there. You need to push a big boat and your power will come in much later. As you said 5200 was your peak HP. This is probably going to take you some time, money and trial and error. I don't know if there are any other boats around running a similar set-up for you to compare to.

I really don't even know where you would want to start with a prop or gear.

There are plenty of people on here that know a whole lot more than me about this stuff. Hopefully they will be able to help you more than I can.

 

[Outdrive1]

No way are you pulling a 33 gear in a 27’ vdrive with 700hp. You’re way off imo.


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[Blownbillybob]

Most direct drive velvet drives in big boats are under driven cause they have big props so I would imagine u should do the same!!