What does 2:1 Transmission mean and why is it significant?

[sarasetp]

Stupid question...What does 2:1 Transmission mean and why is it significant? I have the xr7 550 engine.


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[t.franscioni]

Two revolutions of the engine for every one revolution of the transmission/your prop. The significance has everything to do with boat size/weight, available engine power, prop size and pitch.

[t.franscioni]

The significance is greater with the smaller engines because they need the lower gear ratio to push those big boats. In your case the significance could mean that you can weight your boat down even more than if you had the smaller engine with 2:1 and still have no problem pushing all the weight, or it could mean you can run a higher pitched prop and get more top end speed out of your G than one without the 550. It could mean a few different things depending on what you were wanting to do but in short you theoretically have more options than those without your setup. Does your 2:1 with 550 come with the same prop that the smaller engine boats come with?

[Sailfun]

It really means nothing as far as torque multiplication or RPM. All that can be adjusted with prop pitch changes. What it does allow is using a larger diameter prop within the pitch ranges that produce the best performance by a prop. The old rule of thumb was you wanted to keep pitch and diameter roughly the same. Most direct drive boats ran 13x13 props. When V drives became popular and inboards doubled and tripled in weight you needed a lot more power. A13x13 can't move enough water. Vdrives went to 1.5 to 1 gear sets and 14x18 props but the pitch was getting up there and not as efficient as you want. Now you have 2 to 1 drives using 17x17 props which is a efficient combination.

[t.franscioni]

Oh ya, I forgot about the V drive factor....So the 2:1 means 2 revolutions of the tranny input shaft for every revolution of the transmission output shaft. Not engine to prop....

[nyryan2001]

Sara step, I'd be intersted to know your 0-23mph speed with full 2850lbs ballast.

the 0-23mph for a 450 1.48:1 on a 2315 prop was ~13 seconds

450hp on a 2:1 17" prop was 9-10seconds

550hp on a 1.48:1 15x14.75 prop was ~8seconds

550hp on a 2:1 17" prop????

[ScrewPusher]

I remember a good rule of thumb is a larger diameter propeller turns slower, and is more efficient (up to some point). This was very clear when I had SN with the power plus 1.23:1 trans versus someone w/o and 13X13 prop. Dang that was a fun boat!!!!

[beaster]

I have a 2014 G21.
I had to have my VDrive replaced over winter. My previous Vdrive was 2.0. The new Vdrive is a 1.48, dealer sourced and installed. That's roughly a 25% difference in ratio.
Since the replacement I have a heck of a time getting on plane with 3 crew and a few hundred pounds of ballast, it literally takes me minutes, not seconds. Its a 17" prop (2561) pushing a lot of weight. The 1.48 gives me less revolutions of the prop per revolutions of the engine (I think).
Is this what's causing me to have a hard time getting on plane?

[t.franscioni]

If the dealer didn’t install the same ratio that was in it before and didn’t warn you there will be some noticeable differences then that’s not a dealership I would trust. I’d think changing the ratio that much would certainly cause you issues getting onto plane. To run a higher ratio gear box you’ll now need to try and compensate for that with a lower pitched propellor. Id contact your prop manufacturer and have them work the math on what pitch is needed to compensate for the higher geared box you have now.

[functionoverfashion]

If the dealer didn’t install the same ratio that was in it before and didn’t warn you there will be some noticeable differences then that’s not a dealership I would trust. I’d think changing the ratio that much would certainly cause you issues getting onto plane. To run a higher ratio gear box you’ll now need to try and compensate for that with a lower pitched propellor. Id contact your prop manufacturer and have them work the math on what pitch is needed to compensate for the higher geared box you have now.

Seriously, we replaced an old 1.23 with a 1.46 (can't remember why) and had to change props to get the same performance, I can't imagine your boat would be happy with a 2:1 to 1.48:1 change, if the prop stayed the same.

[JRW160]

I have a 2014 G21.
I had to have my VDrive replaced over winter. My previous Vdrive was 2.0. The new Vdrive is a 1.48, dealer sourced and installed. That's roughly a 25% difference in ratio.
Since the replacement I have a heck of a time getting on plane with 3 crew and a few hundred pounds of ballast, it literally takes me minutes, not seconds. Its a 17" prop (2561) pushing a lot of weight. The 1.48 gives me less revolutions of the prop per revolutions of the engine (I think).
Is this what's causing me to have a hard time getting on plane?

I think the 2013 G23s had the old 1.5:1. They switched to 2:1 in 2014 for all of the engines except the 550. You may be able to mitigate it by changing props, but I'd go back and get the 2:1 installed.

[Jonny Quest]

If you keep the new V-drive gear ratio, you will definitely need a new prop…smaller pitch for sure and maybe even smaller diameter. I can’t understand why the dealer didn’t discuss this with you prior to installation. To go from 2:1 to 1.48:1 is a big jump. No way would the boat perform the same with the prop sized for the 2:1 and now running 1.48:1. It would be like riding your 10-speed bicycle uphill in high gear from a standing start.

JQ