Changing direction of a velvet drive input/maintaining output.

[7228sedan]

Hoping folks can assist with a few questions and observations on the input and output directions of 71/72 series Velvet drives.

The current boat, 78 33 Egg Harbor is powered by twin 270 crusaders with 1.91:1 71 series. I am trying to understand what re-clocking the pump on the transmission accomplishes. We are looking to re power with twin LH rotation motors. I understand that there are nuances with this particular gear reduction as well where the output is reversed (LH flywheel input, RH transmission output and visa versa for the other side). I found a pair of low hour, crusader 5.7's that will essentially be plug and play except they are both LH (standard) rotation.

Is it the correct understanding that swapping the pump position on the transmission behind the current RH rotation engine will essentially make it the same as the LH rotation motor? Meaning they both would be RH output? Does anyone know if this is limited to the 1.91 gear reduction? Would the same exercise on 2.57:1 gear reduction 71C's result in the same result?

 

[gonzo]

The pump has to be oriented to the rotation of the engine. The output rotation depends on the rotation of the engine and not the pump. Velvet drive engines can not be used in reverse. That is, if you have two engines turning LH, the output should be LH. Putting a propeller of the oposite rotation and using Reverse as Forward and viceversa will damage the transmission. The thrust bearings and clutches are not designed to run backwards. There are other transmissions, like ZF and Volvo that can be used in any direction.

 

[7228sedan]

Agree, that much I think I follow. If that's the case, were counter rotating twin engine installations not possible using 2 LH rotation motors and velvet drive transmissions?

Or, is there another factor at hand with the gear reduction units?

 

[gonzo]

If you reverse the input and adjust the pump, the output is also reversed.

 

[sdowney717]

There is a velvet drive version that can use a LH engine and output either direction full time all the time. But is not common.

 

[gonzo]

I never heard of it. Do you have a model number? Are you not confusing them with ZF which bough Velvet Drive?

 

[7228sedan]

Thank you both for the time. Ideally, what I'm looking to do is re-clock the pump on the current RH motor's transmission accepting LH input. However, I'll need it to remain LH rotation. As these are 1.91:1 ratio I am almost certain that that gear reduction was the only one which reverses output. I also have access to a pair of 2.57:1 gear boxes as well. Props would need to be recalculated and changed with the different ratio, however I was planning on new props anyway with the new motors.
What I think is correct is as follows:

• Input matches output on most (all but 1.91:1?) when the pump is clocked to match engine rotation. LH in/LH out
  
• 1.91:1 ratio reduction boxes reverse the output Currently RH in/LH out
• clocking the pump on the RH 2.57:1 I have would create another LH output matching the other side (existing LH rotation engine) eliminating counter rotating props.

Assuming this is correct, does anyone know if a velvet drive 71 (10-17-012) can be rebuilt to facilitate RH rotation with a LH input? e.g. an idler in the reduction box or such?