LH and RH gear ratios in Volvo MS15A transmission -Can I use any of them to go ahead?

[svlamorocha]

Hello everyone.

Volvo says that this tranny has a 2.63:1 ratio for "right handed rotation" and a 1.95:1 ratio for "left handed rotation". As far as I know (and unlike Yanmar) they do not say which one of the two ratios is "forward" and which one is "reverse"

One boat I know has a right-handed propeller so that when it goes forward the 2.63:1 ratio applies and when it goes astern the 1.95:1 ratio applies (this means that with a fixed-blade prop chosen to go forward you get lousy rpm going back).

Another boat *seems* to have it the other way around with a left-handed propeller so that when it goes forward the 2.63:1 ratio applies and when it goes astern the 1.95:1 ratio applies. This means you need a smaller prop to go forward and it is more balanced forward vs astern.

My crazy question is: Is it possible to use this transmission either way or will it suffer if you use it to go forward in the "longer" 1.95:1 ratio using a left-handed prop?

I look forward to some wisdom.

C

[GordMay]

Standard recommendation is for left hand rotation for forward.
Pg 39 ➥ http://www.polarpowerinc.com/volvo_p...ion_manual.pdf

[svlamorocha]

Originally Posted by GordMay

Standard recommendation is for left hand rotation for forward.
Pg 39 ➥ http://www.polarpowerinc.com/volvo_p...ion_manual.pdf

Thanks; since my post I came across this lhat calls for *right* hand prop for the MS1

[svlamorocha]

Originally Posted by GordMay

Standard recommendation is for left hand rotation for forward.
Pg 39 ➥ http://www.polarpowerinc.com/volvo_p...ion_manual.pdf

Thanks a lot; this instalation manual in fact calls for use of *right* hand prop for the MS15 in p40; the left hand prop recommendation in p39 is for saildrives .. Does anyone know if Volvo's recommendation of a spcific hand of prop is b

[svlamorocha]

Originally Posted by GordMay

Standard recommendation is for left hand rotation for forward.
Pg 39 ➥ http://www.polarpowerinc.com/volvo_p...ion_manual.pdf

Thanks a lot; this instalation manual in fact calls for use of *right* hand prop for the MS15 in p40; the left hand prop recommendation in p39 is for saildrives .. Does anyone know if Volvo's recommendation of a specific hand of prop is required to avoid damage to the transmission (as other brands that have a specific direction to be used going forward and the other one is only for exceptional use) or some other reason?
C

[JayH]

Originally Posted by svlamorocha

Hello everyone.

Volvo says that this tranny has a 2.63:1 ratio for "right handed rotation" and a 1.95:1 ratio for "left handed rotation". As far as I know (and unlike Yanmar) they do not say which one of the two ratios is "forward" and which one is "reverse"

One boat I know has a right-handed propeller so that when it goes forward the 2.63:1 ratio applies and when it goes astern the 1.95:1 ratio applies (this means that with a fixed-blade prop chosen to go forward you get lousy rpm going back).

Another boat *seems* to have it the other way around with a left-handed propeller so that when it goes forward the 2.63:1 ratio applies and when it goes astern the 1.95:1 ratio applies. This means you need a smaller prop to go forward and it is more balanced forward vs astern.

My crazy question is: Is it possible to use this transmission either way or will it suffer if you use it to go forward in the "longer" 1.95:1 ratio using a left-handed prop?

I look forward to some wisdom.

C

I'm wondering if you might be confused about the ratios. The 2.63 means the engine turns 2.63 times for every 1 time the prop turns. That is intended to be the forward gear.

The MS15A is probably a ZF15MA. ZF refers to the 2.63 ratio as "forward". They also say this gear needs an oil cooler if using more than 25kW in position "B" (1.95:1, or "reverse").

So it sounds like it is possible to run it backwards (with an oil cooler) but I'm not sure why you'd want to. Sailboats typically benefit from larger, slower-turning props.

http://www.tadiesels.com/transmissio...s/ZF_15_MA.pdf

[svlamorocha]

Originally Posted by JayH

I'm wondering if you might be confused about the ratios. The 2.63 means the engine turns 2.63 times for every 1 time the prop turns. That is intended to be the forward gear.

The MS15A is probably a ZF15MA. ZF refers to the 2.63 ratio as "forward". They also say this gear needs an oil cooler if using more than 25kW in position "B" (1.95:1, or "reverse").

So it sounds like it is possible to run it backwards (with an oil cooler) but I'm not sure why you'd want to. Sailboats typically benefit from larger, slower-turning props.

http://www.tadiesels.com/transmissio...s/ZF_15_MA.pdf

Great stuff. Thank you! Now I know there is a real reason not to use the thing backwards. I knew that for Yanmar but had not seen it written for Volvos.

There is no confusion regarding the meaning of the ratios. I did swap the numbers for the second boat when I wrote the post though. The one reason to use the 2.63 ratio for reverse would be to let the engine reach more rpm in reverse for those infrequent but important situations when you need lots of power astern. The differential pitch in the Maxprops can be made to adjust for that but I did not know how much to trust that...Note that the relative ratio between forward and astern ratios is the opposite in Volvo than Yanmar which means that in Volvo shaft trannies you do not get high rpm astern unlike in Yanmar... Hence the exploration of options.

Back to the ZF info that is very useful. Do you think that the innards are the same even though the housing is not identical? Thanks in advance for your wisdom!

C