"JAXAshby" wrote in message
...

There is also a thrust bearing needed for going in reverse as well.
However,
as the horsepower used in reverse is much less and the time it is used is
hugely less the reverse thrust bearing need not be anywhere near as big.

Now, change the prop so the former reverse thrust bearing becomes the new
forward thrust bearing and operates at 100% power over extended time the
potential to trash that bearing becomes very real.


Either I am not following what you are saying or I am envisioning something
totally different.

As you said, the thrust on the shaft must be countered someplace, and that
someplace is the thrust bearing(s). The thrust will either "push" or
"pull", it shouldn't matter which direction the shaft is rotating.

If you attempted to drive the boat by having the propeller in front, like an
airplane, then the shaft will be pulling and the thrust bearing surface
associated with "pull" will bear the brunt of the load. But I didn't think
this is what we were talking about.

I know that several models of Velvet Drive transmissions don't care which
direction the input and output shafts turn, as long as they turn the same
direction in "forward". You can have a Left Hand and Right Hand rotating
engine turning Left Hand and Right Hand props and the transmissions don't
care. If you attempted to have the Left Hand engine turn the Right Hand
prop, however, then the transmission would be using the "reverse" clutch for
forward which is not nearly as robust as the "forward" clutch and you would
likely have reliability issues.

The web page for the Hurth transmissions indicated that many of their models
were capable of full engine horsepower in either "forward" or "reverse"
operation. I don't know if that really means you can use them for reversing
the rotation for counter rotation or not.

There are many outdrive designs that has the drive shaft come down and drive
two gears, one towards the front and one towards the rear. A "dog" or cone
clutch will engage one gear or the other, which will make the prop shaft
turn one way or the other. The clutches are identical and the thrust is
carried on the shaft bearing (not the gears) so it doesn't matter if the
gear more towards the front is considered "forward" or not.

Rod