For what it's worth, I deal often with one of the foremost drivetrain
and propulsion specialists in the country in connection with designing
boats like this:

http://home.maine.rr.com/rlma/WHOIrv.htm

The shipyard that builds these boat specializes in fast,
sophisticated, high powered craft. Both told me that they hate
"Drivesavers". The boat in the picture has two 710 horsepower engines
with the engines flex mounted and the shafts connected with solid
couplings. There is just one bearing, in the shaft strut. They run
smooth as silk.

I do have a drivesaver disk in my boat but they cut the shaft short
when they installed it so I have to buy a whole new shaft to take it
out. It's not causing any problems that I can see though other than
making it a pain to repack the stuffing box.

Skip the drive saver. Line up your shaft carefully calculating the
overhanging weight of the shaft and using a scale to hold the end up.
Make sure the flanges are true and the pilot concentric. Then hard
mount it. The metal parts will then be more precision than a plastic
disk can ever be and will stay that way. It will run fine.

There's a whole range of prop strike forces where the drive saver
could break but the solid coupling would still leave you able to limp
off a lee shore with the engine vibrating and shaking. I like that
scenario better. I've heard of a lot more broken shafts and totally
trashed props than gear boxes that failed due to prop strike. The
gears are a lot more rugged than you would think. Remember that there
is a friction clutch in the system that will give some under an
extreme shock load.

--

Roger Long



"Skip Gundlach" skipgundlach at gmail dotcom wrote in message
...
Hi, Lists,

Thanks for all the responses to my line cutter question. To put one
on will require some more space, and, in general, I've come to think
that a break-away (with built-in safeguards to allow continued use
until replacement) spacer is also a good move.

Who here has had one, and, best, has had to use it to save their
gear?

Thanks again.

L8R

Skip
Morgan 461 #2
SV Flying Pig KI4MPC
http://tinyurl.com/384p2 The vessel as Tehamana, as we bought her

"Twenty years from now you will be more disappointed by the things
you
didn't do than by the ones you did do. So throw off the bowlines.
Sail
away from the safe harbor. Catch the trade winds in your sails.
Explore.
Dream. Discover." - Mark Twain