"Roger Long" wrote in message
...
I would just put in a very accurately machined spool piece or steel disk
with proper pilots. As I understand it, having just had the opportunity to
sit at the feet of some masters and listen but not being an expert myself,
the really critical alignment issue is that the shaft be exactly centered.
Steel will do this better than plastic. Bolts will not maintain it
reliably. You need those machined pilots.
I know that the drivetrains I have used so successfully must develop some
angular misalignment as the engine moves around on the mounts but the
shaft accommodates it without a problem. The single stern bearing and
flexible stuffing box (or shaft seal) on these boats is actually almost
exactly the same setup as on many sailboats.
If you are relying on something between the flanges to accommodate
misalignment, it has to be very, very, soft. Otherwise, there will still
be enough force transmitted to create vibration. Just think how hard it
is to dent or deform that drivesaver disk even a small amount and then
imagine that force on your system a few hundred times a minute. If the
coupling is soft enough to accommodate misalignment, then you will need a
thrust bearing and all sorts of other complications. I've designed and
built successful shaft lines for auxiliary equipment with big rubber tire
couplings, CV joints and thrust bearings, etc. None ran a smoothly as
these high power research vessels do.
Say, I'm awake too early, how about a sea story?
Marvelous story, Roger,
Back to mine, however, the spacer is just between a couple of flanges, both
flat on the mating surfaces, with no pilot or other bearing or bushings or
pins. If the shaft and the tranny plates aren't perfectly aligned fore-aft,
they aren't going to want to go together. Twiddling, if needed, the engine
mounts will take care of any minor differences (I'm into tight tolerances -
I think .005 or less? might do it). Whenever it was converted from bronze
to SS shaft, the intermediate bearing was removed (still aboard, but would
require removing the Max prop and flange and pulling the shaft far enough
for remounting. As it made it for however many years it was from the change
to now, successfully, it's my presumption that it wasn't needed any more,
perhaps due to the greater rigidity of the SS over the original bronze.
I understand and "get" what you are saying about the drivesavers - but years
of use by others, successfully, makes me wonder why the problems you
cite/project don't make it so nobody uses them?
I also don't "get" what you are saying about spool piece or pilot - I need a
spacer of some sort to accommodate the line cutter. If I wanted to save a
bunch of money (having to buy it originally; there may be one in my cockpit
when I get there from someone who had it available, and if it fits, it's
cheap), I'd just get the proper thickness scrap steel machined to fit the
proper size and holes, easily enough done by a rubbing of both pieces, I'd
think. (Curiously to me, some of the line cutter folks want several
hundred - as much as the device - for their machined steel spacer...)
However, if I align it first, then slide it aft only enough to use the
spacer (whatever it is), should not that alignment persist through the use
of - the only difference I'd see - longer bolts? Of course, I'd check,
using the modus recommended by DriveSaver, if that turns out to be what I
use, but I'd expect that it would come out right.
Thanks for your insight(s) - and thanks again for the story, as well as
getting to see your Titanic thoughts.
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