I haven't had a chance to read it yet due to the rare opportunity to
actually earn a little money.

He may well be right. When I stop and think how stubborn and
difficult vibration issues are in high powered boats and how rare
problems are in almost universally neglected drive trains like ours, I
can believe it.

The shaft on one of my research vessels is about 3" dia. Three times
the diameter for over 30 times the horsepower so the relationships are
quite different.

You've got my curiosity up so I think I'll take a break....

You'll feel better after you do all that work anyway

--

Roger Long



"Skip Gundlach" wrote in message
oups.com...
Did you read the article on alignment I cited? It's by a primarily
high-end powerboat surveyor, so has that bias.

The best I can read out of his stuff is that alignment in our boats
isn't worth much...

Despite that, I''m still going to pull the tranny, the shaft, take
off
the prop (of course, required) and take the couplings and shaft off
for
truing, should it need it. Another list I'm on where a similar
discussion is taking place has it that the only reliable
truing/observation of a shaft is a calibrated roller bed. His (the
surveyor) article suggests it's not needed in our sizes, based on
all
the other factors...

L8R

Skip

Morgan 461 #2
SV Flying Pig KI4MPC
http://tinyurl.com/p7rb4 - NOTE:new URL! 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

Just skimmed it.

I think he's right but he's talking about something different than the
couplings faces being true and square to the shaft. If you have a
true running shaft pulled out of line by the engine moving on the
mounts or not being perfectly aimed towards the strut, that's one
thing and probably not a big issues as he says. If the engine is
trying to wave the far end of the shaft in a circle under the same
circumstances, I think you are going to have some noise.

--

Roger Long

In article , Roger Long
wrote:

Just skimmed it.

I think he's right but he's talking about something different than the
couplings faces being true and square to the shaft. If you have a
true running shaft pulled out of line by the engine moving on the
mounts or not being perfectly aimed towards the strut, that's one
thing and probably not a big issues as he says. If the engine is
trying to wave the far end of the shaft in a circle under the same
circumstances, I think you are going to have some noise.

I'd agree with you. What I don't understand, though, is why, *ever*,
you wouldn't have flange faces that weren't at right angles to the
shaft(s) to within extremely close tolerances. But then I'm a
fitter/machinist amongst other things and have a couple of lathes about
the place. Facing a flange off square is a 30 second job. Boring it to
a close sliding fit on a shaft, not much longer.

The whole issue of small boat drive trains strikes me as something that
shoulda been left in the ark. If I ever get my shed finished so I can
move onto the boat, I'm planning on mounting my engine/trans with a CV
joint between it and the shaft. This will require a thrust bearing on
the end of the shaft, but so what. I can mount the engine pretty much
wherever I want, on soft vibration reducing mounts, and forget about
drive train misalignment. We're only talking 30 HP or so. My tractor
PTO handles way more than that reliably. No thrust loads there of
course, hence the need for a thrust bearing on the shaft.

I can't understand why drive systems are hard coupled other than it's
cheap to do the first time and any subsequent maint probs aren't coming
home to the builder.

PDW