"Skip Gundlach" skipgundlach at gmail dotcom wrote

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?

They aren't really a problem by themselves but sort of a band aid
solution for not doing it right in the first place. Of course, most
pleasure boaters, and plenty of boatbuilders, don't want to do it
right. They just want to take stuff out of boxes and bolt it
together. A drivesaver probably won't make things any worse in that
situation, it may even help a little bit with a boost from the placebo
effect.

In the commercial world, the flange on the gear is trued up so that
the outside edge is exactly concentric and the face exactly
perpendicular to the shaft. That flange is then mated to the
propeller shaft flange which is trued up after being installed on the
shaft with the whole thing being turned in a lathe or other fixture.
A male/female pilot or disk; not the bolts, keeps the two halves
concentric.

If you're not going to do this stuff, maybe a drivesaver will help but
it won't be as good as doing it right.

If you do it right, you won't need the drivesaver and it just makes
things more likely to slip.

Still, I wouldn't bother taking the one out of my shaft system except
to make it less of a pain to repack the stuffing box.

--

Roger Long

In article ,
"Roger Long" wrote:

"Skip Gundlach" skipgundlach at gmail dotcom wrote

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?

They aren't really a problem by themselves but sort of a band aid
solution for not doing it right in the first place.

Sorry if I'm misinterpreting -- it's late and I'm catching up on 1400
messages -- but my post seems to be the genus of this.

Our Drivesaver is solely there to try to protect the engine and drive
shaft in the case of a wrapped mooring line or similar. We snapped a
shaft once. I only mentioned that it helped moderate vibration as a
slight benefit.

Every couple of years, I take the drivesaver out, check the alignment
and would correct if necessary, but it hasn't been.

BUT with the Yanmar's flexible mounts, there will be some misalignment
under some power loads, merely because the engine has shifted in its
mounts slightly due to torque.

I wasn't talking about the vibrations a 700 HP setup would generate. I
was talking about vibrations a sailor would notice, one who spent about
70 days out and about last season and who used a grand total of 13
gallons.

I may be hyper-sensitive to noise and vibration, but the drivesaver
makes my motoring time more enjoyable.... Okay, less objectionable.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

"Jere Lull" wrote

I may be hyper-sensitive to noise and vibration, but the drivesaver
makes my motoring time more enjoyable.... Okay, less objectionable.

I have no doubt that it does. My point was that setting up everything
PROPERLY would very likely produce an even smoother running system.
The key word is properly. Few boats have their shaft systems machined
properly which makes a good market for the Drivesaver. At least this
is the opinion of the people who have set up the demanding drive
trains in my 1400+ HP boats so they run far smoother than my sailboat.

Doing it right probably would cost quite a bit more than a drivesaver
which may also help keep those folks in business.

One thing I hadn't thought of:

The shafts on the boats I'm used to dealing with are very
conservatively designed and I've almost never heard of one breaking,
even when the wheels are totally trashed. With the small shafts
common on many yachts, it might make sense to have a "fuse" in the
system that is cheaper than the shaft.

I'll have to confess that I don't deal with the nitty gritty details
of shafts; just the basic layout and sizing. I'm simply passing on
what a guy who has solved shaft problems that others couldn't on boats
from fast patrol boats to aircraft carriers told me when I said,
"shouldn't we have a Shaftsaver?"

I'm sure opinions vary. The shaft shop you talk to may love to just
take stuff out of boxes and sell it to you alone with a Shaftsaver for
the same price as doing it the right way. They may not even know the
right way in which cast the Shaftsaver is your best option.

Like I said, taking the one out of my shaft line is about item number
6374 on my list of things I'd like to do.

--

Roger Long

I'm sort of disagreeing with Roger here with his suggestion (I think)
of flexibly mounted engines but a rigid shaft coupling. On all the
vessels that we design, 95% use flexible mounts. We like Lo-Rez
because they are very soft (~0.5" static deflection). But to use them
you HAVE to have a flexible coupling because otherwise all that
vibration will get into the structure via the shaft and stuffing box.

Evan Gatehouse

"Evan Gatehouse" wrote

I'm sort of disagreeing with Roger here with his suggestion (I
think) of flexibly mounted engines but a rigid shaft coupling.

It's probably not a disagreement but having lost track here of a point
in the thread. I'm talking about a specific drive train configuration
which is common on sailboats.

There must be a flexible stuffing box or shaft seal and there must be
no other bearings other than the stern strut. The engine can be on
very soft mounts. There is then nothing except the cutlass to pick up
any shaft vibration. The shaft is long enough to flex and accommodate
the engine motion. The full length version of this video

http://marine.unh.edu/Images/Gulf%20Challenger.wmv

shows a cup of coffee sitting on the quarter bit while the boat is
going 20 knots and there isn't a ripple on the surface. The struts
pick up very little vibration.

As soon as you introduce a second bearing into a the shaft system with
soft engine mounts, you have to have something flexible between the
gear and the shaft. I've made the shafts slightly oversize on my fast
research vessels to eliminate the need for a second bearing, way, way,
cheaper than installing and lining up that second bearing.

BTW there is a direct relationship between how much the engine can
move and the frequency of vibration isolated. Thin rubber pads take
out the high whine but getting the low throb and rumble out requires
letting the engine move 3/8" to 1/2" as you say you are doing.

--

Roger Long

Evan,

I'm curious. What kind of boats does a phone company design or is
your header showing something odd for an organization?

--

Roger Long



"Evan Gatehouse" wrote in message
...
I'm sort of disagreeing with Roger here with his suggestion (I
think) of flexibly mounted engines but a rigid shaft coupling. On
all the vessels that we design, 95% use flexible mounts. We like
Lo-Rez because they are very soft (~0.5" static deflection). But to
use them you HAVE to have a flexible coupling because otherwise all
that vibration will get into the structure via the shaft and
stuffing box.

Evan Gatehouse

In the commercial world, the flange on the gear is trued up so that
the outside edge is exactly concentric and the face exactly
perpendicular to the shaft. That flange is then mated to the
propeller shaft flange which is trued up after being installed on the
shaft with the whole thing being turned in a lathe or other fixture.

Amen. For years I had an minor vibration in the auxiliary on my 36'
sailboat, which engine realignment, new cutlass bearing, and new engine
mounts didn't change. On last haulout, after a transmission swap (with
a trued output flange), the yard recommended the above procedure and
voila', vibration gone.