PART ONE: DRIVETRAIN INSTALLATIONS
CV joints, there was no problem with this
at all.Drivesaver Disks
When there isn’t room or budget for Aquadrive,
I still prefer to build some flex into the drive
system. In this case, I’ll specify the Babbit or
Globe Drivesaver disk. PYI also makes a rather
different flexible shaft coupling that achieves
similar results. Again, the engine mounts and
the coupling should match. When installing a
Drivesaver disk, I try to spec matching engine
mounts from the same manufacturer.
These Drivesavers add just a small
amount of flex, which helps isolate engine
noise and slightly reduces potential align-
ment problems—though the entire drivetrain
still must be aligned to standard straight-
shaft tolerances.
It’s a good idea to be certain to install
these on shaft installations where the distance
from the coupling to the stern bearing is less
than 20 times the shaft diameter. Such a short
distance can result in too much rigidity, which
the Drivesaver disk reduces nicely.Stuffing Boxes
It used to be that stuffing boxes were
pretty much all the same: screw-down
packing nuts around the shaft that com-
pressed flax packing against the shaft
(Figure 3-12). Of course, the flax had to be
kept wet (lubricated) to keep it from burn-
ing up when the shaft spun. This meant
backing off the compression nut just
enough to allow a drip or two of water to
flow every few hours at anchor and every
15 minutes or so underway.
These days, many of my clients are in-
stalling slip-ring-type stuffing boxes, with an
elastic bellows that presses the slip-ring seals
together. PSS Shaft Seal and Duramax are
two brands that work fine. However, a prob-
lem occurs in conjunction with the
Aquadrive. During maneuvering—when you
go into reverse—the Aquadrive thrust bear-
ing allows the shaft to pull aft roughly^3 / 8 to(^1) / 2 inch (9 to 13 mm); then when you shift into
“ahead,” the shaft pushes forward again. In
that instant, the pressure comes off the shaft
seal and a perfect circular fan of water sprays
Figure 3-10.
Drivesaver-type
coupling
(Courtesy Globe
Composite
Solutions, Ltd.)
Figure 3-11.
Cutaway view of a
rigid stuffing box
(Reprinted with
permission from
Boatowner’s
Mechanical and
Electrical Manual,
by Nigel Calder,
2005)