BOAT DOCTOR /// WHAT TO LOOK FORLIP SEAL
Lip seals, like the Tides Marine
shaft seal, are dripless seals.
The seal is made by a composite
plug that bears directly against
the shaft, preventing water
from getting past the shaft at
the stern tube. The shaft turns
inside the seal, and lubricat-
ing water is plumbed from the
engine’s raw-water discharge.
There is no dripping. No pe-
riodic tightening is required.
Lips seals come with a spare
seal that slides onto the shaft
ahead of the seal assembly
so that a worn seal can be re-
placed without having to haul
the boat. They are self-aligning
to some extent, thanks to the
fl exible hose used to connect
them to the stern tube. Lip
seals require a pristine shaft
surface and may require more
distance between the gear cou-
pler and stern tube (shaft log to
you old salts) than other seal
types. The water supply must
be regularly checked to ensure
safe and proper operation, but
lip seals can last for years.PACKING BOX
A stu ng or packing box,
such as those by Buck
Algonquin (now HydrasearchRecreational), is a shaft seal,
usually attached to a hose, that
the shaft runs right through as
it exits the boat. Made in two
parts, one part screws down
and compresses strands of
wax-impregnated fl ax (dense,
thick cotton strips) packingmaterial against the shaft and
the inside of the fi xed sec-
ond part to create a seal. One
cranks down until just a drip
every 20 seconds or so occurs
when the shaft is rotating and
no drips occur when the shaft
is stopped. Water in the bilge
is tolerated in exchange for
keeping the seal cool. Periodic
tightening and annual packing
replacement is required. Over
time the shaft can become
grooved. Packing boxes are in-
expensive and easy to service.FACE SEAL
Face seals, such as the PSS
shaft seal by PYI, are also drip-
less shaft seals, requiring less
maintenance than a packing
box, and like lips seals, they
get cooled by the engine’s
discharge water. Face seals
rely on two machined faces
pressed together at 90 degrees
to the shaft. One face — the
rotor — is split and bolted inplace onto the shaft. The oth-
er half — the carbon face — is
pressed against this split ring
with pressure exerted by a
sprung bellows. Because face
seals do not seal against the
shaft directly, they can pro-
vide a good seal if the shaftsurface is less than perfect,
such as an older shaft that has
seen service but is still struc-
turally in good shape, making
them popular for retrofi ts.
Face seals need to be regularly
inspected for leaks, but in
practice last for years.INBOARD
SHAFT SEALS
PHOTOS: (CLOCKWISE FROM TOP LEFT) TIDES MARINE, HYDRASEARCH RECREATIONAL, PYI INC., DEFENDER INDUSTRIES INC.If your boat needs to be towed
and has dripless shaft seals,
the shafts must be immobi-
lized. The props will freewheel,
but no engine-cooling water
will be fed to the seal if the
engine cannot be kept running.
Twin-engine boats can have
redundant crossover plumbing
so that each engine’s cooling
serves both shaft seals. If only
one engine is broken down, the
other engine can supply lube
water to the other’s shaft and
the shaft need not be locked.TOWING WITH
DRIPLESS SEALSIf your boat uses an inboard engine, then it’s important that
you know something about shaft seals. Whether you run a
twin-engine convertible sport-fi sher, a sedan cruiser or a wa-
tersports boat; whether you are buying new, buying used or
retrofi tting a faithful family heirloom; or whether you cruise
the bl ue water or ride the endless wave of a wakesurfer, it is
the prop-shaft seal that keeps the water out and lubricates the
shaft at its point of exit from the hull. Here’s what to look for in
shaft seals. —Kevin FalveyQUICK TIP
Shaft seals are also used to seal the rudder shafts of inboard-powered boats.THIS BUCK ALGONQUIN SHAFT PACKING TOOL
is a must-have for removing old, compressed flax
packing from a stuffing-box shaft seal. It comes in 9-
and 12^1 / 2 -inch lengths. $7.99 and $8.99, respectively;
defender.com