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 Conventional stuffing boxes are now being replaced, after two centuries of service, with a revolutionary device patented by an Italian company, allowing for a complete water-tightness and eliminating bilge water leakage, thus improving safety on board. Let's analyze this innovation, built thanks to a professional engineer with a long experience in industrial applications and, of course, a real boating fan. |
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THE STUFFING BOX ERA IS OVER
My first meeting with Engineer Antonio Pedone and his son took
place in a charming ancient villa, located in the center of Milan,
Italy, where I first saw the new Hydraulic Hydro-tightness for
shaft lines. The introduction of such a revolutionary concept in
such an historical place made me focalize, even more if possible,
my attention on the great importance of this innovative device and
on its real value. The system consist of a hydrodynamic device
which replace conventional stuffing boxes, preventing bilge water
leakage and preserving the propeller shaft as well, thus
performing an active and passive safety work both in case of
damage or collision. Its particular design makes it a long
resistance device, and it is covered by a five years complete
warranty from the date of installation.
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A time tested design
"Seven years ago, during a sailing holiday, a mooring line got
warped around the propeller shaft, which moved a couple of
centimeters from its position, damaging the stuffing box. Only
thanks to a scuba-diver who immediately applied a proper putty,
the boat did not sunk. This episode, together with the
continuously care required by conventional stuffing boxes, makes
me think about a new tight concept, able to definitely solve the
problem", Eng. Pedone explains. Thanks to his thirty years
experience on electro-chimic industrial applications design, Eng.
Pedone, assisted by his soon, tested, in 1989, the first Hydraulic
Hydro-tightness on his boat. The new device, developed together
with several technicians, has, since then, fully satisfied Eng. Pedone.
A complete range of tests were carried out for more than
5000 hours in salty and sandy environments, before the marketing
of the actual version. The result of all this is a clear market
success, as confirmed by the several yards which fit theirs
production yachts with the Hydraulic Hydro-tightness; some of them
are: Cantieri Riva, Cantieri di Sarnico and Cantieri del Golfo-Italcraft.
The latter has recently ordered 50 Hydraulic Hydro-tightness
to be installed on Italian Coastguard patrol boats. The
system, manufactured by Technosystemes, consist of a special
mechanical tightness using the rotating shaft line as an impeller
(just like a common pump rotor or turbine) inside a special
bearing with no additional gears, vibrating diaphragm or any other
wearable part. This particular "pump" carries out basically three
main functions: it produce, inside the Hydraulic Hydro-tightness,
a counter pressure which avoid water entrance and oil leakage (at
very high shaft rpm as well); it ensure a perfect lubrication of
the tightness' self-centering bearing thus protecting it, the
elastic rings and the shaft from wear; it ensure the system
cooling thanks to a simple but efficient heat exchanger coil. This
solution avoid, therefore, all the problems related to sea water
cooling, where most often than not, it is possible to have
imperceptible but highly abrasive suspended sand grains.
A one to one scale demo version of the Hydraulic Hydro-tightness
was ready in the room where we met, fitted with an alternate
current engine simulating the shaft rotation. As shown in the
pictures, this patented system (for boat and ships) consist of a
main cylindrical structure made of a special antifriction and
anti-corrosive bronze. It is a custom built case (thus suitable
for installation on any shaft diameter) allowing for the shaft's
axial and radial sliding. In case of installation on existing
boats, it has been studied to ensure the connection to all the
stuffing boxes currently in the market, simply removing the
packing and the head bushing. The groove at the case's aft outer
side end serves this purpose. The Hydro-tightness is made of two
main parts: the first is the one directly touching the water which
can be called the "fastening body". It is filled up with a high
viscosity grease, purposely studied by Technosystemes'
technicians, which ensure water tightness. This is made possible
by two elastic rings which, by keeping the grease, build up a
barrier against water infiltration. A greaser, fitted with an air
outlet valve, supply the greasy oil. The second part is a oil-bath
ring housed, again, between two elastic rings, where the ball-bearing
(bushing) trough which the shaft goes, is placed. The
system basic concept is in the particular bushing's shape which
serves the purpose of supporting and rotating the shaft and act as
an innovative pump. The bushing, together with the shaft speed,
create a pressure on the oil in order to completely avoid both
water entrance and oil leakage. This produce a counter hydraulic
pressure which force the oil, stored in the tank, into the
circuit. Observing the demo version I have noticed that the oil,
flowing from the tank trough two rubber pipes, fills up the two
external grooves placed between the bushing and the sleeve then
lubricating the elastic rings. From here the oil is forced into
the bushing's center where a longitudinal groove, located in its
internal side, acts as the pump body. Here is produced the counter
pressure permitting the oil circulation. Consequently a compact
layer of oil is created between the bushing and the shaft ensuring
an optimal fluid-friction situation. It is a sort of "shaft
planning state on the oil layer", without any contact between the
shaft and the bushing thus eliminating friction. The oil flow
along the elastic rings creates, due to the capillary effect, an
oil layer between the rim and the shaft which is bounded at its
ends by a convex meniscus (a thin convex surface) whose
superficial tension avoid any fluid leakage, also at very high rpm.
Now that we have briefly described the system, (PCT Patent Pending
n. 96/05100; RINA n. MAC/217/95) lets take a look to the
installing techniques, the safety level obtained and the
reliability achieved on both pleasure and working crafts. Some of
the most important advantages are: - the heat exchanger ensure a
correct functioning on fast boats as well, where usually cooling
is performed by mean of sea water inlets, which can be obstructed
by underwater bodies. - Long working life is ensured by its tight
concept and thanks to the forced oil circulation as well, which
guarantee service throughout the years without any particular
maintenance. - The system allows a boat to remain a long time at
berth without any water leakage. - It allows shaft axial shifts,
which can happen due to sudden accelerations and deceleration or
with slight engine movements, without damaging the system in any
way. This usually do not happen on conventional stuffing boxes. -
The perfect forced oil lubricating system is able to preserve the
shaft longer. In fact , on conventional installations, sand grains
may infiltrate trough sea water inlets, wearing the shaft thus
increasing water bilge leakage. - A simple but reliable shaft
shifting monitoring system is available on request, and it is able
to stop the engine in case shaft shifting reach a fixed adjustable
value thus avoiding dangerous situations which could lead to the
craft lost. - Safety is probably one of the most important
characteristics of the Hydro-tightness. Conventional stuffing
boxes, although manufactured from more and more reliable
materials, have a limit which depends on their own working
criterion. The shaft is actually warped by the packing which, to
prevent water infiltration, must press on the shaft surface, thus
inducing friction. Forced water cooling (with consequent water
leakage) increase the shaft stress which, on working boat such as
fishing vessels, must be replaced every two years. The Hydro-tightness,
on the other hand, cure those problems with its
innovative idea. Benefits range from operating costs savings to
cleaner engine rooms leading to even longer equipment life.
"Anyone who own a beautiful car equipped with a good engine care
about it and keeps it in a proper parking space. Nobody knows why,
on the other hand, one or more engine whose cost is often more
than a brand new Ferrari are kept in a dirt, humid and sometime
wet place.
The new Hydro-tightness can make of every engine room a
clean place for our engines", Eng. Angelo Pedone says. We would
like to add that, following to the upcoming CEE rules on bilge
water pollution, the system can really help in dramatically reduce
engine room water leakage which, once mixed with oil or fuel,
become an highly polluted solution. Nowadays it is forbidden to
pump bilge water overboard, but the Hydro-tightness can save us
expensive additional tanks which should be discharged in
structures not even found in all marinas. Not-practical bilge
inspection can be avoided, and an additional cost saving is
obtained eliminating the expensive traditional stuffing box
maintenance. In addition, the system, when installed on sail
boats, will allow to re-charge the batteries with the shaft's free
rotation when steering under sail. In conclusion we hope all
pleasure boats manufacturers will fit this revolutionary system on
their production models, so to improve safety, reliability and
cleanness. The possibility to install this device on existing
boats is probably even more important. It can be easily done on
every kind of pleasure, working, displacement or planning crafts
including, of course, sailing yachts with inboard auxiliary engine
and motorsailers.
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