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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.


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.

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.

What it is

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.

The oil, once in the pump body and thanks to the hydrodynamic lift, the superficial tension and the boundary layer adhesion is pressed near the inlet opening and then pumped outside the sleeve. Then the oil goes trough an effective heat exchanger made of a special copper coil where the heat removed from the system is dissipated. From here the oil goes back to the tank, closing the circuit. By observing the Hydro-tigthness, it is clear that the forced oil circulation is essential to the entire system concept. In fact it ensure the perfect lubrication of both bushing and elastic rings, which will, otherwise, wear quickly. It is ,then, the oil circulation which makes the system time reliable. Without it, the oil will remain next to the elastic rings edge, increasing its temperature till its lubricating capabilities will decrease. In such a case the elastic ring edge will wear, dragging dry on the shaft, scratching it and with unavoidable oil and water leakage.

The technological pluses

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.

For further information please contact Technosystemes, tel. +377-93-256926 Munich Pricipate, which will point you to the nearest authorized dealer.