PARTIALLY SUBMERGED PROPELLER DRIVE SYSTEM

Description

The present invention relates to a marine drive system of the kind having a partially submerged propeller, provided with one or more propellers positioned at the lower part of the transom of a watercraft, with the drive shaft projecting astern.

Many different types of the above specified system are known, available e.g. in the Italian Patent No. 1 ,184,406 and in the international patent applications Publ. No. WO 92/06000 and WO 96/40550.

In this drive system typology, the propeller is intended to remain only partially submerged in the operation thereof, causing a driving flow localized at the water surface. This system, being generally adoptable on every watercraft, in the current state of the art finds its preferred application in the field of high speed planning watercrafts, for competition, sporting and yachting.

It is understood that the propeller efficiency, as the ratio between the driving power actually transferred to the water and actually exploited and the power at the drive shaft, is optimized in the partially submerged operation, wherein the water level, obviously considering the wave generated by the wake, substantially corresponds to the propeller centre line, i.e. about to the drive shaft (50% disc area submerged).

In order to help the propeller to remain substantially at this condition during the normal motion conditions, US 5,290,182, in the name of Mondelo, discloses a marine drive comprising two flaps arranged lengthwise the propeller member at the end adjacent the propeller, for generating a vertical upward force.

However, these flaps will affect the position of the propeller only in high speed conditions and, therefore, the condition for the propeller to be only partially submerged will not generally occur in all other motion conditions. As a matter of fact, when the watercraft moves at the rated design speed, she assumes a different configuration with respect to that assumed when the watercraft is still, when it is fully displaced, which is planing or in a partially displaced configuration. In fact, increasing the speed until the rated design speeds are reached, the watercraft continuously varies the immersion and the longitudinal trim angle thereof, passing from a hull hydrostatic displacement phase to an intermediate or temporary phase and finally to a phase wherein a considerable part of the watercraft weight is supported by the hydrodynamic lift of the hull.

Moreover, at the rate speed, the wake wave is located at a certain distance from the transom, so as not to interfere with or to partially interfere with the propeller.

In lower speed conditions than the rate speed, wherein the cruise configuration is not assumed by the watercraft yet, the propeller is in a completely submerged configuration or in an intermediate configuration, wherein it does not transfer drive

power to the water with the rated efficiency and even it forces the engine to provide a high drive torque at low rpm.

This strain in the power transmission delays the reaching of an optimal configuration, allowing the propellers to work in a partially submerged condition. This drawback further limits the available speed range of the watercraft to those higher, making the partially submerged propeller-driven watercraft of the known art less manoeuvrable and efficient at the intermediate speeds.

Further, it is understood that the above difficulties may be only partially obviated, even in an unsatisfactory way, modifying the watercraft hull at the transom. For example, US 1 ,553,160, in the name of Hickman, discloses a boat comprising a surface extending from the transom apt to prevent the rising the wake wave. As a matter of fact, such modification, being in addition not adoptable on the existing modern watercrafts, varies in a substantial manner the wake, regardless the motion condition of the watercraft, in general negatively influencing the performances thereof at the cruise speed and the manoeuvrability thereof.

Alternatively, modified hulls also US 3,793,980 in the name of Sherman, discloses a boat wherein a tunnel is provided in the underbody thereof, the tunnel housing the drive shaft and being provided with openings allowing the flow of water inside the tunnel. Also in this solution is not adoptable on the existing watercrafts, required a complete modification of the hull and, in general of the structure thereof, and, above all, is does not prevent the flow of water to wash the propeller in low speed driving.

The technical problem at the root of the present invention is to devise a marine drive system allowing to obviate to the drawbacks mention with reference to the prior art.

Such a problem is solved by a partially submerged propeller marine drive systems according to claim 1.

The main advantage of the marine drive system according to the present invention lies in the more affective directing of the wake wave, so as to allow the propeller(s) to operate, at lower speeds, in a condition nearer to the optimum, without affecting the propeller(s) operation at the rated cruise speed of the watercraft.

The present invention will be described hereinafter, according to a preferred embodiment thereof, provided for an exemplifying and not limiting purpose with reference to the annexed drawings wherein: * Figure 1 shows a perspective view in a partial cross-section of a first embodiment of the marine drive system according to the invention;

* Figure 2 shows a side view of the marine drive system of figure 1 ;

* Figure 3 shows a bottom view, i.e. astern, of the marine drive system of figure 1 ;

* Figure 4 shows an elevation view, toward the transom, of the marine drive system of figure 1

* Figure 5 shows a perspective view of a second embodiment of the marine drive system according to the invention; * Figures 6A, 6B and 6C illustrate the behaviour of a watercraft having the marine drive system of the preceding figures; and

* Figures 7A, 7B and 7C show a flap of the marine drive system of the invention according to a different embodiment.

In the figures, a drive system is only partially depicted with reference to a sole propeller, but it will be apparent how the system may use more propellers, e.g. a pair, mirroring, for each propeller, the structure which will be described hereinafter, so as to apply it on the transom of every watercraft, in particular a displacing or semi-displacing or planning watercraft, possibly with one or more propellers for one or more hulls. In such configurations, the propellers are placed so as be counter rotating, and consequently all the details, which will be described hereinafter, will be mirrored from one propeller to the other.

With reference to figure 1 to 4, a first embodiment of a partially submerged propeller drive system is indicated as 1. It comprises a propeller 2 and a supporting structure 3 which in turn has a fastening plate 4, apt to be secured to the transom of a watercraft. As will be clear in the following, the supporting structure 3 and the propeller 2 can be alternatively secured directly to the transom, without the use of the fastening plate 4.

At the fastening plate 4, the system has, in connection with the transmission of the driving torque to the propeller 2, a stern tube 7 housing the drive shaft between said fastening plate 4, if present, and the propeller 2. Said tube simultaneously works as hydraulic sealing, preventing the water leaking inside the watercraft; thrust bearing, for transferring the thrust generated by the propeller to the lower part of the fastening plate 4; and possibly structural support for the propeller shaft. According to the present embodiment, the tube 7 housing the drive shaft is linked to means for positioning the drive shaft, in the present embodiment of the kind having an active-type hydraulic cylinder 14, able to absorb the thrusts involving the shaft, along any direction, and to actively modify the height of the propeller, e.g. for adjusting the latter in connection with different load or speed conditions of the watercraft.

In the present embodiment, the means for positioning the drive shaft are placed below a projecting case 10 which will be detailed in the following.

At the present issue, the drive shaft can be oriented on a vertical plane, achieving

the adjustment of the propeller immersion. This typology is suitable for cargos and recreational crafts, having a planing-type bottom suitable for medium-high speeds.

The propeller 2 is mounted to the drive shaft, the propeller being of the type with five blades appropriately shaped for this kind of propeller. At the drive shaft, i.e. at the stern tube 7 thereof, the marine drive system 1 according to the present embodiment comprises a flap 100, substantially positioned between the transom, i.e. the fastening plate 4, and the propeller 2.

As it will become apparent from the following description, the flap is positioned so as to intercept and control the wake wave, at least when the wave tends to excessively submerge the propeller disc.

More precisely, the flap 100 is mounted separated from the transom T, i.e. the position of the flap 100 is such that a gap is defined therebetween and it does not project directly from the transom T.

This feature advantageously allows the passage of a flow of air above the flap, so that, as will be better understood in the following, the water eventually flowing to the propeller will be mixed with this flow of air, improving the working conditions thereof.

Also, the gap will allow the flow of water under the watercraft S when moving astern, improving the efficiency of the drive. In the present embodiment, the flap 100 has a substantially convex shape, with the convexity facing the top side, so as to direct bottomwise a V-shaped camber.

The flap is positioned just below the drive shaft and it is linked to the latter, i.e. to the stern tube 7 thereof. Due to the presence of the means for positioning the drive shaft, it can suitably adjust the position of the flap 100 too, varying it according to the different cruise conditions.

In the present embodiment, the flap 100 is delta-shaped, with the apex directed toward the transom of the watercraft, and it comprises a longitudinal centre portion 102, corresponding to the drive shaft section between propeller 2 and fastening plate 4. From the centre porting 102, two half-flaps 103 branch away, directed so as to result in said top-open convexity. Further, the flap 100 comprises a rear edge 104 faced to the propeller 2, extending along a width of about 50% of the propeller diameter, preferably equal or greater than the 80% of the propeller diameter, to reach or to slightly overcome the width of the propeller diameter. Such width, and even the flap area, can be modified and adapted according to the features of the single applications and can be at least 20% of the propeller diameter.

In particular, in order to assure an adequate deflection of the wake wave, the flap

100 extends along a width of at least 20% of the propeller diameter, and along a length of at least 20% of the propeller diameter.

Due to the shape and to the position, only the wake of part actually involving the propeller is influenced. However, it is understood that the shape of the flap 100 can be modified just to adapt itself to peculiar design requirements concerning the watercraft manoeuvrability or the performances thereof.

In particular, it is understood that the area, the plan shape, the cross-section and the longitudinal section of the flap can be appropriately sized and optimized for each single application.

Further, it could be possibly provided means (not shown) for modifying the position and/or the configuration of the flap 100 with respect to the drive shaft.

According to a further alternative, the flap 100 can be positioned just above the drive shaft, i.e. above the tube thereof. In the present embodiment, a suitably shaped projecting case 10 extends from the fastening plate 4, overlapping the region of the propeller 2. Such case 10 is sealed on the plate 4, so as to prevent the water leaking inside. It has, at the region of the propeller, a curved surface 11 connecting to the transom, i.e. with the bottom end 12 of the connection plate 4. The curved surface 1 1 is shaped so as to gradually direct the propulsive flow of the propeller driven astern, suitably orienting it in order to maximize its effectiveness at such a speed. Thus, the efficiency of the drive, astern and in handling, is significantly improved.

However, it is understood that the projecting case is not an essential feature of the present invention, i.e. linked to the presence of the flap 100. Even in the present embodiment, the system 1 comprises a shroud 20 positioned above the propeller 2 and connected, through a joint 21 , to the projecting case 10.

Such a shroud 20 may be rotated about a substantially vertical axis 22. In the present embodiment the shroud 20 is basically constituted by a curved plate, shaped so as to envelop the region of the propeller 2 along a significant circular sector.

Therefore, the shroud 20 is positioned so as to intercept the flow generated by the propeller and, thanks to the peculiar shape of the former, the flow is suitably directed to maximize its effectiveness. Between the shroud 20 and a horizontal plane surface corresponding to the ideal immersion line 9 of the propeller 2 lies a channel 23, extending longitudinally and having a cross-section whose area is decreasing, starting from the transom.

This shape effect is achieved by assuring that, along said direction of flow, the

bottom surface 25 of the shroud 20 varies its position with respect to the axis of the propeller 2.

Laterally, the shroud 20 extends vertically with a rudder blade 24, positioned so as to remain well-immersed. Hence, by rotating the shroud 20 it is achieved the dual effect of directing the propulsive flow, since also the longitudinal axis of the channel 23 is rotated. Concomitantly, the rotation of the shroud 20 actuates the rudder 24.

Therefore, into the projecting case there will be housed the actuators, e.g. wire- driven, hydraulic, etc., of the shroud 20 and of the rudder 24. The case 10, by being watertight, protects these actuators which accordingly do not need specific details.

Again, it is understood that the shroud 20 is not an essential feature of the present invention, i.e. linked to the presence of the flap 100.

In this embodiment, said means for varying the position of the propeller shaft is positioned below the projecting case, in a zone of the curved surface comprised between the shroud 20 and the bottom end 12 of the connection plate 4.

The functionality of the shroud 20 and of the rudder 24 is identical to that described with reference to the first embodiment.

However, it is understood that the projecting case 10, apart from housing the actuators of the shroud 20, will contain, shielding them from water, the actuators and the connections required to said means for positioning drive shaft.

The above-described flap 100 can be applied to a drive shaft of partially submerged propellers regardless the presence of a projecting case 10 overlapping the shaft itself, or with a projecting case having a shape different from that previously disclosed.

In particular, the projecting case 10 and the drive shaft can be even more elongated with respect to as they are shown in the figures. This typology is suitable for particularly fast crafts, e.g. race crafts.

Even according to this alternative, means for positioning the drive shaft can be present, located in a manner similar to that previously described.

In any case, the projecting case can be possibly modelled so as the bottom curved surface 1 1 of the case 10, in an area located at the propeller, is shaped so as to envelope the propeller, so as to operate as previously described with reference to the shroud 20 but remaining fixed, with the rudder released from it. It is noted that, in the embodiment herein described, the mutual position between the fastening plate 4, the drive shaft and the flap 100 as well has been already

established and adjusted in the manufacture plant, and hence further adjustments in the application of the system 1 to a transom are not required.

It is understood that the marine drive system 1 disclosed in connection with the above reported embodiment can be applied, with some variants and adjustments not depending upon the inventive core, to any watercraft, of either the displacing or semi-displacing type, or anyhow using partially submerged propellers.

Similarly, a shorter projecting case 10 and drive shaft may be provided with respect to those depicted in the figures, and possibly without any means for positioning the shaft, as it will be suitable on slower or commercial watercrafts. Of course, it is understood that the principle at the root of the present invention can be applied to systems having more elongated drive shafts, designed for greater cruise speeds, e.g. of the kind employed in the field of motorboat races.

With reference to figure 5, a further embodiment of a marine drive system is indicated as 1 , wherein the same reference numerals indicates the same or analogous parts. It comprises a propeller 2 and a supporting structure 3 which in turn has a fastening plate 4, apt to be secured to the transom of a watercraft. Moreover, a stern tube 7 is provided to house the drive shaft between the fastening plate 4 and the propeller 2, similar to that of the preceding embodiment.

The tube 7 housing the drive shaft is linked to means for positioning the drive shaft, in the present embodiment of the kind having an active-type hydraulic cylinder 14, positioned below the projecting case 10 so as the drive shaft can be oriented on a vertical plane, achieving the adjustment of the propeller immersion.

At the drive shaft, i.e. at the stern tube 7 thereof, the marine drive system 1 according to the present embodiment comprises a flap 100, substantially positioned between the transom, i.e. the fastening plate 4, and the propeller 2, so as to intercept and control the wake wave at every speed, and in particular when the wave tends to excessively submerge the propeller disc.

Again, the flap 100 has a substantially convex shape, with the convexity facing the top side, so as to direct bottomwise a V-shaped camber. The flap 100 is delta- shaped, with the apex directed toward the transom of the watercraft, and it comprises a longitudinal centre portion, corresponding to the drive shaft section between propeller 2 and fastening plate 4 and two half-flaps, directed so as to result in said top-open convexity.

It is understood that the shape of the flap 100 can be modified just to adapt itself to peculiar design requirements concerning the watercraft manoeuvrability or the performances thereof.

According to a further alternative, the flap 100 can be positioned just above the drive shaft, i.e. above the tube thereof.

In the present embodiment, the projecting case 10 comprises, at the distal end thereof, i.e. directed astern, a rudder 24 controlled through tie rods 30 driven through the case 10.

However, it is understood that the projecting case 10, even housing actuators of the rudder 24, will contain, shielding them from the water, the actuators and the connections required to said means for positioning the drive shaft.

According to a further embodiment, as illustrated in figures 7A to 7C, the flap 100 further comprises an upper surface 105 located above the stern tube 7 and connected to the half-flaps 103 so as to form a box-like structure enveloping the stern tube 7. the box-like structure formed by the upper surface 105 is substantially wedge- shaped so that when the watercraft moves astern the flow of water will be directed under the watercraft.

On the contrary, during cruise conditions, the performances of the flap 100 will not be affected by the presence of the upper surface 105.

Moreover, in particular in this embodiment, the box-like shaped flap 100 could be advantageously made in a composite material.

With reference now to figures 6A, 6B and 6C, the operation of the above-described marine drive system will be disclosed, e.g. on a planing-type watercraft. With reference to figure 6A, a watercraft S is depicted as still, in a condition preceding the start.

The transom T, and the corresponding portion of hull H as well, are submerged. Accordingly, the propeller 2 and the related drive shaft are also substantially submerged. With reference to figure 6B, the watercraft S is depicted in an intermediated or temporary phase, after the start, when the speed thereof has not reached the rated cruise or design speed yet.

The transom T is still at least partially submerged, while the propeller 2 has not reached the condition of partially submerged operation yet, i.e. with the immersion line corresponding to about the hub of the propeller 2.

At the propeller region, a relative water flow is present, resulting from the travelling of the watercraft. The flap 100 acts on said flow causing a lowering of the dynamic pressure of the flow at the propeller 2. In such a way, the propeller itself operates at a lower pressure, more similar to the normal working condition partially submerged, with a higher efficiency.

Further, the flap 100, being totally or partially submerged, generates a lift with

respect to the rotation centre C of the watercraft S, located substantially in the middle between stern and stem. The distance between the flap 100 and said rotation centre, with the lift of the flap 100, results in a torque whose entity is relevant considering the width of the lever arm. Such torque opposes the forces mainly acting at the stem and results in a rotation of the watercraft, i.e. a lowering of the stem P with respect to the buoyancy line.

Hence, this rotation has the effect of promoting the planing, decreasing the longitudinal trim angle and hence the resistance of the hull through the transition to the planing. Moreover, the wake wave generated by the watercraft and raising back near the propeller 2, at least when the watercraft moves at a speed lower than the rated one, is substantially deflected and lowered just at the propeller itself, improving the operation efficiency thereof.

In other words, the flap 100 is apt to deflect the flow of the water so that at least a portion of the propeller is prevented to be directly washed by the flow. Therefore, the flow of the wake wave is partially blocked in its flowing by the presence of the flap 100. Experimental tests permitted to note that the total efficiency of the propeller, i.e. the ratio between the driving power actually transmitted to the water and actually exploited, and the power at the drive shaft is substantially improved at low speeds.

Further, it is understood that, at speeds lower than the rated speed, the position of the drive shaft and therefore the position of the flap 100 can be varied for exploiting its lift.

Therefore, to promote the planing it can be possible to lower the drive shaft and the flap 100. At high speed, the flap 100 may be raised in order to not interfere with the wake wave W.

In the same way, the position of the flap 100 may be modified according to the load conditions of the watercraft, influencing the buoyancy line.

Similar variations may be adopted in the reverse motion or in a deceleration phase of the watercraft.

With reference to figure 6C, the watercraft is depicted moving at a rated cruise speed. It is planing with the propeller 2 operating partially submerged.

In this configuration, the wake wave W is located at a certain distance from the transom T, so as to not interfere with the propeller 2, and the flap 2 is in a position substantially corresponding to the propeller immersion line, without affecting the wake and even helping to maintain the transom and the propeller 2 in the correct configuration.

To the above-described marine drive system a person skilled in the art, in order to

satisfy further and contingent needs, could effect several further modifications and variants, all however encompassed in the protective scope of the present invention, as defined by the appended claims.