DE9116840U1 - Sheath propeller system for a sailboat - Google Patents

Description

93-3911

Serge Harrison
Lachine, Quebec H8S 1A7 / Canada

DUCT PROPELLER SYSTEM FOR A SAILBOAT

This invention relates to propeller systems that can be both attached to an existing outboard engine and inserted into an outboard engine during its construction.

It is widely known that an outboard motor generally comprises an internal combustion engine unit, usually enclosed in a suitable housing and provided with means (such as a clamp) for securing it generally to a stern rung of a boat. At the base of the housing of the engine unit is a shell which contains water passages for engine coolant as well as an exhaust passage and a propeller drive shaft. At the base of the shaft a bevel gear is provided in a suitable shell, to the output shaft of which a propeller is attached. This shell also contains cooling water inlet and outlet ports and generally discharges the engine exhaust gases into the water. Such outboard motors are commonly used on a variety of small craft, particularly sailing boats of a size not large enough to accommodate an inboard motor. Such sailing boats use an outboard motor as auxiliary propulsion energy in adverse weather conditions, such as against frontal winds and in calm conditions and especially during docking and casting off maneuvers.

Conventional outboard motors have certain significant disadvantages when used in a vehicle such as a sailboat. Outboard motors currently available have been designed primarily for boats that use high speed propellers and are often equipped with planing hulls. These propellers produce high thrust at high propeller speeds (and therefore at high engine speeds). These propellers produce very low thrust at low propeller (and engine) speeds.

However, sailing boats do not have planing hulls but displacement hulls. Consequently, the maximum speed of a sailing boat is much lower than that achieved by a planing hull vehicle with a shorter overall length. A sailing boat cannot therefore use the high thrust of the conventional outboard motor, as this only develops at high engine speeds. Conversely, a sailing boat is difficult to steer at low engine speeds, which are more realistic for sailing boat use, as sufficient thrust is not available from the outboard motor. In addition, operating an outboard motor under these circumstances is not very economical in terms of fuel consumption.

A further difficulty arises when using a conventional outboard motor as an auxiliary propulsion system on a sailboat when the propeller is used in reverse. This is either used as a means of slowing the boat or to move it backwards, for example during a docking maneuver

J —

done. A typical outboard motor propeller is designed for high forward thrust at high propeller speed; such a propeller produces very little thrust in the reverse direction, which in turn leads to deterioration of the handling of a sailboat with such an engine. A separate problem arises when operating the propeller in reverse, because the exhaust gases in conventional outboard motors are always discharged rearward through the moldings containing the propeller drive shaft. In larger motors, this is done by openings through the propeller hub, and in smaller motors, at least one opening is usually provided in the underside of the cavitation plate near the propeller. When reversing, this gas flow is impeded by the water flow, which then goes in the other direction. This adds to the difficulties of using a conventional outboard motor in reverse.

Although the disadvantages of the conventional outboard motor have been described above in connection with a displacement hull, as is usually found on sailing boats, these disadvantages apply everywhere. Similar problems arise when other displacement hulls have to be moved at low speeds, such as a small barge or fishing boat, or when a planing hull has to be moved at low speed for a period of time, for example when using a planing hull boat for trolling. Under these circumstances, the efficiency of a conventional outboard motor, equipped with the

conventional, inclined high-speed propeller is far from the desired objective. In addition, operating such an outboard motor under conditions for which it was neither designed nor intended will shorten the life of the motor and result in excessive fuel consumption.

The present invention aims to avoid these difficulties by providing a combined propeller and nozzle system which, in combination with an otherwise conventional outboard engine, is intended to provide a relatively high thrust at low engine and propeller speeds in both forward and reverse directions and which vents the exhaust gases to the output side of the propeller. This means that the exhaust gases are degassed into the turbulence zone behind the propeller in both forward and reverse directions of rotation.

Thus, in its broadest aspect, the invention comprises a combination of a Kort nozzle with a special propeller, both of which are fitted to a conventional outboard motor either as a retrofit kit with parts replacing an existing propeller or as an integral part of the underwater parts of an outboard motor during its construction.

Kort nozzles are well known. Examples of such nozzles

-5-

can be found, among others, in US patents 3,179,081 (Backhaus et al); 3,455,268 (Gordon); 4,106,425 (Gruber); 4,509,925 (Wuhrer); 4,694,645 (Flyborg et al); 4,789,302 (Gruzling); and 4,832,633 (Corle H.). While some of these publications deal with small engines, none of them seem to address the problems of using an outboard engine on a sailboat or the like.

In a first embodiment, the present invention aims to provide an outboard motor unit comprising in combination:

(i) a motor device adapted to drive a propeller in both forward and reverse directions of rotation and having a housing incorporating means by which the outboard motor unit can be attached to the hull of a boat;

(ii) a first shroud means extending generally downwardly from the housing and including a first propeller drive shaft means, engine cooling water passages, and at least one first engine exhaust passage;

(iii) a second shroud assembly attached to the first shroud assembly and including a second propeller drive shaft driven by the first shaft and extending substantially aft therefrom, engine cooling water passages, and at least one second exhaust passage connected to the first exhaust passage;

-6-

(iv) a substantially symmetrical Kort accelerator nozzle mounted on the second shroud concentrically about the axis of the second shaft;

(v) a reversible propeller comprising blades and a hub attached to the second drive shaft and rotatable in a plane substantially perpendicular to the axis of the Kort nozzle at its centre, wherein

(a) the blade slope decreases outwards in the longitudinal direction of the blade;

(b) the leaf width increases outwards* in the longitudinal direction of the leaf; and

(c) each blade is curved symmetrically in a plane parallel to the axis of rotation so that both the leading and trailing edges serve to accelerate the water flowing over the propeller regardless of the direction of rotation of the propeller;

(vi) at least one first exhaust gas outlet opening communicating with the second exhaust duct and arranged to vent exhaust gas behind the nozzle; and

(vii) at least one second exhaust gas outlet opening communicating with the second exhaust duct and arranged to vent exhaust gas upstream of the nozzle,

and wherein the exhaust gas outlet openings are constructed and arranged to substantially cover all of the exhaust

·

vent gases into the turbulence zone behind the propeller in both forward and reverse rotation of the propeller.

In a second embodiment, the present invention aims to provide a propeller-nozzle combination for an outboard motor unit, comprising:

(i) a motor device adapted to drive a propeller in both forward and reverse directions and including a housing containing means by which the outboard motor unit can be attached to the hull of a boat;

(ii) a first shroud means extending generally downwardly from the housing and including a first propeller drive shaft means, engine cooling water passages, and at least one first engine exhaust passage;

(iii) a second shroud assembly attached to the first shroud assembly and including a second propeller drive shaft driven by the first shaft and extending substantially aft therefrom, engine cooling water passages, and at least one second exhaust passage communicating with the first exhaust passage; the combination comprising:

(iv) a substantially symmetrical Kort acceleration nozzle arranged to be mounted on the second shroud concentrically about the axis of the second

• ■· * * * mt

-8th-

shaft to be attached;

(ν) a reversible propeller comprising blades and a hub adapted to attach the second drive shaft and rotatable in a plane substantially perpendicular to the axis of the Kort nozzle at its center, wherein

(a) the blade slope decreases outwards in the longitudinal direction of the blade;

(b) the blade width increases outwards in the longitudinal direction of the blade; and

(c) each blade is curved symmetrically in a plane parallel to the axis of rotation so that both the leading and trailing edges serve to accelerate the water flowing over the propeller regardless of the direction of rotation of the propeller;

(vi) at least one first exhaust gas outlet opening communicating with the second exhaust duct and arranged to vent exhaust gas behind the nozzle;

(vii) at least one second exhaust gas outlet opening communicating with the second exhaust duct and arranged to vent exhaust gas upstream of the nozzle,

and wherein the exhaust gas outlet openings are constructed and arranged to vent substantially all of the exhaust gases into the turbulence zone behind the propeller in both the forward and reverse directions of rotation of the propeller.

-9-

Preferably, the at least one first exhaust gas outlet opening comprises a first set of exhaust gas outlet openings communicating with the second exhaust gas passage, extending through the propeller hub and having axes substantially parallel to the second shaft.

Preferably, the at least one second exhaust gas outlet opening comprises at least one second set of exhaust gas outlet openings in extension of the propeller hub, which is connected to the second exhaust gas channel, has axes which are substantially perpendicular to the second shaft and which is located between the propeller and the second shroud.

Alternatively, the first and second exhaust port outlet opening(s) comprise either channels in a spacer used to mount the Kort nozzle and/or openings provided adjacent to the nozzle in the second shell.

It is thus apparent that the concept of this invention can be applied in two different ways. Firstly, an existing outboard motor can be modified by removing the existing propeller and fitting both the Kort nozzle and a replacement propeller to the outboard motor. In some cases, some special exhaust openings may be necessary. Secondly, the improvements can be made to the outboard motor during its manufacture, thus enabling an engine that is specifically designed for high

► ft * · · &phgr;&phgr;

-10-

performance at low speed. In both cases, no changes need to be made to the internal combustion engine parts of the outboard motor.

The invention will now be described using an embodiment with reference to the accompanying drawings, which show:

Figure 1 is a partially sectioned side view of the lower parts of an outboard motor; Figure 2 is a partially sectioned propeller; Figure 3 is a front view of a propeller of Figure 2;

Figure 4 is a front view of a portion of the assembly of Figure 1; and

Figure 5 shows in outline a conventional outboard motorexnhext.

In these figures, equal parts are assigned equal numbers.

Referring first to Figure 5, there is shown a conventional outboard motor which essentially comprises a motor unit, designated 100, which drives a propeller in either a forward or reverse direction. Smaller motors are generally powered by two-stroke gasoline engines, while larger ones use four-stroke engines. The motor unit of the outboard motor also includes

-11-

a conventional clamping device 102 by which the motor is secured to the hull 103 of the boat. The clamping system usually includes links for pivoting the motor out of the water when not in use and also links for rotating the motor about a substantially vertical axis to thereby steer the boat. A gear box is also provided by which the rotation of the propeller can be changed from forward to reverse. A first shroud 104 extends generally downwardly beneath the motor unit. Within this shroud are provided a first propeller drive shaft 105, first engine cooling water passages 106 and at least one first exhaust passage 107. Generally there are at least two water passages, an "inlet" and an "outlet". The bottom or base of the motor unit includes a bevel gear whereby the second propeller drive shaft 109 is driven by the first shaft 105. The propeller 101 is usually keyed to the second shaft 105 and retained thereon by a nut or the like. As shown, the second shaft generally projects rearwardly from the engine unit. The base or second shroud also contains second engine coolant passages which terminate in an air hole, such as slots 113. The second shroud also contains a second exhaust passage which vents the exhaust gases into the water, generally in one of two ways. In larger engines, an exhaust port 110 is provided through the hub of the propeller 101 which communicates with the second exhaust port. In smaller engines, a similar air hole as that provided in the

• *

-12-

Engine water flow is generally provided at the rear of the second jacket and is connected to the second exhaust port.

In Figure 1 only the lower parts of an outboard motor modified according to the invention are shown. The first shell 1 is connected upwards to the engine unit proper (not shown) and houses the first propeller drive shaft, cooling water passages and exhaust gas passages. The first shell is connected to a second shell 2 which generally includes an engine cavitation plate 3. The second shell receives the lower end of the first propeller drive shaft which drives the second propeller drive shaft 4 generally through a bevel gear (not shown). The second shell contains cooling water openings as shown at 5 which are connected to the coolant passages within the first shell and exhaust gas passages.

The Kort nozzle 6, as shown in section at 6A and 6B, is secured to the cavitation plate 3 by means of a molded spacer 7 (which may be integral with the nozzle) by bolts shown at 8. When the nozzle is installed during manufacture of the engine, the spacer 7 and bolts 8 may be replaced by integral construction means. The lower periphery of the nozzle is, if desired, anchored to the bottom of the second shell in a suitable manner by the clamping members 10.

-13-

While the outer surface of the Kort nozzle generally tapers towards the rear, as can be seen from the sectional views in 6A and 6B, the inner shape of the nozzle is ideally essentially symmetrical. Consequently, the acceleration effect of the nozzle is essentially the same in both directions of rotation of the propeller. Thus, the distances X and Y are essentially the same. For the boat operator, this means that the behavior of the boat is essentially the same in forward and reverse travel, depending on the power developed. Experiments have shown that a certain deviation from the symmetrical shape is permissible, provided that it is not such that the desired power in the forward and reverse directions of rotation is different. The nozzle types designated as types 19B and 37B from the Marine Research Institute in Wageningen, Holland, have proven to be suitable, with nozzle type 19B being preferred.

The propeller 9, which has four blades as shown, is mounted on the second shaft 4, which lies in the longitudinal axis of the nozzle. The propeller mounting is adjusted so that the blades 11 are centrally located in the longitudinal direction of the nozzle. Again, this central arrangement contributes to the equality of the output power in the forward and reverse directions. As can be seen in Figure 1, the blade pitch decreases outwards along the blade, and, as Figure 3 shows, the blades widen outwards. In addition, the blades have a symmetrical curvature (Figures 1 and 2).

•♦

·

·

-14-

along their entire length, so that both the leading and trailing edges serve to accelerate the water as the propeller rotates in any direction. Again, this symmetry contributes to the equality of power output in the forward and reverse directions.

The propeller hub also provides two ways through which the exhaust gases can be vented. The first, usual way, comprises a plurality of arcuate passages 12 passing through the propeller hub 13 substantially parallel to shaft 4. When the boat is travelling forward, the exhaust gases are exhausted through these openings into the turbulence zone behind the propeller. A second set of openings 14 are also provided between the hub 13 and the shroud 2. These can be achieved either by cutting off the extension of the hub as at 15 in Figure 2 or by providing a suitably slotted spacer between the hub and the shroud 3 on the shaft 4. When the boat is travelling astern, the exhaust gases are exhausted through the second set of openings again into the turbulence zone behind the propeller, thus avoiding any hydrostatic back pressure which would otherwise develop in the exhaust system and interfere with engine operation.

It has also been found that the blade tips 16 should be adapted to the inner curvature of the nozzle, and preferably the gap between the blade tips and the nozzle should be as small as possible.

·

-15-

In practice, it has been shown that the Kort nozzle and propeller arrangement significantly improves the handling and steering of a sailboat hull when it is driven by an otherwise conventional outboard motor intended for use with the planing hull type. It has also been found that fuel consumption is reduced; in a comparative test, a fuel saving of about 15% was achieved when using a sailboat driven by an outboard motor at a speed of about 6 knots.

In the foregoing description of Figures 1 to 4, a particular embodiment of the invention has been described. The design may be modified in two relatively significant ways when a Kort nozzle and an adapted propeller are to be retrofitted to an existing outboard motor. These modifications relate to the positioning of the Kort nozzle and the redirection of the exhaust gases.

As for the Kort nozzle, its position is determined by the fact that the propeller shaft also determines the nozzle axis. The power required from the outboard motor after its modification determines the desired diameters of the propeller and nozzle. Finally, the nozzle itself must be sufficiently robust to withstand the load acting on it. In order to find a reasonable compromise between these two

• *

·

·

-16-

In order to achieve this, it may be necessary for the cavitation plate to be modified more than is shown in Figures 1 and 4, so that it in effect becomes part of the nozzle. For example, instead of the simple screw connection on the underside of the cavitation plate as shown in Figures 1 and 4, the latter may be modified to be provided with a tongue or tab which fits into a slot or cutout provided in the nozzle.

With regard to exhaust venting, the design shown in Figures 1, 2 and 3 is suitable for larger outboard engines. In some smaller outboard engine designs, the exhaust gases can be vented through an opening pointing downward and rearward through the cavitation plate. The gases are vented into the turbulence zone a short distance behind the propeller when moving forward. Engine performance problems always arise when reversing with the propeller rotating in reverse, as the exhaust opening is pressurized when facing against the oncoming water and the gases exhaust into the unturbulent water in front of the propeller. In addition, fitting a nozzle to such an engine effectively blocks a downward-facing exhaust opening. If a new design is considered, suitable steps can be taken to redirect the exhaust gases. In a retrofit situation, at least two possibilities exist depending on the nozzle size and the distance between the cavitation plate and the axis of the propeller shaft.

-17-

If the nozzle size is such that a spacer as indicated at 7 in Figure 4 is fitted, the exhaust gases can, if the spacer is deep enough, be diverted by having exhaust openings through the spacer as shown schematically by A in Figure 4, which face both forwards and rearwards and communicate with the second exhaust duct in the upper part of the second shroud. Thus, the exhaust gases are always exhausted through an opening towards the propeller barrel.

If the nozzle size prevents the exhaust gases from being diverted by the spacer, the shrouds will require modification to create new exhaust ports. Usually a single rear-facing port is sufficient, but a forward-facing port on each side of the shroud may be required, as shown schematically at B or C in Figure 1.

In this situation, it is not desirable to simply provide a replacement for a single exhaust port facing the stern, because the water pressure on the exhaust system will adversely affect engine performance when travelling stern-on, especially if the engine is a two-stroke engine. The performance of such an engine is directly affected by the back pressure in the exhaust system. Therefore, failure to provide exhaust ports unaffected by the direction of water flow would result in the operation of a

outboard motor designed to provide equal power in both forward and reverse directions may be adversely affected.

Claims (20)

-19- EXPECTATIONS An outboard motor unit comprising in combination: (i) a motor device adapted to drive a propeller in both a forward and aft direction and a housing containing means for attaching the outboard motor unit to the hull of a boat; (ii) a first shroud means extending generally downwardly from the housing and including a first propeller drive shaft means, engine cooling water passages, and at least one first engine exhaust passage; (iii) a second shroud assembly mounted on the first shroud assembly and including a second propeller drive shaft driven by the first shaft and extending substantially aft therefrom, engine cooling water passages, and at least one second exhaust passage connected to the first exhaust passage; (iv) a substantially symmetrical Kort acceleration nozzle mounted on the second shroud concentrically about the axis of the second shaft; (&ngr;) a reversible propeller having blades and a hub attached to the second drive shaft and is rotatable in a plane which is substantially perpendicular to the axis of the Kort nozzle at its centre, a) the blade slope outwards in longitudinal direction of the leaf; (b) the blade width increases outwards in the longitudinal direction of the blade; and (c) each blade is curved symmetrically in a plane parallel to the axis of rotation so that both the leading and trailing edges serve to accelerate the water flowing over the propeller regardless of the direction of rotation of the propeller; (vi) at least one first exhaust gas outlet opening communicating with the second exhaust duct and arranged to vent exhaust gas behind the nozzle; and (vii) at least one second exhaust gas outlet opening communicating with the second exhaust duct and arranged to vent exhaust gas upstream of the nozzle, and wherein the exhaust gas outlet openings are constructed and arranged to vent substantially all of the exhaust gases into the turbulence zone behind the propeller in both the forward and reverse directions of rotation of the propeller. 2. Propeller-nozzle combination for an outboard engine unit, comprising: · -21- (i) a motor device adapted to drive a propeller in both forward and reverse directions and including a housing incorporating means by which the outboard motor unit is attachable to the hull of a boat; (ii) a first shroud means extending generally downwardly from the housing and including a first propeller drive shaft means, engine cooling water passages, and at least one first engine exhaust passage; (iii) a second shroud assembly attached to the first shroud assembly and including a second propeller drive shaft driven by the first shaft, extending substantially aft therefrom, engine cooling water passages, and at least one second exhaust passage communicating with the first exhaust passage; the combination comprising: (iv) a substantially symmetrical Ko rt accelerator nozzle adapted to be attached to the second shell concentrically about the axis of the second shaft; (v) a reversible propeller comprising blades and a hub adapted to attach the second drive shaft and rotatable in a plane substantially perpendicular to the axis of the Kort nozzle at its center, wherein (a) the blade slope is directed outward in the longitudinal direction -22- tion of the leaf decreases; (b) the blade width increases outwards in the longitudinal direction of the blade; and (c) each blade is curved symmetrically in a plane parallel to the axis of rotation so that both the leading and trailing edges serve to accelerate the water flowing over the propeller regardless of the direction of rotation of the propeller; (vi) at least one first exhaust gas outlet opening which is in communication with the second exhaust channel and is arranged to vent exhaust gas behind the nozzle; (vii) at least one second exhaust gas outlet opening communicating with the second exhaust duct and arranged to vent exhaust gas upstream of the nozzle, and wherein the exhaust gas outlet openings are constructed and arranged to vent substantially all of the exhaust gases into the turbulence zone behind the propeller in both the forward and reverse directions of rotation of the propeller. 3. The engine unit of claim 1, wherein the Kort nozzle is internally shaped to produce the same power in forward and reverse directions. 4. The combination of claim 2, wherein the Kort nozzle is internally shaped to produce the same power forward and reverse. -23- 5. The motor unit of claim 1, wherein the propeller has at least three blades. 6. The combination of claim 2, wherein the propeller has at least three blades. 7. The motor unit of claim 1, wherein the propeller has four blades. 8. The combination of claim 2, wherein the propeller has four blades. 9. Motor unit according to claim 1, wherein: (i) the at least one first exhaust gas outlet opening comprises a first set of exhaust gas outlet openings communicating with the second exhaust gas passage, extending through the propeller hub and having axes substantially parallel to the second shaft; and (ii) the at least one second exhaust gas outlet opening comprises a second set of exhaust gas outlet openings in extension of the propeller hub, communicating with the second exhaust gas passage, having axes substantially perpendicular to the second shaft and located between the propeller and the second shroud. 10. The combination of claim 2, wherein: (i) the at least one exhaust gas outlet opening has a first set of exhaust gas outlet openings communicating with the second exhaust gas passage, through the propeller hub and having axes substantially parallel to the second shaft; (ii) the at least one second exhaust gas outlet opening has a second set of exhaust gas outlet openings communicating with the second exhaust gas duct in extension of the propeller hub, the axes of which are substantially perpendicular to the second shaft and which are located between the propeller and the second shroud. 11. The engine assembly of claim 13, wherein the propeller hub extension comprising a slotted spacer mounted on the second shaft abutting the propeller hub. 12. The combination of claim 14, wherein the propeller hub extension comprising a slotted spacer mounted on the second shaft abutting the propeller hub. 13. The engine assembly of claim 1, wherein the at least one first exhaust gas outlet port is included in the attachment of the nozzle to the second shell. 14. Engine unit according to claim 1, wherein the at least one second exhaust gas outlet opening is included in the attachment of the nozzle to the second shell. 15. The combination of claim 2, wherein the at least one first exhaust gas outlet opening is included in the attachment of the nozzle to the second shroud. 16. The combination of claim 2, wherein the at least one second exhaust gas outlet opening is included in the attachment of the nozzle to the second shroud. 17. The engine unit of claim 1, wherein the at least one first exhaust gas outlet opening is contained in the second shell. 18. The engine unit of claim 1, wherein the at least one second exhaust gas outlet opening is contained in the second shell. 19. The combination of claim 2, wherein the at least one first exhaust gas outlet opening is contained in the second shell. 20. The combination of claim 2, wherein the at least one second exhaust gas outlet opening is contained in the second shell.