GB2046689A

GB2046689A - Mechanically propelled boats

Info

Publication number: GB2046689A
Application number: GB8012731A
Authority: GB
Original assignee: Kanzaki Kokyukoki Manufacturing Co Ltd
Current assignee: Kanzaki Kokyukoki Manufacturing Co Ltd
Priority date: 1979-04-18
Filing date: 1980-04-17
Publication date: 1980-11-19
Also published as: FR2454404A1; IT8021489A0; SE8002899L; DE3013609A1; JPS55140697A

Abstract

The whole propulsion mechanism of a boat including an engine 30 is assembled into a housing 37 which carries a propeller 31, thus forming a propulsion unit which may be manufactured and assembled independently of the boat. The housing 37 is received by a well 28 formed in the hull of the boat. The walls of the housing 37 and well 28 isolate noise and vibration of the engine 30. The boat is buoyant both when the propulsion unit is received in and removed from the well 28 and fitting of the unit requires no water-tight seals to be made. In preferred embodiments of the invention the hull is moulded from fibre-reinforced plastics material. In alternative embodiments the boat has a water-jet propulsion system. The housing may be circular and rotatable to effect steering. <IMAGE>

Description

SPECIFICATION Mechanically propelled boats This invention relates to mechanically propelled boats such as pleasure boats including yachts and motor boats, fishing boats and cargo boats.

There are known and are used in practice various kinds of drive systems for such boats.

These drive systems include drive systems in which a power transmission path from an engine to a propeller is linear and inclined, V-drive systems in which a power transmission path from an engine to a propeller is formed into a V-shaped configuration, drive systems in which an engine and a succeeding propulsion mechanism are integral and are mounted in an upright position, a propeller shaft being arranged in a horizontal direction, stern drive systems in which a propulsion mechanism succeeding an engine is arranged behind the stern of a boat in an upright position, and water jet drive systems in which boat propulsion is attained by pumping water through a jet by means of an impeller.

It is much preferred that a propulsion device for a boat be manufactured and assembled easily and can be also inspected, repaired or exchanged easily. It is further preferred that a propulsion device is quiet and vibration-free.

According to the present invention there is provided a mechanically propelled boat comprising a hull having an open-topped well receiving a removable housing containing propulsion mechanism which includes an engine connected by transmission means to propelling means operative externally of the housing.

Recently, hulls of boats have often been manufactured from a plastics such as fibrereinforced plastics (FRP) by moulding. The well may be formed with ease in a hull when the hull is manufactured from a FRP by moulding. The housing may also preferably be manufactured from a FRP or a similar material.

In a mechanically propelled boat according to the present invention, the whole propulsion unit including the engine transmission and the propelling means may be assembled into a unit with the housing. The housing is fitted into the well of the hull through the open top of the well.

Such fitting of the housing may be carried out even when the boat is afloat by workers on board the boat. Consequently, the propulsion unit having previously been manufactured and assembled may be put into the hull of the boat from the deck of the boat when the boat is afloat, the boat being buoyant irrespective of whether the propulsion unit is in the well. A boat according to the present invention is thus easy to manufacture and assemble and is cheap to manufacture. The propulsion unit is also easy to inspect and repair because removing of the propulsion unit for such inspection and repair may be achieved by lifting the unit upwardly out of the hull when the boat is afloat and because re-mounting of the unit may be carried out in similar circumstances.

With the exception of units of the stern drive type, the well of the hull may be provided in the hull at any selected longitudinal location.

Consequently, the propulsion unit may be located where it does not interfere with other equipment of the boat and where longitudinal distribution of load in the boat is made even. Stability of the boat is thus enhanced. The propulsion unit permits prompt responses by a manufacturer to demands of users in a case when the manufacturer has standard sizes and mounting locations for such units. Generally speaking, the marine propulsion unit enhances freedom in designing boats and makes standardization easy.

In the boat according to the invention, the engine is shut off from the hull by a twofold wall structure comprising walls of the housing and walls defining the well. Consequently, noise and vibration due to operation of the engine are isolated. Advantageously, cushioining means such as cushioning rubber are disposed between the housing and the walls of the well, the cushioning means support in a vibration-preventing manner not only the engine but the whole propulsion mechanism succeeding the engine. In other words, a boat according to the invention advantageously has a structure which supports both the engine and the propulsion mechanism succeeding the engine in a vibration-preventing manner by a cushioning system.Further, because the well for fitting the housing carrying therein the whole propulsion mechanism is formed so that it is isolated from the interior of other portions of the hull by walls integral with the hull, fitting of the propulsion unit involves no watertight seal being made to the hull. It is thus only necessary to ensure water-tightness of the propulsion unit, thus simplifying ensuring water-tightness of the boat.

Moreover, even if the water-tight structure of the propulsion unit becomes ineffective, welter enters only the housing and does not enter the hull.

Safety is thus enhanced.

The well may be such that its lower wall is defined by the bottom of the hull or may be such that is passes through the bottom. In the latter case, the well is easier to form. In a boat in which the well is formed so that it passes through the bottom of the hull, it is preferred for simplicity that the opening of the well be closed by the lower wall of the housing so that the lower wall constitutes a part of the bottom of the hull.

In general, the housing carrying therein the whole of the propulsion mechanism is secured in the well of the boat by securing the housing to the hull by means of bolts or the like. In some embodiments of the invention, however, the housing is supported by the hull sq that it may be lifted and lowered. In such cases, when a boat is in shallow water the propulsion unit may be lifted so as to raise the propelling means.

The propulsion unit may be fashioned so that the housing is rotatably supported by the hull of the boat. In this case, the boat may be steered by varying the direction of the propelling means by rotation of the housing. In another embodiment of the present invention, a steering rudder is supported on the housing so that the propulsion unit also includes the rudder. This has advantages in manufacturing and assembling aspects of the boat.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a vertical sectional view of a boat, Fig. 2 is a schematic plan view, partially in section on the line Il-Il of Fig. 1, showing the outline of the boat shown in Fig. 1; Fig. 3 is a vertical cross-section on the line Ill-Ill of Fig.1; Fig. 4 is a view from below showing a part of the boat shown in Fig. 1; Fig. 5 shows a side elevation, partially in section, of a second embodiment of the invention; Fig. 6 is a vertical cross-section taken along the line VI--VI of Fig. 5:: Fig. 7 is a view seen in the direction of the arrows VIl-VIl of Fig. 5; Fig. 8 is a plan view of a part of the hull of the boat shown in Fig. 5; Fig. 9 shows a side elevation, partially in section of a third embodiment of the invention; Fig. 10 is a view from below showing a part of the boat shown in Fig. 9; Fig. 11 shows part of Fig. 9 in a state different from that shown in Fig. 9; Fig. 12 shows a side elevation, partially in section, of a fourth embodiment of the invention; Fig. 1 3 is a vertical cross-section taken along theXlll-Xlll of Fig. 12; Fig. 14 is a plan view of a part of the boat shown in Fig.12;; Fig. 1 5 is an enlarged vertical cross-section of a part of Fig. 12; Fig. 1 6 shows a side elevation partially in section, of a fifth embodiment of the invention; Fig. 1 7 is a view from below of the boat shown in Fig. 16; Fig. 18 shows a side elevation, partially in section, of a sixth embodiment of the invention; Fig. 19 is a view seen in the direction of the arrows XIX--XIX of Fig. 1 8; Fig. 20 shows a side elevation, partially in section, of a seventh embodiment of the invention; Fig. 21 is a vertical cross-section taken along the line XXl-XXl of Fig. 20;; Fig. 22 shows a side elevation, partially in section, of an eighth embodiment of the invention; and Fig. 23 is a perspective view of a part of the boat shown in Fig. 22.

In Figs. 1 to 4, there is shown a first embodiment of the invention. A boat shown in Figs. 1 to 4 has a series of holds 20 arranged longitudinally along its hull, as shown in Fig. 1, and is typically used as a cargo boat or fishing boat. Hatchways of each hold 20 are closed by hatches 21. Bitts 22 and 23 for mooring and towing ropes are installed at the bow and stern of the boat and a bar 24 for mooring the boat and for receiving a fishing net is provided at the bow. At the stern is mounted a rudder 26 which may be rotated in a rudder post 25 and is operated manually by a tiller 27 or, alternatively, may be remote-controlled by wires.

The hull of the boat is made of a fibrereinforced plastics (FRP) material by moulding.

The hull is formed near its stern with a well 28 having an open upper end and having a rectangular cross-section, as ciearly shown in Figs.

1,2 and 3. The well 28 is formed integrally with the hull during moulding and has side walls 29 which are thus integral with the hull. A propulsion unit is made as a separate assembly and is attached to the hull by utiiizing the well 28.

The propulsion unit includes an engine 30 and a propeller 31. In this embodiment, a V-drive system is employed. As shown in Fig. 1 ,the engine 30 is arranged so that its output shaft is directed toward the bow. The engine 30 is connected through a reversing gearing 32, which provides an output selectively for ahead or astern directions of propulsion, to a transmission 33 which converts the path of transmission of power into a rearwardly- and downwardly-inclined direction by means of, for example, bevel gears (not shown). To an output shaft of the transmission 33 is coupled by a coupling 35 a propeller shaft 34 carrying the propeller 31 at its end. The transmission path from the engine 30 to the propeller 31 is thus V-shaped.A stern portion of the bottom 36 of the hull is inclined upwardly towards the stern from a point close to the middle of the well 28 so as to provide clearance for the propeller shaft 34 and the propeller 31, as shown in Fig. 1.

As shown in Figs. 1 to 3, the whole of the engine 30, reversing gearing 32 and transmission 33 and a portion of the propeller shaft 34 are enclosed within a housing 37 which is fitted into the well 28 and is supported by the hull. The housing 37 is made also of FRP and has an open upper end. A floor of the housing 37 has an upwardly-inclined stern portion which corresponds to the inclined stern portion of the bottom 36 of the hull. At a step formed at the forward end of the upwardly inclined stern portion the floor of the housing 37 has an aperture 38 through which the propeller shaft 34 projects, as shown in Figs. 1 and 4.

As shown in Figs. 2 and 3, a pair of hollow mounting bases 39 are moulded integrally with the side walls and floor of the housing 37. The engine 30 has two pairs of mounting legs 40. The engine 30 is supported within the housing 37 to prevent vibration by mounting the legs 40 onto the bases 39 through cushioning materials 41, for example, rubber, and by securing the legs 40 to the bases 39 by bolts (not shown). The reversing gearing 32 is fixed to the engine 30 and the transmission 33 is fixed to the gearing 32. The gearing 32 and transmission 33 are thus supported within the housing 37. At the inner end of the aperture 38 and on the inner surface of the floor of the housing 37, a journal 42 which supports the propeller shaft 34 is fixed. The aperture 38 is sealed at an end face of the journal 42 by conventional means.The bottom 36 of the hull has at a forward end of its upwardly inclined stern portion an opening 43 through which the propeller 31 and the end portion of propeller shaft 34 may be passed in a vertical direction, as shown in Figs. 1 and 4. The propeller shaft 34 is rotatably supported near its end by a shaft bracket 44 which is secured to the bottom of the housing 37 and projects downwardly through the opening 43.

As shown in Figs. 1 and 3, cushioning material 45, for example rubber, is positioned between the bottom surface of the housing 37 and the inner surface of the hull bottom 36 and between the outer surfaces of the walls of the housing 37 and the side walls 29 of the well 28. The housing 37 has an integral upper flange 37a which is received by an upper surface of the hull around the well 28 through cushioning material 46. The housing 37 is fixed to the hull by securing the flange 37a to the hull by bolts or the like (not shown). For closing the upper opening of the housing 37, a cover 47 is provided which is put on top of the housing 37 so that it is received at its lower end by the flange 37a. An air-inlet pipe 48 and an outlet pipe 49 for the engine 30 may extend upwardly th tough the cover 47, as shown in phantom in Fig. 3.

Alternatively, exhaust gas from the engine 30 may be discharged through the floor of the housing 37 which may also provided with an inlet or kingston valve (not shown) for cooling water for the engine 30.

The propulsion unit is fitted in the boat by assembling the engine 30, reversing gearing 32, transmission 33, propeller shaft 34 and propeller 31 in the housing 37, fitting the housing 37 into the well 28 of the hull downwardly from above so that the propeller shaft 34 and propeller 31 pass downwardly through the opening 43 of the bottom wall 36 of the hull and, finally, by securing the flange 37a to the hull. The cushioning materials 45 and 46 are placed in the positions shown when the housing 37 is fitted into the well 28. The fitting of the propulsion unit may be carried out when the boat is afloat and by workers on board the boat.The propulsion unit shown in Figs. 1 to 4 may be manufactured and assembled with ease because it is a single unit, because fitting the unit into the hull is carried out from above, because such fitting may be carried out when the boat is afloat, and because such fitting may be carried out by workers on board the boat.

The whole of the propulsion unit may be taken out of the hull for inspections and repairs with similar ease by workers whilst the boat is afloat. After an inspection and/or repair the propulsion unit may be re-fitted easily.

The propulsion unit shown in Figs. 1 to 4 operates, in use, to propel the boat selectively in an ahead or an astern direction by rotation of the propeller 31 by the power of the engine 30. The reversing gearing 32 changes selectively the direction of propulsion. During propulsion, noise and vibration caused by the engine 30 are hardly transmitted outwardly or to the hull because the engine 30 is shielded by the walls of the housing 37 and the walls 29 and bottom 36 of the hull.

This effect of avoiding transmission of noise and vibration is further enhanced by twofold cushioning comprising cushioning materials 41 between the engine 30 and the housing 37 and cushioning materials 45 and 46 between the housing 37 and the hull. The hull shown in Figs. 1 to 4 is formed such that it is watertight when the propulsion unit is removed.

Consequently, fitting of the propulsion unit to the hull requires no additional water-tight seals to be made. As described before, the aperture 38 of the housing 37 is sealed at the end of the journal 42. If such sealing failed, water would enter only the housing 37 and not the hull. The propulsion unit shown in Figs. 1 to 4 is thus very advantageous in this respect.

As can be understood with ease, the well 28 for receiving the housing 37 carrying the whole propulsion mechanism may be formed at any selected location in the hull. Consequently, location for the well 28 and, therefore, the engine 30 and so on may be selected for a particular boat by taking into consideration longitudinal distribution of load along the hull, which distribution is varied by the location of auxiliary machinery and the like, so that the centre of gravity of the boat is located so as to balance the load distribution. Well-balanced longitudinal load distribution of a boat enhances stability. Further a manufacturer of the marine propulsion unit shown would be able to respond to demands of users promptly by standardizing sizes and mounting locations of propulsion units.

In Figs. 5 to 8, there is shown a second embodiment of the invention. As shown in Fig. 5, the propulsion mechanism is fitted centrally in the boat. A standard drive system having a linear, inclined power transmission path is employed in which an engine 30 is arranged having its output shaft directed toward the stern and inclined downwardly, a reversing gearing 32 is disposed on the front of the engine 30, and a downwardly inclined propeller shaft 34 carrying a propeller 31 is coupled to an output shaft of the gearing 32.

The hull of the boat has a groove 51 which extends from a central point to the stern end of the hull, as shown in Figs. 5 and 7. The propeller 31 is located within the groove 51.

As best seen from Fig. 5, a propulsion unit including the engine 30, the propeller 31 and a housing 37 is arranged such that an end portion of the propeller shaft 34 projects from the housing 37. A well 28 having an open upper end which is formed integrally with the hull for receiving the housing 37 and, in particular, passes through a bottom 36 of the hull, as shown in Figs. 5 and 6.

The location of the housing 37 in a vertical direction is determined by an upper surface of the hull on which a flange 37a provided at the uppermost end of the housing 37 is engaged around the well 28. A floor 52 of the housing 37 is aligned with the bottom 36 of the hull so that the floor 52 of the housing 37 closes a lower opening 43 of the walls 28 and thus forms a part of the bottom 36 of the hull. As in the first embodiment, the well 28 is surrounded by walls 29 which are integral with the hull. The floor 52 of the housing 37 has an upwardly inclined stern portion 52a which is aligned with the groove 51. The propeller shaft 34 projects through the inclined portion 52a.

As is the case of the first embodiment, the housing 37 supports a journal 42 and a shaft bracket 49 for carrying the propeller shaft 34.

The propeller shaft 34 and propeller 31 are connected to the output shaft of the gearing 32 by a coupling 35 after the housing 37 has been fitted into the well 28. Preferably, the hull is formed with a vertical passage 28a (Fig. 8) having a relatively small width which is interconnected with the well 28, and which allows an end portion of the propeller shaft 34 and the propeller 31 to pass downwardly through the hull. In this case, the whole propulsion mechanism including the propeller shaft 34 and the propeller 31 may be assembled beforehand into the housing 37 which may then be fitted into the well 28 from above.

The passage 28a receives a corresponding projecting portion (not shown) of the housing 37 when the housing 37 is inserted into the well 28.

The casing 37 has an open upper end which is closed by a cover 47.

The mounting structure for the engine 30 and other parts of this second embodiment are similar to the corresponding parts of the first embodiment shown in Figs. 1 to 4.

The propulsion unit of the second embodiment shown in Figs. 5 to 8 may be manufactured and assembled with ease. The propulsion unit may be removed from the hull with ease for inspections and repairs. Noise and vibration from the engine 30 are suppressed because of a twofold covering of the engine 30 by the walls of the housing 37 itself and by the walls 29 defining the well 28. As can be understood, the propulsion unit of the second embodiment is also advantageous with respect to water-tightness. This propulsion unit may be mounted at a location in a boat at which it creates a well-balanced load distribution in the boat.

In a case where the well 28 passes through the hull in a vertical direction and a part of a bottom 36 of a boat is constituted by the floor 52 of the housing 37, as is the case in this second embodiment, there is an advantageous reduction in weight of the boat. The hull and the well 28 may also be moulded easily as a unit. The location of the propeller 31 within the groove 51 on the bottom 36 of hull is advantageous when the boat encounters shallow water.

Figs. 9 to 11 show a third embodiment of the invention. As shown in Fig. 9, a sail drive system is employed in which an engine 30 is arranged so that its output shaft is directed downwardly and a power transmission 54 is integral with the engine 30 and has a horizontal propeller shaft 34. As is usual, the power transmission 54 comprises, although not shown in the drawings, bevel gears for converting the direction of power transmission from the vertical to the horizontal and a reversing clutch mechanism. As in the case of the second embodiment, a housing 37 having a floor 52 which constitutes a part of a bottom 36 of a hull of a boat is fitted into a well 28 which passes through the hull in a vertical direction. The power transmission 54 extends downwardly from the bottom of the housing 37 through an aperture8 of the floor 52 of the housing 37.In Figs. 9 and 11 numeral 55 designates a sealing material for preventing water from entering the housing 37 through the aperture 38.

In the third embodiment shown in Figs. 9 to 11 a well 28 is defined by a wall 29 and has a circular horizontal cross-section, as can be seen from Fig.

10. A housing 37, carrying therein an engine 30, has a corresponding circular cross-section. At the lowest position of the housing 37 shown in Fig. 9, an uppermost flange 37a of the housing 37 engages an upper surface of the wail 29 around the well 28 so that the casing is supported in that position. The housing 37 is, however, not secured to the hull by the flange 37a but is merely supported by the hull so that it may be both rotated within the pit 28 and moved vertically. The housing 37 is rotated by a handle, or the like, (not shown) attached to a cover 47 closing the open upper end of the housing 37 and it is lifted and lowered by winch or similar means (not shown).

Consequently, a boat equipped with the propulsion unit of this third embodiment may be steered by rotating the housing 37 about its vertical axis so as to vary the direction of the propeller 31, as shown in Fig. 1 0. A separate steering rudder is thus not needed. Further, when the boat is in shallow water the housing 37 may be lifted to place the propeller 31 within the well 28 of the hull, as shown in Fig. 11.

Other advantages of the propulsion unit of the third embodiment shown in Figs. 9 to 11 will become apparent to those skilled in the art without any further description.

Turning to a consideration of Figs. 12 to 15, there is shown in these figures a fourth embodiment of the present invention. A propulsion unit of this fourth embodiment is mounted at the stern of a boat and has a stern drive system in which a power transmission 57 for transmitting power from an engine 30 to a propeller 31 is outside the boat. An output shaft 34 of the transmission 57 carries at its end a propeller 31. The transmission 57 is similar to that of a conventional stern drive system. The engine 30 is fixed within a housing 37 which is fitted through cushioning materials 45 into a well 28 of the hull. A lower wall of the well 28 is formed by a bottom 36 of the hull. As clearly shown in Fig. 15, a tubular casing 58, fixed at one of its ends to the engine 30, and a rubber boot 59, fixed at one of its ends to the transmission 57, are secured at their other ends to a rear wall of the housing 37. A transmission shaft mechanism 60 having a universal joint 60a transmits power from the engine 30 to the transmission 57 through the tubular casing 58, an aperture formed to the rear wall of the housing 37 and the boot 59. A cover 47 of the housing 37 is received by the upper surface of the hull through cushioning material 46 and is secured to the hull by bolts 61.

As can be seen from Figs. 12, 14 and 1 5 a rear wall 29A of the well 28, has a cut-out 62 which receives the boot 59 and allows the power transmission 57 to be put in position from above the hull. The whole of the propulsion unit having the housing 37 as a supporting structure may be mounted on a boat as a whole in this fourth embodiment, too.

The propulsion unit of this fourth embodiment of the invention has advantages similar to those of the unit in the first embodiment. The universal joint 60a and rubber boot 59 permit the transmission 57 to pivot upwards when the transmission 57 runs against flotsam or a rock during sailing. The transmission 57 is thus protected.

All of the embodiments described hereinbefore are concerned with propulsion units which propel a boat directly by a propeller 31. A device of the water-jet type in which propulsion of a boat is achieved by a water jet from a nozzle is also within the scope of the present invention. Figs 1 6 and 1 7 shows a fifth embodiment of the invention in which the propulsion unit is of a water-jet type.

In the fifth embodiment of the invention shown in Figs. 1 6 and 17, an engine 30 is mounted within a housing 37 which is fitted into a well 28 of a hull. The well 28 has walls 29 which are integral with the hull. A floor 52 of the housing 37 forms a part of a bottom 36 of the hull. An impeller shaft 34A is connected by a coupling 35 to an output shaft of the engine 30. The output shaft is arranged horizontally and is directed to the stern. The impeller shaft 34A projects outwardly from the housing 37 and carries at zits end an impeller 31 A. The floor 52 has a circular opening 64. A similar circular opening 65 is formed in a rear wall of the housing 37 close to the bottom.

The opening 65 opens into a forward end of a groove 66 which is formed in the bottom 36 of the hull and extends along the lengthwise direction of the hull from the stern end of the well 28 to the stern end of the hull.

As shown in Figs. 1 6 and 17, an arched suction pipe 67 is provided within the housing 37 and is secured at its ends to the inner surfaces of the floor 52 and the rear wall of the housing 37 so that it connects the openings-64 and 65.

The impeller 31A is disposed within the suction pipe 67 near the rear end of the pipe 67. A nozzle 68 which is secured to a rear surface of the housing 37, is aligned with the opening 65 and lies in the groove 66 on the bottom 36 of the hull.

The nozzle 68 is fitted with a rudder and deflector, not shown in the drawings, for steering the boat.

When the impeller 31 A is rotated water is sucked through the opening 64 into the suction pipe 67 and is pumped through the opening 65, through the nozzle 68 within the bottom groove 66 and the boat is thus propelled. The suction pipe 67 may, of course, be fitted beforehand to the housing 37. The nozzle 68 may be attached to the rear surface of housing 37 after the housing 37 has been put into the hull. However, it is preferable for fitting the propulsion unit, that the hull is formed with a vertical passage having a relatively small width corresponding to the vertical passage 28a shown in Fig. 8 which communicates with the well 28 and which allows the nozzle 68 to pass downwardly through the hull having previously been attached to the housing 37.

Advantages of this fifth embodiment will be apparent to those skilled in the art without any particular explanation.

Figs. 1 8 and 1 9 show a sixth embodiment of the invention which also includes a water-jet type propulsion unit. The propulsion unit of this sixth embodiment is mounted at the stern of a boat and comprises a housing 37 which is supported by the hull in a manner similar to the one described for each of the preceding embodiments. The housing 37 carries an engine 30 whose output shaft is directed forwardly and downwardly, a power transmission 70 which outputs power of the engine 30 rearwardly by altering the direction of transmission of power, an impeller shaft 34A which is fixed to the output shaft of the transmission 70 by a coupling 34 and an impeller 31 A which is mounted on the end of the impeller shaft 34A.A terminal portion of the impeller shaft 34A and the impeller 31 A project rearwardly from the housing 37. The propulsion unit of this sixth embodiment is thus also a V-drive device.

In this sixth embodiment, a water passage corresponding to the one which is formed in the fifth embodiment by the suction pipe 67 and nozzle 68 is formed by a pipe 71 which is integral with the housing 37. A well 28 of the hull does not pass through a bottom 36 of the hull. The bottom 36 has an opening 72. The lower end of the pipe 71 is aligned with the opening 72 through which water is sucked into the pipe 71. A rear wall 29A of the well 28 has a cut-out portion 73 which permits, when the housing 37 is fitted into the well 28, the terminal portion of pipe 71 to attain the position shown in Fig. 1 8. Advantages of this sixth embodiment will be recognised now with ease by those skilled in the art without any particular explanation.

The suction pipe 67 and nozzle 68 employed in the fifth embodiment shown in Figs. 1 6 and 1 7 may be replaced by a suction pipe and nozzle which are formed integrally with the housing 37 similarly to the sixth embodiment. Further, for the purpose of easy moulding, only a part of the water passage for a water jet-type device may be formed by a pipe which is integral with housing 37. Figs.

20 and 21 show a seventh embodiment of the invention in which only a part of a water passage is formed integrally with the housing 37.

As shown Figs. 20 and 21, a housing 37 has a groove 75 which is aligned with an aperture 72 formed in a bottom 36 of a hull. The groove 75 may be formed at the same time as when the housing 37 is moulded. A nozzle 68 which is positioned within a groove 66 on the bottom 36 of the hull and is secured at a flange 68a to a rear surface of the housing 37 so that the nozzle is open at one end to the groove 75. As is apparent, moulding of the housing 37 can be made with ease. In this seventh embodiment; a well 28 of the hull does not pass through the bottom 36 of hull.

An eighth embodiment of the invention is shown in Figs. 22 and 23. A propulsion unit has a V-drive system similar to the system of the first embodiment shown in Figs. 1 to 4 but is positioned nearer to the stern of the boat when compared with the first embodiment. In this eighth embodiment, a steering rudder 77, replacing the rudder 26 shown in Fig. 1, is provided and is supported by the rear wall of a housing 37. The rudder 77 is mounted to rotate about a vertical shaft 78 in a bracket 80 which is secured to the housing 37 by for example, bolts 79, as clearly shown in Fig. 23. Steering of the boat is carried out by a tiller 81 which is fixed to the upper end of the shaft 78. Steering may, of course, also be carried out by a remote control system for rotating the shaft 78 in place of the tiller 81. Although the well 28 of the hulls shown in each of the embodiments has substantially vertical walls these walls may also be inclined within the scope of the invention.

As can be understood from the embodiments shown, the propulsion unit may have various drive systems. The propulsion unit is advantageous because it may be manufactured and assembled with ease and also may be inspected and repaired with ease. The propulsion unit is advantageous also in reducing noise and vibration and in watertightness, as described above. A further advantage of the boats of in the described embodiments is that they are buoyant both when the propulsion unit is received in the well and when it is removed.

Claims

1. A mechanically propelled boat comprising a hull having an open-topped well receiving a removable housing containing propulsion mechanism which includes an engine connected by transmission means to propelling means operative externally of the housing.

2. A boat according to claim 1 in which the well has an aperture in its bottom wall which is closed by a floor of the housing from which the propelling means projects.

3. A boat according to claim 1 or 2 in which cushioning means are positioned between the housing and the hull.

4. A boat according to any preceding claim in which the housing may be lifted to retract the propelling means into the well or lowered to a lowermost position in which the propelling means projects below the hull.

5. A boat according to any preceding claim in which the housing is rotatable in the well.

6. A boat according to any of claims 1 to 4 in which a rudder is attached to the housing.

7. A boat according to any preceding claim in which the propelling means is of a water-jet type including an impeller and a portion of a water passage.

8. A boat substantially as hereinbefore described with reference to the drawings.