Improvements In and Relating To Underwater Excavation Apparatus

Abstract

An excavation apparatus (5), such as an underwater excavation apparatus and/or a controlled flow excavation apparatus, comprises a rotor (10) comprising a plurality of first rotor blades (12) and a plurality of second rotor blades (14). The second rotor blades are provided between adjacent pairs of first rotor blades. The first rotor blades (12) define a plurality of primary rotor blades of the rotor (10). The second rotor blades (14) define a plurality of secondary, splitter, rotor blades of the rotor (10).

Claims

1. An underwater excavation apparatus, comprising: a housing comprising: at least one inlet; and an outlet; a rotor disposed in the housing; a stator disposed in the housing; wherein the rotor comprises a plurality of first rotor blades and a plurality of second rotor blades, wherein the first rotor blades comprise or define primary rotor blades of the rotor, wherein the second rotor blades are each provided between a pair of adjacent first rotor blades and comprise secondary, splitter, rotor blades the rotor, and wherein a leading edge of one or more of the second rotor blades commences part way along a length of an adjacent first rotor blade.

2. (canceled)

3. An excavation apparatus as claimed in claim 1, wherein the leading edge of said one or more second rotor blades commences at 35% to 45% along the length of the adjacent first rotor blade, e.g. 38% measured at a bub and 42% measured at the housing.

4. An excavation apparatus as claimed in claim 1, wherein at least one of: a distance between and/or an area of a flow path between adjacent first and second rotor blades increases along the length of the respective first and second rotor blades; a distance between and/or an area of a flow path between adjacent second rotor blades increases along the length of the respective second rotor blades; a distance between and/or an area of a flow path between adjacent primary rotor blades increases along the length of the respective primary rotor blades.

5. An excavation apparatus as claimed in claim 1, wherein a height of one or more of the first rotor blades and/or the second rotor blades reduces along a length of the respective first and/or second blades.

6. (canceled)

7. (canceled)

8. (canceled)

9. An excavation apparatus as claimed in claim 1, wherein at least one of: the rotor is provided proximal to the at least one inlet; the rotor comprises a first body, wherein the first and second rotor blades are disposed on the first body, and wherein optionally the first body comprises a first cone member, and/or an apex of the rotor faces the at least one inlet.

10. An excavation apparatus as claimed in claim 1, wherein at least one of: the plurality of first rotor blades comprise impeller blades; the plurality of first rotor blades comprise aerofoil blades; the plurality of second rotor blades comprise aerofoil blades.

11. (canceled

12. (canceled)

13. (canceled)

14. (canceled)

15. An excavation apparatus as claimed in claim 1, wherein the rotor has a rotor rotation axis.

16. (canceled)

17. An excavation apparatus as claimed in claim 15, wherein, in use, flow of fluid past or across the rotor is at a first angle a from the rotor rotation axis, and wherein optionally the first angle a diverges away from the rotor rotation axis in a direction away from at least one of the inlets and towards the outlet. and wherein further optionally the first angle is in the range of 55 to 75, e.g. 65 .

18. (canceled)

19. (canceled)

20. An excavation apparatus as claimed in claim 1, wherein the housing comprises an axis, e.g. longitudinal axis, and wherein optionally at least one of: the rotor is arranged coaxially upon or with the axis of the housing. the stator is arranged coaxially upon or with the axis of the housing the outlet is substantially coaxial with the axis of the housing; and/or the housing is circumferentially/rotationally symmetrical about the axis of the housing.

21. (canceled)

22. An excavation apparatus as claimed in claim 1, wherein the stator comprising a plurality of first stator blades, and wherein optionally the plurality of first stator blades comprise aerofoil blades.

23. An excavation apparatus as claimed in claim 22, wherein the stator comprises a plurality of second stator blades, and wherein optionally the plurality of second stator blades comprise aerofoil blades.

24. (canceled)

25. (canceled)

26. An excavation apparatus as claimed in claim 1, wherein at least one of: the stator is provided proximal to the outlet of the housing; the stator is provided between the rotor and the outlet the stator comprises a second body, wherein optionally the second body of the stator comprises a second cone member; an apex of the stator faces the outlet.

27. (canceled)

28. An excavation apparatus as claimed in claim 23, wherein: the first stator blades comprise a plurality of primary stator blades; the second stator blades comprise a plurality of secondary, splitter, blades; and one or more of the second stator blades is provided between a pair of adjacent first stator blades.

29. An excavation apparatus as claimed in claim 23, wherein at least one of: a leading edge of one or more of the second stator blades commences part way along, e.g. 45% to 55% along, a length of an adjacent first stator blade; a height of one or more of the second stator blades reduces along a length of the respective second stator blade; a distance between and/or an area of the flow path between adjacent first and second stator blades decreases along the length of the respective first and second stator blades; a distance between and/or an area of the flow path between adjacent second stator blades decreases along the length of the respective second stator blades.

30. An excavation apparatus as claimed in claim 22, wherein a distance between and/or an area of the flow path between adjacent first stator blades decreases along the length of the respective first stator blades.

31. An excavation apparatus as claimed in claim 1, wherein the stator is coaxial with the rotor.

32. (canceled)

33. An excavation apparatus as claimed in claim 15, wherein in use, flow of fluid past or across the stator is at a second angle from the rotor rotation axis, wherein optionally the second angle converges towards the axis in a direction away from the at least one inlet and towards the outlet. and wherein further optionally the second angle is in the range of 55 to 75, e.g. 65.

34. (canceled)

35. (canceled)

36. (canceled)

37. (canceled)

38. (canceled)

39. (canceled)

40. An excavation apparatus as claimed in claim 1, wherein at least one of: one or more of the inlets are provided on or at a side or sides of the housing; one or more of the inlets is provided on or at an end of the housing; one or more of the inlets are provided around, e.g., circumferentially or peripherally around, the housing; one or more of the inlets are provided at a non-zero angle, e.g., perpendicularly or substantially perpendicularly, to the outlet; one or more of the inlets are provided near or adjacent an end of the housing; and/or one or more of the outlets are provided on or at another end of the housing

41. An excavation apparatus as claimed in claim 20, wherein at least one of: one or more of the inlets are inclined and/or offset from the axis of the housing; one or more of the inlets are provided perpendicularly or substantially perpendicularly to the axis of the housing; one or more of the inlets are provided non-parallel to the axis of the housing; one or more of the outlets are provided on and/or parallel to the axis of the housing.

42. (canceled)

43. (canceled)

44. An excavation apparatus as claimed in claim 1,

wherein the apparatus is adapted to provide and/or direct a flow of water at a pressure of 200 KPa to 400 KPa and/or a volume flow of 0.5 m.sup.3/s to 4 m.sup.3/s.

45. An excavation apparatus as claimed in claim 1, wherein there is provided a fluid flow path or passage extending from the at least one inlet to the outlet.

46. (canceled)

47. (canceled)

48. An excavation apparatus as claimed in claim 45, wherein the fluid flow path comprises: a first section; a second section; a third section; and/or a fourth section.

49. An excavation apparatus as claimed in claim 48, wherein at least one of: the first section extends from the at least one inlet; the second section contains at least part of the rotor; the third section contains part of the stator; the fourth section extends to the outlet.

50. (canceled)

51. An excavation apparatus as claimed in claim 48, wherein at least one of: the second section diverges away from an axis, e.g. longitudinal axis, of the housing; and the third section converges towards an axis, e.g. longitudinal axis, of the housing.

52. An excavation apparatus as claimed in claim 45, wherein the fluid flow path comprises: a first portion, e.g. first inlet portion, which is provided at or adjacent the one or more inlets; a second portion, e.g. second inlet portion, which extends or continues from the first portion, a third portion, e.g. rotor portion, which extends or continues from the second portion: a fourth portion, e.g. intermediate portion, which extends or continues from the third portion, a fifth portion, e.g. stator portion, which extends or continues from the fourth portion, a sixth portion, e.g. first outlet portion, which extends or continues from the fifth portion: and/or a seventh portion, e.g. second outlet portion, which extends or continues from the sixth portion, said seventh portion being provided at or adjacent the outlet.

53. An excavation apparatus as claimed in claim 52, wherein at least one of: said first portion converges towards an axis of the housing, e.g., at a non-zero angle, e.g., between 0 and 90, 45, and 90, or at 90, said first portion is substantially horizontal, in use, and/or perpendicular to an axis of the housing; said first portion is substantially straight; said second portion is curved, bent, arcuate and/or convex relative to an axis of the housing; said third portion is substantially straight, is coincident with or contains at least a part of the rotor, said third portion diverges away from the axis of the housing, e.g., in a flow direction from the inlet to the outlet, e.g., at an angle of 55 to 75, e.g., 65 said fourth portion is curved, bent, arcuate and/or concave relative to the axis of the housing; said fifth portion is substantially straight, is coincident with or contains at least a part of the stator, said fifth portion converges towards the axis of the housing, e.g., in a flow direction from the inlet to the outlet, e.g., at an angle of 55 to 75, e.g., 65; and/or said sixth portion is curved, bent, arcuate, and/or convex relative to the axis of the housing.

54. An excavation apparatus as claimed in claim 1, wherein: in a first mode of operation, which optionally comprises an excavation mode, the outlet faces an area to be excavated, and in such mode the one or more inlets are provided above, e.g., directly above, the outlet; and/or in a second mode of operation, which optionally comprises a suction mode, the one or more inlets are provided proximal to an area which has been excavated, and in such mode the one or more inlets are provided below, e.g., directly below, the outlet.

55. An excavation apparatus as claimed in claim 1, wherein at least one of: an inside of the housing converges from the at least one inlet towards the rotor; an inside of the housing diverges from an inlet end of the rotor towards an outlet end of the rotor. an inside of the housing converges from the stator towards the outlet.

56. (canceled)

57. An excavation apparatus as claimed in claim 1, wherein at least one of: the outlet is substantially coaxial with the rotor, the outlet is substantially coaxial with the stator.

58. (canceled)

59. (canceled)

60. An excavation apparatus as claimed in claim 1, wherein: the excavation apparatus comprises means or an arrangement for dampening reactive torque on the excavation apparatus caused by rotation of the rotor, in use, and wherein optionally at least one of; the torque dampening means comprise or include anti-rotation vanes; and/or the torque dampening means does not comprise a second rotor, such as a second rotor configured to counter-rotate relative to the rotor.

61. (canceled)

62. (canceled)

63. (canceled)

64. (canceled)

65. An underwater excavation system or tool, comprising at least one underwater excavation apparatus according to claim 1.

66. A method of underwater excavation, the method comprising: providing at least one underwater excavation apparatus according to claim 1; and excavating an underwater location, using said excavation apparatus.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0098] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, which are:

[0099] FIG. 1 a schematic sectional side view of an excavation apparatus according to a first embodiment of the present invention;

[0100] FIG. 2 a view from above of a rotor of the excavation apparatus of FIG. 1;

[0101] FIG. 3 a side view of the rotor of FIG. 2;

[0102] FIG. 4 a view from below of a stator of the excavation apparatus of FIG. 1;

[0103] FIG. 5 a side view of the stator of FIG. 4;

[0104] FIG. 6 a view from below of an alternative stator of the excavation apparatus of FIG. 1; and

[0105] FIG. 7 a side view of the alternative stator of FIG. 6.

DETAILED DESCRIPTION OF DRAWINGS

[0106] Referring to FIGS. 1 to 5, there is shown an excavation apparatus comprising an underwater excavation apparatus, generally designated 5, according to a first embodiment of the present invention.

[0107] The excavation apparatus 5, such as a controlled flow (underwater) excavation apparatus, comprises a rotor 10 having or comprising one or more rotor blades 11 comprising one or more or a plurality of first (impeller) rotor blades 12 and one or more or a plurality of second (splitter/splitter impeller) rotor blades 14.

[0108] Provision of the second rotor blade(s) 14 between adjacent first rotor blades 12 effectively narrows a width of an end of a fluid passage 16 between adjacent first rotor blades 12. This can obviate or mitigate a need to increase a diameter of the rotor 10 if the excavation apparatus 5 is to be used for hard soils, e.g., above 100 KPa such as 100 KPa to 400 KPa.

[0109] The excavation apparatus 5 comprises a stator 15. The stator 15 has or comprises a plurality stator blades 45 comprising first stator blades 46 and (optionally/beneficially) a plurality of second (splitter) stator blades 47.

[0110] The excavation apparatus 5 beneficially comprises a single rotor.

[0111] The excavation apparatus 5 beneficially comprises a single stator.

[0112] The apparatus comprises a housing 20.

[0113] The housing 20 comprises or has at least one inlet 25 and at least one or an outlet 30.

[0114] The first (impeller) rotor blades 12 comprise one or more, i.e., a plurality of primary (impeller) rotor blades.

[0115] The second (splitter) rotor blades 14 comprise one or more, i.e., a plurality of secondary or splitter rotor blades.

[0116] A/each second rotor blade 14 is provided between adjacent (pairs of) first rotor blades 12.

[0117] A leading edge of a/each second rotor blade 14 commences or starts midway along, e.g., 35% to 45% along, a length of a/an adjacent first rotor blade 12, e.g., 38% measured at a hub and 42% measured at the housing 20.

[0118] A height of the first rotor blade(s) 12 and/or second rotor blade(s) 14 reduce along a length of the respective blade.

[0119] A distance between and/or an area of a flow path between adjacent first and second rotor blades 12, 14 and/or a distance between and/or an area of the flow path between adjacent primary rotor blades and/or between adjacent splitter rotor blades increases along the length of the respective rotor blades 12, 14. (In each case, the length of the respective rotor blade 12, 14 can be measured from the at least one inlet 25 towards the outlet 30).

[0120] Such arrangement can be of benefit in providing an excavation apparatus adapted for use in firmer seabed or riverbed conditions which require higher pressure in order to excavate the soil.

[0121] The rotor 10 and/or the stator 15 are provided in the housing 20. The housing 20 comprises an axis or longitudinal axis A, the rotor 10 and the stator 15 being arranged coaxially upon or with the axis A.

[0122] The rotor 10 is provided proximal the inlet(s) 25. The stator 15 is provided proximal the outlet 30.

[0123] The rotor 10 has a rotor rotation axis, which comprises or is coincident with the longitudinal axis A of the housing 20.

[0124] The rotor 10 comprises a first body 39. The plurality of first and second rotor blades 12, 14 are provided within the housing 20.

[0125] In use, flow of fluid past or across the rotor 10 is at a first angle from the axis of rotation.

[0126] There are excavation and optionally suction modes of the excavation apparatus. In excavation and/or in suction mode fluid can flow from the at least one inlet 25 to the outlet 30 of the excavation apparatus 5.

[0127] The rotor rotation axis extends between (a level of) the at least one inlet 25 and the outlet 30.

[0128] The first body comprises a first cone member.

[0129] The first angle diverges away from the axis A in a direction away from at least one of the at least one inlets 25 and towards the outlet 30.

[0130] An apex of the rotor 10 or first cone member faces the inlet 25 or an inlet end of the housing 20.

[0131] The plurality of first and/or second rotor blades 12, 14 comprise aerofoil blades, which can be optionally disposed, such as circumferentially disposed, on the first cone member.

[0132] The first stator blades 46 comprise one or more, i.e., a plurality of primary stator blades.

[0133] The second stator blades 47 comprise one or more, i.e., a plurality of secondary or splitter blades.

[0134] A/each second stator blade 47 is provided between an adjacent pair of first stator blades 46.

[0135] A leading edge of a/each second stator blade 47 commences or starts midway alone, e.g., 45% to 55% along, a length of an adjacent first stator blade 46, e.g., 48% measured at the hub and 52% measured at the housing 20.

[0136] A height of the first and second stator blades 46, 47 can reduce along a length of the respective stator blade 46, 47.

[0137] A distance between and/or an area of the flow path between adjacent first and second stator blades 46, 47 and/or a distance between and/or an area of the flow path 49 between adjacent primary stator blades and/or between adjacent splitter stator blades may decrease along the length of the respective stator blades 46, 47. In each case the length of the stator blade 46, 47 can be measured from inlet towards outlet. Such arrangement can be of benefit in creating an excavation apparatus 5 adapted for use in firmer seabed or riverbed conditions which require higher pressure in order to excavate the soil.

[0138] Such arrangement can be of benefit in excavation apparatus 5 adapted for use in relatively shallow waters, e.g., as such may allow relatively low profile/height excavation apparatus.

[0139] The stator 15 is coaxial with the rotor 10 and the stator is provided between the rotor 10 and the outlet 30.

[0140] In use, flow of fluid past or across the stator 15 is at a second angle from the axis of rotation of the rotor 10.

[0141] The stator 15 comprises a second body 40, such as a second cone member.

[0142] The second angle converges towards the axis A in a direction away from the inlet 25 and towards the outlet 30.

[0143] An apex of the stator 15 or second cone member faces the outlet 30.

[0144] The plurality of first and second stator blades 46, 47 comprise aerofoil blades, which can be disposed on the second cone member.

[0145] The first angle can be selected from either: in the range of 55 to 75, or 65.

[0146] The second angle can be selected from in the range of 55 to 75, or 65.

[0147] The at least one inlet 25 is provided on or at a side or sides 26 (or alternatively on or at an end) of the housing 20.

[0148] The at least one inlet 25 is provided around, e.g., circumferentially or peripherally around a/the side of the housing 20.

[0149] The housing 20 comprises longitudinal axis A. The housing 20 is symmetrical with respect to the longitudinal axis A.

[0150] The one or more inlets 25 are provided inclined and/or offset from or transversely or substantially transversely to the longitudinal axis A.

[0151] The one or more inlets 25 are provided perpendicularly or substantially perpendicularly to the longitudinal axis A.

[0152] The/each of the one or more inlets 25 are provided non-parallel to the longitudinal axis A of the housing 20.

[0153] The/each of the one or more inlets 25 is provided at an angle, e.g., non-zero (0) angle, e.g., perpendicularly or substantially perpendicularly, to the/each of the one or more outlets 30.

[0154] The/each at least one inlet 25 is provided near or adjacent an end 29 of the housing 20.

[0155] The/each of the one or more outlets 30 are provided on or at an/another end 31 of the housing 20 such as on and/or parallel to a/the longitudinal axis A.

[0156] The apparatus 5 is adapted to provide an inclined or horizontal or substantially horizontal or a non-vertical or substantially non-vertical flow of fluid/water into the housing 20, in use, such as in a first or excavation mode of operation.

[0157] The fluid/water flow into the housing 20 is inclined at a converging angle to the longitudinal axis A of the housing 20.

[0158] The excavation apparatus 5 is adapted to provide a coaxial or substantially coaxial or vertical or substantially vertical or a non-horizontal or substantially non- horizontal flow of fluid/water out of or from the housing 20, in use.

[0159] The excavation apparatus 5 is adapted to provide and/or direct, in use, a flow of fluid/water, e.g., at a pressure of 200 KPa to 400 KPa and/or a volume flow of 0.5 m.sup.3/s to 4 m.sup.3/s.

[0160] There is provided a fluid flow path F or passage extending from the/each at least one inlet 25 to the outlet 30. The at least one rotor 10 and/or the at least one stator 15 is provided in the flow path F.

[0161] The fluid flow path F comprises a first (inlet) section, which extends from the at least one inlet 25.

[0162] The fluid flow path F comprises a second (rotor) section, which contains at least part of the rotor 10. Said second section diverges away from the longitudinal axis A of the housing 20.

[0163] The fluid flow path F comprises a third (stator) section, which contains at least part of the stator 15. Said third section converges towards the longitudinal axis A of the housing 20.

[0164] The fluid flow path F comprises a fourth (outlet) section, which extends to the at least one or the outlet 30.

[0165] The fluid flow path F comprises a first inlet portion/first portion F.sub.1 which is provided at or adjacent the/each at least one inlet 25. Said first inlet portion/first portion F.sub.1 advantageously converges towards the longitudinal axis A of the housing 20, e.g., at a non-zero angle, e.g., between 0 and 90, 45, and 90, or at 90. Said first inlet portion/first portion F.sub.1 advantageously is substantially horizontal, in use, and/or perpendicular to the longitudinal axis of the housing 20 and/or said first inlet portion/first portion F.sub.1 is substantially straight.

[0166] The fluid flow path F comprises a second inlet portion/second portion F.sub.2, which extends or continues from the first inlet portion/first portion F.sub.1. Said second inlet portion/second portion F.sub.1 is advantageously curved, bent or arcuate and convex relative to the longitudinal axis A of the housing 20.

[0167] The fluid flow path F comprises a rotor portion/third portion F.sub.3, which extends or continues from the inlet section/second inlet portion/second portion F.sub.2. Said rotor portion/third portion F.sub.3 is advantageously substantially straight, coincident with or contains at least a part or parts of the rotor 10, and diverges away from the longitudinal axis A of the housing 120, e.g., in a flow direction from the inlet 25 to the outlet 39, e.g., at an angle of 55 to 75, e.g., 65.

[0168] The fluid flow path F comprises a further or intermediate portion/fourth portion F.sub.4, which extends or continues from the first rotor portion/third portion F.sub.3. Said further or intermediate portion/fourth portion F.sub.4 is advantageously curved, bent or arcuate, and concave relative to the longitudinal axis A of the housing 20.

[0169] The fluid flow path F comprises a stator portion/fifth portion F.sub.5 which extends or continues from the further or intermediate portion/fourth portion F.sub.4. Said first stator portion/fifth portion F.sub.5 is advantageously substantially straight, coincident with or contains at least part or parts of the stator 15, and converges towards the longitudinal axis A of the housing 20, e.g., in a flow direction from the inlet 25 to the outlet 30, e.g., at an angle of 55 to 75, e.g., 65. Such arrangement can be of benefit for excavation apparatus adapted for use in relatively shallow waters, e.g., as such may allow for a relatively low profile/height excavation apparatus.

[0170] The fluid flow path F comprises a first outlet portion/sixth portion F.sub.6, which extends or continues from the stator portion/fifth portion F.sub.5. Said first outlet portion/sixth portion F.sub.6 is advantageously curved, bent or arcuate, and convex relative to the longitudinal axis A of the housing 20.

[0171] The fluid flow path F comprises a second outlet portion/seventh portion F.sub.7, which extends or continues from the first outlet/sixth portion F.sub.6. Said second outlet portion/seventh portion F.sub.7 is provided at or adjacent the outlet 30. Said second outlet portion/seventh portion F.sub.7 is advantageously substantially vertical, in use, parallel to the longitudinal axis A of the housing 20, and substantially straight.

[0172] In a first mode of operation, which comprises an excavation mode, the outlet 30 faces an area to be excavated, and in such mode the inlet 25 is provided above, i.e., directly above, the outlet 30.

[0173] In a second mode of operation, which comprises a suction mode, the inlet 25 is proximal an area which has been excavated and/or requires to be cleared, and in such mode the inlet 25 is provided below, i.e., directly below, the outlet 30.

[0174] An inside of the housing 20 converges from the at least one inlet 25 towards the rotor 10.

[0175] The inside of the housing 20 diverges from the inlet end of the rotor 10 towards the outlet end of the rotor 10.

[0176] The inside of the housing 20 converges from the stator 15 towards the outlet 30. The outlet 30 is substantially coaxial with the rotor 10 and the stator 15 and the axis A of the housing 20.

[0177] The housing 20 is circumferentially/rotationally symmetrical about the axis A of the housing 20.

[0178] The excavation apparatus 5 comprises means or an arrangement (not shown) for dampening reactive torque on the excavation apparatus 5 caused by rotation of the rotor 10, in use.

[0179] The excavation apparatus 5 and/or the at least one rotor 10 beneficially comprise a single rotor.

[0180] The torque dampening means beneficially does not comprise a second rotor, such as a second rotor counter-rotating to the at least one (single) rotor.

[0181] The excavation apparatus 5 and/or the at least one stator 15 beneficially comprise a single stator.

[0182] The housing 20 comprises a hollow body.

[0183] The rotor 10 and the stator 15 are provided in the housing 20. The housing 20 comprises axis A. The rotor 10 and the stator 15 are arranged coaxially, such as upon the axis A. The housing 20 is provided upon the axis A. The rotor 15 is provided proximal the at least one inlet 25 and the stator 15 is provided proximal the outlet 30.

[0184] The rotor 10 comprises first body 39, such as a first cone body, and the plurality of first and second rotor blades 12, 14 are disposed on the first body 39. The stator 15 comprises a second body 40, such as a second cone body, and the plurality of first and second stator blades 46, 47 are disposed on the second body 40.

[0185] The torque dampening means can comprise or include anti-rotation vanes.

[0186] The excavation apparatus may comprise a motor 70 for driving the rotor 10. The rotor is provided (longitudinally) between the at least one inlet 25 and the at least one outlet 30.

[0187] Referring to FIGS. 6 and 7, there is shown an alternative stator 15a for use in the excavation apparatus 5. The stator 15a is similar in many respects to the stator 15, like parts being denoted by like integers, but suffixed a.

[0188] The present invention provides an excavation system or tool 205, such as an underwater system or tool, comprising at least one excavation apparatus 5 as hereinbefore described.

[0189] The present invention provides a method of excavation, such as a method of underwater excavation, the method comprising: [0190] providing at least one excavation apparatus 5 as hereinbefore described; and excavating a location, such as an underwater location, using said excavation apparatus.

[0191] It will be appreciated that the embodiment of the present invention hereinbefore described is given by way of example only, and is not meant to be limiting of the invention in any way.

[0192] It will be particularly appreciated that the arrangement of the at least one inlet is adapted and/or designed to provide and/or encourage fluid flow ingress from a side or sides rather than an end/top of the housing. This is of particular benefit when operating at or near a surface of a body of fluid/water and/or in relatively shallow depths, e.g. so as to reduce any vortex effects at the inlet. Another key feature of such an excavation apparatus, particularly for such use, is a relatively large stator path converging angle relative to the longitudinal axis A, as such reduces the required height of the housing. To achieve the shorter, low profile, housing height, the provision of the secondary/splitter blades is of particular benefit.

[0193] As shown in FIG. 1, height A.sub.1 minus A.sub.2 is greater than height C.sub.1 minus C.sub.2. A second rotor blade(s) 14 start at B. Also, first rotor blade(s) 12 and second rotor blades 14 end at position C.

[0194] Referring to FIG. 1, a first stator blade(s) 46 start at position D and end at position F. Also, second stator blade(s) 47 start at position E and end at position F.

[0195] As shown in FIG. 2, a distance between first rotor blades 12 increases along a length of the first rotor blades 12see 1a, 1b to 2a, 2bi.e., 1a to 2a is less than 1b to 2b. Also, distance 3a to 4a is less than distance 3b to 4b.