TWIN HULL SEMI-SUBMERSIBLE DERRICK BARGE

• US 3,835,800 A
• Filed: 07/09/1971
• Issued: 09/17/1974
• Est. Priority Date: 02/13/1968
• Status: Expired due to Term

• Current Assignee: Samuel Harry Iii Lloyd, Yorman Goren
• Original Assignee: Samuel Harry Iii Lloyd, Yorman Goren
• Inventors: Lloyd, Samuel Harry III, Goren, Yorman
• Primary Examiner(s): Halvosa, George E. A.
• Assistant Examiner(s): Frankfort, Charles E.
• Application Number:
  US05/161,865
• Time in Patent Office: 1,166 Days
• Field of Search: 114/.5D,.5R,43.5,61 61/46.5 212/3
• US Class Current: 114/265
• CPC Class Codes: B63B 1/107 Semi-submersibles; Small waterline area multiple hull vessels and the like, e.g. SWATH
• CPC Class Codes: B63B 2001/044 with a small waterline area compared to total displacement, e.g. of semi-submersible type
• CPC Class Codes: B63B 35/44 Floating buildings, stores, drilling platforms, or workshops, e.g. carrying water-oil separating devices construction methods for floating offshore platforms B63B75/00
• CPC Class Codes: B66C 23/52 Floating cranes floating dredgers E02F

Abstract

The derrick barge comprises a pair of laterally spaced elongated hulls having a plurality of upstanding columns spaced therealong supporting a working platform and a heavy duty derrick or crane in spaced relation above the hulls. The hulls bouyantly support the vessel including its deck load in the floating condition with the hulls having freeboard. The hulls have ballast compartments to submerge the hulls and portions of the stabilizing columns to a distance of approximately one-half the effective height of the stabilizing columns to maintain the vessel in a semisubmerged floating condition with the platform and derrick elevated above the waterline. However, the vessel also may be ballasted or deballasted to submerge or emerge to a greater or lesser extent from the semisubmerged condition such that the distance between the mean water surface and either the underside of the deck or top side of the hull is not less than 0.75 of the mean wave height. The columns stabilize the vessel in the semisubmerged condition about roll and pitch axes. The heavy duty derrick is located adjacent the stern portion of the vessel with its vertical axis of rotation intersecting the vessel centerline. This novel twin hull column stabilized derrick barge arrangement has excellent motion minimizing characteristics under wave action in operations at sea.

Claims

1. A column stabilized semi-submersible derrick barge comprising:

a pair of elongated hulls disposed in spaced side-by-side relation;

a working platform spaced above said hulls a predetermined height;

means for supporting said platform in fixed spaced relation above said hulls including columns connected to said hulls and said platform;

the distance between the extremities of said barge along the longitudinal centerline of said barge being substantially greater than the distance between the extremities of said barge along the transverse centerline of said barge;

a heavy duty crane located adjacent one end of said barge and mounted for rotation about a substantially vertical axis, said crane having a rated capacity and a boom of sufficient length capable of performing lifting operations off both barge beams and off the end of the barge adjacent to which said crane is mounted;

said hulls having ballast compartments for ballasting said barge to alter its draft between a low draft hull supported floating condition and a high draft semi-submerged column stabilized floating condition;

said columns having predetermined cross-sectional areas and being located on the hulls to provide righting moments about the pitch and roll axes of said barge when in high draft condition;

the area of said columns, the number thereof and the distance of said columns from the longitudinal and transverse centerlines of said barge being such as to provide a greater righting moment about the transverse pitch axis than the righting moment about the longitudinal roll axis when said barge is in high draft semi-submerged condition.

2. A derrick barge according to claim 1 wherein:

said crane load capacity and boom outreach length are such that when said crane is rotated in high draft condition of the barge with load and outreach of predetermined values the resultant moment with respect to the roll axis causes substantial heel of said barge about said axis which if uncorrected would exceed the maximum slew limiting angle of said crane;

said barge having ballast means for counteracting such angle of heel caused by such crane operations to provide a counter-righting moment for said barge about its roll axis sufficient to maintain the angle of heel of the barge during crane operations within said slew limiting angle of said crane.

3. A derrick barge according to claim 2 wherein:

said ballast means is operable to transfer ballast from one hull to the other hull in a manner to achieve said counter-righting moment to maintain the heel of said barge within the crane slew limiting angle, with said ballast being transferable as the crane slews during load operating conditions.

4. A derrick barge according to claim 2 wherein:

said ballast means is operable to transfer ballast between said hulls in relation to the moment caused by operation of said crane to provide sufficient counter-righting moment to maintain the heel of said barge within the predetermined crane slew limiting angle.

5. A derrick barge according to claim 2 further including:

ballast means for counteracting the angle of trim caused when said crane boom extends outwardly away from the end of said barge in the direction of the barge'"'"''"'"'s longitudinal axis with load and boom outreach of high magnitude causing a high resultant moment with respect to the pitch axis of said barge so that the latter mentioned ballast means may provide a counter-moment for reducing the angle of trim of the barge about its pitch axis.

6. A derrick barge according to claim 1 wherein:

at least one column on each hull is located adjacent the end of said barge at substantially the same longitudinal position at which said crane is mounted and at a distance from the transverse centerline of said barge at least substantially the same as the distance between said transverse centerline and the crane'"'"''"'"'s axis of rotation.

7. A derrick barge according to claim 1 further including:

additional structural support means adjacent said crane for increased support of said heavy duty crane both in unloaded and loaded condition.

8. A derrick barge according to claim 7 wherein:

said additional structural support means includes support members directly connecting between the base of said crane and each of said pair of hulls for at least partially structurally supporting said crane from said hulls.

9. A derrick barge according to claim 1 wherein:

at least one of said columns on each of said hulls has a cross section whereby the column dimension extending in the direction of the barge roll axis is greater than the transverse dimension of the column.

10. A derrick barge according to claim 1 further including:

a plurality of longitudinally spaced structural means for reinforcing the structural relationship of said hulls, platform and columns.

11. A derrick barge according to claim 1 including:

additional structural supporting means adjacent said crane for increased support of said heavy duty crane in loaded and unloaded operations;

a plurality of longitudinally spaced structural members for reinforcing the structural relationship of said hulls, platform, and columns;

said structural members including substantially transversely extending members interconnecting said hulls adjacent the uppermost portions of said hulls and restraining said hulls against lateral displacement relative to one another;

at least one column on each hull being located adjacent the end of the barge at substantially the same longitudinal position at which said crane is mounted at a distance from the transverse centerline of said barge at least substantially the same as the distance between said transverse centerline and the crane'"'"''"'"'s axis of rotation.

12. A derrick barge according to claim 1 wherein:

there are at least three columns connecting with each of said hulls and with said platform, said columns being located at spaced intervals along each of the hulls;

at least one column on each hull being located adjacent the end of said barge at substantially the same longitudinal position at which said crane is mounted and at a distance from the transverse barge centerline at least substantially the same as the distance between said transverse barge centerline and the crane axis of rotation, another of said columns on each hull being located adjacent the opposite end of the barge, with at least one additional column at an intermediate position on each hull;

a plurality of longitudinally spaced structural means reinforcing the structural relationship of the hulls, platform and columns;

said structural means including substantially transversely extending members interconnecting said hulls adjacent the uppermost portions thereof and restraining said hulls against lateral displacement relative to one another;

said barge including additional structural support means adjacent said heavy duty crane for increased support of said heavy duty crane both in unloaded and loaded condition.

13. A derrick barge according to claim 1 wherein:

said barge is elongated so that it has a length to width ratio such that the barge length is at least a plural number of times as great as the barge width.

14. A derrick barge according to claim 13 wherein:

the barge'"'"''"'"'s length to width ratio is approximately 400 to 100.

15. A derrick barge according to claim 13 wherein:

the boom of the crane is of such length that it reaches beyond the transverse centerline of the barge when the crane boom is disposed in a rest position.

16. A derrick barge according to claim 13 wherein:

the boom of the crane is of such length that the end of the boom reaches to adjacent the end of said barge opposite the end at which said crane is mounted when said boom is disposed in the rest position.

17. A derrick barge according to claim 1 wherein:

said crane has a predetermined angle of inclination from the crane'"'"''"'"'s normal substantially vertical axis of rotation beyond which said crane cannot slew;

the configurations, areas and locations of said columns being such as to provide the barge in high draft semisubmerged condition with stabilizing characteristics with respect to inclination about the roll and pitch axes for enabling the barge to maintain an attitude keeping the axis of rotation of said crane within said predetermined slew limiting angle for predetermined magnitudes of load and boom outreach.

18. A derrick barge according to claim 1 wherein:

the upper and lower surfaces of each of said hulls have a non-streamlined configuration to provide increased added mass and thereby increased resistance to movement of said hulls through water in a vertical direction when said barge is in said high draft column stabilized semisubmerged condition;

said crane having a predetermined angle of inclination from said crane'"'"''"'"'s normal substantially vertical axis beyond which said crane cannot slew;

the configurations, areas and locations of said columns being such as to provide the barge in high draft semisubmerged condition with stabilizing characteristics with respect to inclination about the roll and pitch axes sufficient for enabling the barge to maintain an attitude keeping the axis of rotation of said crane within said predetermined slew limiting angle for predetermined magnitudes of load and boom outreach;

the crane load capacity and boom outreach length being such that when the crane is rotated in high draft condition of the barge with load and outreach of predetermined values the resultant moment with respect to the roll axis causes substantiAl heel of said barge about said roll axis which if uncorrected would exceed the maximum slew limiting angle of said crane;

said barge having ballast means for counteracting excessive angle of heel caused by such crane operation with beam outreach to provide a counter-righting moment for said barge about its roll axis sufficient to maintain the angle of heel of said barge during crane operations within said slew limiting angle of said crane;

a plurality of longitudinally spaced structural means reinforcing the structural relationship of said hulls, platform and columns with said structural means including substantially transversely extending members interconnecting said hulls adjacent the uppermost portions of said hulls and restraining said hulls against lateral displacement relative to one another;

said vessel including additional structural supporting means adjacent said crane for increased support of the heavy duty crane in both loaded and unloaded condition.

19. A column stabilized semi-submersible derrick barge comprising:

a pair of elongated hulls disposed in spaced side-by-side relation;

a working platform spaced above said hulls a predetermined height;

means for supporting said platform in fixed spaced relation above said hulls including columns connected to said hulls and said platform;

the distance between the extremities of the barge along its longitudinal centerline being substantially greater than the distance between the extremities of the barge along its transverse centerline;

a heavy duty crane located adjacent one end of said barge and mounted for rotation about a substantially vertical axis, said crane having a rated capacity and a boom of sufficient length capable of performing lifting operations off both barge beams and off the end of said barge adjacent to which it is mounted;

said barge hulls having ballast compartments for ballasting said barge to alter its draft between a low draft hull supported floating condition and a high draft semisubmerged column stabilized floating condition;

said crane having a predetermined angle of inclination from said crane'"'"''"'"'s normal substantially vertical axis of rotation beyond which said crane cannot slew;

the configurations, areas and locations of said columns being such as to provide the barge in high draft condition with stabilizing characteristics with respect to inclination about the roll and pitch axes sufficient for enabling the barge to maintain an attitude keeping the axis of rotation of said crane within said predetermined crane slew limiting angle for predetermined magnitudes of load and boom outreach;

a plurality of longitudinally spaced structural means reinforcing the structural relationship of said hulls, platform and columns;

said structural means including substantially transversely extending members interconnecting said hulls adjacent the uppermost portions thereof and restraining said hulls against lateral displacement relative to one another.

20. A derrick barge according to claim 19 wherein:

the crane load capacity and boom outreach length are such that when the crane is rotated in the high draft condition of the barge with load and outreach of predetermined values the resultant moment with respect to the roll axis causes substantial heel of said barge about said axis which if uncorrected would exceed the maximum slew limiting angle of said crane;

said barge having ballast means for counteracting excessive angle of heel caused by such crane operations with boom outreach to provide a counter-righting moment for the barge about its roll axis sufficient to maintain the angle of heel of said barge during crane operations within said slew limiting angle of said crane.

21. A derrick barge according to claim 19 wherein:

at least one column on each said hull is located adjacent the end of the barge at substantially the same longitudinal position at which said crane is mounted and at a distance from the transverSe centerline of said barge at least substantially the same as the distance between said transverse barge centerline and the crane axis of rotation.

22. A derrick barge according to claim 19 including:

additional structural supporting means adjacent said crane for increased support of said heavy duty crane both in loaded and unloaded condition.

23. A derrick barge according to claim 19 wherein:

at least one of the columns on each said hull has a longitudinal dimension greater than its transverse dimension whereby the cross-sectional dimension of each such column is greater in length than in width.

24. A derrick barge according to claim 19 wherein:

the area of said columns, the number thereof, and the distance of said columns from the longitudinal and transverse centerlines of said barge are such as to provide a greater righting moment about the transverse pitch axis than the righting moment about the longitudinal roll axis when said barge is in high draft semi-submerged condition.

25. A derrick barge according to claim 19 wherein:

the upper and lower surfaces of each hull have a non-streamlined configuration such as to provide increased added mass providing higher resistance to movement of the hulls and portions thereof through the water in a vertical direction when said barge is in high draft semi-submerged condition;

the area of said columns, the number thereof, and the distance of said columns from the longitudinal and transverse centerlines of said barge being such as to provide a greater righting moment about the transverse pitch axis than the righting moment about the longitudinal roll axis when said barge is in high draft semi-submerged condition.

26. A derrick barge according to claim 25 wherein:

each hull is of generally rectangular cross section with the longer axis of the hull cross section extending in like direction as the transverse barge centerline.

27. A derrick barge according to claim 19 wherein:

there are at least three columns connecting with each of said hulls and with said platform, said columns being located at spaced intervals along each of the hulls;

at least one column on each hull being located adjacent the end of said barge at substantially the same longitudinal position at which said crane is mounted and at a distance from the transverse barge centerline at least substantially the same as the distance between said transverse barge centerline and the crane axis of rotation, another of said columns on each hull being located adjacent the opposite end of the barge, with at least one additional column at an intermediate position on each hull;

said barge including additional structural support means adjacent said heavy duty crane for increased support of said heavy duty crane both in unloaded and loaded condition.

28. A column stabilized semi-submersible derrick barge comprising:

a pair of elongated hulls disposed in spaced side-by-side relation;

a working platform spaced above the hulls a predetermined height;

means supporting the platform in fixed spaced relation above the hulls and including columns connected to the hulls and the platform;

the distance between the extremities of the barge along its longitudinal centerline being substantially greater than the distance between the extremities of the barge along its transverse centerline;

a heavy duty crane located adjacent one end of said barge and mounted for rotation about a substantially vertical axis, said crane having a rated capacity and a boom of sufficient length capable of performing lifting operations off both barge beams and off the end of said barge adjacent to which it is mounted;

said barge hulls having ballast compartments for ballasting the barge to alter its draft between a low draft hull supported floating condition and a high draft semisubmerged column stabilized floating condition;

said columns having predetermined cross-sectional areas and being located to provide righting Moments about pitch and roll axes, when said vessel lies in high draft condition;

the upper and lower surfaces of each said hull having a non-streamlined configuration to provide increased added mass to provide higher resistance to movement of the hulls and portions thereof through the water in vertical direction when said barge lies in high draft condition;

the area of said columns, the number thereof, and the distance of said columns from the longitudinal and transverse centerlines of the barge being such as to provide a greater righting moment about the transverse pitch axis than the righting moment about the longitudinal roll axis when said barge lies in high draft semi-submerged condition;

a plurality of longitudinally spaced structural means reinforcing the structural relationship of the hulls, platform and columns;

said structural means including substantially transversely extending members interconnecting the hulls adjacent the uppermost portions thereof and restraining said hulls against lateral displacement relative to one another.

29. A derrick barge according to claim 28 wherein:

said crane has a predetermined angle of inclination from the crane'"'"''"'"'s normal substantially vertical axis of rotation beyond which said crane cannot slew;

the configurations, areas and locations of said columns being such as to provide the barge in high draft semi-submerged condition with stabilizing characteristics with respect to inclination about the roll and pitch axes for enabling the barge to maintain an attitude keeping the axis of rotation of said crane within said predetermined crane slew limiting angle for predetermined magnitudes of load and boom outreach;

said barge having ballast means for counteracting excessive angle of heel caused by crane operation with beam outreach to provide a counter-righting moment for said barge about its roll axis sufficient to maintain the angle of heel of the barge during crane operations within said slew limiting angle of said crane.

30. A derrick barge according to claim 29 wherein:

said ballast means is operable to transfer ballast from one hull into the other hull in a manner to achieve said counter-righting moment to maintain the heel of said barge within said crane slew limiting angle, with said ballast being transferable as said crane slews during load operating conditions.

31. A derrick barge according to claim 29 wherein:

said ballast means is operable to transfer ballast between said hulls in relation to the moment caused by operation of said crane to provide sufficient counter-righting moment to maintain the heel of said barge within the slew limiting angle of said crane.

32. A derrick barge according to claim 29 further including:

ballast means for counteracting the angle of trim caused when said crane boom extends outwardly away from the end of said barge in the direction of said barge'"'"''"'"'s longitudinal axis with load and boom outreach of high magnitude causing a high resultant moment with respect to the pitch axis so that the latter ballast means may provide a counter moment for reducing the angle of trim of said barge about its pitch axis.

33. A derrick barge according to claim 28 wherein:

at least one of said columns on each said hull has a cross section whereby the column dimension in direction of the barge longitudinal axis is greater than the transverse dimension of such column.

34. A derrick barge according to claim 28 wherein:

the cross section of each hull is generally rectangular with the longer axis of the hull cross section extending in like direction as the barge'"'"''"'"'s transverse centerline.

35. A derrick barge according to claim 28 wherein:

at least three columns connect with each of said hulls and with said platform, said columns being located at spaced intervals along each of the hulls;

at least one column on each said hull being located adjacent the end of said barge at substantially the same longitudinal position aT which said crane is mounted and at a distance from the transverse centerline at least substantially the same as the distance between the transverse barge centerline and the crane axis of rotation, another of said columns on each hull being located adjacent the opposite end of the barge, with at least one additional column at an intermediate position on each hull.

36. A derrick barge according to claim 35 wherein:

the upper and lower surfaces of each hull are substantially planar for at least most of their length and substantially perpendicular to a vertical plane through the barge'"'"''"'"'s longitudinal axis.

37. A derrick barge according to claim 28 wherein:

said barge is elongated so that it has a length to width ratio such that the barge length is at least a plural number of times as great as the barge width.

38. A derrick barge according to claim 37 wherein:

the boom of the crane is of such length that the end of the boom reaches to adjacent the end of said barge opposite the end at which said crane is mounted when said boom is disposed in the rest position.

39. A derrick barge according to claim 28 wherein:

each of said hulls has a streamlined bow portion for minimizing resistance to movement through water in the low draft condition.

40. A column stabilized semi-submersible barge comprising:

a pair of elongated hulls disposed in spaced side-by-side relation;

a working platform spaced above said hulls a predetermined height;

means for supporting the platform in fixed spaced relation above the hulls and including at least three columns connecting with each of the hulls and with said platform;

the distance between the extremities of the platform along the barge'"'"''"'"'s longitudinal centerline being substantially greater than the distance between the extremities of the platform along the barge'"'"''"'"'s transverse centerline, with the barge length being at least a plural number of times as great as the barge width;

means located adjacent one end of said platform for mounting a heavy duty crane which rotates about a substantially vertical axis and has a rated capacity and a boom of sufficient length capable of performing lifting operations off at least one beam of the barge and off said end of said barge adjacent which said crane mounting means is located;

said hulls having ballast compartments for ballasting the barge to alter its draft between a low draft hull supported floating condition and a high draft semisubmerged column stabilized floating condition;

said columns having predetermined cross-sectional areas and being located on said hulls to provide righting moments about pitch and roll axes of said barge when in high draft semi-submerged condition;

the area of said columns, the number thereof, and the distance of the columns from the longitudinal and transverse centerline of the barge being such as to provide a greater righting moment about the transverse pitch axis than the righting moment about the longitudinal roll axis when the barge is in high draft semi-submerged condition;

the upper and lower surfaces of each said hull having a non-streamlined configuration to provide increased added mass providing higher resistance to movement of the hulls through the water in vertical direction when said barge is in said high draft semi-submerged condition;

at least one column on each said hull being located adjacent the end of said barge at substantially the same longitudinal position of said crane mounting means and located at a distance from the transverse centerline of said barge at least substantially the same as the distance between said transverse centerline and the center of said crane mounting means, another of said columns on each hull being located adjacent the opposite end of the barge, with at least one additional column at an intermediate position on each hull;

said structural means including substantially transversely extending members interconnecting said hulls adjacent the uppermost pOrtions thereof and restraining said hulls against lateral displacement relative to one another;

said barge including additional structural supporting means adjacent said mounting means for increased support of the crane when mounted and operated on said barge.

41. A barge according to claim 40 wherein:

said additional structural supporting means includes support members directly connected between said crane mounting means and said hulls for at least partially structurally supporting said mounting means and the crane when mounted and operated on said latter means.

42. A barge according to claim 40 wherein:

at least one of the columns on each said hull has a cross section with longitudnally extending dimension greater than its transversely extending dimension.

43. A barge according to claim 40 wherein:

the centroid of the cross-section of at least one column on each hull lies outboard of the longitudinal centerline of the associated hull.

44. A barge according to claim 40 wherein:

said barge has ballast means for counteracting angle of heel caused by operation of a crane having a slew limiting angle and disposed on said mounting means so as to provide a counter-righting moment for said barge about its roll axis sufficient to maintain the angle of heel of the barge during crane operations within the slew limiting angle of such crane;

said ballast means being operable to transfer ballast from one hull to the other hull in a manner to achieve such counter-righting moment to maintain the heel of said barge within said slew limiting angle, with said ballast being transferable as such crane slews during load operating conditions.

45. A barge according to claim 44 further including:

ballast means operable for counteracting the angle of trim caused by operation of a crane on said mounting means with its boom extending outwardly away from the end of said barge in the direction of the barge'"'"''"'"'s longitudinal axis so that the latter-mentioned ballast means may provide a counter-moment for reducing the angle of trim of the barge about its pitch axis.

46. A column stabilized semisubmersible derrick barge comprising a pair of elongated hulls disposed in spaced side by side substantially parallel relation with each hull having substantially parallel planar top and bottom horizontal surfaces disposed substantially perpendicular to a vertical plane through the longitudinal centerline of the barge and extending substantially the length of each hull, with the transverse horizontal dimension of each hull being greater than its vertical dimension;

a working platform spaced above said hulls a predetermined height;

means for supporting said platform in fixed spaced relation above said hulls including at least three columns connecting with each of said hulls and said platform and located at spaced intervals along said hulls;

the distance between the extremities of said barge along the barge'"'"''"'"'s longitudinal centerline being substantially greater than the distance between the extremities of said barge along the barge'"'"''"'"'s transverse centerline, with the barge length being at least a plural number of times as great as the barge width;

a heavy duty crane located adjacent one end of said barge and mounted for rotation about a substantially vertical axis, said crane having a rated capacity and a boom of sufficient length capable of performing lifting operations off both barge beams and off the end of the barge adjacent to which said crane is mounted, the boom of said crane being of such length that it reaches beyond the transverse centerline of the barge when the crane boom is disposed in a rest position, and said crane having a predetermined angle of inclination from the crane'"'"''"'"'s normal substantially vertical axis of rotation beyond which said crane cannot slew;

at least one column on each hull being located adjacent the end of said barge at substantially the same longitudinal position at which said crane is moUnted and at a distance from the transverse barge centerline at least substantially the same as the distance between said transverse barge centerline and the crane axis of rotation, another of said columns on each hull being located adjacent the opposite end of the barge, with at least one additional column at an intermediate position on each hull;

a plurality of longitudinally spaced structural means reinforcing the structural relationship of the hulls, platform and columns;

said barge including additional structural supporting means adjacent the crane for increased support of the heavy duty crane in both loaded and unloaded condition;

said hulls having ballast compartments for ballasting said barge to alter its draft between a low draft hull supported floating condition and a high draft semisubmerged column stabilized floating condition;

said columns having predetermined cross-sectional areas and being located on the hulls to provide righting moments about the pitch and roll axes of said barge when in high draft semi-submerged condition;

the area of said columns, the number thereof and the distance of said columns from the longitudinal and transverse centerlines of said barge being such as to provide a greater righting moment about the transverse pitch axis than the righting moment about the longitudinal roll axis when said barge is in high draft semi-submerged condition;

the configurations, areas and locations of said columns being such as to provide the barge in high draft semisubmerged condition with stabilizing characteristics with respect to inclination about the roll and pitch axes for enabling the barge to maintain an attitude keeping the axis of rotation of said crane within said predetermined crane slew limiting angle;

said barge having ballast means for counteracting excessive angle of heel caused by crane operation with beam outreach to provide a counter righting moment for said barge about its roll axis sufficient to maintain the angle of heel of the barge during crane operations within the slew limiting angle of said crane;

additional ballast means for counteracting the angle of trim caused when said crane boom extends outwardly away from the end of said barge in the direction of said barge'"'"''"'"'s longitudinal axis with load and boom outreach of high magnitude causing a high resultant moment with respect to the pitch axis so that the latter ballast means may provide a countermoment for reducing the angle of trim of said barge about its pitch axis.

47. A barge according to claim 46 wherein said ballast means is operable to transfer ballast from one hull to the other hull in a manner to achieve said counter-righting moment to maintain the heel of said barge within the crane'"'"''"'"'s slew limiting angle, with said ballast being transferable as the crane slews during load operating conditions.

48. A barge according to claim 46 wherein said structural reinforcing means includes substantially transversely extending members interconnecting said hulls adjacent the uppermost portions thereof and restraining said hulls against lateral displacement relative to one another.

49. A barge according to claim 46 wherein said structural support means adjacent the crane includes support members directly connected between the base of said crane and said hulls for at least partially structurally supporting said crane from said hulls.

50. A barge according to claim 46 wherein:

the barge'"'"''"'"'s length-to-width ratio is approximately 400 to 100.

51. A derrick barge according to claim 46 having at least eight stabilizing columns and wherein:

there are at least four columns connecting with each of said hulls and with said platform, with at least one pair of columns on each hull located adjacent opposite ends of said barge as above-stated and with at least one additional pair of columns at two intermediate positions on each hull.

52. A derrick barge according to claim 51 wherein the last-mentioned pair of additional columNs are longitudinally positioned on each hull so that the centroid of each of said latter columns is located on opposite sides of the barge'"'"''"'"'s transverse pitch axis.

53. A derrick barge according to claim 46 wherein:

at least one of said columns on each of said hulls has a cross section whereby the column dimension extending in the direction of the barge roll axis is greater than the transverse dimension of the column.

54. A derrick barge according to claim 46 wherein:

each of said hulls has a streamlined bow portion for minimizing resistance to movement through water in the low draft condition.

55. A column stabilized semi-submersible derrick barge comprising:

a pair of elongated hulls disposed in spaced side by side substantially parallel relatiOn with each hull having a substantially right quadrilateral cross section with substantially planar top and bottom horizontal surfaces disposed substantially perpendicular to a vertical plane through the longitudinal centerline of the barge, and extending substantially the length of each hull;

a working platform spaced above said hulls a predetermined height;

means for supporting said platform in fixed spaced relation above said hulls including at least three columns connecting with each of said hulls and said platform and located at spaced intervals along said hulls;

the distance between the extremities of said barge and its platform along the barge'"'"''"'"'s longitudinal centerline being substantially greater than the distance between the extremities of said barge and its platform along the barge'"'"''"'"'s transverse centerline, with the barge length being at least a plural number of times as great as the barge width;

a heavy duty crane located adjacent one end of said barge and mounted for rotation about a substantially vertical axis, said crane being mounted and having a rated capacity and a boom of sufficient length capable of performing lifting operations off at least one beam and one end of the barge, with the boom of said crane being of such length that it reaches beyond the transverse centerline of the barge when the crane boom is disposed in a rest position;

said crane having a predetermined angle of inclination from the crane'"'"''"'"'s normal substantially vertical axis of rotation beyond which said crane cannot slew;

at least one column on each hull being located adjacent the end of said barge at substantially the same longitudinal position at which said crane is mounted and at a distance from the transverse barge centerline at least substantially the same as the distance between said transverse barge centerline and the crane axis of rotation, another of said columns on each hull being located adjacent the opposite end of the barge, with at least one additional column at an intermediate position on each hull;

a plurality of longitudinally spaced structural means reinforcing the structural relationship of the hulls, platform and columns;

said structural reinforcing means including substantially transversely extending members interconnecting said hulls adjacent the uppermost portions thereof and restraining said hulls against lateral displacement relative to one another;

said barge including additional structural supporting means adjacent the crane for increased support of the heavy duty crane in both loaded and unloaded condition, such means including support members directly connected between the base of said crane and said hulls for at least partially structurally supporting said crane from said hulls;

said hulls having ballast compartments for ballasting said barge to alter its draft between a low draft hull supported floating condition and a high draft semisubmerged column stabilized floating condition;

said columns having predetermined cross-sectional areas and being located on the hulls to provide righting moments about the pitch and roll axes of said barge when in high draft semi-submerged condition;

the area of said columns, the number thereof aNd the distance of said columns from the longitudinal and transverse centerlines of said barge being such as to provide a greater righting moment about the transverse pitch axis than the righting moment about the longitudinal roll axis when said barge is in high draft semi-submerged condition;

the configurations, areas and locations of said columns being such as to provide the barge in high draft semisubmerged condition with stabilizing characteristics with respect to inclination about the roll and pitch axes for enabling the barge to maintain an attitude keeping the axis of rotation of said crane within said predetermined crane slew limiting angle;

said barge having ballast mens for counteracting excessive angle of heel caused by crane operation with beam outreach to provide a counter righting moment for said barge about its roll axis sufficient to maintain the angle of heel of the barge during crane operations within the slew limiting angle of said crane, said ballast means being operable to transfer ballast from one hull to the other hull in a manner to achieve said counter-righting moment as the crane slews during load operating conditions;

additional ballast means for counteracting the angle of trim caused when said crane boom extends outwardly away from the end of said barge in the direction of said barge'"'"''"'"'s longitudinal axis with load and boom outreach of high magnitude causing a high resultant moment with respect to the pitch axis so that the latter ballast means may provide a countermoment for reducing the angle of trim of said barge about its pitch axis.

56. A barge according to claim 55, wherein:

the barge'"'"''"'"'s length-to-width ratio is approximately 400 to 100.

57. A method for transferring loads between horizontally spaced locations utilizing a variable draft derrick barge of the type characterized by a pair of spaced elongated hulls, a working platform spaced above the hulls a predetermined height at least equal to the height of the maximum anticipated wave, a derrick having a generally vertically extending axis of rotation substantially coincident with the centerline of the barge, and a plurality of stabilizing columns connecting between the hulls and the platform and upstanding from the hulls a distance at least equal to said predetermined height comprising the steps of:

moving the barge in a low draft condition with the hulls having freeboard to a work site;

ballasting the barge to respectively submerge the hulls and portions of the columns below the waterline to provide a high draft floating condition with the mean waterline located a distance above the hulls at substantially one-half the height of said stabilizing columns, lifting a load at one location, slewing the derrick and the load carried thereby to transfer the load from said one location to another location, depositing the load at said other location, the steps of lifting, slewing and depositing being performed when the barge lies in said high draft floating condition, and deballasting the barge to return the barge to the low draft condition with the hulls having freeboard.

58. A method of claim 57 including the step of ballasting and deballasting the barge to vary its submergence when in the high draft floating condition such that the distance between the mean waterline and either the underside of the platform or the topside of the hulls is not less than 0.75 of the mean wave height for wave heights less than the maximum anticipated wave to preclude amplification of barge motion due to interaction of wave and barge motions.

59. A method according to claim 57 wherein each of said hulls includes a plurality of ballast compartments and including the further step of selectively ballasting the compartments in each of the hulls to alter the natural period of the barge about at least one of its pitch and roll axes.

60. The method according to claim 57 wherein the derrick includes an elongated boom and a counterweight and including the steps of Ballasting one of the hulls to incline the barge to one side about its roll axis, slewing the derrick such that the boom lies outboard of the barge on said one side thereof whereby the counterweight inclines the barge about the roll axis in the opposite direction, and lifting the load on said one side thereof.