Abstract:
This application describes apparatus ( 200, 6200, 8200 ) for laying elongate articles from a vessel ( 100 ) at sea. The apparatus comprising tensioning means ( 204, 6204, 8204 ) for controlling paying out of said articles along an axis of said tensioning means, and a structure tiltable ( 202, 6202, 8202 ) between upright and horizontal states. The apparatus is operable in a first mode, wherein the tensioning means is carried by said structure with its axis at an elevated angle and said structure for example also carries a radius controller ( 220, 6220, 8220 ) and a straightener ( 212, 6212, 8212 ), and in a second mode wherein the tensioning means is arranged with its axis substantially horizontal. The tiltable structure may be detachable from the tensioning means in the second mode, so as to assist in transferring in-line accessories overboard. Alternatively a separate A-frame may be provided for that purpose. This allows the same apparatus to be adapted for laying rigid and flexible pipes at different times, and/or in different depth ranges.

Description:
[0001]    The present invention relates to methods and apparatuses for laying elongate articles at sea, and especially to pipe laying vessels. 
         [0002]    Various methods and apparatus are known for laying continuous steel pipe (known as rigid pipe) from a vessel at the sea surface onto the seabed. The pipeline may be welded on board from sections, as disclosed in U.S. Pat. No. 5,975,802 (Willis/Stolt), or may be laid from a pre-loaded reel, as in U.S. Pat. No. 4,917,540 (Recalde/Santa Fe). For deep water, a steep angle of departure of the pipeline into the water must be arranged, using track tensioners, or other tensioning means such as movable clamps, in order to align with the natural catenary curve of the suspended pipeline. Bending of the pipe under this very high tension is liable to cause damage. 
         [0003]    In addition to rigid pipes, flexible pipeline and cables may be laid from a vessel, typical from a coil in a carousel located below deck. Conventionally, the flexible pipe follows a horizontal path and is diverted over board via a sheave (wheel), to protect it against excessive bending. Vertical lay arrangements are known for flexible pipe, for example from EP 0717222 A (Stolt) and WO 91/15699 A (Coflexip Stena Offshore), but the horizontal path has advantages. In any case, generally vessels are specialised to one type of product (rigid or flexible), or are provided with separate apparatus for each type of product. This requires a larger vessel, and of course a greater cost of equipment. One vessel advertising capacity to handle both rigid and flexible product in a single apparatus is Technip/Coflexip ‘Deep Blue’, described in WO 00/66922 A1. However, this is a very large capacity and costly vessel, and therefore not necessarily adapted to all types of operation. Moreover the tensioners are fixed in vertical orientation which is not necessary or optimal for handling the flexible product in particular. 
         [0004]    The invention aims to provide cost-effective methods and apparatus whereby a single vessel can be adapted readily between a configuration suitable to lay rigid pipe along a vertical path, and a configuration suitable for laying flexible pipe along a substantially horizontal path. 
         [0005]    In a first aspect of the invention, there is provided an apparatus for laying elongate articles from a vessel at sea, the apparatus comprising tensioning means for controlling paying out of said articles along an axis of said tensioning means, a structure tiltable between upright and horizontal states, wherein the apparatus is operable in a first mode wherein the tensioning means is carried by said structure with its axis at an elevated angle, and in a second mode wherein the tensioning means is arranged with its axis substantially horizontal. 
         [0006]    The tiltable structure in the first mode may carry a radius controller and a straightener for conditioning rigid pipe, at a position upstream of the tensioning means. 
         [0007]    The radius controller and/or straightener may be provided at least partially in the form of modules to be removed when the structure is in the horizontal state. This alleviates space constraints and allows use of a smaller vessel. 
         [0008]    The apparatus may further comprise overboarding means for receiving flexible elongate product from the horizontal tensioning means in the second mode. The overboarding means may comprise a sheave. 
         [0009]    The overboarding means may be provided at least partially in the form of a module to be removed when the apparatus is in the first mode. Again, a compact apparatus is facilitated, and particularly avoiding congestion in the region where the pipe is launched from the vessel into the water. 
         [0010]    The tiltable structure may be operable in the first mode to orient the tensioning means vertically and at a range of angles below vertical. 
         [0011]    The tensioning means may be detached from the tiltable structure in the second mode, the tiltable structure being returned to an upright orientation for supporting loads independently of the tensioning means. The tiltable structure may in particular be operable in the second mode at a range of angles either side of vertical, to support in-line accessories as the product travels over said overboarding means. 
         [0012]    The tensioner in the second mode may be located at a position displaced horizontally from a location from which it will be elevated by said tiltable structure in the first mode. Such an arrangement allows the centre of mass to be kept reasonably low when the tensioner is elevated in the first mode, while affording increased clearance between the tensioning means and the overboarding means in the second mode. 
         [0013]    In a preferred embodiment, the tensioning means is detached from the tiltable structure in the second mode, and displaceable horizontally while detached from the tiltable structure. 
         [0014]    The tiltable structure may for example take the form of a pair of legs pivoted to the deck of the vessel at their lower ends and joined by a crossbeam at their upper ends, the tensioning means in the first mode being carried between the legs below the crossbeam, with a straightener and radius controller mounted above the crossbeam and being detachable when adapting the apparatus into the second mode. 
         [0015]    In alternative embodiments, the tiltable structure is movable bodily in order to provide said horizontal displacement of the tensioning means. This may be achieved as part of a single operation with lowering the structure about single pivot by placing the pivot point away from an axis of the tiltable structure. 
         [0016]    The tiltable structure may alternatively be connected to the vessel by one or more arms pivotally connected at one end to the tiltable structure and at another end to the vessel. This can permit independent modes of movement for (i) lowering the structure from upright to horizontal and (ii) retracting the structure away from a launch point of the product, with various advantages. Alternative arrangements to support and reconfigure the structure are also possible. 
         [0017]    In such alternative embodiments, the tensioning means may remain attached to the tiltable structure in both first and second modes. 
         [0018]    The invention further provides methods of laying rigid articles and flexible elongate articles using such apparatus and methods of configuring such apparatus for different modes of use. 
         [0019]    These and further features and advantages of the invention will be understood by the skilled reader from a consideration of the embodiments described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0020]    Embodiments of the invention will now be described, by way of example only, by reference to the accompanying drawings, in which: 
           [0021]      FIG. 1  presents various general arrangement (GA) views of a pipe laying vessel incorporating novel pipe handling apparatus according to a first embodiment of the invention; 
           [0022]      FIG. 2  is an enlarged partial side view of the vessel, showing the novel pipe handling apparatus in an upright mode; 
           [0023]      FIG. 3  is an enlarged partial side view of the vessel, showing the novel pipe handling apparatus in a horizontal mode; 
           [0024]      FIG. 4  is an enlarged partial plan view of the vessel corresponding to the side view of  FIG. 3 ; 
           [0025]      FIG. 5  is an enlarged partial plan view of the vessel corresponding to  FIG. 4  but at a lower deck level; 
           [0026]      FIGS. 6(   a ) and ( b ) are enlarged partial side views of an apparatus according to a second embodiment of the invention, in upright and horizontal mode respectively; 
           [0027]      FIG. 7  illustrates steps (a) to (h) in the lowering and retraction of the apparatus of the second embodiment between vertical and horizontal modes; 
           [0028]      FIGS. 8(   a ) and ( b ) are enlarged transverse section (looking sternward) and side views of an apparatus according to a third embodiment of the invention, in upright mode; 
           [0029]      FIGS. 9(   a ) and ( b ) are enlarged transverse sectional views, and  FIG. 9(   c ) is an enlarged partial side view of the apparatus of the third embodiment in horizontal mode; 
           [0030]      FIG. 10  illustrates steps (a) to (f) in the conversion of the apparatus of the third embodiment between vertical and horizontal modes; and 
           [0031]      FIG. 11  illustrates steps (a) to (c) in the operation of a movable linkage in an optional variation of step (e) in the third embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
     General Arrangement (First Embodiment) 
       [0032]    Referring to the general arrangement (GA) view shown in  FIG. 1 , a pipe laying vessel is shown in two different modes of operation in a partially cut-away side view in parts (a) and (b) of the drawing. Part (c) is a plan view corresponding to side view (b), in particular at a shelter deck level, being the highest deck on which most operations will be conducted. Part (d) shows additional features at and below a main deck level, below the shelter deck. 
         [0033]      FIGS. 2 ,  3 ,  4  and  5  are enlarged views of the stern portion of the vessel, corresponding respectively to views (a), (b), (c) and (d) of  FIG. 1 . Accordingly, the following description applies to all of the  FIGS. 1 to 5 , in which the reader is invited to look at  FIGS. 2-5  for more detail. 
         [0034]    The vessel naturally comprises a hull  100  with a superstructure  102 , located in this case forward of a larger working area. The vessel has various thrusters  104  to provide dynamic positioning (position holding) during pipe laying operations. The novel pipe handling apparatus to be described in detail below is configurable for the laying of rigid continuous pipe or alternatively flexible pipe. Such conduits and other elongate articles such as cables and umbilicals are known to the skilled reader. The reader will also appreciate that the arrangements required for laying these different types of articles generally mean that different equipment is used for the two purposes. 
         [0035]    In the present example, a large reel  106  is provided for continuous rigid pipe and oriented with a horizontal axis. An extended spooling arm  108  is also provided. As an alternative or supplement to the reel  106 , means may be provided on deck for welding pipeline from discrete sections, in a manner well known per se. For the storage and dispensing of flexible product, on the other hand, a carousel  110  located below deck level is provided. A second storage space  112  is provided, for cable and the like. 
         [0036]    Various ancillary equipment in the form of winches, ROV garaging, and particularly cranes  120 ,  122 ,  124  and  126  is shown. The aft cranes  120 ,  124  are removed in most of the drawings, to allow a clear view of the apparatus  200 . As will be appreciated by the skilled reader, these cranes play an important part in the pipe laying operations, particularly where end terminations or mid-line modules must be included, as well as in other hoisting operations of a more general nature. The outer cranes  120  and  124  are shown in alternative working positions, for illustration only. One such module  130  is shown in  FIG. 2 , for the sake of example, which would be suspended from crane  120  (not shown in  FIG. 2 ). 
         [0037]    At the main deck level ( FIG. 1(   d ) and  FIG. 5  show this most clearly), a retractable working platform  132  is provided for handling such modules and connecting them to suspended pipe, for example. This platform is associated with a hang off clamp  133  in a known manner. Similarly, an A-frame  134  is mounted on a raised working deck  136  for further versatility in handling objects other than continuous pipe cable, this being best seen in  FIGS. 3 and 4 . 
         [0038]    At the stern of the vessel is mounted the novel pipe handling apparatus  200 , which is operable in different orientations, according to whether rigid or flexible pipe is being laid. Apparatus  200  comprises primarily a tiltable support structure  202  and a tensioning means in the form of a track-type tensioner  204  which can pay out pipe under considerable tension. The tensioner in this example comprises four rolling tracks arranged about the axis of the product being handled, which can be pressed together by hydraulic rams to squeeze the pipe, in a known manner. The tensioner  204  is shown always with its tracks open, in the accompanying drawings. 
         [0039]    In  FIGS. 1(   a ) and  2 , the apparatus  200  is shown in an upright position adapted particularly for the laying of continuous rigid product. The structure  202  is shown both completely vertical and with the same structure in an off-vertical position shown with label  202 ′. In  FIGS. 1(   b ),  1 ( c ),  3  and  4 , the apparatus  200  is shown in an alternative configuration, with the structure  202  and tensioner  204  lying horizontally for use in laying flexible product. Further differences between these configurations will be described in more detail below. 
         [0040]    Also surrounding the tiltable structure  202  is an extension of working deck  136 , supported on a fixed structure. This is not shown, for clarity, in  FIGS. 1 to 5 , but a similar fixed structure will be seen in detail in the example of  FIGS. 6 and 7 . 
       Upright Configuration for Rigid Pipelay 
       [0041]    Referring in particular to  FIGS. 1(   a ) and the enlarged view in  FIG. 2 , it will be seen that additional modules are fitted to the structure  202  to enable it to perform the laying of rigid pipe in the vertical or near-vertical orientation. That is to say, in the present embodiment the equipment specific to rigid pipe laying is provided in modules  208  and  210  and  220  which can be detached to change from the upright mode of operation to the horizontal mode, described further below. Module  208  comprises a straightener  212  of well-known three-track type, a winch  214  and a tiltable working platform  216 . Module  208  is also shown separated from the structure at the left hand side of  FIG. 2 . Module  208  also effectively extends the height of the tiltable structure  202 . At the top or upstream end of structure  202  a radius controller  220  is fitted, and module  210  comprises an extension of this. As can be seen at  216 ′ in  FIG. 2 , the platform  216  can rotate to remain horizontal for workers thereon, as the structure  202  moves from its vertical position to an off-vertical position  202 ′. 
         [0042]    In operation, continuous rigid product is unreeled from reel  106 , via spooling arm  108  to the top of radius controller  220 / 210  where it is bent, potentially involving plastic deformation, to align with the lay axis and pass through the jaws of straightener  212 . It will be noticed that spooling arm  108  reduces the span travelled by the continuous pipe laying between reel  106  and the apparatus  200 , as indicated at  230  and  232  in  FIG. 1(   a ). The straightener  212  removes the bending imparted by the reeling and radius controller  220 , to supply a substantially straight product into the jaws of the tensioner  204 . Tensioner  204  feeds the pipeline slowly down into the sea, while the reel  106  unwinds synchronously, with a certain back tension maintained for control and safety. The suspended weight of pipeline when operating at great depth can be very considerable (hundreds of tonnes), and the orientation of the structure  202 , and hence tensioner  204 , is controlled, together with positioning of the vessel, to ensure that the structure aligns very closely with the natural catenary path of the suspended pipeline. Accordingly, the part of the pipe which is under the heaviest tension is not subject to bending, and is less prone to damage. 
         [0043]    It will be noted how the positioning of tensioner  204  on structure  202  allows the pipeline end termination (PLET) or other bulky module  130  to be accommodated in line between the outlet of the tensioner  204  and the retractable working platform  132 . Hang off clamp  133  is used for suspending the pipeline ( 234  in  FIG. 2 ) while this operation is conducted. Tensioner  204  can open to the position shown in the drawings, and winch  214  can be used to assist in manipulating module  130  into line, and for other abandonment and recovery operations. 
         [0000]    Horizontal Configuration for Flexible Pipe laving 
         [0044]    Referring now to  FIGS. 1(   b ) and ( c ) and to  FIGS. 3 and 4 , structure  202  can now be seen in a fully horizontal position, which is convenient for flexible pipe to be laid. In reaching this configuration, tiltable structure  202  has moved about a pivot  236  under control of hydraulic rams or similar jacking means (not shown). The pivot  236  is level with the foot of the structure  202  when upright, but is offset from the line of the structure  202 . By this arrangement, the structure  202  not only tilts from vertical to horizontal, but also moves bodily inboard, away from the line where the pipe, cable etc. is desired to enter the sea. This makes room for the overboarding sheave to be mounted to the downstream end of the structure  202 . 
         [0045]    In changing from vertical to horizontal configuration (which can be done at a shore base if necessary), the apparatus  200  has also been modified by the removal of modules  208  and  210 , and the replacement of module  220  directly onto the end of structure  202 , where module  208  was formerly located. Clearance  238  is indicated in  FIG. 3 , where the segment  210  has been removed and stowed elsewhere, on or off the vessel. It will be appreciated that the extended section  210  could be also a permanent part of radius controller  220 , if a recess could be provided in the deck to accommodate it, or if space between the deck and structure  202  in its horizontal position were sufficient to accommodate it in any case. However, it is clearly more convenient for it to be removable. 
         [0046]    While module  208  including the straightener  212  has been removed from the upstream end of the structure  202 , a different module  240  has now been mounted at the downstream end, which comprises primarily an overboarding sheave  242 , which is a wheel adapted to support and turn with a flexible pipe (not shown) as it passes from tensioner  204  over the stem of the vessel and into the sea. Using the radius controller  220  and other guiding means (not shown) it is therefore possible to unload a continuous flexible product from carousel  110 , under control of tensioner  204 , and pay it over the side without excessive bending or other damaging treatment. 
       Design Considerations 
       [0047]    Various considerations arise from the desire to use tensioners for handling both rigid and flexible pipelines and umbilicals. An important consideration for handling flexible pipes (and also coated rigid pipes) is to respect the maximum crush load of each product, whilst achieving the necessary friction to support the weight of suspended pipeline safely. Conventionally, tensioners adapted for handling rigid pipe are much shorter than flexible pipe tensioners, because they can squeeze harder without damaging the pipe and therefore require less contact length to achieve the necessary friction to hold the product. Compared with a normal rigid pipe tensioner, therefore, it will be seen that tensioner  204  in the apparatus  200  has a greater length than would be expected. 
         [0048]    The squeeze pressure and pad design are also important parameters. The hydraulic control system of the tensioner unit in the novel apparatus will therefore be modified to provide a wider range of squeeze pressures. In particular, it proposed that a dual hydraulic system be used, whereby a number of the squeezing cylinders can be “turned off”. This will reduce the overall squeezing pressure without requiring fine adjustment of the hydraulic pressure, and effectively gives a dual range system. 
         [0049]    With regard to pad design, a number of pad sets are provided to cover the range of different products. In a preferred embodiment, these are manufactured in two parts. A base piece is bolted to the tensioner track and stays in place for all operations, while an insert fitted with a quick release mechanism can be changed for a different insert relatively quickly. In particular, a number of sets of inserts with different radii and/or pad material will be used to cover the variety of products, while being light and easy to change. 
         [0050]    Deck layout is also an important factor, in order to meet the requirements of both configurations. The tensioner position in each mode is generally pre-determined by the specification. Accordingly, in this example the tower rotation point  236  must be selected such that the tensioner always ends up in the desired place. Crane location is important to achieve adequate coverage for both types of operation and similarly winch location, lay routes and load-out methodology require consideration. 
         [0051]    The apparatus and general arrangement of the vessel presented above and illustrated in the drawings satisfy these various considerations. In particular, in order to perform rigid lay in a vertical configuration and flexible lay in a horizontal configuration, there is provided a tower structure that can operate from 0° to 90° from horizontal. It is attractive to lay flexible products horizontally for operational reasons, including easier access, easier working and a general preference by particular customers. On the other hand, the vertical configuration can also be used for laying flexible products where necessary. 
       Second Embodiment 
       [0052]      FIG. 6  illustrates an alternative for the apparatus  200 , with in particular a different pivoting and jacking mechanism from the apparatus of  FIGS. 1-5 .  FIG. 6(   a ) shows the apparatus in the upright configuration, while  FIG. 6(   b ) shows it in the horizontal mode. The same reference signs are used for the various components of the second apparatus, but with prefix ‘6’ to distinguish them from the corresponding parts of the apparatus of  FIG. 1 to 5 . Only the differences will be specifically described. 
         [0053]    Firstly it will be seen in  FIG. 6(   a ) that the extension of the raised working deck  6136  is visible, and supported below by a fixed structure  6300 . Radius controller segments  6220  and  6210  are fitted on top of a removable module  6208 , but in this example the winch  6214  is located lower in the module  6208 , and it co-operates with a sheave  6302  mounted in the radius controller section  6220 . The functions of these elements is the same as in  FIG. 1 , however. 
         [0054]    The structure is again moved from upright to horizontal by pivoting about a pivot  6236 , and in this example the hydraulic ram  6304  responsible for this movement is shown (in practice two or more rams will be provided and operate in parallel). In this second example, however, the pivot point  6236  is not fixed with respect to the deck, but is moveable. Specifically, pivot  6236  is at the end of an arm  6306 , which in turn is connected to the deck at a pivot  6308 . Ram  6304  acts not between the structure  202  and the deck, but between the structure  202  and an intermediate point on arm  6306 . As will be illustrated with reference to  FIG. 7(   a ) to ( h ), this allows the same ram  6306  to perform the two actions of pivoting the structure down to horizontal and retracting it inboard to make room for the overboarding sheave  6242 , while also separating those actions. This provides more design freedom than the single pivot  236  in the first example. The articulated structure  6202 / 6306  can be moved using significantly less powerful rams than would be required to move the structure  202  as a unit. Depending on the exact layout, it may also allow the heavy tensioner  6204  and the working deck  6136  to be mounted lower, aiding stability of the vessel overall. 
         [0055]    In  FIG. 7 , steps in the movement of the structure  6202  and associated parts are shown, with all surrounding structure removed for clarity. Steps (a) to (d) describe the lowering of the structure from vertical to horizontal, while steps (e) to (h) show the subsequent process of retraction. Step (a) corresponds to the state of the apparatus shown in  FIG. 6(   a ), while step (h) corresponds to the state shown in  FIG. 6(   b ). 
         [0056]    In all of steps (a) to (d), it should be appreciated that the arm  6306  is pinned somewhere along its length to a part of the fixed structure  6300 , so that it maintains a fixed orientation. Pivot  6308  is fixed to the deck, so in this phase of operation pivot  6236  is also fixed with respect to the vessel. In step (a), the structure  6202  is vertical, and indeed is in use for the laying of continuous rigid pipe  6320  under control of the tensioner  6204  (shown open here but in practice clamped shut to grip the pipeline  6320 ). Step (b) shows the structure still in use for laying pipe, but inclined to achieve a lay angle of 35 degrees or so off-vertical. To reach this position ram  6304  has contracted a little. 
         [0057]    In steps (c) and (d), ram  6304  contracts still further by stages, until the tiltable structure  6202  is fully horizontal and within the fixed structure  6300  which supports the working deck  6136  (not shown). Part of the fixed structure  6300  is shown in  FIGS. 7(   d ) to ( h ), to provide a point of reference for the reader to follow the subsequent movement of the structure  6202  as it retracts inboard from the stem of the vessel. 
         [0058]    For steps (e) to (h), the pin connecting arm  6306  to the fixed structure  6300  is now removed, so that the arm is free to pivot now about the second pivot  6308 , fixed on deck. This changes the action when the ram  6304  subsequently expands again. Following the sequence of steps (e) to (h) in the drawing, and watching the position of structure  6202  relative to the portion of fixed structure  6300  which is show for comparison, it will be seen how expansion of ram  6304  now causes the structure  6202  to cant slightly, but also to be displaced horizontally away from the stem of the vessel. At the end of the movement, with ram  6304  fully extended, the structure  6202  is again fully horizontal. 
       Third Embodiment 
       [0059]      FIGS. 8 and 9  illustrate a further alternative for the apparatus  200 . This also includes a different pivoting and jacking mechanism from the apparatus of  FIGS. 1-5 . Most significantly, the functions of the separate tower  202  and A-frame  134  of the first two embodiments are combined in a single A-frame structure  8134 . For horizontal operation, the tensioner detaches from the A-frame/tower, so that it may again elevate to be used for handling bulky accessories. 
         [0060]      FIGS. 8(   a ) and ( b ) show the apparatus in the upright configuration, while  FIGS. 9(   a ), ( b ) and ( c ) show it in the horizontal mode. The same reference signs are used for the various components of the first apparatus, but with prefix ‘8’ to distinguish them from the corresponding parts of the apparatus of  FIGS. 1 to 7 . Only the differences will be specifically described. 
         [0061]    Referring firstly to  FIGS. 8(   a ) and ( b ), it will be seen that the combined tower and A-frame  8134  is substantially stronger than A-frame  134  of the first example, comprising box sections to form port (PT) and starboard (SB) legs  8400 ,  8402  and crossbeam  8406 . Again there is provided a raised working deck  8136  supported on a fixed structure  8300  not shown in detail. The A-frame  8134  is again moved from upright to horizontal by pivoting about a pair of pivots  8236 , and in this example the pivot points are fixed on the structure  8300  and do not move between modes. At each side (port PT and starboard SB) a pair of hydraulic rams  8304  are arranged to control this movement, extending between the respective leg  8400 / 8402  and a bearing point  8414  on the fixed structure  8300 . In parallel, at each side a strut  8420  is provided to brace the structure at a range of angles (from vertical to over 60° forward) using removable pins and arrays of pinning points  8422  at both port and starboard sides. This provides additional safety against failure of the hydraulic system powering rams  8304 . The strut and rams acting on each leg  8400 / 8402  are strong enough to hold the A-frame  8134  and its loads at the desired angle independently of those on the other leg. 
         [0062]    Tensioner  8204  (shown in outline) is permanently mounted on a tensioner frame  8408 . In the vertical mode for rigid Pipelaying, frame  8408  is held between the legs of the A-frame by a locking mechanism  8410  comprising, for example, four retractable locking pins and corresponding sockets. In this example, extensions  8412  of the tensioner frame are also provided which end in pivot points for suspending the lower working table  8132  and hang off clamp on the product axis at a suitable distance below the tensioner  8204 . ( The mounting of the working table on these extensions allows for a greater off-vertical orientation of the apparatus. In an alternative embodiment where such extreme inclination is not required, the lower working table  8132  is supported on the vessel or the structure  8300 , and slides in and out to maintain its position on the product axis. In that case the extensions  8412  of the tensioner frame  8408  can be dispensed with.) 
         [0063]    Radius controller segments  8220  and  8210  are fitted on top of a removable module  8208 , which again carries straightener  8212  and tiltable working platform  8216  (not shown in  FIG. 8  (a) for clarity). In this example a double-drum winch  8214  is located permanently on the forward side of A-frame  8134  rather that on module  8208 . This co-operates with sheaves  8302  mounted in the radius controller section  8220  to provide the same functions as in  FIGS. 1-7 . The winch also provides a hoist function in the second mode, however. 
         [0064]    In operation, rigid product (typically steel pipe) is hauled over the radius controller  8210 / 8220  and through straightener  8212 , passing through tensioner  8204  and into the sea. The A-frame  8134 , and hence the tensioner  8204 , are kept aligned with the desired product axis, according to the depth of water, tension in the product and so forth. This is done primarily using the rams  8304 , assisted also by the struts  8420 . The supply of product can be from a reel as in  FIG. 1 , or from welding on board as shown in U.S. Pat. No. 5,975,802, mentioned above. These operations will be well-known to those skilled in the art and not described further in detail. 
         [0065]      FIGS. 9(   a ) to ( c ) show the same apparatus converted to a second mode for laying flexible product from the storage tanks  8110  and  8112 . The sequence of conversion will be described in detail with reference to  FIGS. 10 and 11 . In  FIG. 9  it can be seen that the components  8208 ,  8210 ,  8212  and  8220  have been removed from the top beam  8406  of the A-frame  8134 . An overboarding sheave  8242  has been added generally at the base of the A-frame to receive flexible pipe from tensioner  8204  and support it as it is diverted to a more vertical path for launching to the seabed. 
         [0066]    The tensioner  8204  has been left horizontal and fixed to the structure  8300  through its frame  8408  and locking mechanism  8410 . In  FIG. 9(   b ), boxes  8400 ′ and  8402 ′ indicate spacers to maintain a usable and safe working deck, where the structure provides space for the legs  8400  and  8402  of A-frame  8134  to lie down to deposit and pick-up the frame  8408  carrying the tensioner  8204 . Compared to the first two examples, it can be seen how there is no longer a need for a massive tower structure ( 202  in  FIGS. 1 to 5)  to lie down passively merely because the tensioner is being operated in the horizontal mode. Skidways  8430  are provided for the frame and tensioner to be shifted several metres fore and aft in the process of conversion between modes, as will shortly be described and illustrated in more detail with reference to  FIG. 10 . This allows space between tensioner  8204  and sheave  8242  for working on the pipe and for deflecting it to pass in-line accessories over it without clashing with the tensioner. As shown partially in  FIG. 9(   b ) and the other figures, tensioner  8204  opens to allow passage of such items when the need arises. 
         [0067]    Also compared with the first configuration of the apparatus as shown in  FIG. 8 , it will be seen that the bearing points  8414  for the rams  8304  have been moved upward to new positions  8414 ′. This is to facilitate the complete range of outboard movement illustrated in  FIG. 9(   c ). This is at the expense of a reduced range of inboard movement compared with the first mode, but allows a more compact footprint and use of shorter rams  8304 . The struts  8420  are also not used in this configuration, as the A-frame is not carrying the tension of the suspended pipeline, and is required to move smoothly inboard and outboard over the suspended pipe, in order to pass bulky accessories, joints etc overboard without bearing on the sheave  8242 . The winch  8214  serves to hoist these loads. 
         [0068]      FIG. 10  shows steps (a) to (f) in the conversion from the rigid lay or vertical mode to the flexible pipe lay or horizontal mode. These steps can be simply reversed to perform the reverse conversion. Only the key moving parts as seen from the starboard side are shown to allow clarity. The same reference signs are used for these components as in  FIGS. 8 and 9  and they will not be reiterated here. 
         [0069]    In Step (a) the apparatus is in the same “vertical” mode as in  FIG. 8 , although the tower is shown inclined at an angle some way of vertical, to suit for example pipe  8234  being laid in shallower water. In this first mode the frame  8134  can be inclined to steeper or shallower angles as illustrated by dashed arrows. The rams  8304  provide the motive force for this, while the struts  8420  can be unlocked and locked at different positions on the array  8422  of locking points. In operation the suspended weight of the pip being laid is carried by tensioner  8204 , and hence through the A-frame and struts. 
         [0070]    In Step (b), a rectangular portion of working deck  8136  forward of A-frame pivots  8236  has been removed for conversion to the second mode, and A-frame  8134  has been lain down completely. Components  8210  etc. have been detached from it ready for stowage on- or off-board the vessel. The locking mechanism  8410  of the tensioner frame  8408  is disengaged from the A-frame legs  8400 / 8402 , to break the link between the tensioner frame  8408  and A-frame  8134 . It goes without saying that the locking mechanism must be sufficiently strong in each mode to support the entire tension in the pipeline, as well as the weight of the tensioner and frame in the vertical mode. The weight of the tensioner and tensioner frame  8408  is then taken on the skidways  8430  (seen in  FIG. 9(   b )). 
         [0071]    In Step (c) the A-frame  8134  is lifted using the rams  8304  sufficiently high that the tensioner  8204  on its frame  8408  can be skidded several metres forward along the skidways  8430 . This can be done using a winch (not shown), although obviously rack-and-pinion, hydraulic rams or other drive means would also be suitable. 
         [0072]    In Step (d) the frame and tensioner have reached the appropriate position for the horizontal mode of operation and the locking mechanism  8410  are engaged into suitable sockets in the fixed structure  8300 . At some point the spacers  8400 ′ and  8402 ′ (seen in  FIG. 9(   b )) are inserted alongside the tensioner frame and a smaller portion of working deck restored between the tensioner frame and pivots  8236  of A-frame  8134 . 
         [0073]    In Step (e) the bearing points of the rams  8304  are moved from their position  8414  to their higher position  8414 ′. Remembering that only the starboard side components are shown in  FIG. 9(   e ), it is explained that the starboard side rams  8304  can be disconnected at  8414  and reconnected at  8414 ′ while the port side rams support A-frame  8134 . Once the starboard side rams are secure in their new bearing point, the port side rams can be disconnected and reconnected at their higher bearing position. Tracks or the like can be provided to guide the ram ends between these two positions. ( FIG. 11 , described below, shows a more elaborate system of links whereby the bearing position of rams  8304  can be moved from  8414  to  8414 ′ without disconnection.) 
         [0074]    Step (f) shows the finished horizontal mode configuration in which the overboarding sheave  8242  has been fitted to the rear of structure  8300  and A-frame  8134  can swing fully inboard and outboard over it, for laying of flexible pipes, cables etc., under control of tensioner  8204  in its horizontal orientation. Also shown in  FIG. 10(   f ) is the sliding version of working table  8132 , in both extended and retracted positions. 
         [0075]      FIG. 11  shows a system of links whereby the bearing position of rams  8304  can be moved from  8414  to  8414 ′ without disconnection, in going from vertical to horizontal mode and vice versa. 
         [0076]    The bearing point  8414 / 8414 ′ in this modification is provided not by fixed points on the supporting structure  8300 , but by a bearing point on a first link  8440  pivotally connected at its forward end to a fixed point  8442  on the structure  8300 . The first link  8440  at its stem end is to one end of a second link  8444  at floating pivot point  8446 . The opposite end of link  8444  is pivotally mounted on a slider  8448  which is constrained to slide fore and aft in a short track  8450 . In the first mode of operation, slider  8448  is locked at the forward end of the track and thus the entire linkage  8440 - 8444  are locked in the V-shaped configuration shown in  FIG. 11(   a ). This provides a fixed bearing point  8414  for the rams  8304  to support and control the attitude of A-frame  8134 . 
         [0077]    In order to transfer this bearing point to the upper position  8414 ′ for the second mode of operation, the lock on the slider  8448  is first released, and then the ram  8304  is retracted. With the slider free to move aftward in its track  8450 , linkage  8440 - 8444  is free to be drawn upwards by ram  8304 , as shown in an intermediate position in  FIG. 11(   b ). It is recalled that only the starboard side components are shown, the A-frame  8134  being supported throughout this operation by the rams  8304  of the opposite side, or alternatively by a strut  8420 . 
         [0078]    The linkage is designed such that, once the ram  8304  is fully retracted (or nearly so), the links  8440 ,  8444  are in the inverted-V configuration shown in  FIG. 11(   c ), and slider  8448  has returned to the forward end of track  8450 . At the same time, the bearing point on link  8440  at the foot of ram  8304  is in the desired upper bearing position  8414 ′. Locking slider  8448  again at the forward end of the track fixes the bearing point  8414 ′ in its new position and the starboard ram  8304  can once again take the weight of A-frame  8134 . The same steps can then be repeated at the port side, until the rams  8304  are fixed at  8414 ′ on both port and starboard sides, and the A-frame can be swung inboard and outboard as shown in  FIG. 9(   c ). To revert to the first mode, the process is simply reversed. 
       Conclusion 
       [0079]    The above three examples show a range of different implementations of a “dual-mode” pipe laying apparatus, and further variations within those implementations have also been described. Further modifications can be considered, for example:
       Features from the different examples can be combined with each other in various ways according to the needs of a given project.   Other types of tensioning means may be substituted for the track tensioners shown.   Other types of drive besides hydraulic rams can be used in the tensioner and other parts of the apparatus.   Radius controllers may be smooth chutes as shown, and/or may comprise sheaves or tracked arches.   Tracks and sheaves may be powered or passive.   Instead of being located at the stem of a vessel, the apparatus may be adapted to launch the product over the side or the bow, or through a “moonpool”.       
 
         [0086]    The apparatus can also be configured for handling flexible pipe with the tower and tensioner in the vertical orientation, offering yet further versatility in the range of depths and types of pipe handled. In particular, pipe or other product may be damaged by being bent over the overboarding sheave at a high tension, corresponding for example to a greater than usual depth of water. If the tensioner is aligned with the catenary curve of suspended flexible pipe by using the apparatus in its vertical orientation, the risk of such damage is reduced. 
         [0087]    Of course various further modifications of the above examples can be envisaged by the skilled person, without departing from the spirit or scope of the invention in one or more of its aspects.