The present invention relates to tapered line splice systems and methods for forming a line having a tapered splice.
Tapered lines are long lengths of rope of one diameter attached to a shorter length of rope of a smaller diameter by way of a splice. In one example application, a tapered line is commonly used in riser pull-in applications in offshore applications. The long length of rope is used to do the bulk of the work during a riser pull-in. The smaller diameter line on the lead end improves winch efficiencies by decreasing the overall weight of the lifting system and increasing drum capacity. The small diameter line on the lead end is easier to handle when compared to using a rope that is a larger diameter the full length of the line.
The need thus exists for improved tapered lines and especially for tapered lines used in riser pull-in applications in the offshore market.
The present invention may be embodied as a tapered rope structure comprising a first rope region, a second rope region, and a splice region. The splice region is between the first and second rope regions and comprises a taper portion, a finish portion, and an overlap portion. The finish portion is arranged between the taper portion and the first rope region. The overlap portion is arranged between the taper portion and the second rope region. A diameter of the first rope region is smaller than a diameter of the second rope region. A diameter of the overlap portion is greater than the diameter of the second rope region. A diameter of the splice region generally decreases from the overlap portion to the first rope region.
The present invention may also be embodied as a method of forming a tapered rope structure comprising the following steps. First and second rope members are provided. A first portion of the first rope member partly inserted into the second rope member at an insertion point. A portion of the second rope member between the insertion point and a bitter end of the second rope member is unbraided. Sub-strands are formed from the unbraided portion of the second rope member. At least a portion of each of the sub-strands is tucked into a second portion of the first rope member.
The example taper systems and methods of the present invention are implemented by splicing two ropes of differing diameter together and works, for example, for both 12-strand single braid and 12-strand jacketed rope constructions. A gradual smooth transition takes place in the taper area. When the technique is used on a 12-strand single braid, the appearance is similar to a standard eye splice. Because the splice method of the present invention results in a continuous jacket covering the entire length of the tapered line, the appearance of the finished rope structure does not change in the taper region when used on a 12-strand jacketed rope.
Referring initially to
As shown in
The SD rope 40 and the LD rope 50 are combined or spliced together to form the example tapered rope structure 20 as follows.
Initially, the SD rope 40 and the LD rope 50 are measured and marked in preparation for formation of the splice region 22.
As will be discussed in further detail below, an inserted portion 60 (
The insertion length LI of the inserted portion 60 of the SD rope 40 is calculated to obtain sufficient overlap between the SD rope 40 and the LD rope 50 within the splice region 22. Overlap between the SD rope 40 and the LD rope 50 within the splice region 22 is sufficient when tension loads on the tapered rope structure 20 are adequately transferred through the splice region 22 while minimizing the overall length of the splice region 22. As shown in
The SD mark 64 is formed by marking every S- and Z-strand around the circumference of the SD rope 40. In the example SD rope 40, six (6) strands are marked around the circumference of the SD rope 40 as shown in
The insertion length LI will generally correspond to a length of the overlap portion 30 of the splice region 22 as will be described in further detail below.
The unbraid length LU is determined to ensure that a sufficient length of the LD rope 50 is available for tucking to form the taper portion 32 and finishing to form the finish portion 34 as will be described in further detail below. The unbraid length LU may be calculated as follows.
First, a number of sub-strands to be used in a picking and tucking process is calculated or predetermined. As one example, the number of sub-strands to be used may be equal to a cross-sectional area of the LD rope 50 divided by a cross-sectional area of the SD rope 40.
Given the number of sub-strands to be used, a total number of picks of the SD rope 40 is determined. For each pick of the SD rope 40, one tuck process of the sub-strands of the LD rope 50 is performed, so the total number of picks is typically the same as the total number of tucks. In the example tapered rope structure 20 of the present invention, the total number of picks/tucks will be equal to approximately 11-13 times the number of sub-strands to be used. However, the total number of picks/tucks may be calculated or predetermined using different methods. The following Table A provides one example method of determining the number of picks/tucks given typical numbers of sub-strands of the LD rope 50 formed as will be described in further detail below:
Once the total number of picks/tucks is determined, the unbraid length LU can be calculated or predetermined by as the total number of picks/tucks (TNPT) multiplied by the inverse of the picks per unit length of the SD rope 40 (e.g., picks per inch associated with SD rope or SDPPI) plus an arbitrary margin (e.g., 24″). One example formula for calculating the unbraid length LU is as follows:
LU=TNPT×1/SDPPI+24″
Once the unbraid length LU is determined, the insertion location 62 is determined by forming an LD mark 66 on the LD rope 50 at the insertion location 62 as determined by measuring a distance corresponding to the unbraid length LU from the LD rope bitter end 54.
With the SD mark 64 and the LD mark 66 formed as described above, the SD rope 40 and LD rope 50 are measured and marked for splicing.
After the SD rope 40 and SD rope 50 have been measured and marked, the SD rope 40 is inserted into the LD rope 50 as described in FIGS. 5-8. As shown in
At this point, a rope securing member 70 may be applied to the LD rope 50 adjacent to the insertion point 62 and the LD mark 66 as shown in
After the SD rope 40 has been inserted into the LD rope 50 as described above, a portion of the LD rope 50 is unbraided as follows. Initially, an S-series 80 of consecutive S-strand picks 82 is identified along the length of the LD rope 50 from the LD mark 66 towards the bitter end 54. The insertion location 62 is included between two of the S-strand picks 82 in the series of consecutive S-strand picks 82. Next, a Z-series 84 of consecutive Z-strand picks 86 is identified along the length of the LD rope 50 between the LD mark 66 and the bitter end 54.
In the following discussion, the use of a letter suffix appended to a numerical reference character indicates a particular instance of an element generally described by the numerical reference character and does not indicate a new element. Accordingly, a numerical reference character used in the text to refer to an element in general (e.g., “S-strand pick 82”) may not be found in the drawing without a corresponding reference character (e.g., “82a”). The use of a numerical reference character in this specification without a letter suffix should not be considered inconsistent with the drawing so long as that same reference character is used in the drawing with a reference character.
In the example LD rope 50, six (6) S-strand picks 82a, 82b, 82c, 82d, 82e, and 82f are identified and marked as shown in
Next, as shown in
In the example tapered line structure 20 as shown in
Subsequent strand pairs 92 are formed in the manner generally described in the previous paragraph until the entire length of the LD rope 50 between the LD mark 66 and the LD bitter end 54 has been unbraided. In the example tapered line structure 20 in which the LD rope 50 is a 12-strand braided rope, first, second, third, fourth, fifth, and sixth strand pairs 92a, 92b, 92c, 92d, 92e, and 92f are formed of strand portions 90a and 90b, 90c and 90d, 90e and 90f, 90g and 90h, 90i and 90j, and 90k and 90l, respectively, as shown in
Starting with the SD rope 40 inserted into the LD rope 50 and the LD rope 50 partly unbraided as shown in
The individual strand portions 90 forming each of the strand pairs 92 are then disassembled and reformed into a number of sub-strands 96 as generally described above in Step 1 and depicted
As described above, the example LD rope is formed of fibers that are in turn arranged in yarns 58. One method of forming the sub-strands 96 is to determine the number of total yarns 58 in each pair 92 of strand portions 90 and dividing this number of yarns by the number of sub-strands 96 required. In the example LD rope 50, each strand contains nine (9) yarns 58, yielding a total of eighteen yarns 58 in each pair 92. Dividing the total number of yarns 58 (18) by the number of sub-strands 96 required (6) for each pair 92 of strand portions 90 yields three (3) yarns per sub-strand 96. As yarns 58 and/or fibers are grouped into the sub-strands 96, yarns/fibers that are closest to each other are desirably arranged into the sub-strands 96. Sub-strand securing members 98 (e.g., tape) may be used to maintain the sub-strands 96 together during subsequent tucking and finishing operations.
The first group of sub-strands 96 formed will be identified as a signal strand. In the example depicted in
If the number of yarns 58 per sub-strand 96 is not even, at least some of the yarns 58 may be separated into fibers and reformed as necessary to the proper number of sub-strands 96 to obtain sub-strands 96 of approximately even or substantially equivalent volume. Substantially equivalent volume may be obtained by arranging approximately the same number of yarns or fibers in each of the sub-strands 96. The term “substantially volumetrically equivalent” as used herein means that the resulting splice region 22 is substantially, but not completely, symmetrical or balanced about an axis of rotation defined by the longitudinal axis of the tapered rope structure 20. Working with intact yarns or other sub groups is preferred to working with individual fibers for ease of fabrication.
The last sub-strand 96f formed from the first strand pair 92a is first tucked under the first S-strand 120a as shown in
At this point, one of the sub-strands 96 is laid along the pic line 122 parallel to the axis of the SD rope 40 and another of the sub-strands 96 is tucked along the pic line 122 as shown in
The process of laying one of the sub-strands 96 parallel to the pic line 122, tucking the remaining sub-strands 96 around the parallel laid sub-strand 96, and then cutting the parallel laid sub-strand 96 to remove an exposed portion thereof may be repeated until only the pilot sub-strand 96a remains. In the example tapered rope structure 20, once the number of remaining sub-strands 96 reaches a predetermined number (e.g., 4) as shown in
The sub-strand 96b is then cut such that, at this point, only the signal sub-strand 96a remains as shown in
The sub-steps of Step 4 are repeated for each of the strand pairs 92 until all of the sub-strands 96 of all of the strand pairs 92a, 92b, 92c, 92d, 92e, and 92f have been spliced into the SD rope 40 as described above. Once all of the strand pairs 92 have been divided into sub-strands 96, tucked into the SD rope 40 along a unique pic line parallel to the example pic line 122, pruned down to only the respective pilot sub-strands 96a, and then divided into finish strands 130 and 132, a plurality of the finish strands 130 and 32 will extend from the SD rope 40. In the example depicted in
To complete the splice, the first finish strands 130a, 130b, 130c, 130d, 130e, and 130f may be combined into three groups of first final strands 140a, 140b, and 140c, and the second finish strands 132a, 132b, 132c, 132d, 132e, and 132f may be combined into three groups of final strands 142a, 142b, and 142c as shown in
With the finish strands 140 and 142 thus formed, the first finish strands 140 (e.g., closest to the SD mark 62) are each buried into the SD rope 40 until the tails of the strands 140 meets a first exit location 150 at which the second finish strands 142 (e.g., farthest from the SD mark 62) exit the SD rope 40 as shown in
This application (Attorney's Ref. No. P218718) claims benefit of U.S. Provisional Application Ser. No. 62/092,166 filed Dec. 15, 2014, the contents of which are incorporated herein by reference.
Number | Date | Country | |
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62092166 | Dec 2014 | US |