DESC:FIELD OF INVENTION:
The invention relates generally to the field of ship building and particularly relates to innovative shaft lowering method during ship building.
BACKGROUND OF INVENTION:
The build strategy for vessel to be constructed is mainly decided based on the method and sequence of propulsion shaft installation during construction as it is one of the precision and critical activities. The other construction activities are sequenced accordingly. Delay in delivery of shafts due to unavoidable reasons may lead to deferment of many sequential activities scheduled after shaft lowering. This would delay the progress of the planned concurrent activities and will impact the time lines of the ship building or ship repair project.

the shafting work commences with the lowering of the shafts on the bearing blocks located inside the shaft tunnel using the overhead crane. Once the shaft is lowered, subsequent blocks above it could be lowered. This conventional procedure can be planned and a suitable erection strategy could be adopted in the Build strategy. But sometimes, the delivery of the shafts could be delayed due to various reasons. In such cases progressing with the vessel construction as per the original procedure can result in deferment of many sequential activities scheduled to be undertaken after shaft lowering and can impact the time lines of the project. Following conventional method of shipping of delayed shafts by cutting of decks could lead to restricted progress of work on above decks, extensive fabrication and erection works leading to both time and cost overruns.

Various methods were introduced for maintaining the ship building even if the propulsion shaft has been delayed. For instance, KR101195686 discloses a method for installation of a drive shaft system for a special ship for reducing the period for ship construction by installing a drive shaft system during construction of a ship. However, the method for installing the drive shaft use laser guiding system in addition to a jig which is very expensive.

Hence, it is an endeavour of current inventors to develop a novel method for inserting the propulsion shaft in a constructed vessel.

SUMMARY OF THE INVENTION:
In view of the above, the primary object of the invention is to provide a method for lowering the shaft in a vessel which is economical and does not upset the ship-building schedule.

Therefore, in view of the above it is a primary aspect of the invention to provide a method for lowering the shaft.
In an embodiment, the method comprises of:
- inserting a shaft through a stern tube;
- transporting the shafts within the shaft tunnel to its designated location using a low bed transporter;
- lowering the transporter into a building dock;
- inserting the shaft into the ship through a bossing where the working clearance is very less;
- moving the shaft from behind the ship and below the aft cut up and into the stern tube, which is facilitated using the Low Bed Transporter;
- adjusting rake, vertical displacement and eccentric loading of the hub by means of a jig to enable smooth travel of the shaft piece into the shaft tunnel avoiding any scoring of the shaft or damage to the stern gear of the ship; and
- moving the shaft within the tunnel using blocks and tackles.

Accordingly, the method provided does not require reworking of the vessel.
The provided method allows for insertion of propulsion shaft with a help of low jig and the fine alignment are effected by grouped pneumatic arrangement.

BRIEF DESCRIPTION OF DRAWINGS:
Fig, 1 illustrates method of shaft lowering by using low bed transporter to insert shaft from aft stern tunnel.
Fig. 2 illustrates the subsequent step of insertion of shaft using low bed transporter.

DETAILED DESCRIPTION OF INVENTION:
The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated. As used herein, the following terms and phrases shall have the meaning set forth below.

Unless specified otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art, to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described.

Unless stated to the contrary, any of the words “contains”, “containing”, "including," "includes," "comprising," and "comprises" mean "including without limitation" and shall not be construed to limit any general statement that it follows to the specific or similar items or matters immediately following it. Embodiments of the invention are not mutually exclusive, but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention.

Further, words like “a”, “an”, “at least” and “the” should be construed to not only cover singular quantities but also plural quantities of the elements immediately following them.

Described herein is a method for installing a propulsion shaft which is economical and does not require reworking on the vessel.

Hence, the revised build strategy of the invention could be adopted which includes progressing with the aft sections of ship and erection of steel blocks and equipment outfit inside and above the engine room and insertion of all the shafts through the stern tube once the shaft reaches the location.

The method of the invention helps in meeting the launch deadlines cutting down on the time frame by months and cost saving of money.

Accordingly, a special jig is designed to undertake the fine adjustments of rake, vertical displacement and eccentric loading of the hub and is used together with a low bed transporter to guide the shaft in a narrow shaft tunnel. This enables smooth travel of the shaft piece into the shaft tunnel avoiding any scoring of the shaft or damage to the stern gear/stern tube of the ship with clearances of about 1.5 mm. This movement of shafts within the tunnel is arranged using grouped pneumatic balancer and tackles for smooth and controlled movement.

In an embodiment, the method comprises of:
- inserting a shaft through a stern tube;
- transporting the shafts within the shaft tunnel to its designated location using a low bed transporter;
- lowering the transporter into a building dock;
- inserting the shaft into the ship through a bossing where the working clearance is very less;
- moving the shaft from behind the ship and below the aft cut up and into the stern tube, which is facilitated using the Low Bed Transporter;
- adjusting rake, vertical displacement and eccentric loading of the hub by means of a jig to enable smooth travel of the shaft piece into the shaft tunnel avoiding any scoring of the shaft or damage to the stern gear of the ship; and
- moving the shaft within the tunnel using blocks and tackles.

The present invention enables to address the issue of shaft lowering with minimum impact on concurrent progress through resequencing of tasks and completion of all activities as per schedule.

In accordance with above embodiment, the insertion of shaft through the stern tube and transport of the shafts within the shaft tunnel to its designated location is shown in Figure 3. The low bed transporter is a material handling equipment normally used in specially laid broad roads to shift large structural panels on ground. This huge transporter may be lowered into the building dock where the manoeuvrability option is limited with the various vessels under construction and other structures erected to progress construction activities in the vicinity.

The movement of the shaft from behind the ship and its travel below the aft cut up and into the stern tube is facilitated using the Low Bed Transporter as shown in figure 4. A specially designed jig is configured to make the fine adjustments of rake, vertical displacement and eccentric loading of the hub to enable smooth travel of the shaft piece into the shaft tunnel avoiding any scoring of the shaft or damage to the stern gear of the ship. The movement of shaft within the tunnel is arranged using blocks and tackles.

Advantages and/or uses of Invention:
During Ship building practice, the delivery of the shafts could be delayed due to various reasons. In such cases progressing with the vessel construction as per the original procedure can result in deferment of many sequential activities scheduled to be undertaken after shaft lowering and can impact the time lines of the project. Following conventional method of shipping of delayed shafts by cutting of decks could lead to restricted progress of work on above decks, extensive fabrication and erection works leading to both time and cost overruns. Multi degree freedom shaft insertion method helps us to save both time & cost. For example against a timeline of 8 weeks planned for shaft mounting following the deck cut and vertical lowering, the entire job is completed in 3 days thus accruing a saving of 2 months in timeline. The effort saving is of the order of 400 mandays as most of the operation is automated. The present invention enables yard to address the issue of shaft lowering with minimum impact on concurrent progress while meeting all the quality requirements. This innovative process is repeatable especially for major platforms to maximize on accrued savings in time and cost. With this all underwater-activities could be completed on time and the vessel can be launched as per the schedule.
,CLAIMS:1. A method of insertion of multi-degree freedom shaft in a vessel comprising:
inserting a shaft through a stern tube;
transporting the shafts within the shaft tunnel to its designated location using a low bed transporter;
lowering the transporter into a building dock;
inserting the shaft into the ship through a bossing where the working clearance is very less;
moving the shaft from behind the ship and below the aft cut up and into the stern tube;
adjusting rake, vertical displacement and eccentric loading of the hub by means of a jig to enable smooth travel of the shaft piece into the shaft tunnel avoiding any scoring of the shaft or damage to the stern gear of the ship; and
moving the shaft within the tunnel using blocks and tackles.
2. The method as claimed in Claim 1, wherein the movement of the shaft into the stern tube is facilitated by the Low Bed Transporter.