GST RATE TO BE CHARGED BY SUB CONTRACTOR TO PRINCIPAL CONTRACTOR OTHER THAN WORKS CONTRACT - Goods and Services Tax - GST

My query is with respect to the subject captioned above. One GST Registered Contractor is engaged in Maintenance, repairs and overhauling of vessels, ships, floating structures. It also manufactures the same. It also carries out manufacturing services in the nature of job work on the goods owned by others which is also related to ships and vessels only. Now, If this registered person entrusts the work (in case of maintenance and repairs) relating to one or two activity namely fabrication or say piping to another sub contractor,at what rate the sub contractor should charge GST to the principal contractor? In the second scenario of manufacturing of ships, vessels if it entrusts some of the work to a contractor (and not sub contractor as here they are principal manufacturer) say surface blasting,piping,color , what rate of gst should be charged by said contractor to the manufacturer? In the third scenario of manufacturing job work, if it entrusts either in full of some the work to another job worker, at what rate GST would be levied by the said job worker from the principal job worker ? I will be highly obliged if any one share his/her knowledge,opinion here. Thanks