Response of a Converted T-2 Tanker^'* 



The T-2 tanker has been found to be one of the best of the currently 

 available ships for conversion to special applications such as heavy lift. For 

 exannple, Project ARTEMIS, which required lifts of approximately 190 tons 

 to 1,200 feet, employed a converted T-2 tanker with a large free-flooding 

 well near the center. The principal characteristics and dimensions of the 

 enlarged 7'-2 tanker used in Project ARTEMIS are as follows: 



Length 503 feet 



Beam 68 feet 



Mean draft 27 feet 



Displacement 17,000 long tons 



Natural pitching period 7.0 seconds 



Natural heaving period 7.2 seconds 



Natural rolling period 12.2 seconds 



The T-2 tanker is a relatively large ship which has power sufficient to 

 support a heavy-lift system. It is fairly stable and is large enough to provide 

 ample room for both facilities and crew. However, most T-2 tankers are 

 showing signs of age, thereby making it doubtful that one could be converted 

 to heavy-lift operations without extensive modifications. Nevertheless, the 

 amounts of heave, pitch, etc. of the T-2 in a fully developed sea are excellent 

 inputs for computing the dynamc stresses imposed on lines suspended from 

 ships of this size. 



Of interest is a report entitled "Seaworthiness Tests on a Model of a 

 T-2 Tanker With a Well Arrangement Near Amidships."-''* This report is 

 concerned primarily with the effect of the well on the heave and pitch of 

 the ship. The motions of the ship were observed in a fully developed sea 

 state 5 with 21 -knot winds. Table B-6 summarizes the average heave 

 amplitudes for a T-2 tanker. 



To get a better grasp on exactly how the ship heaves, the response 

 amplitude operators for heave motion in long-crested seas is multiplied by the 

 Neumann spectrum. The result is shown in Figure B-12. The figures in the 

 graph compare favorably with those in Table B-6. 



Assuming that the sea is in a steady-state condition, it is then 

 possible to compute the axial force due to heave in the pipe string by 

 multiplying the value of the heave spectrum by the force/heave diagram 

 derived earlier. Figure B-13 illustrates the relationships between dynamic 

 force and heave period for various depths for a T-2 tanker. There is little 

 possibility of these values being exceeded. The graph indicates that the 

 maximum dynamic stress is about 5% of the static stress. 



127 



