Page 273 - Practical Ship Design
P. 273

23 1












                                       Chapter 8

                                  Design of Lines






                                    8.1 OBJECTIVES

         In previous  chapters the design has progressed  to  the point  at which  the main
         dimensions,  the  block  coefficient and  possibly  the  LCG  and  LCB  have  been
         decided.
           A lines plan is now needed for a number of reasons.
           (i)  So that a General Arrangement plan can be drawn. Whilst this may not be
                essential at the initial design stage for large, full lined ships, it is an early
                requirement for fine lined ships, where the arrangement must be tailored to
                a major extent to suit the space and shape of the deck lines which contain it.
                This applies very strongly to the design of warships, research vessels and
                smaller passenger ships.
           (ii)  So that quantities can be taken off and used for weights, centres of gravity
                and cost estimates.
           (iii)  So that cargo spaces and tanks can be arranged and their capacities checked.
           (iv)  So that hydrostatics can be calculated and trim and stability checked.
           (v)  To send to the Tank for use as the basis for model tests.
         Later, after any modifications found necessary as a result of tank testing have been
         made, the lines plan becomes the basis for the offsets, loft work, numerical coding
         and all the structural and arrangement drawings.
           The lines plan has to meet a large number of different objectives all of which
         will have been set by the stage in the design at which it is drawn:
           (i)  Required displacement at the load draft.
           (ii)  Required cargo space and tank capacities.
           (iii)  Required deck areas to accommodate all aspects of the arrangement.
           (iv)  Features conducive to minimising the powering requirements; low resist-
                ance, good hull efficiency  and an ability to accommodate the propeller
                with clearances that make vibration unlikely.
   268   269   270   271   272   273   274   275   276   277   278