To ascertain the accurate maximum strains tending to produce longitudinal bending, or, in excessive cases, to break the ship across at the transverse section where the strains reach their maximum, involves a careful and most laborious consideration of the relative weight and buoyancy of individual sections throughout the length, and is a task not generally undertaken in mercantile shipyards.[8] References to the nature of the transverse and other strains above enumerated and the extent to which they have been investigated will be made further on. With regard to such fundamental properties of vessels as displacement, weight, and carrying capability, nothing new has for a long period been added to the fund of scientific knowledge. One of the conditions now most commonly laid down by the owners of a proposed ship is that which provides for a certain carrying capability on a given draught of water and at a certain speed, the principal dimensions of the vessel also being stipulated. The problem of determining what total displacement will be required, involves consideration and an estimate of—1st, The total weight of hull having regard to structural strength; 2nd, the total weight of machinery having regard to speed required. By using “co-efficients” deduced from the weights of vessels of similar type already built,[9] these are determined; and adding them to the carrying capability or dead-weight stipulated, the required displacement can be closely approximated to. For vessels of abnormal proportions or of very unusual construction careful and detailed calculations of the weight of materials are undertaken previous to tendering for them. In some yards, indeed, a like degree of care is observed in ordinary cases: methods of approximation involving the use of co-efficients such as that based on cubic capacity being distrusted. The further problem of determining what form of hull will give the required displacement is the essential and all-embracing feature of the work of design, as it involves consideration of almost all other properties. The methods of designing ships are various, and a very common method, at one time more followed than it now is, consists in shaping a block model direct, and from it taking the necessary measurements for displacement, and for full-size delineation in the moulding loft. The disadvantages pertaining to this somewhat antiquated method are becoming more recognised as shortened and exact methods of linear or “draught plan” design are put forward.