Development of the ships   

   The form and rig of ocean-going, cargo carrying merchant ships throughout earlier centuries had been primarily adopted for the carriage of as much cargo as possible. The slow, lumbering argosies of Spain were in keeping with the general pace of life in their day , which changed little until the 19th century. The complete dependencc on wind power with the absence of power-driven tugboats often meant a delay in leaving an estuary of days, weeks, and sometimes months. Whole fleets ofa hundred or more East Indiamen and varied craft could be seen in the bay off the Isle of Sheppey at the mouth of the Thames, for days on end, as also in the Downs awaiting a fair wind. One instance is recorded of two ships leaving Liverpool on the same day, one of which caught a wind which took hcr to the West Indies. Upon her return to Liverpool she found the other ship still waiting for enough wind to move her. In contrast to this, another eyewitness in 1828 gives a delightful description of 140 shi ps sailing out of the river on one tide, with their sails stretching as far as the cye could see down the channel.

   The system of assessing a ship's size in the I 8th century, for taxation or harbour dues and for its own valuation in building cost or salc or charter , was based on the assumption that the physical proportions of length, beam, depth and hull shape betwcen light and load line were approximately the samc for all ships, which was a reasonable assumption for the time. The value of a ship was considcred to lie in the weight of cargo it would carry, and therefore a formula was evolved whereby the actual volume of a ship's hull between the light and load drafts (thc deadweight capacity) could bc easily assessed and converted into equivalent weight in tons of seawater. It should be remembered that many vesscls werc built more or lcss by rule of thumb with the minimum, if any, of builders' drawings on which to make calculations. This assessment of deadweight or burden (burthen) was in tons of weight, known as Builder's Tonnage, and in use officially up to 1836, after which it was referred to as Builder's Old Mcasure.

   The formula used the length of keel, the beam, and for the depth bctween light and load linc, a proportion of the beam, the product of these three figures being divided by a factor which gave actual tons weight.
In the event of the ship having no certificate originally, the Customs officer could measure the assumed length ofkeel with the vessel afloat, by means of a formula which made appropriate deductions from a length measured between certain perpendiculars above the waterline. Unfortunately there were loopholes in this assessment, of which unscrupulous shipowners took advantage. Within the confincs of the standard shape of block which these measurements gave, a ship could be either vcry bulky or slim, yct giving the same resultant tonnage, because the actual depth to the keel could be increased dangerously without increasing the tonnage figure, which had originally been intended for vessels of a reasonable depth. Undue depth of hull was used all too often, resulting in an unseaworthy and inefficient ship which, however, satisfied greed and allowed the extra stowage height for West Indian sugar or whatever cargo the owners dealt in.