Thanks to the fact that nowadays more and more books are digitized we are able to read books that are some times for decades no longer available for the public for several reasons. That’s quite a pity while these books contains useful information while the archives are destroyed, incomplete or nor accessible.
P. 257: “The Spanish trade to South America is carried on by annual ships, usually divided into three classes, the Flota, the Register Ships, and Galleons; of which the following is the most accurate account I could meet with.
P. 258: “Register ships are sent out by merchants at Cadiz or Seville , when they judge that goods must be wanted at any certain port in the West-Indies. The course is, to petition the council of the Indies for licence to fend a ship of 300 tuns burthen, or under, to that port: they pay for this license 40,000, or 50,000 dollars, besides presents to the officers, in proportion to the connivance necessary to their design. For tho’ the license runs only to 300 tons at most, the vessel fitted out is seldom less than 600. This ship and cargo are registered at the pretended burthen. It is required too, that a certificate be brought from the King's officer at the port to which the register ship is bound, that she does not exceed the size at which she is registered; all this passes of course. These are what they call Register ship, and by these the trade of Spanish America has been carried on principally for some years past: which practice has been thought as much to the prejudice of their trade, as it is contrary to all their former maxims for carrying it on.”
Source
Rev. Edward Clarke. Letters concerning the Spanish nation: written at Madrid during the years 1760 and 1761. London , 1763.