Ok, but what purpose does the gold bar serve?
I don't have to transfer gold-coin via a ship to a location to use it. If the gold-bar is only a version of currency, similar to bullion in your explanation, why transport it? Why not have it converted to gold-coin(or in this game, why convert it to gold bars at all) which is more easily spent, stored and apparently not subject to the fluctuations of the market as are gold bars.
I suppose it might sit easier with me if gold-bars were made at a smelter, who had to get the gold ore from a mine, then the bars that resulted were transported to a goldsmith and could then be used to create gold coin.