Interesting quotes from http://warandgame.wordpre.../alternative-operations/ :

[...] the number of barges assembled in the Channel ports declined steadily after mid-September, dropping from 1004 on 18 September to 691 by the end of the month.

[...] on 12 October, General Wilhelm Keitel, the Chief of Staff of the Oberkommando der Wehrmacht (OKW – Hitler’s replacement for the War Ministry), acknowledged that it was now continuing ‘only as a means of exerting political and military pressure on England’ and that its execution would ‘possibly’ take place the following year. In the meantime, this ‘bluff’ had been an expensive one, dramatically slowing down industrial production, producing food shortages at home, and putting at risk the 1941 harvest. Iron ore and coal built up at the Baltic ports, with insufficient barges to transport it to the Ruhr, and even priority programmes (U-boat construction for example) began to slip. Barges were actually converted and crewed for their new role, consuming 75,000 cubic metres of concrete, 30,000 tonnes of iron girders and 40,000 cubic metres of wooden planks, plus 4000 towlines and huge quantities of canvas, chain and armour plate. Huge numbers of former seamen were transferred from the army and Luftwaffe, and the Kreigsmarine mobilised its reserves.