RodentRevolution
Banned
Never heard of previous attempts, when were they done? "Heavily supportd from the landward side" = map shows islands taken only by seaborne troops and operation 100 miles away that has no direct impact. The invasion was a successful multi-division operation involving significant land, sea, and air forces against 22,000 defenders equipped with coastal guns up to 15" calibre that did affect German doctrine. Looks like the only thing that would convince you that a successful Sealion operation could be mounted would be a successful Sealion operation - actually no, that wouldn't be enough, as probably you would say they didn't do it properly and it would have to be done again so it could be done the way you think it should be done.
McPherson is not the one moving goalposts here. Okay let us look at the above cited operation and see how it matches up to the Sea Lion prerequisites
Negligible interdiction by enemy airpower? Check
Substantial local naval superiority covering the invasion force? Check
Manageable logistic scenario? Check
Sea Lion itself was failing on all three any one of which had the power to scupper all of it by itself
But the RN didn't know that, and they said they would not put their capital ships into the channel as it was unsuitable for capital ships, unnecessary (50 cruisers and destroyers available) and too risky (plus they expected the Germans to do what was planned - send raiders into the Atlantic sea lanes as a diversion). It took most of the Home fleet plus Force H just to track down and sink one ship in May 1941 (the Bismark) and at the end of 1940 German capital ships did break out into the Atlantic. The Germans had broken the British naval code and had better radar on their capital ships (in 1940 many British ships had no radar) which is why the Scharnhorst was able to evade the British ships early in the war (later in the war the Sharnhorst got sunk because it was afraid of using its radar so it didn't know that it was being shot at until it was too late). So the Germans had to deal with the 50 or so destroyers and light cruisers - well they were scattered around England and on convoy escort duties so they weren't going to be there on S Day. Combats between the German destroyers (your figures are too low and do not include the "T" boats which were the same size as Hunt class destroyers) and the British destroyers in the Channel prior to 1942 usually were resolved in the Germans' favour, as the British destroyers had had most of their torpedoes removed (and had Mountbatten in command) - that's if the British found the German destroyers, who several times came close to the British coastline without detection. So to blockade the invaders the huge number of RN ships have to survive being shot at by channel guns (which got very close to hitting them and made them run away even when they were travelling at high speed at night), the minefields, Luftwaffe attacks, u-boat attacks, S-boat attacks, and the close-in es/corts (which were actually of similar numbers and reasonably well armed - the British called the German minesweepers "channel destroyers"). It's unlikely that the Germans would succeed but this thread is about making them succeed, and it's not impossible, just unlikely. The Germans could build more coastal ships S-boats, minesweepers, and destroyers and fewer capital ships without upsetting any treaty requirements or the British prior to the war.
You really want to be careful with your use of figures here. In 1940 total RN strength was above 50 cruisers plus above 150 destroyers. The 50 destroyers number so often cited in these debates is exclusive of the 22 destroyers assigned to convoy escort and the Western Approaches. There are also additional cruisers plus the battleship Revenge from 15 September.
As to sneaking up on the coast the initial landing required the movement of 640 barges, 215 tugs, 550 motorboats and 45 transport ships for the first wave per German Plans for the Invasion of England 1940 that I have linked previously and draws on among other sources the German Naval war diaries.
It is also worth noting that the Kriegsmarine's Western Command was not at all sanguine about the abilities of its destroyers to hold off the Royal Navy forces in the Channel instead being forced to rely mainly on mining operations which were themselves deemed insufficient (cf part 68 of the German Plans for the Invasion of England linked above). The German war diaries complain of the Royal Navy stationing its forward pickets off the Franco-Belgian coasts, hardly indicative of a situation where German destroyers utterly dominate British ones.