I believe from experience that a ship doesn't need to be sitting on the golden bridge at straits to blockade enemy crossing, but even when a small fleet is sitting on that bridge it doesn't seem to prevent enemy battle reinforcements from crossing back and forth.

Having demolished the Spanish fleet and taken Gibraltar, then blockaded the straits, the Spanish counterattacked repeatedly from the mainland and were joined by their garrison in Morocco (an interesting sandwich, since the reinforcements come right in the left rear of the only decent defensive position for an army there. Crowding the straits made no difference - the only solution after a second assault was to seize Morocco and then return to Gibraltar, letting the Moroccans recover their country and facing assault from only one side.

Is this familiar? Intended? It was a nasty surprise at first.

Thanks