How to maintain a blockade?

[wargamingDave44]

Playing in a PBEM game and the Japanese player can't seem to maintain a blockade of the Philippines for more than 3 turns. What are the rules for a blockade? They have a fleet counter of 3 ships at each port which intially blocks supply for the Philippines ground units but whenever the Japanese ships run out of supply or oil the blockade drops. It also seems as though whenever they try to move and replace the ships in those hexes with freshly supplied ships the blockade also breaks. How is the Japanese player supposed to effectively blockade the Philippines if all the ground units receive supplies right when they become super weak?

[AlvaroSousa]

They have to swap fleets in and out or use oilers to keep the fleets at sea supplied. But they do lose effectiveness.

You should only have to blockade 2 ports: Manila and Lingayen.

You should invade Aparri and Legaspi 1st turn.

You can invade the Southern Island, cut across the roads with the invader and blockade Davao.

It just takes some planning.