Why local supply made blockade duty easier

Did local resupply and laundry make the harbour much easier for the British squadron to blockade?

Yes; reliable supply and clean clothing reduced both logistical strain and the risk of disease disrupting the blockade.

A squadron gains a decisive advantage when it can meet daily needs locally and avoid major resupply problems. Regular washing also reduces the risk that disease will disable ships even when no enemy breaks the line. The Cádiz laundry trade was therefore an operational asset as well as a convenience. Blockade endurance depended on health and provisioning as much as on the ability to defeat sorties.