The first wharves were built here in 1825 but the harbour we see today evolved over decades, as the slate industry prospered.
Each of the main slate quarries to the east of Porthmadog built its own wharf. The area to the left of the slipway, for example, was the Oakeley Wharf, where slates were exported from the giant Oakeley quarry in Blaenau Ffestiniog. There were similar private wharves in the railway yard at Mumford where some slate was transhipped to main-line.
Slates came to the harbour on narrow-gauge railways, and the wharves were covered with a web of railway tracks. Each wharf had an unloading track along its quayside, usually connected to other tracks by simple turntables on which individual wagons were rotated manually. The rail system continued to the “public” wharves at the harbour mouth (on the right as you look from the slipway area) which were not linked to specific quarries.
A ship-building industry emerged in Porthmadog to serve the slate-export trade. Hundreds of vessels were built at the harbour and Borth-y-Gest (700m south of the slipway). Ship-builders needed only a patch of sloping beach to construct and launch new vessels, and commonly ships would to be under construction at several locations simultaneously. In the early years, some ships were built on the north side of the harbour, as slate export was then focused on the wharves opposite. This activity was relocated as the wharves on this side were installed.