Slip #4 is the most intact of the many launching slips that once edged the Potrero shipyards. The two mobile gantry cranes are probably Pier 70's most recognizable landmarks. The cranes moved alongside the slip as the ships' hulls took shape, carefully moving the prefabricated sections, steel plates, and other large parts into position, where they would be welded in place.
Aerial View of Slip 4 in 1976 - Large Barge Under Construction
Many ship hulls were constructed and launched from this slip, usually with considerable fanfare and celebration. The hulls were then towed to nearby berthing piers for the extensive work needed before the ships were completed.
The process of launching was delicate and carefully planned. The slope of the launching slip was carefully chosen to allow the hulls to slide into the water at a rate fast enough to allow them to enter cleanly, but not so fast that they would be damaged by the impact. The slip ways (launching tracks) were usually greased in preparation for launching. Wooden blocks supported the ship until launching. Many of these thick wooden blocks appear to be still present on the site.
See Building a Ship for more information.
Artist's Conception: Future Shoreline Park at Slip 4 - Courtesy John Borg
Slip #4 has frequently been mentioned as the site of a possible future shoreline park. The preservation of the landmark gantry cranes is a high priority, but presents challenges.