"casters"appear to be a subset of shipwrights who were forming unionsand causing trouble for employers

Anno 33° Geo. III. A.D. 1793.
CHAP. LXVII.
An Act for better preventing Offences in obstructing, destroying, or damaging Ships or other Vessels,
and in obstructing Seamen, Keelmen, Casters, and Ship Carpenters, from pursuing their lawful
Occupations. [17th June 1798.]
g WHEREAs many Seamen, Keelmen, Casters, and Ship Carpenters, have of late assembled themselves in great
e Numbers, and have committed many Acts of Violence; which Practices, if continued, may occasion
'great Loss and Damage to Individuals, and injure the Trade and Navigation of this Kingdom: