§ 111.05-11 Hull return.
(a) A vessel's hull must not carry current as a conductor except for the following systems:
(1) Impressed current cathodic protection systems.
(2) Limited and locally grounded systems, such as a battery system for engine starting that has a one-wire system and the ground lead connected to the engine.
(3) Insulation level monitoring devices if the circulation current does not exceed 30 milliamperes under the most unfavorable conditions.
(4) Welding systems with hull return except vessels subject to 46 CFR Subchapter D.