If a ship’s hull or tank breaks, the ship may sink, or oil spills can cause enormous damage to the environment. If the ship is equipped with a capable, cost-effective oil or liquid flow stop emergency device, casualties and marine pollution could be reduced. Many magnetic-type liquid spill stop emergency devices developed since 1904 have limitations, such as difficulties with installation and impossibility of use during sailing. This study demonstrated the applicability of a magnetic-type liquid spill stop emergency device through tests for water pressure and leakage, attachment, magnetic fields, and the generation of sparks. Results showed that the device can be applied to the ship’s side hull and bottom with a specified minimum diameter at a pressure depth of 1.0 kg/cm2 while sailing at a speed of 18 kts (9.26 m/s). If the distance from the device was at least approximately 750 mm, the magnetic field had no effect, and there was no risk of explosion due to sparks. A cost–benefit analysis based on the International Maritime Organization-approved guidelines for formal safety assessment confirmed the cost effectiveness of the device. This experimental study confirmed that the magnetic liquid stop emergency device is generally applicable to a ship’s hull.