The objective of this study is to develop viable surface-treatment technologies for offshore and underwater structures. The study focused on cavity formation, which is a prerequisite to underwater plasma spraying using a fluid-stabilized local dry-wet method. Factors affecting cavity formation that were investigated in the study include slit angles on protection tubes, jet velocity of water curtains, and clearances between protection tubes and plate surfaces. All plasma-sprayed coatings formed underwater were made with pure Ti wire and then assessed to determine the influence of various factors on cavity formation. Macroscopic examination of the coatings revealed neither cracks nor peelings. X-ray analysis confirmed that coatings consisted mostly of Ti phase.