Designing a mechanical seal for an ROV thruster operating at depths of 100 meters in salt or fresh water presents challenges, particularly regarding pressure differentials and material selection. Recommendations include using lip seals or O-rings, with O-rings being a cost-effective option for limited use, while lip seals may require careful consideration of shaft alignment and material durability. The proposed design involves a .375-inch polished stainless steel shaft and an aluminum casing, with suggestions for using Delrin for the end cap housing. Concerns about seal performance under pressure and potential shaft flexure highlight the need for precise engineering, particularly in maintaining a consistent seal under varying depths. Overall, the discussion emphasizes the importance of selecting appropriate seal types and materials to ensure functionality and reliability in underwater applications.