Thank you for submitting your item for appraisal. The unterwater landscape painting in your possession is highly unusual. Very few people in Asia might have had the chance to see unterwater mountains in the 1920s. The overall appearance would remind me more of japanese art, e.g the stylistics of japanese ukiyo-e. I can´t find any comparables in chinese art nor in japanese art. My educated guess would be that the watercolour was made by a talented japanese artist and bought by your grandfather on his way home at a stopover in a japanese port town. The estimate is based on similar sea life kakemono by lesser known japanese artists of the 1920s.