His Summer Harem: Part Five: Setting Sail (His Asian Summer Harem #5)
O. L. Tyme

The best things happen at sea as an off-the-cuff comment turns into a maritime adventure as Tom, Izumi, and Eshima rent a yacht and head for open waters.
As Eshima takes the wheel, Izumi takes Tom below deck to see if she can get him up on his sea legs.
Once fully recovered, Tom heads back on deck to relieve Eshima, adopting his rightful position as captain, upon which he fulfils his duties, taking full control of his vessel and the crew serving under him...