How many photos do I need?
At least five of the boat, one of which is set as the cover. More is better, and photographs of the actual vessel matter far more than stock imagery.
Five is the floor, not the target. The cover photograph is the one carrying your listing in search results, so it deserves the most thought.
Photographs of somebody else's boat, or generic stock imagery, will not pass review. Guests book what they can see, and they notice.
Upload JPEG, PNG, WebP or HEIC straight from a phone — send the original rather than a screenshot, because large files are fine and small ones look poor on a big screen. Landscape orientation works best for the cover, since that is the shape it is shown in on search results. You can reorder photographs and change the cover at any time from your workspace without a new review.