Collapsible boats with foldable rigid transoms and a brace for the transom are disclosed. A collapsible boat includes a collapsible hull formed from a plurality of panels that extend from a first end to a second end of the collapsible/inflatable boat. Each of the panels is connected with at least one the other panels. The collapsible hull is configurable between a collapsed configuration and an expanded configuration. A folding rigid transom is used to constrain at least two rear margins of the panels when the hull is in the expanded configuration. The folding rigid transom and seats remain attached to the hull when the hull is in the collapsed configuration. A collapsible boat can have one or more interior members that are inflatable to support the collapsible hull in the expanded configuration.