Find great deals on ebay for model boat plans in radio-controlled boats and hovercraft. shop with confidence.. So what is the smallest (shortest length) boat with an inboard you have seen or read about? any limitations to boat length besides shaft angle and space?. Free plans: the 13′ rowing dory assay (free downlaodable plans with full-size pattern from classic wooden boat plans); absolutely free plans (links to free online boat plans).