The little big boat. And it’s not just a fantasy definition. Her hull waterlines comes, in facts, from inside a more extended research on stepped hydroplane hulls, a program with the aim to realize boats in 12-18m size range, suitable for civilian and military duties, able to perform high cruise speed, in rough seas and with high payloads, able to operate efficiently in an extended range of speed, with low dynamic attitude variations. A difficult mix of requirements to be satisfied, with a lot of variables, often counteracting each other, to be “tuned” in the best possible way. The potential answer to this challenge could be found only in the “stepped” hydroplane hull architecture, so ancient as planing hulls themselves are, but absolutely up to date to respond to modern challenges. Still considered by many people arduous, difficult in design and construction, the solution, if scientifically analyzed, displays all the enormous potentialities in designing crafts aimed to operate in an “extended performance range” (EPR), as given by the mission requirements. Even if more complex, the formula, in facts, allows to combine at the best the basic hydrodynamic parameters involved in the design. To the designing hypothesis, to the preliminary drafts, to the analyses performed by special software and designing methods, specifically developed, had to follow experimental verifications. Instrumentals tests on scale models, by towing and self-propelled, were set-up. To the first point, an answer was given by means of a 2m scale model, to the second, by means of a larger hull model, 4m length, engine powered and driven by pilot on board, testing different speed and load conditions. Tests confirmed what was expected, for some aspects with better results respect to the prevision. In particular, the “pilot on board” model boat showed the attended quality in rough water navigation, with high load capability, low trim variation attribute. Why not to think about these qualities as good even for a real production small boat? The following step seems natural, so, from that scale model, comes a small complete boat, incorporating all the characteristics of her bigger sisters: arises the first of “Idroplan” line, the smallest, but not for this the less important, the “4k8”. The “little big boat”.