Read "Storm Over Warlock" by Andre Norton online for free on Textopian. Full text with search, annotations, highlights, and AI-powered reading aids.
Once again the beach was a wide expanse of shingle, drying fast under a sun hotter than any Shann had yet known on Warlock. Summer had taken a big leap forward. The Terrans worked in partial shade below a cliff overhang, not only for the protection against the sun's rays, but also as a precaution against any roving Throg air patrol.
Under Thorvald's direction the curious shell dragged from the sea -- if it were a shell, and the texture as well as the general shape suggested that -- was equipped with a framework to act as a stabilizing outrigger. What resulted was certainly an odd-looking craft, but one which obeyed the paddles and rode the waves easily.