Please view Hokusai's gradual working towards The Great Wave Off Kanagawa, over a period of 39 years.
An early exploration of the themes Hokusai would keep coming back to is Spring in Enoshima, done in 1793 when he was 33. The wave is small and there are no boats, but Mt Fuji is clear in the background, and Enoshima is in Kanagawa, so we are clearly beginning to work towards something here.
A second pass, eleven years later in 1803 when he was 44. The title of this one begins to get more familiar: The View of Honmoku Off Kanazawa. It has a towering wave over a smaller boat, but Mt Fuji is not present, and the boat is considerably larger and has a sail. But the feeling of danger in the wave and the smallness of the boat are here, and of course the general composition is definitely recognizable.
This is A View Of Express Delivery Boats, done in 1805, merely two years later at age 46. Here we find the wave and the boats almost exactly as we'll find them in The Great Wave Off Kanagawa, though Mt Fuji isn't present, and the location is uncertain. And it's a good picture! The wave is threatening, the boats are small -- but the feeling of "ocean" isn't really there yet, is it? It's unlikely this picture would have become a classic for the ages. But that's okay, there's still time.
And here we have it, a full 26 years later, done by Hokusai in 1831 at the age of 72. The Great Wave Off Kanagawa, one of the most recognizable pieces of art in the world. The boats are there, the mountain is there, the wave is there, and the FEELING is there. He did it! He reached the apex of his ongoing motif and theme!
Or did he? Because the whole point of a motif is not that you're striving to get to the perfect version of it, the one idealized image you carried in your head all along, and when it is done, you are also done. Hokusai is on record at the age of 73 saying he'd only just begun to feel like he was learning how to draw things properly, and that "if I keep up my efforts, I will have even a better understanding when I was 80 and by 90 will have penetrated to the heart of things. At 100, I may reach a level of divine understanding, and if I live decades beyond that, everything I paint — dot and line — will be alive." He had drawn The Great Wave, but he didn't believe he was finished -- he thought that he was still just beginning to get started.
And he wasn't finished with his ocean motif, either. Please check out his Mt Fuji At Sea, done in 1834 at the age of 75.
It's all there; Mt Fuji, the ocean, the wave. The boats are gone, but replaced with birds, flying with the wave instead of fighting against it. It's not as famous as The Great Wave Off Kanagawa, but that's not what motifs are for -- each successive work does not have to surpass the previous in terms of success, especially in terms of external success. They're there for you to keep playing with, keep remixing and re-experiencing, for as long as you think you have something to say.