간만(干滿) means the "ebb and flow" of the tide. 간조(干潮) is "low tide," and 만조(滿潮) is "high tide." 간(干) and 만(滿) are supposed to be opposites, but they did not seem like opposites to me, so I looked up their definitions.
간(干) means "shield," but it also has a few other meanings, including "attack," "pursue," "participate," and "dry." Among these meanings, "dry" seems to be the only one that comes closest to being the opposite of 만(滿), which means "full" or "abundant." "Dry" and "full" do not really seem like good opposites to me, but if you are talking about water, which is implied by the "water" radical, 氵(수), in 만(滿), then maybe they could be considered opposites. Nevertheless, I still do not like it.
So, a literal translation of 간조(干潮) and 만조(滿潮) would be "dry tide" and "full tide," respectively.
By the way, if you add "water" to "dry," what do you get? Well, the Chinese think you get "sweat," 汗(한). The logic? You charge in and penetrate the skin with your "shield" (干) and "water"(氵) comes out. Inscrutable? Yes, I think so, too.