Under water gliders do not need to 'porpoise' a simple hydrostatic controller alters the hydro vanes from the climb phase to the dive phase at a set depth and vis a versa. The steeper the climb or dive angle is set the faster the water glider travels. the ideal path is a continuous flattened wave form such maximises forward travel at the optimum speed.
They don't need too, true, but so far they have in tests.
As for what they look like and what they do?
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