I haven't used a single thole pin with rope grommet. I have used a single pin with an oar which widened out at that point such that there can be a hole through it to accept the pin; or with an oar that has a fitting affixed to its side that accepts the pin. Examples of these are found in the Irish currach/naomhog,
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the Northumberland and Yorkshire Cobles, and the boats that are launched from Chesil Beach. I made a miniature currach for use as a tender, years ago, and found this single thole pin to be just as appropriate as in an inshore fishing boat. In both uses, you need to be able to let go of the oars to attend to something else. I find them much easier to use in a seaway than the more usual horseshoe shaped oarlock.
In all cases, the oar blade tends to be very narrow, as rotation to feather the blade is impossible. The thole pin plus grommet, as used on a Norwegian Faering, is generally used with a quarter round sectioned loom to the oar. The coble and currach use a square sectioned loom.
There are also boats with pairs of thole pins, with the oar working between them. I have no experience of those.![]()