Apart from that it's worth noting that especially before, but even after the Renaissance most, if not all fleets in the North Sea were in fact composed of ships primarily designed for mercantile purposes.
(As a matter of fact the arche-type Frisian mercantile ships for the North Sea (designed for the coastal waters, for intermediate distances, and mostly for carrying relatively much cargo with very little crew), aka the Cog, did in so form or another (Tjalk) remained in use even in the 20th century. And still does, but only for the purpose of racing.) [...]
4) sdk80: yes, and they are basically the odd mercantile fleet that is either confiscated or just decides to go pirate (a common thing to do around the North Sea, very common - afterwards you just sell the goods back to the previous owners

). So that part is about covered by the abundant presence of mercantile ports.
In the North Sea, real navies, with the explicit and sole purpose of being a military asset were not common to the point of non-existant altogether I'd say. Mind you if you look at the landscape of modern-day Netherlands you can still see why: in Frisia the old villages were located on what is called a 'Terp'; for the sake of comparison that's basically a sand dune. Those sand dunes were the only things that did not flood every odd 6 hours or so. In other words "Habukolandam" was more like "Habuko-Sea" half the time.
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