However I believe one can't win even a Trade Conflict war ingame without using anything but ships - but since I never tried, please correct me if I'm wrong.
Point of a trade war is full blockades giving 25% warscore and demanding cash is cheaper.
Declare, fully blockade, grab half their money, peace out before the year is over.
Sounds great on paper, doesn't it?
Whoever came up with its design has never played the game, sadly.
Length of war + ally in war modifier means fully blockading someone doesn't give enough warscore to demand anything from them unless they're warleader.
It will barely suffice for a white peace, oftentimes not even that.
Meaning trade war cb only lets you take cash from your target and nothing from their allies.
Saves you 2 years compared to walking into their land and sieging down their capital.
Except sieging down their capital allows you to take much, much more.
A huge design flaw.
I want to lower warscore for demanding cash so I can ask for more, but the warscore gained from blockades means I can ask less than someone who sieges them down could? What?
Why would I need a warscore reduction on something that's below 100%?
It's like someone handing you a single grape and telling you not to eat it all at once while your brother has five cakes and twenty steaks on his table.
You can use trade war cb against Lübeck as Brandenburg or Denmark to farm cash early on when half their treasury can already exceed 100% warscore because you're able to siege them down with either nation.
That's it. These are the only two nations who are able to make use of the cb. One of these nations won't even get a ticking warscore since it has no navy.
On top of that you won't get enough with trade war cb to justify building a navy early on.
The main idea behind the cb (build ships, blockade, become a naval power) will get ignored.
Not even as Denmark if you want to invade England since it's easier to invade Scotland first and you can do that with the navy you're starting with.
Potential fix could be that you can demand unlimited amounts of cash once your ticking warscore hits 25, additional trade efficiency for winning a trade war or similar.
Sadly those ideas go beyond what PDX is willing to do with any kind of cb. Any kind of suggestion players have come up with has been thoroughly ignored.
Trade cb is worthless and will always stay worthless.