"Just wondering if there are ways to cooperate without talking?"
Yes, absolutely.
The biggest thing I didn't realise when I was new to gunboat is that positioning is key. You can signal that you want to work with someone by just being in a far better position to attack them than to attack someone else. A clear example is F Sev->Rum - this says to Austria that you want peace, and (probably) want to fight Turkey together. Gunboat is about reading the board.
You can also signal by helping others - if you move somewhere that your intended ally can support you to, it signals that you want support there. Or, you can move somewhere to cut support. If Italy is in Piedmont, and France has armies in Mars and Bur, with Germany in Ruh and Mun, then Pie->Mar shows Germany that Italy wants to attack France with him.
This is contentious, but I personally think that gunboat requires more experience than full press games, because experience of how alliances usually work allows you to predict supports.
For example, in a typical R/T alliance, Turkey gets Bulgaria, Serbia, Greece and Trieste, whereas Russia gets Rumania, Budapest and Vienna. In an R/T, it's usually clear which centre is "next" for the alliance, and so supports are easy to construct, even in gunboat. Of course, in a press game, the R/T alliance might end up with a different distribution of centres, because you can talk about it.
Sometimes it does involve just throwing a support out there, when there's no other way to have previously signalled (or when your intended ally hasn't interpreted your signal correctly). Because of this, sometimes supports take a couple of turns to set up. And then, there are dishonest supports - where you really want someone to tap an enemy unit, you can support them one turn, and then not do it again the next turn.
Also, there's support for moves that you know don't need support, to signal that you're expecting them. For example, as an E/G against Russia, with an English fleet in Sweden and a German fleet in the Baltic (and no relevant Russian units), England can support Baltic->GoB. This says "I want to work with you". And since you're moving Germany closer to St P, England is also saying "I think you should have St P".
The beauty of gunboat is that the board does the talking for you.
I think many mid-level press players ignore what the board is saying, and playing some gunboat (well) is a great way to learn to listen to the board.