Apologies for posting this in chunks, but I am writing from an Android phone and bluetooth keyboard, and if I accidentally hit the home key, when I reopen Chrome, the page refreshes and I lose my post, so I typed it up in Gmail, but it's too big to copy and past in one go. This is my workaround.
Instead of taking the more common way from Costa Rica to Ometepe Island in Nicaragua, I decided to cross by river at Los Chiles and take the 10-11 hour ferry from San Carlos
I arrived in Los Chiles from Arenal around 1pm. My research had told me that there was a boat somewhere between 3-4pm to San Carlos, but it was hard to pin down an exact time. It was a 10-15 minute walk from where the bus dropped me off to immigration. I didn't have a map, so I just stepped aside into a discreet place and used my cellphone gps to figure out where I had to go.
I waited about 15 minutes to get my exit stamp. When I left the building, and man asked me if I needed a taxi, and I said no, I was going to San Carlos. He led me to a card table set up across the street, where a woman told me they'd start selling tickets in 15 minutes. Unlike the rest of Costa Rica, they didn't seem to speak English, at least they didn't offer after hearing my bad Spanish, so Spanish is helpful here, as it has proved to be throughout Nicaragua.
Since I had time, I walked down the street to find the building I read in LP where I would need to pay my 600 colones exit fee. It wasn't hard as a man sitting at another card table flagged me down, asked if I was going to San Carlos, and waved me over when I said I was.

