I am working my way out of a similar situation.
First, get familiar with the checklists that relate to your situation. If you have been running a boat over 50 tons, you likely qualify for at least a 500 or 1600 ton mates ticket, if not a master 500. Get this credential, and a radar endorsement if you don’t all ready have one. at the very least get the five hundred ton mate, it will open doors a bit later if you decide to pursue a mate of towing. i’ll leave it to you to find out how.
Second, and most likely before you get said 500 ton ticket, get the AB special. For sure. Right now. Commit to it. Immediately. You will also need BST, and lifeboatmen/PSC. Don’t skimp on the STCW side of things and only do the national lifeboatman, you will be screwing yourself hard. Get set up with Rates forming part of a nav watch as well, and you will be on your way to being competitive for an entry level position in the workboat industry.
Understand that you will not be the captain at your new job. Prepare to humble thyself. You will be a hand learning the ropes and treated as such. I hope you haven’t been a dick to your present crew just for the sake of it, because karma is a PITA, and on a tug it comes in the form of needle guns, grinders, clogged heads, and officers that think you can whip up super fancy coffee on a whim using a second rate Bun coffee maker and Chock Full O Nuts coffee. Learn everything you can, as fast as you can, including the coffee thing.
About my situation, and hopefully a little motivation for you to get that ab special; I came out of the small boat business, just like you. I was the captain or senior guy at my outfit for a lot of years. I decided to get serious about making this industry a career. I applied everywhere that I could walk into. After not hearing back from places that were hiring, I asked a manager during an interview what I could do to be more competitive in the local market. He said: “every hotshot that comes through that door has a 100 ton. Get an AB.” So I did, went back in to the same office with the sticker still drying on my credential two months later, and got hired immediately. I’m now working on upgrades for my license while running a boat and decking on tugs when I can.
Get the AB special, it’s the door opener you need. good luck!