Adjusting V Belt tension and removing alternator Yanmar 1GM

[Overlord34]

Hi all,

I have a Yanmar 1GM 10 on my boat which I bought a few months ago. I'm slowly learning more about the engine. I know this is pretty basic but I would greatly appreciate any advice on how to adjust the V belt on the engine because it's way too loose and my efforts at adjusting it this afternoon were a dead end . To show you what I did, I've attached a photo (left most photo). The yellow arrow points to a bolt on the top of the alternator. My first step was to loosen the nut that was on the back of the bolt behind the alternator (I made sure I had a wrench holding the bolt as I loosened the nut with a 2nd wrench). I thought this was the "pivot" bolt but the alternator did not move after I completely loosened this nut. i then loosened the nut that the blue arrow is pointing too, which I thought was the "adjusting" bolt (also had a wrench holding the bolt behind it in place as I loosened the nut). However the alternator was still fixed in place and I couldn't move it even after I loosened the 2nd nut. I saw a mechanic tighten the belt a couple of months ago and I thought this was what he did but he did it so fast that I can't be sure. Any suggestions or ideas would be greatly appreciated! I've also attached a second overhead photo if that helps illustrate what I'm doing. The reason I'm also interested in possibly removing the alternator is because the zinc plate is behind it and I spent an hour and a half today trying to get at it but the alternator (and to a lesser extent the starter) is blocking access.