Serpentine Belt Tensioner?
 

I replaced my impeller on my new to me boat (09 tige 22ve) for the first time last night and I'm glad I did as the impeller was completely shot but I'm having issues trying to get the belt back on. I have loosened the belt tensioner but I still can't get the belt around all of the pulley's as there isn't enough slack. I must be missing something here but I can't figure it out. Any ideas?

the tensioner is spring loaded. put a long wrench or socket with a long ratchet for leverage over the nut and push it in toward the circulation pump. If you're just loosening the nut that wont do anything. the whole pulley articulates in then slip the belt over it and release the tensioner back into place. that nut should be all the way tight and as you turn clockwise it will rotate off center towards the circ pump.

Exactly what he said. It's counter intuitive, but you have to crank it like you're tightening it and the entire pulley will kind of pivot inwards towards the rest of the pulleys and let you put the belt around it. It works this way so it will have tension when the boat is running. It's the same on most cars too.

Great thanks guys! I will try again tonight.

I replaced the belt on my PCM EX343 this weekend and found it was easier to go ahead and put the belt on the tensioner pulley, push the tensioner pulley towards the circ pump with a large ratchet and then slide the belt under the circ pump.