Marc,
No disrespect to what others are telling you is intended here. I use VC-17 in fresh water too. Most all the local racers at our club (lake Erie - warm water, 70 degrees) use VC-17. But... VC-17 for fresh water is a totally different chemical make up than VC-17 for salt water.
What we tell you about VC-17 may not apply to your condidtions. Do some research, talk to the local racers. Here's one article on bottom paint. http://www.sailingworld.com/article/The-Bottom-Line-on-Bottom-Paint