Works, but don't expect miracles.
Used for pontoon boat that had about 8 years of freshwater lake build up.  Read directions and mixed the ratio and sprayed it on, but it didn't do too much, and just left it really spotted.<br /> Increased the ratio each time and ended up using a brass soft brush to remove the build up along the water line.  Even then it wasn't coming off.  This stuff just seemed to turn the lower half water build up darker.  After I lightly used the brass brush on the top half, I used it again and it seemed to foam up right away and made the top half a look half decent, but under the water line it didn't seem to work and I pretty much gave up.  It did improve the look of the top sections however, and I was able to lower the ugly water line build up with a sander.  I would say, if you have a lot of hard water build up, you Will definitely have to increase the ratio by a good bit to get it to do anything.
Rating: 3 stars