Thanks for all the replies.

As far as wax, I give the hull a good coating of high quality boat wax before the
spring launch, and it doesn't seem to help protect the boat. This fresh water river

must have some nasty chemicals in it. I certainly wouldn't go in this water to try
and
clean the boat during the season. I have tried various products containing bleach,
oxalic acid, etc. and haven't found an effective cleaner yet. I am still wondering
if
using these acid products full strength might do damage to the fiberglass, so maybe
they should be diluted (how much?). If they use muriatic acid to etch concrete,
that
sounds scary. I will check out the 'on and off' product. I eventually got most of
the
stain off using a heavy duty liquid cleaner, but it took a lot of rubbing. I have
used
most of the commercial products mentioned in this thread, with not much luck.

Sherwin

sherwindu wrote:

After pulling my boat from the Root River in Racine Wisconsin, I noticed that
there
was an ugly band of black gunk at the waterline, especially at the upstream side
of
the boat when it was in the slip. A power wash got the mud off, but this band
of
gunk stayed on. I had the same problem last year, and had to rub like hell with

all kinds of cleaners to get it off. Someone recommended using Tidy Bowl as a
cleaner, possibly because it contains Muratic Acid. I know that Muratic Acid is

used to clean and etch concrete, so I was wary to use it on my fiberglass hull.
Was I correct about this? Is there a better way to clean off this river junk?
I
have used Zud and other similar products, but they don't get everything off and
require a lot of elbow grease. Some of this gunk is on the bottom paint, as
well,
so I have to be careful not to dissolve that.

Sherwin