Others have chimed in with Zud, BKF, and the like. Ditto Oxalic acid.
I agree.

However, don't scrub. Just wet it and let it lay. The oxalic acid
will do the job without scrubbing. All you're doing is neutralizing
the ferrous ions; scrubbing, despite how mild the cleansers are, will
dull your gelcoat. OTOH, if you're wanting to give it a new coat of
poli, or whatever, the scrub would probably help the prep :{))

I've got some myself, and I'm using IronOut, a laundry product which is
essentially powdered oxalic acid. I'm also going to try it on my SS
before I try to repassivate - I've got way more staining than I think
appropriate...

L8R

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Morgan 461 #2
SV Flying Pig KI4MPC
http://tinyurl.com/p7rb4 - NOTE:new URL! The vessel as Tehamana, as we
bought her

The Society for the Preservation of Tithesis commends your ebriated
and scrutible use of delible and defatigable, which are gainly, sipid
and couth. We are gruntled and consolate that you have the ertia and
eptitude to choose such putably pensible tithesis, which we parage.

Stamp out Sesquipedalianism