Cleaning hard black/brown film from hull and cockpit

[BillT]

I'm sure some of y'all already know this, but today I discovered an almost magic cleaning to remove that hard, brown/black layer of crud that adheres to a hull when a boat has been neglected and let to sit in water for years.

I picked up this boat for free (yes, free - although there ain't no such thing as a free boat, really) a few days ago. It had been neglected for at least three years or more, and it was highly cruddy and filthy.

It had been left sitting on the edge of a big lake, and evidently it had been partly underwater for some time. It had all kinds of sand, mud, gunk and rotting acorns in it.

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I started power washing it and used my Shop-Vac to suck out probably 100 lbs of gunk, mud, sand, acorns, leaves, etc.

Then I started scrubbing with every cleaning solvent I have - purple stuff, Krud Kutter, bleach, with copious scrubbing and power washing. It made the brown gunk a slight shade lighter, but wasn't really touching the heavy stuff at all.

Then I saw the bottle of muriatic acid. And it said right on it "boat hulls: use full strength".

Amazing.

I poured it into a bucket and just dunked a nylon bristle deck brush in it and then scrubbed on the hard, black/brown cruddy areas. It immediately started just washing right off. A little scrubbing, wait a few seconds, a little more scrubbing.

Here is a before and after that took literally five minutes total from start to finish.

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I'll show interior pics next...

[BillT]

The interior had a hard brown film all over, as did the side decks.

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The muriatic acid made everything bright white again.

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It still needs a few small areas scrubbed with a smaller hand brush, but it's already like a completely different boat.

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[GreenLake]

Wow, she does clean up nice. That must have been satisfying.

A quick internet search reveals that there are some concerns about using undiluted muriatic acid on gelcoat. There are other acid based cleaners explicitly market for boats that are supposedly effective but less aggressive. But clearly, acid was the right choice here. (Bleach definitely attacks the gelcoat, so it's not an alternative).

All the harsh cleaners have the potential of attacking the top surface of the gelcoat, leaving it a bit more rough than it was before, thus more attractive to new dirt. UV exposure over long time periods does something similar. If that's the case, and you find either chalky or dull spots/areas don't try to use wax, but polish the affected areas instead.

You don't want to wax areas in the cockpit or deck that you stand or walk on for safety reasons, and below the water line, wax is supposedly slower than unwaxed. Also, if you ever want to repair dings with gelcoat patches or paint, you may have trouble with adhesion. So, all-around just polishing out dull spots would seem the recommended approach.