Clean Your Dinghy Bottom More Easily

Ugh. Cleaning the dinghy bottom. It was one of the last chores we had to do before re-launching the boat.

Even though we have dinghy davits and pull the dinghy out of the water every night to prevent barnacles growing, there’s still a certain amount of growth on the bottom (on our previous boat, without davits, we hoisted it every night using our whisker pole — see more about how to do that here). If not cleaned periodically, the dinghy motor (or rower!) has to work harder and harder to move the dinghy at all, speed suffers and fuel consumption increases.

So you have to take the dinghy ashore, take the motor off, flip the dinghy over and clean. Really fun. Actually, the first time we did it on our first cruising boat (after not having hoisted it and with a nice crop of barnacles), we didn’t know any better and cleaned it on the deck of the boat. Talk about a big mess!

Two things we learned from that: pull the dinghy out of the water at night both for security and to significantly slow the barnacle growth, and don’t clean the dinghy on the foredeck.

Still, we’d never really hit up on a good way to clean the dinghy bottom. Admittedly, it was easier while the boat was in the yard, hence why we wanted to do it before re-lauching.

A couple of years ago, we hit upon the technique of using a green scrubby over a putty knife and that helped some (read more about that here).

Then, a few months ago, Dave’s brother sent him an article from the Pensacola, Florida newspaper that said WD-40 could help clean boat bottoms. So we tried it. To be honest, we didn’t find it to be a breakthrough. A reader had suggested Krud Kutter, but that didn’t do much for us either.

But it got us thinking about what might make it easier. I went looking for other things to try and found both a can of powdered Barkeeper’s Friend (a cleanser with oxalic acid) and an unopened bottle of Liquid Bar Keeper’s Friend that the previous owner had left on the boat.

I did a quick online check to make sure that oxalic acid wouldn’t hurt hypalon or the fiberglass bottom. Everything that I could find said that it was okay with hypalon, fiberglass and even PVC dinghies.

WOW! The powder Bar Keeper’s Friend (usually abbreviated to BKF) was good, but the liquid was amazing in how fast it cleaned the gunk off.  

I wet the hull, squirted some of the Liquid BKF on it, went over it with a green scrubby folded over a putty knife and it was pretty well clean. I rinsed it off and re-did any stubborn spots, rinsing thoroughly after it was all done. The photo at the top of this article shows the before and after: the side further from the camera is done. Even the little “barnacle footprints” came off completely — and so much more easily!

With Dave and I working together, it only took a little over a half hour to have the whole dinghy bottom and tubes where they were in the water looking almost new — a task that previously took considerably longer. Then we put on two coats of Star-Brite Polish with PTEF, which helps considerably to keep stuff from growing.

I haven’t found Liquid Bar Keeper’s Friend in any local stores but stocked up from Amazon. I discovered that they now call it “Soft Cleanser” but it’s the same formula; a 13-ounce bottle was just enough for our dinghy. Even better — it’s about the cheapest thing we’ve tried other than elbow grease! The Star-Brite is available almost anywhere that sells boat polish, including Amazon.

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  • Ann
    Posted at 16 November 2015 Reply

    I have also heard that the liquid BKF is amazing on glass shower doors!! I haven’t been able to find it locally but now I’ll order it from Amazon! Thanks for the tip!!

    • Susan Creighton
      Posted at 17 November 2015 Reply

      I use liquid BKF to get ride of shower mildew. It leaves the shower shiny and clean and eliminates mildew on contact without scrubbing and without the strong scent of traditional mildew sprays for mildew.

  • Glenda Neild
    Posted at 16 November 2015 Reply

    oxalic acid is great for lots of things around the boat. A 10% solution sprayed on to rust removes it from both cloth and stainless. Don’t leave too long on stainless before washing off though. It helps clean teak also

  • Mark & Cindy - s/v Cream Puff
    Posted at 16 November 2015 Reply

    Great tip. Thanks.

    We use BKF for rust spots. It can be safely used on fiberglass but will also remove any wax or protective coatings. Before waxing the cabin top we will use BKF on any tough marks and stains. It s magical stuff.

    Mark & Cindy
    s/v Cream Puff

  • Jonathan
    Posted at 16 November 2015 Reply

    I guess I just don’t understand this. I have been putting regular ablative bottom paint on my RIB (on the fiberglass and hypalon tubes) for more than ten years. NEVER scrub the bottom. Pressure wash once per year when we haul out. What am I missing?

    • Carolyn Shearlock
      Posted at 16 November 2015 Reply

      If you deflate the dinghy on passage, the paint cracks and chips off. Also, many paints can’t go in and out of the water on a daily basis.

  • Outland Hatch Covers, LLC
    Posted at 16 November 2015 Reply

    Once its clean there is a products called Ellsnot. Its a product developed for skim boards to reduce the water adhesion, but it can be used on the bottom to prevent growth. Ive never tried it myself but getting ready to try it on my waterline to prevent the brown scum line. I have high hopes. Look them up. If I had a dinghy that was not bottom painted, I would surly give it a try.

  • Pam Dean
    Posted at 16 November 2015 Reply

    I saw where you were heading to BKH. I got liquid BKF at the Home Depot there last year. It’s great for all kinds of things. Thanks for the tip.

  • Lynn Cryer Duggan
    Posted at 17 November 2015 Reply

    I love PRISM!

  • Karin Leach
    Posted at 17 November 2015 Reply

    Is the product safe and non-polluting when rinsed? Or should you use away from the water?

    • Carolyn Shearlock
      Posted at 17 November 2015 Reply

      It’s biodegradable, and does not contain bleach or phosphates. Oxalic acid occurs naturally in rhubarb and swiss chard. I’ve never heard that there is anything in it that’s bad . . .

      • Mike Thomas
        Posted at 18 November 2015 Reply

        Hi Guys,
        Oxalic acid is toxic (that’s why we don’t eat rhubarb leaves) and an irritant so needs to be treated with respect. It is ecotoxic and not meant to be disposed of in waterways. It also reacts with oxidisers like bleach (hypochlorite) and alkaline materials (as found in some cleaning materials) so it would be a good idea not to mix it with any other cleaning agents. As with all toxins dose is important and I am not sure what the concentration of oxalic acid in BKF is. If you type “MSDS Oxalic Acid” into your browser you will find a lot more info on this. Don’t forget natural does not equal harmless, arsenic for example.

  • Elinore Craig
    Posted at 19 November 2015 Reply

    We are currently in Marina Mazatlan and we just found the liquid BKH in the local Walmart. Will try it next time the dinghy needs a cleaning.

  • Marion Harrison
    Posted at 19 November 2015 Reply

    can this be used on a aluminium dinghy?
    Hoping yes, and that i can buy it in Australia

    • Carolyn Shearlock
      Posted at 20 November 2015 Reply

      The bottle says NOT to use it on anodizied aluminum. I can’t find anything from the company either for or against using it on regular aluminum, but I find plenty of people online recommending it for that.

  • Cindy Balfour
    Posted at 04 August 2016 Reply

    Thanks again Carolyn, I always learn something from the boat galley. We brought our BKF from the states in an empty plastic parmesean cheese bottle. It stays dry and shakes out. We needed liquid soft cleanser in Fiji and found a product called Jif that works very well.

  • Peter Greika
    Posted at 05 May 2017 Reply

    LA’s Totally Awesome available at dollar stores is oxalic acid and is way cheaper

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