woman scrubbing boat underwater

The first and best advice on this topic you should ever get is this: clean your boat frequently.

The longer between the times you dive on your boat, the more growth there will be and the more developed it will become. This is particularly true around hot areas for growth such as around the waterline, near thru hulls and your prop. For us in Southern California, we dive on our 36’ Union Polaris sailboat at least once a month to give it a scrub. During the summertime, we are in the water more frequently than that so it’s simple to touch up some of the areas that growth happens more quickly. To determine the right frequency for your area, you should to talk to boaters local to where you are as they’ll know best.

Now that frequency is out of the way, let’s get onto what needs to happen to clean your boat underwater.

Get the right tools to clean your boat underwater

Before I decided to take this project on and not hire it out, I spoke with some of the local hull divers. They all advised getting tough scrub pads. I took the save-some-money route one suggested and bought two of the scrub pads that go on the bottom of industrial buffers. I cut the scrubbing pads to about hand-size, so they would be easy to hold while underwater.

Some hull cleaners will use metal scrapers, but personally, I did not want to be quite that rough on the hull of my boat. Instead I opted for a multi-pack of plastic putty knives of various sizes. I used the large ones for the bigger areas and the small ones to get into areas the large one would not fit into like the inside of the thru hulls. A pick of some kind would also work well for this.

Having gloves on your hands can save you from scraping them up on any growth, and from becoming potential sharkbait with blood in the water (kidding, mostly)! This will be particularly true if you’re in waters that tend to result in lots of barnacle growth on the bottom of your boat. Get some gloves that you can wear underwater that won’t inhibit movement too much. I got the large dipped impact glove by Husky and they have worked wonderfully.

Have the right gear for yourself

  • Mask + snorkel, we love anything Cressi like this snorkel set
  • Fins
  • Hookah system

  • Wetsuit (if necessary)

It should go without saying that you’ll need a mask at the very least to clean your boat underwater. I highly recommend you go the extra mile for a snorkel and fins though – this will make a major difference. But to really make it easy (and do it the way the professionals would), use a hookah system so you can stay underwater for extended periods of time. We currently don’t have this so we hold our breath while we dive down and scrub, though this may be a purchase we make eventually. I have heard having a hookah system can be a game changer, but can’t speak on this from experience. Also, if you happen to be in cold waters, do yourself a favor and wear an appropriate wetsuit.

Alternate from side to side to let the sediment settle

So now you’re in the water and you’re ready to start scrubbing. What happens to all that growth that you scrub off your hull? It falls right into your line of sight! To keep this from becoming too inhibitive, I frequently switch from port to starboard to let what I’ve just taken off settle. There’s no real science to this other than your judgement. If you can’t see because the water is too cloudy, head to the other side.

Use your buoyancy to your benefit

If you’ve ever tried to clean your boat underwater before, you may have noticed that you consistently float up, even when you’re down at the base of the keel, and this can get rather annoying. To use this to your benefit, start by diving down and then scrubbing as you come up instead of just scrubbing at random or on your way down. After I made this adjustment I felt so much more productive with each breath I held underwater.

Weather and time of day matters

Your job underwater will be so much easier when you can actually see what you are doing. Not to mention it will help you make sure you’ve done the job properly too. Start as close to mid-day as possible and your visibility will improve drastically. I would not recommend doing this job on a cloudy day (unless you’re in trouble with the first thing mentioned – frequency!) if it can be avoided. If you’re in an area with a strong current, cleaning your boat underwater may be a lot easier during a slack tide so you are not fighting the current to stay nearby.

Some other things to keep in mind when you clean your boat underwater

  • Always, always, always check your zinc’s when you clean your boat underwater. This is the best way to detect any issues that you may have with electrolysis and prevent any bigger issues from coming up. If they need to be replaced, this is not the time to cheap out. Maintain your boat and buy new zincs.
  • Depending on where your boat is located, having a dive flag may be necessary.
  • Try to tackle the toughest parts first. You’ll be grateful you did.

Good luck underwater!

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