How To Keep Your Boat's Bottom Clean

Keeping your boat well-maintained below the waterline starts in the boat yard, with good prep work and a high-quality antifouling bottom paint, properly applied. Once in the water, periodic dive service by a reputable hull cleaner can clean away the marine growth that the antifouling can’t resist, and keeps the paint working properly. A good diver is also invaluable for inspecting the bottom and running gear for problems, replacing zinc anodes when needed, and keeping you up to date on the condition of your boat below the waterline.

There’s no doubt that good paint and a good diver are paramount to a good bottom, but there are also some simple things that you can do to keep your bottom in better shape between dive services and haul-outs. I spent over ten years as a hull diver and thousands of hull cleanings, and in that time I came up with 4 things that time and time again seem to make a noticeable difference in the amount of growth that a boat accumulates. The marinas in which I have worked generally have clear water, so much of the growth issue we see is algae growth fueled by sunlight. Bottom paints are generally very good at keeping off hard growth like barnacles and mussels, but the algae growth always finds a way to accumulate. These tips pertain specifically to boats kept in clearer water, but some will be useful to everyone.

Go Sailing or Cruising!

The easiest way to keep the bottom of your boat cleaner is to use your boat! Sailing or cruising in your boat gets it going through the water at speed, and even a little speed is sufficient to work off some of the algae slime and discourage other types of growth. While this speed is mandatory to allow certain bottom paints (namely ablatives) to shed growth properly, I have always seen frequent use provide solid improvement to bottoms with hard paints as well. Most marine organisms like to establish on surfaces that don’t move, so taking your boat out and working up some speed can discourage quite a bit of the growth that would otherwise love to colonize your bottom. I was always able to tell pretty quickly whether a boat got a lot of use or not, based on the growth I saw on the bottom. 

Alternate the way your tie up your boat

Maybe it’s the direction your boat faces, or maybe it’s tied up closer to one side of the slip than the other. Most boats get more sunlight exposure on one side of the bottom versus the other, and that lighter side generally sees more growth. Likewise, if you have your boat cleaned periodically by a diver, that lighter side eventually gets more wear and tear from the cleaning of that extra growth. I have had some clients who always tie their boat the same way, and get lots of light on one side while the other side gets little. After a couple of years, one side of the bottom looks very tired, and accumulates substantial growth between services, while the other side still looks great and wipes clean easily every cleaning. By periodically changing the direction your boat faces, or tying your boat up to the opposite side of the slip, you can switch off which side of the hull is the “lighter” side, and more evenly distribute the sunlight, and therefore the growth and cleaning impact. This way you the bottom paint will age more evenly, and you can eliminate “problem areas” forming that will attract growth faster than the rest of the bottom. 

Gently brush the waterline and rudder if needed 

Because sunlight spurs algae growth like no other force, it’s the areas that get direct sunlight that growth the fastest and most abundant algae. Thankfully though, these are also the areas that you can generally see and have access to from the dock. The areas in question are generally the waterline and the rudder on a sailboat, and the hull sides / waterline and transom on a powerboat. These are the areas that will likely grow the dreaded “beard”, especially during the summer months. Should growth dis-proportionally accumulate in these areas, a gentle brushing with a soft deck brush should do the trick. While I would recommend against doing this to ablative paint, as even a soft brush can too easily remove paint, hard antifouling should withstand some brushing well with no problems. Even so, be watchful of color (paint) coming off while you scrub, and ease up if this occurs. It’s great to get rid of the beard, but you don’t want to prematurely wear out your paint doing so. While this only takes care of the high-growth areas, it can allow the rest of the bottom that sees slower growth to “catch up” to the high-growth areas before a full cleaning is necessary.

Shade your rudder, trim tabs, and outdrive

This can make a huge difference for small sailboats or power boats that have rudders or trim tabs that attach to the transom of the boat. The problem with these fixtures is that they hang out from the back of the boat with full sun exposure at all times of the day. These areas grow algae like no other, and again, it’s the sunlight that drives this growth. If you can back your boat into the slip or otherwise provide shading for these parts, you can drastically slow down the algae growth. For a powerboat, a swim step can help quite a bit, but further benefit is possible. 


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