How To Clean Your Boat Hull to Remove Stains, so it Looks Like New Again

How To clean your boat hull so it looks new again.

Over time every fiberglass boat hull will become stained. The staining process will happen quicker if you ever use your boat in brackish water, around ocean inlets, or in stained waters found in many inland lakes and rivers. The tanic or tea colored water in all of these areas will cause  your boats hull to eventually become discolored. 

A cleaning of your boats hull will eventually have to happen on boats that do not have bottom paint. But even if you have bottom paint on your boat the area just above the bottom paint will eventually become discolored and stained as well. Those areas will take longer to discolor but eventually a cleaning may be needed to get it looking like new again.

How did this boats hull get so stained?

The picture above is after 6 years of use in the ocean waters around South Florida. Most of which was from fishing in the clean water found over the third reef out to the far offshore areas for mahi and swordfish. Even though this boat was used 90% of the time in clean offshore water the boat still developed a nasty stained hull.

This boat was stored on a rack in a marina and was used mostly for offshore fishing. So how did it develop this type of stain?  Well traveling from the marina to the ocean inlet the boat had to pass through brackish water found in the intracoastal water ways. Then had to return back through these stained waters to get to the marina. If the boat had returned back to the marina late at night the boat would have to be tied up in a on the water slip for the night.  So the boat would sit in the water until the next morning. The marina workers would then come move the boats to the haulout slip. There a fork lift would lift the boat out of the water to put the boat back onto the storage rack. Before going to the rack the marina workers would also rinse off the hull and flush the motors.

Being that the inland waterways in South Florida eventually lead to the everglades, this allows the tea colored stained water from the everglades to travel down the canals to the ocean. Fresh water is lighter than salt water so the tea colored water tends to sit higher near the surface. With the boat traveling through these stained waters to and from the ocean, and often staying in the stained waters over night a deeply stained hull developed.

So what is the best boat hull cleaning product to remove these stains?

After using all kinds of different products I have found the product called On & Off Hull and Bottom Cleaner for Fiberglass to work the best to remove these types of nasty stains from boat hulls. It works fairly quick, isn’t very labor intensive, and the results last a long time.

On & Off Hull and Bottom Cleaner for Fiberglass and Gel Coat

On and Off really does do the best job that I have found for removing tough waterline stains, algae stains, barnacle stains, rust, and exhaust stains. It is pretty strong so you want to take precautions using it as it can cause skin burns and eye irritation. May cause respiratory tract irritation, and vapors while using it can be harmful. Read the entire label before use. You may see all of the bottles precautions and warnings at the bottom of this post as well.

On & Off hull and bottom cleaner can be a dangerous product to use, but I personally have never had any of the warning items listed happen to me. But still take all product label recommended precautions and always have a garden hose turned on and ready while using this in case you experience any of the dangers listed on the warnings.

Step #1 in cleaning your boats hull stains, put the boat on a work rack, or prep the boats trailer to do it on the trailer.

If you have the boat in rack storage like the boat in this example, have the marina move the boat to a work rack or have them place the boat onto work pedestals and blocks.

If your boat is on a trailer you can clean it on the trailer only after taking some precautions to protect the trailer. You will need to place plastic over the aluminum  and steel areas of the trailer. You can do this by using painters drop plastic. Just make sure that you overlap any of the plastic seams where two sections might come together and tape the seams if necessary. 

Most painted surfaces will not be affected by On and Off boat hull and bottom cleaner. But if doing the hull cleaning while the boat is on a trailer I recommend covering as much of the trailer as possible anyway with plastic even if it is a painted trailer.

Step #2 Setup a 5 gallon bucket, a Deck Brush, and a bottle of On and Off hull and bottom cleaner

What I like to do is take a 5 gallon bucket and put about two gallons of water into the bucket from a hose. Then dump about 1/3 of the 1 quart bottle of ON and OFF into the bucket. Then add 5 seconds of hose water into the bucket to get everything mixed well and a little sudsy. The suds help to hold onto the hull a little longer. The longer they hold onto the hull before dripping off the better it works.

The directions found on the label of ON and OFF call for using the cleaner directly with no extra water. I have found that using the direct cleaner does work faster and more complete the first time. But using it with a little water allows me to brush the product all over the hull without worrying that I missed a spot. I’m able to coat the entire hull and hull sides with the water / ON and OFF solution several times to make sure I hit every spot. And I have more solution to move around on the hull so a bottle lasts a lot longer. A one quart bottle of On and Off did this entire hull with some left over.

Doing it this way I can also use a long deck brush instead of using a short handled paint brush as recommended by the manufacturer. This allows me to avoid being dripped on by the solution and keeps this product as far away from me as possible while working with it.

Step #3 use the deck brush to coat the hull with the ON and OFF hull cleaner solution

I use a 10″ Shurhold Polystyrene medium (Yellow) bristle deck brush and brush pole to rub the ON and OFF hull cleaner solution from the bucket onto the hull of the boat. Again this allows me to be far away from the cleaning solution, unlike using the recommended way from manufacturing company of using a short handled paint brush. You do not need to touch every area with the deck brush but try to anyway. With this product gravity is your friend as it will pull the cleaning solution down the hull to those hard to reach areas. As long as the hull is wet with the solution it will work.

Cover the entire hull with the cleaning solution by basically scrubbing the hull with the deck brush. Once you have covered the entire area at least a foot above the water line all the way down to the keel do it again while still wet from the first coat. Starting from the top down to double coat it. As you do it a second time you will see areas that the cleaner didn’t get or didn’t get enough on. So go back over these areas extra well if you see them. 

Having the ON and OFF mixed with water allows you to cover the boats hull several times before having to add more water and ON and OFF from the bottle.

Step #4 Rinse off the boat hull sides and bottom thoroughly with a hose

After scrubing the hull at least twice to start, let the ON and OFF solution sit on the hull for about 5 to 10 more minutes to work. Then take your hose and rinse off the entire hull sides and bottom thoroughly. You may notice areas that have not gotten any hull cleaner on them, or areas that have clean streaks through the stained parts. This is normal, as it is hard to get all areas 100% clean on your first passes.

Step #5 Reapply to areas that have not cleaned entirely or did not get any solution contact the first time

After rinsing the hull you will see areas that are still stained. Simply take the deck brush onto these areas again. You may have to add more water and ON and OFF solution into your bucket to do another coat of cleaner onto the hull.

You may also need to use a long handled paint brush to now reach some of the hard to reach tight areas. Such as in the recesses for trim tabs, around the boat trailer bunks or rollers, or around the blocks the boat is on if on a work rack, along with to access around the engine or engines.

Let sit for a few minutes and look for areas that still may be stained. Reapply to any areas that need it until you see no stained areas left.

Step #6 Clean the hull, all items used in washing the hull, and your clothing, along with take a shower

After you no longer see any stained areas left and you are satisfied with your job, clean the hull and all surrounding areas thoroughly with a hose. Clean the bucket, deck brush, and any long handled paint brushes that may have been used thoroughly with water.

Along with clean / launder any clothes you were wearing, shoes etc, and take a shower. This stuff isn’t anything you want sitting on you for any length of time.

Above: Before and After pictures of the port side hull after using Mary Kate Hull & Bottom Cleaner for Fiberglass boats on this 244 Bluewater Key West center console Boat

Before and After pictures of the stern area between the twin engines on this 244 Key West. You can see that the ON and OFF hull and bottom cleaner did an amazing job bringing this boat back to like new condition.

Port Stern area on the boat before using the On and Off hull cleaner, this is while the boat was being moved on the fork lift to the work rack.

Port Stern area on the boat After using the On and Off hull cleaner, this is while the boat was on the work rack / pedestals.

Now you know how to clean your boats hull so it looks like new again.

This information will also work on any other fiberglass part of your boat. So it is not limited to just the hull and bottom of your boat. I’ve used this with great success removing rust stains, cleaning stains out of deck lockers, and more. Just remember to protect any metal surface near where you are using this product especially if the metal is not painted.

Below is a picture of the back of the On and Off bottle showing the directions, safety information, and more for On and Off Hull and bottom cleaner bottle. Written text of what is found on the label is below the picture as well.

Mary Kate On and OFF Hull and Bottom Cleaner Directions and Precautions Listed On the Bottle

 Below is the information written on the back of the On and Off hull and bottom cleaner bottle:

 The #1 hull cleaner and strongest formula available. MARYKATE ON & OFF HULL & BOTTOM CLEANER works instantly to clean and remove the toughest waterline stains, barnacle & algae stains, and rust & exhaust stains. Easy to apply – Just brush it ON and rinse it OFF! Will not harm gelcoat. For use on fiberglass only. Not for use on metals or painted surfaces. Protect metal surfaces from vapors.

 DIRECTIONS: Read entire label before using this product.
Eye protection and protective clothing must be worn when using this product. Test on a small area prior to use on painted surfaces.

Protect boat trailers with a plastic (polyethylene) cover when using ON & OFF. Pour contents into a bucket or other plastic container. Apply full strength with a natural bristle brush, the hose off or rinse with water. Collect and dispose of rinsate in accordance with local, state and federal laws and regulations.

To remove rust stains: Apply directly to stain with natural bristle paint brush. Wait approximately 60 seconds, then rinse off. If rust is heavily embedded, reapply.

 WARNING: Contains water 7732-18-5, hydrochloric acid 7647-01-0, phosphoric acid 7664-38-2, ethoxylated alcohols 68131-39-5 and oxalic acid 144-62-7. Do not get in eyes, on skin, or on clothing. Can cause skin burns and corneal damage. Do not breathe vapor. Use outside or in area with adequate ventilation. Do not enter where vapors are suspected in high concentrations. Inhalation may cause irritation to respiratory tract. Wear rubber gloves, protective clothing and eye protection. Wash thoroughly after handling. Keep container closed. Store upright between 32 degrees F and 100 degrees F. For small spills, use absorbent and sweep into closed containers for disposal. For larger spills, neutralize with sodium carbonate or absorb on fire retardant material. Use proper protective equipment. Take precautions as necessary to prevent contamination of ground or surface water.

FIRST AID: If swallowed, rinse mouth. DO NOT induce vomiting. In case of eye or skin contact, flush with water for at least 15 minutes. Call a physician immediately. Remove any contaminated clothing. If too much is breathed, remove to fresh air. Consult a physician if breathing becomes difficult or condition persists. For overexposure, call physician immediately. For additional information, consult SDS for this product.

 DISPOSAL: All used and unused product should be disposed of in conformance with local, state, and federal regulations. Do NOT dump in sewers, floor drains, on the ground or into any body of water.

 KEEP AWAY FROM CHILDEREN

 MARYKATE 

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