There are plenty of paint manufacturers who have come out with bottom paints for inflatable boats. The application is two step and starts with the application of a primer coat then followed with superior quality cuprous-oxide bottom paint.
The primer is called Hy-Grip and should be applied after the bottom has been thoroughly clean. First, wash the bottom with soap and water to strip the marine growth after which scrub the bottom with solvent on Hypalon boats and MEK (methyl ethyl ketone) on PVC boats. It is best that no trace of oxidation is evident on the bottom of the boat. To check, soak a clean rag in the solvent. Wipe the bottom of the boat with the clean rag. If no color shows up, then the boat's bottom is clean.
For new boats, you should remove all the surface plasticizers from the bottom fabric. Most plasticizers can be wiped off with a rag soaked in solvent. Some inflatable boats are tougher that you might have to use a stiff-bristled brush to scrub off the plasticizer. The Interlux #202 is very effective in removing silicones. You might want to consider using this to remove plasticizers, oxidized materials and silicone o the fabric's surface for ease in applying the primer.
Once you are 100% sure that the boat's bottom is clean, apply the Hy-Grip with a clean brush. The Hy-Grip is the material that will bond the paint with the boat's bottom. Any bottom paint will do but highly recommended is the Shipbottom Premium Performance antifouling paint. Look for a bottom paint that is hard-drying and flexible with high cuprous oxide content (about 62.5%). This type of bottom paint will last for seasons. The boat can also be easily stored without fear of flaking or cracking paints.
Make sure the paint line of the boat's bottom is above the waterline on a fully loaded boat. Mark the line to make sure. The bottom paint should be good for two seasons at least. The primer should last longer unless you don't take care of the boat.
RIBS should also be painted in the same process as that with any conventional fiberglass or aluminum boats but with the addition of painting the fiberglass or aluminum bottom with the appropriate primer. Note that the side and stern tubes are in the water when the RIB is docked.
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