Using your R/C Boat on salt water
Special care should be taken if you run your R/C model boat in salt water. At the end of the day's activities, wash the hull and all metallic parts with plenty of fresh water and neutral soap. Protect the carb inlet and use a lot of water. If you have access to a air compressor, use it, if not use rags and brushes. Remove the flex cable, prop shaft, prop and all other removable parts, grease everything in the drive system with nautical grease. Take off the radio box lid, check for humidity on the electronics and dry it carefully. Leave the box open to evaporate any remaining moisture. Now, apply spray oil to all metallic parts you can see and even on that ones you can't see but you know are there. Don't forget to oil the rudder pivot.
With proper care and knowing that all our boats use stainless steel, aluminum and brass hardware, your boat is well protected. By the way, when assembling a engine we substitute all the original steel screws with stainless steel ones. It takes roughly 40 screws and insures much better durability.
Before putting your boat on water
Check the tightness of all screws, mainly the ones that mount the engine, the rudders and propeller. On sail boats check, specifically, the mast and rudder screw. The worst enemy of your electronics is water, mainly salt water. It's just impossible to make a completely sealed radio box - too many holes for antenna, accelerator and rudder cables/rods, wires, etc. Make those holes with the small diameter possible; close with silicone when possible. For the ones where this is not possible - rudder and carburetor cables, use rubber boots for protection. Keep the receiver inside plastic bags - make a small hole for the antenna wire and close the bag - including the small hole - with plastic straps.
It is of utmost importance that your boat floats when - and this will happen sooner or later - it turns upside down on the water. Either from aggressive driving or because you faced a big wave or too strong a wind. Sooner or later you will be on the shore, looking at a boat that, hopefully, floats with the bottom end up. The best, cheapest and most effective floatation you can use is an empty plastic soda bottle. Take the cap off, squeeze the bottle and insert as many as you can under the bow. Blow them to their original shape and securely tighten the cap. More over, and as this trick can only be used at the bow, and to prevent your boat to become a buoy when submersed, fix to the hull's open portion as many pools noodles as you can.
Getting rid of ingested water
It happened. Your boat is upside down in the middle of the lake. Of course it was not your fault... But the important thing to know is what to do. As you followed the above tip about flotation ' I hope - your boat will be (hopefully) floating and not sunken. After using all your stock of bad words, it's time to recover your boat and fix the damage:
Empty the gas tank and fuel lines. Take off the spark plug, flip the engine over. Let the water drain. Spray a lot of WD-40 into the spark plug hole and into the carb bore. Connect the ignition coil to the spark plug. Ground it, otherwise your can damage your coil. Pull the starter many times. While there is a brown liquid going out from the hole, there is water inside. More WD-40, more pulls of the starter. When only oil comes out, put the spark plug in place, fill the gas tank with new fuel and start the engine. You must use some kind of refrigeration to cool the engine. See below how to make one. Start the engine a few times, to be sure everything is OK. It is a good idea to take your engine out of the boat and disassemble, dry, clean and oil the starter. The return coil has a bad habit of rusting with water. Take off the plug again. Fill the cylinder with the same oil you mix to gas. Pull the starter slowly. Let the oil go down to the case. The next time you start the engine, you will need to get rid of the excess oil in the case. At that time, take the plug off, put the engine upside down and pull the starter until the excess oil has came out. About the electronics, look below how to repair a wet receiver.
Note: About grounding the spark plug, lets see what my friend William has to say: "If you pull start your engine without grounding the spark plug you will have, at the plug's terminal, an infinite resistance. Without a path to discharge the spark, the high voltage generated at the coil will try to jump trough the coil wires, destroying the isolation and the coil"
Running the engine out of water
Although the final adjustment of the engine just can be done with the boat on water, during normal use, the first adjustments are always made out of water. This requires some sort of cooling, without cooling the engine will overheat with possible damage to it. A cheap and efficient system cam be made at marginal expense using a plastic soda bottle, a few feet of aquarium line, a plastic valve also used on aquariums and a piece of wire. Make a hole in the bottle's cap and epoxy the line in the cap, so the tip of the line barely passes the bottle's neck. Insert the other end of the line onto the valve. On the valve outlet fasten a 5 inch piece of the plastic line. Make a hole on the bottle's bottom, that will double as a ventilation and filling device and also as a support for the wire, that should be bent in a hook fashion. When out of water, fill the bottle with water by the bottom hole, closing the valve. Hang the bottle anywhere higher than your boat, take off one of the original water inlet lines at the water jacket and insert the line from the plastic valve. Open the valve and adjust the water flow, to maintain the normal operating temperature for the running engine - that is, the water jacket should be warm but not so warm that cannot be touched with your bare hands. Presto: you have all the time you need to adjust your engine. REMEMBER: When out of water the engine reaches higher RPM's than recommended. Take care with the accelerator under these circumstances. The prop shaft's thrust washers and bushings are lubricated and cooled by water when the boat is moving. Don't run the engine more than 2 minutes out of water.