On a boat, the time would be shorter before failure. Whether you are in a fresh water or saltwater environment is another key factor. If an amplifier were to be splashed with salt water, turn it off and rinse it with cold, preferably distilled water. Once fully dry, the amplifier will be fine, unless salt residue has remained on circuit components. Salt water is a conductor and mineralized spring water can also conduct electrical currents. Distilled water is the most benign. Therefore, always ensure that wiring bundles drop below the chassis of the gear you are installing rather than running up and over the component. This will act as a drip loop, leading errant water and condensation that could collect on the wiring's insulation away from the chassis of the component.
Electrical effects:The electrical system in a boat is quite similar to a car in that anything over a certain size will have an alternator and battery to supply and store energy rather than a magneto. The first consideration is the amount of current you intend to draw. Keep within the limits of the charging system or plan on alternate energy. There is a good chance your boat will be docked or beached as you party with the music playing and the engine off. This means you are drawing directly from the battery and you can start the clock on how long until you no longer have enough power to start the boat.
An alternate battery system is a mainstream approach for a boat, where in a car the preferred approach is to upgrade the charging system via the alternator(s). Positioning the additional batteries will require that you consider keeping the center of gravity low to reduce messing up the balance of the craft. It is also critical to maintain proper ventilation of the explosive gasses produced by the battery's chemical reaction. Using sealed technology or "gel-cells" is another common solution.
Secondly, most boats do not have a chassis ground. I suspect "hull ground" would be a better term, but the key problem is that most hulls are non-conductive. Wood and fiberglass boats will need to have negative wires returning back to the negative post of the battery bank. The rules we use for determining the appropriate wire gauge in a car will be different because we simply assume that the car's metal body and chassis can be considered a far better conductor than installing a dedicated ground wire. Now we need to calculate the resistance in both the positive and negative conductors to determine the required wire gauge, while also factoring in the greater lengths than we normally encounter in the car. At least we don't need to worry about ground loops, right? Well
Also, don't look at the engine compartment of a sport boat as a suitable location for gear. Although there is a lot more free space in a boat's engine bay in comparison to a car, the same rule applies. The engine bay is no place for electronics, unless it is a yacht with an engine room you can walk into.
Noise interference is another challenge. Since the hull of any small- to medium-sized boat is either aluminum, wood or fiberglass, there is no natural ability to shield or block electrical interference. For that you would need a steel hull where the iron content acts as the noise shield. As a result, if you install the head unit or amplifiers (or speakers for that matter) near a current-carrying wire, the electrical field produced around the wire will infect the gear and sensitive signal cables. Any other electronic gear can also introduce problems, since they will produce either electromagnetic, radio frequency or pulse interference. Maintain an adequate distance away from electrical components and radio and navigation gear or you can expect a variety of hard-to-eliminate noises.
Where you do want to pick up RF radiation is in the tuner section. Receiving broadcast radio or TV stations requires a different antenna than in a car. For radio, the car will use what is called a "dipole" antenna, using a 39" antenna mast balanced with the metal body of the vehicle. This forms one of the simplest antennas available-if you have metal to use. Mounting an automotive antenna on a non-metallic boat will leave you without half of the dipole. In addition, the metal under the antenna in a car forms a "ground plane" which acts as a reflector to intensify the signal at the mast.
I have seen situations in which installing a ground wire to any part in electrical contact with the water will result in making the lake a ground plane, resulting in excellent radio reception. But don't consider this the magic bullet-compared to your car parked at the dock, a boat will probably have much better reception, but if your boat is farther away from the station, the signal strength can only drop. We often don't consider the increased distance from the broadcasting station, but it is an important source of problems. If your receiver has a choice between a fragile signal traveling from miles away and the noise-generating components on the same hull, which do you think will win?
Here is where satellite radio is a clear advantage, since the broadcast source is directly overhead regardless of where you are on the open water. Also, a satellite radio antenna will work well without a ground plane although it will need to be fixed in place since the mounting magnet won't grab a boat. Here is where a marine or residential antenna will excel.