I am currently restoring a 1972 Sea Ray 190 with a Mercruiser 165 sterndrive. I thought this would make a good subject for some articles on the importance of using marine equipment as opposed to automotive. Many people have asked me that question over the years, and it needs restating from time to time that there is a significant difference between marine and auto from a safety stand point.
First the boat. You can follow this at my web site http://newboatbuilders.com/pages/SeaRay190.html.
One of the things I discovered was the previous owners had not been very careful about maintaining the boat and keeping it up to current standards. Cases in point: Alternator and Distributor, Overcurrent protection.
Here are the alternator and distributor that were on the engine.
Neither of the above are ignition protected. Both are automotive parts. Yes, marine costs more but if you don't use marine you are risking your life.
Marine alternators usually use flame screens, or they are hermetically sealed. The screen on the back of this alternator act as a flame arrester. If fumes enter the alternator, and are ignited then the screen cools the flame front and fumes outside the alternator are not ignited. This is the same principal as the flame arrester on the carburetor and the flame screens in the fuel tank vent.
The distributor in the second picture at the top, has a vacuum advance on it. That immediately brands it as automotive. Marine engine distributors do not use vacuum advance. Marine engines have a much heavier duty cycle than auto engines, and are constantly under a much heavier load. The distributors are set up for this duty cycle. Also they are ignition protected. The gold circle on the distributor above is a flame screen. See Ignition protection http://newboatbuilders.com/pages/elect.html#Ignition Protection
Another requirement that is just as important, is overcurrent protection; fuses or circuit breakers. Small boats like mine usually have fuses. Bigger boats that have very complex electrical systems usually have circuit breakers.
Why overcurrent protection? Most boat fires are electrical in origin, and one of the most common causes is a wire getting too hot, melting, and setting the boat on fire. Overcurrent protection is there to protect the wire. If there is too much current in the wire the fuse blows and stops the overheating.
So to protect the wire the protection is required to be within seven inches of the power source, unless the wire is in a sheath, then it can be 40 inches. There are some instances when it may be 72 inches away. See overcurrent protection http://newboatbuilders.com/pages/elect_a.html#Over Current Protection
This boat has overcurrent protection, but is at the instrument console, way to far away. The wires from the battery to the instrument console are not protected. So I am installing a battery switch and a fuse block. These will be very close to the battery.
As an aside, the battery was not fastened down. Batteries are supposed to be fasten down so they can't move. One way to do this is use a strap to hold the battery in place. But I chose to use a battery box which is fastened down. This also provides protection from an acid spill.
Here is a link to a typical wiring diagram for a small motorboat. !4 Steps to Wiring Your Boat. http://newboatbuilders.com/pages/electricity13.html