Bearh- You're sure right about there not being much info around about grounding issues, especially regarding plastic tanks. Perhaps some of the reluctance to put anything in writing is due to the consideration of liability for any erroneous information that might be construed as contributory to any subsequent disaster. (Pat Anderson could comment here on the legal issues).
The above having been said, let me say forthwith, that this is my reasoned opinion for your consideration and should not be taken as necessary final truth or any recommended plan of action.
I may be wrong, but I'm going to give you my thoughts on this subject, as I feel the thinking on this issue is bordering on having a touch of hysteria(!).
To begin with, we all know that the grounding of the tanks as well as the gas delivery nozzle is done to prevent the build up of static electrical charges in the tanks and the delivery system, such that similarly grounded components will have no charge relative to each other and no spark will occur setting off the dreaded explosion and/or fire. The grounding system in the boat works two ways, first to keep the tank grounded at all times, and, secondly, is especially important when filling of the tank(s) takes place, as the transfer to fuel is considered to be a operation that can generate a static charge.
The delivery nozzle is grounded through the wire in the hose to the electrical ground in the pump system and electrical supply. This is understood and accepted.
The gas tank and fuel system in the boat are all grounded together and to the boat's ground system, including motor, drive mechanism, and electrical and electronic components. If this fuel supply system is all metal, the chances that the grounding system will do it's job are generally felt to be very good. The great questions arise when using plastic tanks (and Neoprene hoses).
Typically, the ground system on plastic tanks connects the deck fills, top rings around the tank inlets, and fuel tank level sender units to the boat's ground system. This is just about all that can be done reasonably without adding special grounding plates , and apparently is considered adequate. I have seen some commercial specifications for this for very large storage tanks (on land) that have a surface area to gallonage ratio specified, but never on a boat related basis. We'll have to assume the standard connection/grounding set up is adequate, and in practice it must be or the number of fires and explosions would dictate a change in the status quo.
Now think about the filling process. If you wanted to minimize the danger, what procedures would you take? The boat and the delivery nozzle should be without differential charge when we begin fueling. To be sure, touch the nozzle to some other grounded part of the boat other than the deck fill, or to the deck fill before opening the screw cap. As an added precaution, be sure the motor and all electrical units are off. Most important: Be sure the nozzle stays in contact with the metal components in the deck fill (some boats have fills made of plastic with metal inserts) throughout the filling process to insure the ground in the nozzle will pick up and drain off any developing charge as the tank(s) is/are filled.
That's about it, what else can be done? Call Dave S and have him stand by with the fire boat? The fact that we don't have more problems in this area indicates that the grounding systems currently employed work. My guess is that most gasoline fires on boats come from faulty lines, leaky carburetors, and inadequate blower usage (on inboard boats).
Gas sloshing around in plastic tanks is probably not an issue, since the gas and vapors are in a closed system and are grounded and self-neutralizing.
Filling a tank by hand from a portable tank of some sort is probably not an issue if both are plastic, or if a siphon (slow transfer) is used. A rapid fill from a metal can to a plastic reciever could result in a charged transfer. Connect a ground wire from the metal can to the gas tank ground for safety's sake.
I'm sure there are more possibilities, but we can discuss them as they arise. Hope this helps us all think this through! Joe.
