At 11:14 AM 8/17/98 +1200, Stephen C. Darden wrote: >To recap, we are seeking advice on design/components of the diesel fuel >system for the 52-ft cat we are building. > >We have 4 diesel tanks feeding an 8-hour daytank via the filter manifold. >All 3 engines are feed from the daytank directly, with returns all to the >daytank only. Therefore the fuel pump, filters and daytank are the common >failure mode for propulsion, AC and DC power. [big snip] >Any suggestions on either issue would sure be appreciated! Boy, does this sound familiar. We are building a triple engine cat just a little larger, with a day tank and several bulk tanks, too. You are working some of the same fuel concerns that I'm working. While my design is still a bit flexible, perhaps I can provide a little snapshot into my thinking at this point. I will have eight bulk tanks down near the keels, with four to nine feet of head pressure to the tank in the bridge deck. I will have a ninth bulk tank plus the day tank in the bridge deck. All this adds up to about 4500 gallons of diesel fuel, and then I will have another tank in the bridge deck for about 350 gallons of gasoline. That is generally separate from the diesel system, but can be used for additional diesel fuel when I have no need for gasoline. It will be connected to the keel tanks with a pipe and a valve, so it will be easy to get the diesel from it into the rest of the system, when it is used for diesel instead of gasoline. The one bulk diesel tank in the bridge deck is key to everything. It will have the one and only fill port for the entire diesel system, as well as the only external air vent. It will be the only place where I can pump diesel fuel into my boat. Fuel will drain from it to the keel tanks, with valves to shut the flow off to each keel tank when desired. Vents from all the keel tanks will also be plumbed to the vent for the bridge deck bulk tank, so that I will have only one vent to put a desiccant filter onto. That will prevent moisture and condensation from entering my fuel system. When I buy fuel, I will open all the drain valves and fill all the tanks at the same time--except the day tank, which can only be filled by transferring from the bulk tank in the bridge deck. I will then shut the valves to isolate the tanks. I do not like the idea of sucking fuel out of the lower tanks. I know that I can find pumps that can handle the head pressure and maintain a prime, but they will be less effective and less reliable than if the pumps were installed down low, and then used to push the fuel rather than to pull it up hill. My plans are to install one pump for each two bulk tanks in the hulls, and to mount them down low so that they do not have to draw the fuel out of the tanks. They will be very small pumps, because I really do not care how long it takes to pump the fuel out of the bulk tanks down below. My plans are to install a fuel polishing system onto the bulk tank that is in the bridge deck. It will have a GCF #F-1 fuel filter on it, with a small pump to circulate the fuel more or less continuously. By switching valves, the same pump will be used to transfer to the day tank. I do not like float type valves or sensors at all, and do not plan to install any of them any place on this boat; but all tanks will have a site glass on them. We will also have to develop a routine of topping off the day tank once per watch. Since the day tank actually holds enough fuel for three days of normal operations, I have plenty of reserve in case mechanical or other problems prevents us from topping off the day tank for several watches. The vent for the day tank is also plumbed back to the common vent for all the bulk tanks. I will have an overflow line from the day tank back to the bridge deck bulk tank, in case we let the transfer pump run too long. That line will have a check valve to prevent fuel from flowing in the opposite direction, or perhaps I will be able to put a riser in that line instead of a check valve. Since the fuel in the day tank will always be very clean and dry, I will put nominal filters onto each engine--perhaps a GCF O-1JR for each engine. Nothing more should be required. The day tank will also be very easy to pull the lid off of for cleaning. I want that part of my fuel supply to be extremely clean. I have had troubles before when I run more than one engine off the same day tank, with all the returns also plumbed back to the same tank. The problem is that the fuel can get to be VERY hot. Lets face it, the whole purpose of that return fuel is to lubricant and to carry the heat away from the injectors. I have not decided how to handle this yet, but will probably build the system such that it would be very easy to add a cooler to the return line; and then try it and see if I need the cooler. I know that it is very difficult to find a 12 or 24 VDC fuel pump, which the manufacturer is willing to rate for continuous duty. In fact, I have never found one; but I am hopeful. I know an engineer who is doing a serious market search for one right now for a solar powered fuel polishing system that he is building for an industrial application. I'm sort of waiting to see what he will come up with; but most likely I will do as I have always done before, and buy something off the shelf at my local truck parts store. They will be cheap enough to carry several spares, and they will last long enough so that I do not have to change them out often. The bulk tank on the bridge deck is almost exactly the same size as the day tank, to give you an idea of comparisons. I have already explained how I plan to protect the day tank from over filling, and will do something similar to the bridge deck bulk tank. If I overfill that tank, the surplus will drain back down into the lower bulk tanks. I hope that I have been able to shed some light onto your situation, but feel free to ask additional questions. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ :: Paul and Cindy Kruse :: KJV Joh 14:27 Peace I leave with you, 165 South Kenneth Court :: my peace I give unto you: Merritt Island, FL 32952 :: not as the world giveth, give I unto you. E-mail: plkruse@iu.net :: Let not your heart be troubled, 407-453-6206 :: neither let it be afraid. :: +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++