Adding extra fuel tanks

[ahein]

I have 225hp Volvo Penta I/O on my 24' boat and I would like to add a couple of 20-25 gallon saddle tanks to increase my range. I only have a 57 gal belly tank now, and by burning 12-15 gallons per hour, I have a limited range if I go by the old addage, 1/3 out, 1/3 in, and 1/3 for safety.<br />I would like to add the two new tanks under the pot and starboard gunnels and forward toward the cockpit to help balance the boat (there is a significant amount of weight in the stern now due to the V-8 I/O). The new tanks would be mounted above the top of the existing belly tank. My idea would be that the new tanks would drain into the belly tank using the force of gravity.<br />My question(s) are should I use shutoff valves on the drain lines to the belly tank, and does anyone foresee any problems with this idea? I read somewhere on one of these posts that the fuel would not drain evenly from the two exta tanks into the belly tank. Is this true? <br />Any thoughts (good or bad) on this proposal will be appreciated.

 

[bob58]

Re: Adding extra fuel tanks

I would tie the two new tanks together with a crossover hose. Put a tee inline to a three way valve (fuel crossover valve this could be manual or solenoid operated). Hook the existing line to the other port of the three way valve and the third port (main or common) of the valve would go to your motor. Install fuel shutoff valves at each tank outlet for safety and isolation incase of hose rupture. <br />The problem with tieing the new tanks into the belly tank is the added head pressure of the new tanks full of fuel (1/2 psi. per foot of elevation) on the existing tank would be increasing the possibility of fuel leakage into the bilge, or if you have a vent line on the fuel fill side of your tank you could end up dumping fuel overboard through the vent.

 

[sloopy]

Re: Adding extra fuel tanks

NO DO not have the tanks drain into the one big tank! BIG MISTAKE! Lets say you brought contaminated fuel from XX gas station and poured it into tank 2, then you got good fuel from x gas station and filled up tank 1, when you head out on the water you start with tank 2 and your engine begins to act funny, you quickly switch tanks and add throttle to get burn the bad fuel off, DAY SAVED! If all drained into one you would be stuck.<br /><br />I would add two 32 gallon tempo plastic tanks.

 

[18rabbit]

Re: Adding extra fuel tanks

We just did a 200-gal fuel system re-design for our boat. I am presuming you want a permanent fuel tank installation. Here are a couple things I learned that might help.<br /><br />1- ALL fuel tanks are required to drain from the top with a metal fitting. No way for a crossover to function, as it would have to drain low on the side or bottom to do so. The reason is fuel line is flexible and easily compromised. Any rupture in the line and fuel is pouring, gravity fed, into your boat. Any onboard fire, the line is the first thing to burn thru and the fire is quickly being gravity fed with fuel.<br /><br />2- All of the weight in your boat “wants” to be centered and low. Obviously, it isn’t, like the engine in the stern, but keep working with this in mind. Stability is NOT achieved by even distribution of weight. It is achieved by keeping it centered and low. Adding 50-gal of fuel is adding 400+ lbs of weight. It will make a huge difference in the stability and ride of your vessel. Getting the extra weight where it needs to be will make you much happier.<br /><br />Is there any way at all that you can get an aux tank somewhere down in the center of the boat? Custom-made aluminum tanks are a one-time expense and probably not as expensive as you think. If you go this route, you will want to have the tank built by someone that does marine fuel tanks, specifically. There are some other technical issues required by the USCG that they will know about and incorporate into the tank. They also understand the needs for internal baffling.<br /><br />3- Multiple tanks means fuel use between the tanks cannot be even due to the motion of the ocean. As soon as there is significant consumption from one of the tanks, you will start to list and continue to run alist until all tanks are either emptied or filled. Fuel is not going to run up-hill into the tank with the least fuel in it. This being the other reason crossovers don’t work. It will guarantee one of the two aux tanks is kept full until the other is empty.

 

[ahein]

Re: Adding extra fuel tanks

All of you that have responded have brought up some great points to consider. I have already begun re-designing the auxilary fuel system. However, some of your comments have created new questions.<br /> 1. If I keep the outlets on the top of the tanks as suggested by 18rabbit, how do I move the fuel to the engine without utilizing some elaborate pump/valve switching system?<br /> 2. Can I tie the auxilary tank feed lines into the main tank line using a three-way manifold and use the engine fuel pump to move the fuel to the motor? There doesn't appear to be anywhere I can mount the permanent auxilary tanks "centered and low", as suggested. The tops of the auxilary tanks would be approximately 20-24 inches above the fuel pump. <br /> 3. I plan on using braided stainless steel fuel lines from my auxilary tanks, as well as from the main tank, to the engine. Based on your suggestions, I will also put ball valves (shut-offs) immediately after each tank for isolation in case of bad fuel or fire. Comments or suggestions?<br />My plan is to open the two auxilary tank valves and burn that fuel first, then open the main tank valve if more fuel is needed. If I open both aux. valves at the same time, the fuel should burn evenly from the two tanks, eliminating the listing problem. Am I correct in this assumption? I have trim tabs to correct any slight listing, by the way. I'm probably going to have the aux. tanks fabricated by Florida Marine Tanks. They can give me pretty much any design I need while insuring that the tanks are up to USCG standards.<br />Again, I appreciate any comments or suggestions anyone would like to make. I have found this forum to be the best of any I have visited to get excellent, straight-forward answers to all of my boating questions. The people who participate in this forum are the best! <br />(By the way, Sloopy, how did you get the designation of "Dock Boy"?)

 

[18rabbit]

Re: Adding extra fuel tanks

Ahein – you are on the right track! Talk to the folks at FL Marine Tanks and ask for advice. They will have oodles of first hand experience with what works and what doesn’t and why. They should be able to suggest an aux tank config that will work for you. Please let us know what you decided on when you finally work out the design.<br /><br />The answer to your 1st question is in your 2nd question – your engine’s fuel pump. Ever see those squeeze balls on portable fuel tanks? They are there to start the flow; the engine pulls the fuel after started.<br /><br />The USCG requirement that all fuel tanks drain from the top impresses me as a good idea with potentially bad real-world applications. All tanks need to have a tube inside to pull fuel from the bottom of the tank. From the fuel pump back to the bottom of the fuel tank is an air-tight line. My fuel line drapes down thru the bilge area and back up into the engine. If the fuel line is compromised low, or if there is a fire in the engine room, the fuel line is a ready-made siphon, in place to feed the flames.<br /><br />I have never seen braided steel fuel line used. You do not need it. Today, fuel line is good stuff. USCG has requirements there, as well. You must use the USCG approved gray hose (type B) if in an open boat, exposed to uv; the black hose (type A) if enclosed. (I think I got those right ) Metal fuel tanks, any metal in the fuel line, all of it needs to be grounded.

 

[Bondo]

Re: Adding extra fuel tanks

The USCG requirement that all fuel tanks drain from the top impresses me as a good idea with potentially bad real-world applications. All tanks need to have a tube inside to pull fuel from the bottom of the tank. From the fuel pump back to the bottom of the fuel tank is an air-tight line. My fuel line drapes down thru the bilge area and back up into the engine. If the fuel line is compromised low, or if there is a fire in the engine room, the fuel line is a ready-made siphon, in place to feed the flames.

That's Why tanks have the USCG Spring Loaded Check-Valve Mounted at the tank outlet Elbow.....( aka; the Anti-Siphon Valve)<br />That little fitting is More than just a hose barb.....

 

[18rabbit]

Re: Adding extra fuel tanks

Bondo - My fuel tank does not have the spring-loaded anything. It is custom made, USCG approved for diesel fuel. Does that matter? If you know it to be required, I will go back to the folks that made the tank and get it fitted with whatever is needed. It does have a view glass. That requires valves placed at top and bottom. Actually, all 9 ports on the tank have a ball-type valve. Fill tube doesn't.

 

[Bondo]

Re: Adding extra fuel tanks

18rabbit,<br />Obviously I can't be Sure of Your installation.....<br />But, I'm willing to bet that the Hose Barb, At the top of the tank pickup tube, Will have an Anti-Siphon Valve built into it......<br />They Usually Look like a Standard Hose Barb....... The Differences are all Internal....<br />I Don't have the USCG Regs ava. But I'm pretty sure that Any Fuel Tank is Required to have the Anti-Siphon Valves....... <br /><br />The Simplest way to check is to Blow/Suck on the fuel line.... An Open line will have No Resistence(you'll Easily hear bubbles in the fuel tank), The Anti-Siphon Valve will Not allow you to Blow into the tank,+ Will require More Suction than you can provide with your mouth to Open.....