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Old 18-06-2010, 21:06   #16
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Why not have someone put together a device to check the conductivity of the bilge pump discharge.

If the conductivity is low, it shoudln't go overboard. If it's high, it might be OK. If you have a catastrophic tank leak into the bilge, the conductivity of diesel is fuctionaly 0, and thus the pump should shut off.

It could be as simple as just putting an open circuit for the ground of the bilge pump in the bilge pump intake. As long as the pump is picking up water, it should provide enough conductivity to pump the open circuit, and keep the pump going.

As soon as it starts sucking up nealy 100% diesel, the contact should stop, and the pump should lose it's path to ground, shutting the pump off.

Only problem with that idea is that you have a continuously powered bilge! Bad idea for electrollisis!
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Old 18-06-2010, 21:14   #17
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In such a case having a manually activated lower bilge pump and a float activated upper pump might save you from pumping leaking fuel overboard and allow you some time to get a fuel recovery plan into operation.
That might work on a boat with a deep sump. However many boats today have almost no bilge so a fuel leak in the cabin is going to make for a very messy situation. At sea this could be a disaster as many things will be saturated with fuel, the sole will be slippery, and the stench will be horrid, possibly rendering the crew helpless with sea sickness.

A fuel tank built by a professional tank builder will be tested under pressure. It will also be labeled with the builder's name and other significant information (I've forgotten what that info. is).
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Old 19-06-2010, 05:43   #18
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As someone else said, you need to replace the tank. I had a tank that pitted and developed a pin hole leak. A few tablespoons of diesel makes a mess around your boat. We removed the tank and replaced it with a fiberglass version but you can also get aluminum. Luther's Welding has done several. Marine Tanks, Fuel, Water, Storage Tanks, Luthers Welding
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Old 19-06-2010, 10:53   #19
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Another, simpler, solution is to completely eliminate the possibility of tank distruction from the fresh water. I did this twenty-some years ago by building my own fuel tanks from plywood, sealed with epoxy resin. It gave me the opportunity to create a baffle plate to reduce sloshing of fuel, to install LARGE cleanout ports on either side of the baffle to allow hand cleaning and inspection. Adding a mechanical fuel gauge, a couple years later, was pure simplicity. Since the tank has generous fillet joints, wiping out settled sediment or slime is a breeze. My only regret is that I didn't have the nerve to install a "sight glass" with a valve to drain accumulated water. Insurance companies (and the ABYC) frown on this addition, and since I've built several more of these tanks, over the years, I needed to keep legal. But now, as I prepare to take off on my own adventures, I'll probably add this device for my own boat. Metal tanks are time bombs. All of the aluminum, stainless and black iron tanks I've worked on, over the years, ALL show signs of deteriorating welds, electrolysis and deferred interior maintenance. I suspect anyone who regularly services tanks will concur with this observation. Build your own "cellulose-core, epoxy composite" fuel tank and add big cleanout ports. It's not a big deal, and considerably cheaper and safer than the metal options.

Attached views show tank exterior without cleanout port covers, and an interior view, shot straight down through a cleanout port, showing the pickup tube (bottom) and the mechanical fuel gauge float. All epoxy has graphite powder to give the black color, all joints are glass taped for additional strength. The pickup tube has a 60 degree cut at the base and is one inch above the bottom to avoid water and sediment pickup. The tank weighs about thirty pounds, empty. The fitting on the left, near side of the tank is the 1/4" copper fuel pickup tube. Middle of the tank is the fuel gauge wire connection. Behind, to the left, is a calibrated dipstick, and on the right, the fill hose and vent hose connectors (merely through hull fittings). Tank volume is 55 gallons.
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Old 19-06-2010, 12:07   #20
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We have a WaterWitch bilge pump switch. It is a solid little black box with two metal contacts on it. It has no moving parts or floats. It is activated when water makes a connection between the two contacts. If it senses oil (and I think diesel) it cuts off. So presumably, if we had water & diesel in the bilge, the diesel would float on top, so the pump would pump out all the water and then stop when it got to the diesel.
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Old 19-06-2010, 13:09   #21
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Originally Posted by SvenG View Post
With old tanks I worry about what happens when/if our 80-gallon diesel tank should spring a leak. I've been monitoring channel 16 when a docked fishing boat had a tank burst and started pumping it overboard through a 2" bilge pump outlet, it did not sound pretty.

So, what can one do to prevent it ? I am looking to put a diesel filter in the bilge pump lines but that wouldn't handle gallons and gallons.

Ideas ?
-Sven
1. Check your tanks regularly. If the tank looks suspect then you should consider a second opinion and possible replacement. Don't forget the fuel lines, inspection port (if you have one) and fuel pickup tube.
2. Check your bilge with a flashlight. Diesel or oil float on the water and leave a sheen a bright light might see. Consider dipping the bilge with a transparent container to see if there are any pollutants in the water.
3. Monitor your bilge water, especially when pumping overboard. If you get diesel or oil floating on the surface then you've got a problem. Stop pumping immediately. You should also have an idea of how often your bilge pump goes off - more often or longer would indicate a problem to me.
4. If you can't be there, then consider asking someone to look after the boat. They should have a key so they can look around below, your phone number, and some basic direction.

Spills happen. The best action in that event is to stop the discharge, inform the marina and coast guard and do what you can to absorb the discharge. You'll be in far more trouble by either ignoring the discharge, not alerting the authorities, or not taking prudent and rapid action.
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Old 19-06-2010, 18:45   #22
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Originally Posted by TabbyCat View Post
We have a WaterWitch bilge pump switch. It is a solid little black box with two metal contacts on it. It has no moving parts or floats. It is activated when water makes a connection between the two contacts. If it senses oil (and I think diesel) it cuts off. So presumably, if we had water & diesel in the bilge, the diesel would float on top, so the pump would pump out all the water and then stop when it got to the diesel.
Excellent suggestion. I was going to switch over to a couple of those anyway. It will be fairly easy to test your idea.

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Another, simpler, solution is to completely eliminate the possibility of tank distruction from the fresh water.
Our water tank is SS but the diesel tank is aluminum. I think I saw some of your earlier posts about building tanks out of epoxy-coated plywood and had that on my list of possibilities when I thought the tank was black iron and would have to be replaced due to age.

Thanks,


-Sven
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