Convert Gravity Feed Tank?

[chuckt]

I have a gravity fed tank in my concordia. And the original Gray marine 31hp. I don't had much of an idea of what's invalid to convert. Or do I need to? I'm aware gravity feed is a safety concern. Obviously, I need a pump to convert to top-feed. I'd appreciate any guidance on what is involved in converting?

[The Bigfella]

I don't understand the difference between gravity feed and top feed. Can you tell us?

When I rebuilt my Detroits and fuel system, the engine guys needed to know how the fuel setup worked so they could set up the fuel pumps correctly.

If it works now... why change it?

[seo]

To have a fully "up to code" fuel system, it has to comply with the requirements found in NFPA (National Fire Protection Association) publication 302 "Standards for small vessels". A smart surveyor will tag any non-complying features of a fuel system, because NFPA is the recognized expert on the question. ABYC and USCG standards are just NFPA standards that the other bodies have adopted, and sometimes made more complicated. If your fuel, electrical, and heating systems comply with NFPA 302, underwriters will be happy.
NFPA publication 302 is available from:
National Fire Protection Association
PO Box 9101
Quincy, MA 02269-9959
(800) 344-3555
Assuming you're happy with the size and location of the tank, and that it's in good condition, you need to plug off the bottom feed, and add a top feed. This can be done with mechanical fittings, or by soldering/brazing/welding, depending on the tank material.
In all cases, it will be easiest to do if you can get the tank out of the boat. That makes "hot work" (welding and cutting) a lot safer and more feasible. If your tank has a clean-out plate on the top, you can take just the plate to a shop and fit it with a through-fitting. The very simplest arrangment is a NPT pipe/compression union. The pipe end is threaded into the inspection plate, with the compression fitting UP (outside the tank). The dip (suction) tube is soft copper of the proper length, with the pickup at the low point of the tank. It's held in place by tightening up the compression fitting on the outside of the tank.
If your engine doesn't have a transfer pump, you'll need to add one. Simplest way is with a 12V fuel pump. There are at least a few types on the market. Get one that's UL listed for gasoline and marine use. You should put a siphon-break poppet valve into the feed line as well (It's an NFPA requirement) They're cheap and work well. Tempo part number 478 ASV.
Perhaps the best plumbing arrangement is for the soft copper to run to the edge of the tank, connected to a flare (or compression) /npt pipe 90º adaptor, then to a vertically mounted marine approved shut off valve, with the siphon break valve threaded directing into the discharge of the shut off valve. The discharge of the siphon valve is hose barb, and I'd go type A1 approved neoprene from there to the pump, and on to the fuel filter and carburetor. I use the modern "spin on" type filters that also serve as water traps.
A few more considerations: 1) Make sure the vent fitting is at least 1/2" diameter USCG A2 hose, with an approved flash screen at the vent, vent discharging outboard of the cockpit or vessel interior.
2) Fuel hose USCG A2 hose, connected to a through deck that's located so that a leak will flow overboard, not into the hull interior or the cockpit. In other words, the old-style cockpit sole fuel fill does not comply with current standards, because fuel vapor can't flow out through the cockpit drains, because the cockpit drains are immersed in water when the boat is in the water. An alert surveyor will tag this, and a picky underwriter won't like it. If that's what you have, it usually works to install a close pipe/hose street elbow in the top of the tank, with the hose running out and up to a flush fuel fill fitting mounted out on the waterway.
People argue that the cockpit sole fitting makes it easy to check fuel level, and clean the tank, and I sympathize with them, but the way I read the rules they don't comply.
There has to be a ground jumper wire from fill fitting to tank to vessel ground. A static electricity spark from fuel nozzle to tank is not a good thing. A smart boat owner loosens the fill to finger tight, then touches the fuel nozzle to the fill fitting to dissipate any static charge, and THEN opens the fill fitting. (On tankers, the first thing you do before hooking up the tank manifold to the dockside manifold is to hook up a big (not quite wrist thick) ground jumper from the dock to the ship. )
If you switch to a waterway fill, you may find it necessary to install an electric fuel tank gauge. This seems like retrograde motion, doesn't it?
IF you decide to convert to diesel, you can use a bottom-discharge diesel tank as long as it's less than some threshold around 200 gallons, as I remember. So the only modification to the tank would be a fuel return fitting. I have never heard of an underwriter making trouble over a cockpit sole mounted fill in a diesel system, because the vapor problem is much less. That doesn't mean it couldn't happen, because the tank fill requirements are the same for gasoline or diesel.
Even if you decide to try to keep your old system, at least make sure that the fuel shut off valves comply with current standards (closed bottom), that there isn't a glass sediment bowl in the system, and that the fuel feed hose is USCG type A1 compliant, and that all hose connections are double clamped with stainless clamps.
A gasoline fuel system is also required to have an approved bilge blower drawing from the lowest point of the bilge, with a placard at the ignition switch telling people to use the blower.
Gas engines are quiet and lightweight, but they're also getting old.
As an aside, Sometimes I wonder if there isn't a niche for a marinized and fully compliant gas engine out of a modern car. It could be tiny...
Maybe the three-cylinder Suzuki engine out of a Geo Metro, or the new GM little engine...
http://www.thedetroitbureau.com/2011...engine-family/

[chuckt]

Maybe a dumb question but how does the transfer pump know when to shut off? Do I need a new carb set up to work with a pump?

[seo]

A standard transfer pump is set at something like 6 psi pressure. Often they are the solenoid "clicker" pumps that work on higher pressure keeping the contacts from closing, therefore preventing the next pumping "click." Great idea. Just whatever you do, if someone tries to sell you an English clicker pump, either: a) run away, or b) memorize all the Lucas electric jokes (Lucus, Prince of Darkness) or "Q: why do the English drink warm beeer?" "A: Because they all have Lucus refrigerators."
The other type has (I think) a higher current draw, and was made famous as the Sterwart Warner Conelac pump, Friend of Dragracers, because it could pump enough fuel to feed all that dual-quad four-oh-nine stuff. I think they run continuously, and maintain pressure with a bypass valve.
If you're switching from a gravity system, you might look for a pump with an adjustable pressure delivery, or realize that you may have to rebuild your float bowl and get the needle valve to really seal. The idea of a carburetor is that the fuel is delivered under low pressure, either gravity or pump, and then the pressure is reduced to zero in the float bowl, and the suction of the carburetor sucks the gasoline out of the bowl, through the jets, into the verturi, and like that. Not the same thing as fuel injection, where the fuel is metered under mechanical pressure, and bugger the Venturi, Bernouli, and all those other wops. This is Bosch at work!! Sieg Heil!!"

[chuckt]

Ah! Thanks. That makes sense. I'll probably call Concordia Boats and see what pumps they have put in and any issues. Great explanations Seo--I appreciate it.

[boatkid]

I have a question or two, cuz I don't know the answers. Since it's that old, the surveryor doesn't take into account that it's gravity feed already? I mean isn't something like that grandfathered in? Like I said, I don't know that's why I am asking. If you're allowed to keep the gravity, isn't that far better than adding a bunch of items that will go wrong? I mean doesn't gravity eliminate the pump and so forth? I think I read in Buehlers Backyard Boatbuilding book that gravity is the way to go on these? Anyway, please tell me what if anything I have correct or wrong, cuz I might run into this stuff myself someday.
Thanks.

[chuckt]

Well, I don't know. Gravity feed is not allowed on inspected vessels. The danger, as I understand it, is that you get a leak and then gas or gas fumes in the bilge. So its a safety thing. Top feed is safer.

[Dale Genther]

On our boat, Radiance, the two monel fuel tanks were bottom feed. Since it was diesel I left it that way for simplicity. Had it been gasoline I'd have changed them to top feed for safety. Although I beleive ABYC, etc. doesn't recognize a difference in the fuels, requiring top feed with both. Just one of the several things I disagree with them on.

[seo]

Both NFPA and USCG have an exception for tanks below a certain capacity. ABS does also, recognizing that a lot of small ships and tugs used day tanks in the engine room, which were gravity feed. But those tanks had to have a dump valve that worked at the same time as the engine room fire suppression system, dumping the day tank back into one of the deep tanks.
As far as "grandfathering" goes, that's a legal concept, and marine insurance is not constrained by legal regulation. An underwriter can decide to insure a vessel with tanks made out of old dixie cups if it feels like it. Or they can require that the vessel comply with current NFPA (or some other standard).

Even with shoreside building codes, most places require that commercial buildings comply with current fire (NFPA 1) and life safety code, (NFPA 101). Some may let a building float until they do a repair or modification that requires a building permit, and then require the upgrade. Prospective buyers of old commercial buildings beware!

In any event, the potential downside of insuring vessels with substandard gasoline or propane systems is huge. Not only do underwriter pay off on the boat, but also on salvage costs, environmental remediation, and mostly personal injury to anyone who gets burned. Burns are expensive to treat, and up here in Maine, treatment for a bad burn begins with a $15,000 helicopter ride, and doesn't get cheaper after that. The continuing liability for disfigurement, pain and suffering, loss of companionship, all add up to an uninviting prospect for an underwriter, and the only possible scapegoat he has is the surveyor who decided that he was smarter than the people who wrote the NFPA code, and that "it's worked all these years, so it's okay." That guy is toast.

Speaking of toast, as a kid I watched a gasoline-fueled boat explode at a fuel dock, and took part in recovering a cute teenage girl that I'd been joking with only a minute or so before the deck exploded under her and she disappeared into a bloom of flame, and emerged with her hair on fire, her skin horribly burned. It was a sobering experience. I've also gone through the training and testing to be a "Person in Charge" of liquid cargo operations, and been responsible for gasoline cargo hook-ups. I also had a friend who was one of only three to escape alive from a gasoline tanker that burned while discharging cargo. Gasoline is not an intrinsically safe material, and it doesn't take much vapor to do really serious damage.

As a result of all that, when I inspect a vessel's fuel system I recommend that it be brought into compliance with current standards. If the underwriter decides to let the owner slide, at least the owner and the underwriter have been told what they're getting into.

If the underwriter requires that the fuel system be brought into compliance, and the owner blithely signs a statement that the work has been done, the happy owner might wonder for a moment why the underwriter didn't require a follow-up inspection to see that the work actually was done. The reason is pretty simple. If there's a loss caused by a fault that was required to be fixed, but wasn't, then the underwriter has a very good chance of being off the hook for the casualty. Which means that the owner is on the hook, and maybe doesn't even get his premium back, adding insult to (self-inflicted) injury.

There are a couple gasoline fuel system scenarios that the current standards are designed to avert. The first is when a stuck needle valve in the float bowl allows the fuel tank to empty out through the float bowl vent. It can do this whether the tank is top or bottom feed, as long as the level of the fuel is above the level of the carburetor. If you have a "modern" carburetor, its set up so that the overflow is routed down the carburetor's throat, and into the cylinders, past the rings and into the crankcase. This can also happen with one of those good old cam-actuated diaphragm fuel pumps that almost all carbureted cars have. If the diaphragm gets a hole in it, it can divert enough fuel into the crankcase to fill the crank with hot gasoline vapor. As someone who used to sail as engineer on tugs powered with Fairbanks-Morse engines, which are prone to base explosions (and stack fires), I can attest that a base explosion is not a good thing. An engine with its crankcase full of hot gasoline vapor sounds like a prescription for a blast that could reduce your engine to shrapnel.

Anyway, I don't have anything against gasoline engines in boats. They're quiet, light, and relatively cheap. It isn't difficult or even particularly expensive to upgrade one to comply with current standards. Even an updraft or sidedraft carburetor can be modified so that overflow from an overflowing float bowl is sent into the intake manifold.

One final observation about siphon break valves. There are two kinds. One is an electric solenoid valve, and is expensive. The other is a spring-loaded poppet ball valve. The spring holds the ball against a seat with just enough force that the force of gravity (including siphon suction) won't open it, but the suction of a fuel pump will suck the ball back off the seat, and allow fuel to flow. These are simple and cheap valves, around $10.00. They are reported to work better when install vertically, and then can get stuck. If I had a fuel system with a tank installed so that the fuel level is higher than the carburetor, I'd install one. But I would check it to make sure that it's actually working, by loosening a fitting at the low point of the system, and making sure that fuel doesn't come out, which would indicate that either: a) the valve is defective, or b) that the "head" height of the system generated enough pressure or suction to open the ball valve. I don't know if they make those valves with bigger springs, or maybe in that case you're stuck with an electric solenoid valve...