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#571534 - 08/05/18 01:40 PM Is there a difference? If so, what is it?  
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Whilst standing at the gas pump filling the tank from the Whaler I got to thinking about why I am required to remove the portable, plastic tank from the boat and place it on the ground to fill it?

Supposed for this discussion that a boat on a trailer with a built in tank pulls in next to me. He opens the gas cap on the boat and begins filling it.

Both boats are on top of trailers that sit on rubber tires and are connected to tow vehicles that also sit on rubber tires. Neither truck/trailer combination is capable of allowing a spark to go from the boat to ground because of the rubber tires.

So, why does a person with a portable can have to remove it when the other boat obviously can't remove it?

ouch


"Beachcomber" 1995 Sea Ray 550 Sedan Bridge


Anchor's down......Bottoms Up!
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#571535 - 08/05/18 02:02 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Interesting topic. My understanding was that it is dangerous to fill up plastic tanks on the plastic bedliner in the back of pick up trucks. Would think portable tanks strapped down in the boat should be ok but not 100% sure. I always tank my plastic 6 gallons tank & place them on the ground when filling & then put back in bed of truck.


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#571536 - 08/05/18 04:49 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Jack T Offline
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Good question.

Static electricity does not need to go to ground. All it needs to cause a spark is enough potential difference (voltage) between two charged bodies and a path with low enough resistance.

Since we live is "dry" SoCal, there are many times that I get static charge shocks while removing canvas covers or putting them back on. Don't know what voltage they are, but when they jump, a very audible POP is heard. When this happens, I am standing on carpet on the inside of the fiberglass boat. My point is that a ground is not there, but a difference in potential is still present between the canvas and the boat.

Since some boats have plastic built-in tanks, that might be understood that a plastic tank sitting on fiberglass as in your Whaler might be similar. Is it possible that the filler pipe to the built-in plastic tank is either grounded to the boat through a common ground, or might it be conductive and will not build up a potential?


Have a great day of boating
2012 Monterey 224 FS,
300 HP Volvo Penta with catalytic converters

#571537 - 08/05/18 08:23 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Can't add much to the conversation. Only that the tank on the cobalt is plastic and the fillet neck is grounded to boat ground.


James
2002 Cobalt 226 VP 8.1GIDP
2007 Chevy 2500HD Crew Cab Duramax
1988 Suburban 3/4 Ton
2000 Subaru Forester


#571540 - 08/05/18 09:31 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Grand Poobah

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James, is the filler neck metal or plastic? If the filler neck is connected to boat ground but that isn't connect to actual earth ground, where does a spark go if the boat is on the trailer?


"Beachcomber" 1995 Sea Ray 550 Sedan Bridge


Anchor's down......Bottoms Up!
#571543 - 08/06/18 12:17 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Originally Posted by GoFirstClass
James, is the filler neck metal or plastic? If the filler neck is connected to boat ground but that isn't connect to actual earth ground, where does a spark go if the boat is on the trailer?


Filler neck is metal. I have no idea where the spark goes and no idea if it provides any value.


James
2002 Cobalt 226 VP 8.1GIDP
2007 Chevy 2500HD Crew Cab Duramax
1988 Suburban 3/4 Ton
2000 Subaru Forester


#571544 - 08/06/18 02:05 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Grand Poobah

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I was hoping Capn Morgan might see this and give us some of his insight into how these things work.


"Beachcomber" 1995 Sea Ray 550 Sedan Bridge


Anchor's down......Bottoms Up!
#571545 - 08/06/18 02:56 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Jack T Offline
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"If the filler neck is connected to boat ground but that isn't connect to actual earth ground, where does a spark go if the boat is on the trailer?"

"Static electricity does not need to go to ground. All it needs to cause a spark is enough potential difference (voltage) between two charged bodies and a path with low enough resistance."

Expanding on this, "static" means there is no movement of electrons, as in electrons present but not moving from one point to another. The circuit status is not "static" during this balancing the # of electrons between two charged bodies. In reality, if you have two differently charged bodies, they may or may not be at ground potential (0 volts). As an extreme example, let's say there are two bodies, one charged at 10,000 volts and one at 5,000 volts (both with reference to ground) and neither is connected to ground. If you bring the two bodies together, and they are capable of balancing their electrons, there will be a very short time during which current (moving electrons) will flow (no longer static--called static electricity discharge) and the charge (# electrons) on both bodies will be the same. Upon that balance, there will be no electron flow (current) and the voltage between the two will be 0 . And, if you measure the voltage of both the bodies in reference to ground (0 volts), you would still have 7500 volts on each body.

Hopefully, this helps understanding the answer to the question.

By the way, in normal air conditions, if a spark is 1 cm long, it's voltage is somewhere around 30,000 volts, 2 cm would be 60,000 volts, etc. More information can be found out at

https://sciencing.com/calculate-voltage-spark-gaps-8776030.html


Have a great day of boating
2012 Monterey 224 FS,
300 HP Volvo Penta with catalytic converters

#571549 - 08/07/18 02:30 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Grand Poobah

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Thanks Jack. Your explanation made it clearer than my ("clear as mud") previous thoughts.

Your comments about the length of the spark got me to thinking back to my days in the USAF. We had a radar on the nose (bow???) of an F-4 Phantom. When we had to work on the magnetron unit in the shop, before we removed any of the 3 electrodes from the magnetron we had to use a long screwdriver to short each terminal to the body of the transmitter unit which was connected to the bench ground which was connected to ground.

When the screwdriver tip approached each terminal the first time, the spark would jump about a 2" gap. The second time it would jump about a 1" gap and the third time it would hardly jump any gap at all, at which time grounding straps would be applied to each terminal so they could be removed. Then the straps would be hooked to the terminals on the magnetron to keep it grounded while we worked on the unit.

Seeing that spark jump a 2" gap and the loud ZAP that went along with it was quiet a "shocker" (bad pun) to see and listen to.


"Beachcomber" 1995 Sea Ray 550 Sedan Bridge


Anchor's down......Bottoms Up!
#571552 - 08/08/18 02:33 AM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Quote
my days in the USAF. We had a radar on the nose (bow???) of an F-4 Phantom.

At our air base I was in the photo section. We were warned to not walk in front of any fighter in the hanger for maintenance. As they might be working on the radar and it could fire off any flash bulbs in our pockets! Dunno if that was really true, but it was a fun story.

fireball

#571562 - 08/08/18 02:23 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Grand Poobah

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Fireball Kelly, we used to carry a 24" florescent tube in our tool bag. If the radar was transmitting it would light the bulb if the bulb was held about 5' in front of the radome. How's that for a scientific test?


"Beachcomber" 1995 Sea Ray 550 Sedan Bridge


Anchor's down......Bottoms Up!
#571563 - 08/08/18 04:43 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Jack T Offline
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"If the radar was transmitting it would light the bulb if the bulb was held about 5' in front of the radome. How's that for a scientific test?"

All those little electrons dancing around in the air and to the electrodes of the bulb. And, gee. The bulb was not grounded, just electrons floating around in air space. Right?

By the way, GFC. How come the fluorescent bulb glowed when the electrons were moving around?


Have a great day of boating
2012 Monterey 224 FS,
300 HP Volvo Penta with catalytic converters

#571564 - 08/09/18 06:32 AM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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On the subject of static and risk of fire...

If one considers the magnitude of the sample size (vehicles, gas stations, people refueling vehicles, toys, lawn equipment, etc.) you'd think that we'd be able to find a significant number of electrically-started gasoline explosions, or at a minimum, fires, if this was an issue of material concern. But I looked, and although the number of them is not zero, it is vanishingly small (<150). There were about 114,000 gas stations in the US in 2012. When you multiply the number of daily customers, (maybe 300 per day on average, just a wild guess based on 10% of the US population), you get somewhere north of 34 million opportunities for fire every day. If this was a significant issue, surely we'd be hard pressed to not find raging infernos at every corner and freeway exit.

IMO, the more practical reason for not filling portable tanks inside a vehicle or in a truck bed has more to do with not dripping or spilling gasoline inside your vehicle.


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#571565 - 08/09/18 03:19 PM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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Grand Poobah

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CJS, your statistical analysis pretty much lines up with what I had thought would be the case. Lots of refuelings, not lots of fires.

Thanks for putting the numbers out there, speculative though they may be. You're probably much closer than you realize with your SWAG.


"Beachcomber" 1995 Sea Ray 550 Sedan Bridge


Anchor's down......Bottoms Up!
#571570 - 08/10/18 10:04 AM Re: Is there a difference? If so, what is it? [Re: GoFirstClass]  
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CJS' statistics lead me to believe this might be the result of someone doing something stupid, and then the government deciding to create a law to make sure it never happens again.

As an example, a few years ago there was a politician here in the muddy Midwest that was related to a couple of kids that went missing in a row boat. The finally found the kids safe and sound after a lengthy search. The row boat had blown across the lake and ended up in a sheltered cove. With no nav lights, the row boat was hard to see at night. The politician proposed a law that would require all boats to have a ring of reflective tape around the hull so that it would be easy to see when illuminated by a search light. Had this law passed, we would all have to put a ring around our boats with reflective tape. Just sayin....

Has anyone noticed how 12 packs no longer have that perforated opening hatch that makes is easy to get the bottles out? I assume someone was injured by a falling bottle, and a class action law suit filed, all in the name of protecting us hapless and helpless citizens.


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