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Old 17-10-2016, 04:37   #16
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Re: diesel at the pump vs. diesel at the marina

About delivering directly to the boat: If the delivery hose passes over water, the company and driver must be specially licensed to do that. If the boats on the hard, then no. My commercial boats are fuelled directly from the truck, and there's only a couple local suppliers we can use to do that. And the driver does add the red dye in the truck.
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Old 17-10-2016, 05:29   #17
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Re: diesel at the pump vs. diesel at the marina

Another vote for street fuel. It's the same stuff possibly with dye added.


The big advantage is the street fuel is probably fresher assuming you buy from a truck stop as they turn their fuel over frequently.


Condensation is a myth. Run the calculations some time. I did once and for a 200gal tank 90% empty, absolute worst case scenario was a few grams (a gram is roughly the size of a raisin for reference) over a 6 month winter using unrealistically bad assumptions. I'm of the belief that most water in fuel issues are a lose cap or other means of water getting in.
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Old 17-10-2016, 06:01   #18
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Re: diesel at the pump vs. diesel at the marina

Something only previously mentioned in passing above...

States are now passing laws that mandate road diesel being blended to include 10% Bio-Diesel. Bio-Diesel gels at low temps. To counter this, most commercial road diesel users are now mixing with unleaded to delay the gelling. Just like we use to do with #1 diesel.

Also you will get about 2~5% reduction in fuel mileage with the blend.

IMHO, not only to avoid paying extra tax's, it would be best to buy non-road diesel from a rural station that offers it. Most do.
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Old 17-10-2016, 06:02   #19
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Re: diesel at the pump vs. diesel at the marina

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Originally Posted by Jd1 View Post
I may be off base on this but I believe the diesel at the pump is ultra low sulfur diesel which has considerably reduced lubricity compared to the old style diesel that was just low sulfur and that is still served at the dock.
Having said that, I doubt that a low percentage of ULSD would make a significant difference for you next spring. I would be hesitant to go over 50% myself.
BTW, I also believe that gasoline at the dock does not contain Ethanol .....
Up here in Maine all the diesel is identical except for the off-road dye or ValvTect additives which are added at delivery.

A few years ago I followed the tanker truck from our local Mobil station right to the marina (at about 14MPH in a 35 zone). Before he connected the hose to the marina tank he poured in some red dye and then the ValvTect additives (marked right on the bottles "ValvTect").

He then proceeded to fill the marina tank with the same diesel he just dropped at the Mobil station. When I asked about this he said they had been doing it this way for years as it is far less costly to leave the tank farm with one load of fuel and just change it from taxed to non-taxed (off-road) on-site. Course with the timber industry here in Maine we have a lot of land based stations that sell both on-road and off-road diesel. He said the same about the ValvTect additives but also added that ValvTect will do regular spot audits/testing to ensure the fuel is up to ValvTect standards.

Our marinas have been using the same as on-road fuel for years with no ill effects. From what I understand the ULSD has lubricity enhancers added.
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Old 17-10-2016, 07:34   #20
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Re: diesel at the pump vs. diesel at the marina

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Originally Posted by valhalla360 View Post
Condensation is a myth. Run the calculations some time. I did once and for a 200gal tank 90% empty, absolute worst case scenario was a few grams (a gram is roughly the size of a raisin for reference) over a 6 month winter using unrealistically bad assumptions. I'm of the belief that most water in fuel issues are a lose cap or other means of water getting in.
OK, I guess my original question of using diesel from the gas station is ok. But this changes things. So you are saying that if my 26 gallon tank is only 2/3 full, then adding another 8 gallons really won't make a difference, that at worst there would only be a few ml of water from condensation?
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Old 17-10-2016, 08:04   #21
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Re: diesel at the pump vs. diesel at the marina

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Before he connected the hose to the marina tank he poured in some red dye and then the ValvTect additives (marked right on the bottles "ValvTect").
This was my understanding of how they added the dye. It takes only a very small amount of dye to color a lot of fuel and dying the tanker would limit its use to only delivering dyed fuel.

I talked to an inspector one time who's crew was checking the vehicles in a Technical College parking lot. He told me that if you used off road diesel that you would have to refill the tank quite a few times before the dye was undetectable to the eye. He was more specific than that but it was a long time ago and I've forgotten the exact details.
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Old 17-10-2016, 08:34   #22
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Re: diesel at the pump vs. diesel at the marina

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This was my understanding of how they added the dye. It takes only a very small amount of dye to color a lot of fuel and dying the tanker would limit its use to only delivering dyed fuel.

I talked to an inspector one time who's crew was checking the vehicles in a Technical College parking lot. He told me that if you used off road diesel that you would have to refill the tank quite a few times before the dye was undetectable to the eye. He was more specific than that but it was a long time ago and I've forgotten the exact details.

Yes, and the dye will stay in the filter until it's changed as well.
Right after Katrina the moratorium on Off road Diesel was lifted for a time down here, during that time it was legal to run died Diesel.
I'm sure many farmers do run died Diesel in their pickup trucks more out of convenience than anything, but I believe the fines are stiff.

Valvtect I have been told does contain a "bug killer" but I continue to use BioBor JF anyway.
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Old 17-10-2016, 08:46   #23
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Re: diesel at the pump vs. diesel at the marina

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OK, I guess my original question of using diesel from the gas station is ok. But this changes things. So you are saying that if my 26 gallon tank is only 2/3 full, then adding another 8 gallons really won't make a difference, that at worst there would only be a few ml of water from condensation?
Calculate the amount of water in 99% humidity air (have to factor in temp and pressure).

Assume 100% air change every day as the temps drop and rise and assume 100% of the moisture condenses on the tank walls and doesn't evaporate when the temp goes back up in the morning and yes, it's a miniscule amount.

If you are getting a significant amount of water in your tank over winter with only 8 gal of air space, you are far more likely to have a leak in the fuel fill cap or some other source.
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Old 17-10-2016, 09:02   #24
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Re: diesel at the pump vs. diesel at the marina

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Originally Posted by jbinbi View Post
OK, I guess my original question of using diesel from the gas station is ok. But this changes things. So you are saying that if my 26 gallon tank is only 2/3 full, then adding another 8 gallons really won't make a difference, that at worst there would only be a few ml of water from condensation?
This is one of the never ending arguments on boat forums, but my advice (and the advice of my boat manufacturer) is to keep the fuel tanks filled to minimize the chance of condensation. In your case, adding eight gallons shouldn't be a chore. Fifty gallons would be a chore.

Water in diesel fuel is to be avoided at all costs.
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Old 17-10-2016, 09:07   #25
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Re: diesel at the pump vs. diesel at the marina

OK, was troubling me to not figure this out on the back of the envelope, just roughing it, correct me if I am wrong.

100% RH is 17.3g/m3 of water
1 cubic foot is 7.5 gallons.

I need to fill my tank with about 7.5 gallons or so , this is perfect.

1 cubic foot is about 1/35th of a cubic meter, 17.5/35 ~ 0.5g of water.

A drop of water is 0.05 grams, so

I would potentially have 10 drops of water condensate, at 100% RH.
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Old 17-10-2016, 09:10   #26
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Re: diesel at the pump vs. diesel at the marina

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I can't find a correct answer. I need to add some fuel to my tanks for winterizing. The boat is not able to get to a marina for fuel. So I was going to bring in some 5 gallon containers of diesel.

Can I just get it from a regular gas station or do I need to go a fuel dock? I know the gas stations have bio diesel, not sure if that is different from what is at the marinas?

Oh yeah, assuming I can use my gasoline 5 gallon, emptied, rinsed with water, and let dry. Thinking the ratio of diesel to whatever is in there is like 1000:1
Avoid bio anything especially bio diesel. It's full of little critters. It's not intended to sit unused. It will turn to mush after sitting unused.

Otherwise buy diesel at any gas station. The key is to ensure your tank is free of diesel and water that has turned. Putting fresh diesel into a dirty tank will degrade the new fuel.

Ideally you should inpect your tank and clean it out before putting fresh fuel in.

Also dont wash diesel jerry jugs with water. Clean them with an orange oil degreaser and then flush with water. Remove all the water by rinsing with acetone or vent for a few days. Ensure no acetone remains.

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Old 17-10-2016, 09:12   #27
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Re: diesel at the pump vs. diesel at the marina

Avoid Biodiesel, mostly because it is an unknown how stable it is. Let somebody else experiment.

On road diesel is practically the same as off road diesel, except it MUST be Ultra Low Sulfur, off road can be higher in sulfur but not really too critical. You can buy bottles of stuff to make you feel good about the possibility of wear, but since there is no regulation of additives, I wonder if any works...

I can vouch for cetane booster.

#2 Fuel oil is OK, perhaps not as good, and more expensive than on road diesel.
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Old 17-10-2016, 09:25   #28
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Re: diesel at the pump vs. diesel at the marina

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Originally Posted by jbinbi View Post
OK, was troubling me to not figure this out on the back of the envelope, just roughing it, correct me if I am wrong.

100% RH is 17.3g/m3 of water
1 cubic foot is 7.5 gallons.

I need to fill my tank with about 7.5 gallons or so , this is perfect.

1 cubic foot is about 1/35th of a cubic meter, 17.5/35 ~ 0.5g of water.

A drop of water is 0.05 grams, so

I would potentially have 10 drops of water condensate, at 100% RH.
This is close but not quite correct, because you failed to account for the fact that the tank "breathes". As the temperature changes air expands and contracts allowing some air exchange though the vent as the temperature changes. If you are in New England this is probably not a big deal as cold air contains very little moisture. In the mid-atlantic and south to Florida this is more of a problem because the temperature regularly cycles between cold and warm. If the tank is below the waterline this helps because the water does not change temperature rapidly and the tank tends to stay at or near the temperature of the water. All this said I think you are still more likely to have issues with water seeping though the filler cap seals than condensation. Of course those of us in Florida are using our boats all winter and don't have to worry about it.
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Old 17-10-2016, 09:27   #29
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Re: diesel at the pump vs. diesel at the marina

Having gone through an aircraft certification to run Bio (S-10 in Brazil) I can tell you that Bio can be great, best thing there is to Bio can be horrible, worst thing there is, problem is all Bio means is it came from something that at one time was alive, there are no certs and no standards essentially, it can come from many sources, from rape seed, to animal fats, coconut / palm oil etc.
So since you have no way to determine content, best to avoid if at all possible.
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Old 17-10-2016, 09:41   #30
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Re: diesel at the pump vs. diesel at the marina

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Originally Posted by jbinbi View Post
OK, was troubling me to not figure this out on the back of the envelope, just roughing it, correct me if I am wrong.

100% RH is 17.3g/m3 of water
1 cubic foot is 7.5 gallons.

I need to fill my tank with about 7.5 gallons or so , this is perfect.

1 cubic foot is about 1/35th of a cubic meter, 17.5/35 ~ 0.5g of water.

A drop of water is 0.05 grams, so

I would potentially have 10 drops of water condensate, at 100% RH.
Yes, but you're making a few assumptions. The first is that the air in the tank is static, unmoving, unchanged. Someone else proposed using one change/24 hours, which would coincide with heat/cool/condensing cycles. Thus, over the course of a season (200 days?), under this assumption you might have 200x as much, or 100g of water.

The second is your 17.5g/m^3 number. The water vapor capacity is usually described in g/kg, but 1.168kg of air is about 1 m^3. You're using an equivalent of 15g/kg which is 100%RH at 68degF; however, it is likely cooler than that or your sailing season would continue. At 32degF, 100%RH is only 3.8k/kg. Furthermore, as opposed to the air surrendering all of its humidity to liquid, it will only condense to the RH of the new temperature. For example, if 100% RH humidity air at 41F (5g/kg) is reduced to 100%RH at 32F (3.8g/kg), only 1.2g/kg would have condensed out. This would move the estimate an order of magnitude in the other direction, from 100g -> 8g.

The third assumption is that the environment is always at 100% RH. That depends where you are. Here by the New England coast we average 50-70% RH in the winter months. Perhaps one would discount the 8g estimate by what, 50%? to 4g, not even a teaspoon.

It could be that this teaspoon of water will sink to the bottom of your tank and never get sucked up by the pickup tube. How much water are you comfortable adding to your tank every year? How much can one rely on the fuel/water separator to remove if that teaspoon of water is sucked up? I change my filter approx every year and probably remove 10x that in fuel&water every time I do.



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