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Diesel costs


Dunworkin

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16 minutes ago, doratheexplorer said:

If it's expanded, surely you get more for your money?

No you will get less as the diesel is less dense so will contain less energy per litre.

Edited by Robbo
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I don't see a need to completely fill the tank to the top and would always stop when  fuel can be heard rising up the filler neck leaving some room for expansion. 

More significantly on a sea boat, if used at sea,  the fuel will slosh about a lot more than it would on a canal boat . Even so a certain amount of fuel movement will presumably occur on a canal.

On balance best not over fill. We  don't want to cause any pollution if it can be avoided - do we?

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46 minutes ago, MartynG said:

I don't see a need to completely fill the tank to the top and would always stop when  fuel can be heard rising up the filler neck leaving some room for expansion. 

More significantly on a sea boat, if used at sea,  the fuel will slosh about a lot more than it would on a canal boat . Even so a certain amount of fuel movement will presumably occur on a canal.

On balance best not over fill. We  don't want to cause any pollution if it can be avoided - do we?

Mine dosen't have a neck, the filler is in the top of the tank.I would have thought the fuller the tank the less it could slop?

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21 hours ago, Tony Brooks said:

OK, so yesterday I filled with 100 litres @ 60/40 split and paid £114.

 

I was a Burk, first fill up since autumn so should have declared more like 20/80 but there you go.

But the declaration is for the predicted future use of the diesel not what the stuff you have used was used for.

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On 24/06/2018 at 17:37, OldGoat said:

It's really a matter of what YOU think is reasonable as there are no hard and fast rules.

I go on the basis that if 60/40 was deemed by the RYA as reasonable for a fuel guzzling sea going cruiser, then 80/20 would be a generous declaration on your part as most of the fuel is spent on heating the engine and hot water and charging your huge battery bank.  

 As we're leaving the EU this charge should disappear *. Prior to some miserable Belgian MP boating diesel was charged at the domestic rate anyway 

 

* In your dreams Boo Boo

I doubt if being out of the EU will affect fuel prices, go up instantly there is a price rise & takes ages to come down after falls in prices UK pays more at the pumps for road  diesel of which HM Gov pockets a goodly amount in tax most of Europe pays less & prices vary over the whole fuel supply throughout the separate countries

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2 hours ago, ditchcrawler said:

I would have thought the fuller the tank the less it could slop?

I guess so but at sea and  at 20 odd knots I am burning 30 litres per hour each engine so the fuel  tanks don't stay full for long.

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10 hours ago, Mike the Boilerman said:

 

I don't see what that has to do with the price of eggs. We are considering the rise in the temp of the diesel between dispensing it into the tank at say 8.30am (when it might have cooled overnight in the yard tank) and later afternoon when the sun might have warmed it up in the boat tank.

 

The forth factor is the rate at which the sun can transmit heat energy into the diesel raising its temperature, through the limited surface area of steel.

For all of these 'factors' you still haven't offered an explanation as to why, when I fill my tank to within a couple of centimetres of the filler tube on a hot day I end out with a large slick of diesel around my boat bubbling out of the vent.  As a rough rule of thumb 1.5 cm on my dipstick equates to about 5 litres of fuel.

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18 minutes ago, Wanderer Vagabond said:

For all of these 'factors' you still haven't offered an explanation as to why, when I fill my tank to within a couple of centimetres of the filler tube on a hot day I end out with a large slick of diesel around my boat bubbling out of the vent.  As a rough rule of thumb 1.5 cm on my dipstick equates to about 5 litres of fuel.

 

I've no idea why without seeing the construction of your tank.

 

I do however know it is NOT because the volume of the diesel has risen by 10%, from a 10C temperature rise.

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2 minutes ago, Mike the Boilerman said:

 

I've no idea why without seeing the construction of your tank.

 

I do however know it is NOT because the volume of the diesel has risen by 10%, from a 10C temperature rise.

Any idea how the vents are designed? (it's inside the starboard side mooring bollard so annoyingly covers my ropes in diesel as well).

Edited by Wanderer Vagabond
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If the breather has a length of pipe that sticks down into the tank there will be an air pocket above it. Air expands more than diesel, I think, and the expanding air may push diesel out of the vent. I think the trim of the boat coudl allow an air pocket as well.

 

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I have notice some diesel pumps at the waterside deliver fuel at a rapid rate. The pump at the marina where I keep my boat is like that compared to the marina a mile away where the delivery rate is comparably gentle.

I find , if using the faster pump the fuel is more prone to create foam and this can lead to the fuel backing up and foam flowing out of the vent. Therefore if using this faster pump I usually end up with something less than a full tank. 

The trick is to not fill the tank so high or operate the trigger on the filler at part open to deliver the  fuel at a slower rate.

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9 hours ago, Wanderer Vagabond said:

Any idea how the vents are designed? (it's inside the starboard side mooring bollard so annoyingly covers my ropes in diesel as well).

 

This is helpful as I think we can from this deduce your tank IS in the counter block rather than down in the bilges. Consequently if you are filling to within 1cm or 2cm of brim full (you said earlier), the surface level of the fuel must only be 1-2cm below the underside of the counter deck itself. Now the vent being in a bollard welded to the top surface of the cants means the builder must have installed an extension pipe from the underside of the dolly before welding it on, down through the height of the cants (2" or so) to penetrate the top of the tank. SO as Tony says, this tube probably penetrates an inch or two down through, so is 'underwater' when you fill to the top. I'd say just the momentum of the diesel sloshing slightly from side to side as the boat rocks will easily lead to splashing up the vent pipe, partially arrested and converted to froth by the flame trap gauze.

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15 hours ago, Wanderer Vagabond said:

For all of these 'factors' you still haven't offered an explanation as to why, when I fill my tank to within a couple of centimetres of the filler tube on a hot day I end out with a large slick of diesel around my boat bubbling out of the vent.  As a rough rule of thumb 1.5 cm on my dipstick equates to about 5 litres of fuel.

Diesel has a coefficient of volume expansion of about 0.00083

When 200 litres of diesel increases in temp by 25c it will expand by 4litres.

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7 minutes ago, Chewbacka said:

Diesel has a coefficient of volume expansion of about 0.00083

When 200 litres of diesel increases in temp by 25c it will expand by 4litres.

 

0.00083 is the expansion by 1 degree increase in temperature.

 

With a 0.00083 expansion 200 litres would increase by 0.166 litres per degree (so yes 4 litres per 25 degree temp increase)

 

When / How is the diesel in a tank pretty much surrounded by coldish water going to increase by even a couple of degrees ?

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2 minutes ago, Alan de Enfield said:

 

0.00083 is the expansion by 1 degree increase in temperature.

 

With a 0.00083 expansion 200 litres would increase by 0.166 litres per degree (so yes 4 litres per 25 degree temp increase)

 

When / How is the diesel in a tank pretty much surrounded by coldish water going to increase by even a couple of degrees ?

I’ve not measured it but would guess that over half my tank is above the water line, and being about 4inches across means the surface area is quite large compared to it’s volume.  The inside of the tank is the end wall of the engine hole, which is about 50c after a good run.  Hot diesel will sit above cold diesel, so on a very sunny hot day it would not surprise me if the average diesel temp in the tank was over 35c.  Even the water close to a non moving boat can be warm to the touch, so cooling into the water is maybe less than you would expect.

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8 hours ago, Tony Brooks said:

If the breather has a length of pipe that sticks down into the tank there will be an air pocket above it. Air expands more than diesel, I think, and the expanding air may push diesel out of the vent. I think the trim of the boat coudl allow an air pocket as well.

 

 

7 hours ago, Mike the Boilerman said:

 

This is helpful as I think we can from this deduce your tank IS in the counter block rather than down in the bilges. Consequently if you are filling to within 1cm or 2cm of brim full (you said earlier), the surface level of the fuel must only be 1-2cm below the underside of the counter deck itself. Now the vent being in a bollard welded to the top surface of the cants means the builder must have installed an extension pipe from the underside of the dolly before welding it on, down through the height of the cants (2" or so) to penetrate the top of the tank. SO as Tony says, this tube probably penetrates an inch or two down through, so is 'underwater' when you fill to the top. I'd say just the momentum of the diesel sloshing slightly from side to side as the boat rocks will easily lead to splashing up the vent pipe, partially arrested and converted to froth by the flame trap gauze.

I think I'll run with Tony's idea that it is air that is driving the diesel out of the tank, can't say I'm convinced in any way by this idea of the diesel 'sloshing slightly from side to side' and coming out of the vent since it is something that happens exclusively when it is hot, never in winter, so we only slosh the diesel around during the summer months?:unsure: (we are CC'ing).

 

If it is air driving the fuel out (and I think it is), it makes this discussion about co-efficient of expansion of diesel all rather irrelevant. In simple terms however, if I refuel on a hot day like today and don't leave a substantial gap below the filler pipe, I'll be pumping diesel into the canal (and over my ropes, and taking the paint off the side), that is all I need to know.

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28 minutes ago, Wanderer Vagabond said:

and coming out of the vent since it is something that happens exclusively when it is hot, never in winter,

 

I didn’t grasp that bit. In which case I agree with Tony it is air expanding when the vent extension tube is dipping into the fuel. The volumetric coefficient of expansion of air is massive and could easily expel half a litre or so of fuel of a hot day. 

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JUst for the record, we paid 76ppl domestic at Stone Chandlery today. I was told that the inspector never queries a 30% propulsion/70% domestic split, except for hire boats who are expected to declare 60/40.

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1 hour ago, BruceinSanity said:

JUst for the record, we paid 76ppl domestic at Stone Chandlery today. I was told that the inspector never queries a 30% propulsion/70% domestic split, except for hire boats who are expected to declare 60/40.

Has anyone had any experience of the 'inspector' querying anything? As a CC'er my calculation is that during the winter 90% of my fuel is for domestic use (battery charging and eberspacher) and during the summer 80% is for domestic use so that is what I generally declare. If the 'inspector' knows different I'd like to see his working, he can see mine if he likes. I would have thought that the only declaration that may raise eyebrows would be a 100% declaration since how did you get to the refuelling point if none of your fuel is for propulsion (and more to the point, how are you going to leave the refuelling point again since your declaration is, if I understand correctly, for future use).

1 hour ago, Mike the Boilerman said:

I bought diesel at Napton narrowboats last wed. £1.16 a litre at 60/40, only split option available 

 

I didn’t fill up. 

Try Calcutt marina (just around the corner sort of) they always seemed to have a good price whenever I've overwintered in the area.

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