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LadyG

RYA quiz, diesel tanks

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This was noted in the RYA members magazine. I will post their answer later, but I wonder what you would have answered?

Q why should diesel tanks be kept reasonably topped up?

Clue, two reasons.

 

Edited by LadyG

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If you keep little diesel in the tank you will run out of diesel sooner than if you kept it topped to the brim.

 

or

 

Less space at the top of the diesel tank = less condensation = less chance of diesel bug.

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Less chance of picking crap up from the bottom of the tank if it is full.

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Still waiting, but volume is  involved, I think.

 Answer 1 is condensation

Edited by LadyG

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1 hour ago, Rob-M said:

Less chance of picking crap up from the bottom of the tank if it is full.

I agree, esp salty water boats which swish the diesel inside the tank in stormy seas,, but not mentioned in this (Yachtmaster level quiz) In my experience the Volvo Penta is particularly sensitive, Cure: throw engine overboard, and replace, or clean tank and fit a decent filtering system .

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1 hour ago, Nightwatch said:

If you keep little diesel in the tank you will run out of diesel sooner than if you kept it topped to the brim.

 

or

 

Less space at the top of the diesel tank = less condensation = less chance of diesel bug.

Condensation is defo one but not sure of the other.

I was thinking range is important ie on long passages ie more than 24 hours, you may need a tank full if you end up in a flat calm.

However, as an ex sailor, I have a different reason. Our 40ft yacht took its feed from the fuel tank a little bit up on the staboard side of the tank. We were on a passage from Messolonghi in Greece heading for Messina  in a oner (the bit between Italy and Scilly). By the time we got to the straights, with about 6 hours to run, our tank was around 40% full but we hit a force 9 on the nose so tried motor sailing to get to our destination before dark. The boat was heeling so much that air was sucked in the tank output line and the engine died. I spent half an hour trying to get the damn thing started by bleeding the fuel line, easier said than done bobbing up and down in a force 9.  Eventually we did the reverse of when  it died and heeled the boat the other way to get a head of fuel.

That always taught me to have enough in the tank to survive a big heel when running the engine. Crap boat design!

 

edit just read LGs response which crossed. Yes ours was a volvo penta!

Edited by Dr Bob

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Ok, 

A :  "Keeping diesel tanks reasonably full reduces the amount of OXYGEN in contact with the diesel as well as minimising condensation, inthe tank which in turn assists in deterring the growth of diesel algae"

RYA members msg Summer 2020

Over to you Dr Bob .......

Edited by LadyG

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4 minutes ago, LadyG said:

Ok, 

A :  "Keeping diesel tanks reasonably full reduces the amount of OXYGEN in contact with the diesel as well as minimising condensation, inthe tank which in turn assists in deterring the growth of diesel algae"

RYA members msg Summer 2020

Over to you Dr Bob .......

Minimising oxygen in the diesel tank will mean increased oxygen outside the tank which therefore reduces the density of the air inside the boat allowing the ecofan to spin faster and spread the heat better. Everyone wins!

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25 minutes ago, LadyG said:

Ok, 

A :  "Keeping diesel tanks reasonably full reduces the amount of OXYGEN in contact with the diesel as well as minimising condensation, inthe tank which in turn assists in deterring the growth of diesel algae"

RYA members msg Summer 2020

Over to you Dr Bob .......

In a simple rectangular tank the area of the surface of diesel exposed to oxygen is the same whether the tank is nearly full or nearly empty.

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21 minutes ago, Dr Bob said:

Minimising oxygen in the diesel tank will mean increased oxygen outside the tank which therefore reduces the density of the air inside the boat allowing the ecofan to spin faster and spread the heat better. Everyone wins!

Not everyone wins. What about the poor bloke next door? The stealthy but powerful thrust from the ecofan can slip his mooring pins and the first he knows about it is when he wakes up somewhere he wasn't! :boat:

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28 minutes ago, LadyG said:

Ok, 

A :  "Keeping diesel tanks reasonably full reduces the amount of OXYGEN in contact with the diesel as well as minimising condensation, inthe tank which in turn assists in deterring the growth of diesel algae"

RYA members msg Summer 2020

Over to you Dr Bob .......

 

Keeping the tank reasonably full will not reduce the amount of oxygen in contact with the diesel, unless the tank is shaped such the the surface area reduces at the top of the tank, perhaps with a cruiser that may happen, but for most narrowboats I would have thought the tank would be a constant cross section.

 

I would say there are three good reasons (perhaps more) for keeping a tank full

1. less chance of running out of fuel

2. less chance of the fuel slopping about and stirring up debris from the bottom of the tank

3. less empty volume in the tank for condensation to form in

 

The first being the most important one, as that will certainly happen, the other two may or may not happen.

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Empty tank or a not full tank increases condensation which allows “Diesel bug” to leave on the boundary of the fuel and water. Aircraft have the same issue hence water drain done before and after every refuelling. Each tank has a drain point on the lowest point of the tank it’s nothing to get 1/4 to 1/2 a pint out of each tank, more if lazy out stations not doing the drains on the turn round. Biobor is what is used to add to the fuel to kill the bugs. I’ve seen a A320 scrapped as beyond repair with corrosion in the wings due bug infestation. 

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1 hour ago, Dr Bob said:

We were on a passage from Messolonghi in Greece heading for Messina  in a oner (the bit between Italy and Scilly). By the time we got to the straights, with about 6 hours to run, our tank was around 40% full but we hit a force 9 on the nose so tried motor sailing to get to our destination before dark.

Well, well, well, bringing the Cat back from Croatia we had almost exactly the same (except it was a F8 and bang on the nose),  in the same area - had to turn back to the mainland and hunker down for the night.

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I’ve read somewhere that Diesel  bug grows more on moist tank walls, so keeping it full reduces the surface area of the exposed walls.

 

 With aircraft, the drain is to remove the water directly as this could cause engine failure - never heard a pilot worry about microbial growth

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1 hour ago, Dr Bob said:

Condensation is defo one but not sure of the other.

I was thinking range is important ie on long passages ie more than 24 hours, you may need a tank full if you end up in a flat calm.

However, as an ex sailor, I have a different reason. Our 40ft yacht took its feed from the fuel tank a little bit up on the staboard side of the tank. We were on a passage from Messolonghi in Greece heading for Messina  in a oner (the bit between Italy and Scilly). By the time we got to the straights, with about 6 hours to run, our tank was around 40% full but we hit a force 9 on the nose so tried motor sailing to get to our destination before dark. The boat was heeling so much that air was sucked in the tank output line and the engine died. I spent half an hour trying to get the damn thing started by bleeding the fuel line, easier said than done bobbing up and down in a force 9.  Eventually we did the reverse of when  it died and heeled the boat the other way to get a head of fuel.

That always taught me to have enough in the tank to survive a big heel when running the engine. Crap boat design!

 

edit just read LGs response which crossed. Yes ours was a volvo penta!

Fuel tank needed to be V shaped with pick up pipe down in the V or better still fuel tank on gimbals.

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21 minutes ago, boots said:

I’ve read somewhere that Diesel  bug grows more on moist tank walls, so keeping it full reduces the surface area of the exposed walls.

 

 With aircraft, the drain is to remove the water directly as this could cause engine failure - never heard a pilot worry about microbial growth

I never came across a diesel powered (light) aircraft, but, I know "Jet-A" is almost identical to diesel and can readily be used in a diesel engine if you add a bit of lubricant.

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1 hour ago, LadyG said:

Ok, 

A :  "Keeping diesel tanks reasonably full reduces the amount of OXYGEN in contact with the diesel as well as minimising condensation, inthe tank which in turn assists in deterring the growth of diesel algae"

RYA members msg Summer 2020

Over to you Dr Bob .......

Unless the diesel actually absorbs oxygen in preference to nitrogen, which would imply that diesel slowly oxidises, then this is rubbish. Might be true if the tank was triangular in section, and narrow at the top,I suppose.

The danger of lack of oxygen in enclosed shipboard spaces comes from the oxidation of steel, not presence of diesel.

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54 minutes ago, Oddjob said:

Empty tank or a not full tank increases condensation which allows “Diesel bug” to leave on the boundary of the fuel and water. Aircraft have the same issue hence water drain done before and after every refuelling. Each tank has a drain point on the lowest point of the tank it’s nothing to get 1/4 to 1/2 a pint out of each tank, more if lazy out stations not doing the drains on the turn round. Biobor is what is used to add to the fuel to kill the bugs. I’ve seen a A320 scrapped as beyond repair with corrosion in the wings due bug infestation. 

Suggesting that

The tank were poorly constructed or the metal poor quality?

Not enough water was bring drained off

Or A N other eg contaminated fuel

I thought you meant the wing fuel tanks rather than the outer skin or frames?

Note to self, never fly again

Edited by LadyG
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IRA quiz.  What can you make with a milk bottle, pint of petrol and a bit of string.

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1 minute ago, bizzard said:

IRA quiz.  What can you make with a milk bottle, pint of petrol and a bit of string.

How long is the piece of string?

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Just now, LadyG said:

How long is the piece of string?

Pajama cord is better. Length depends on how far you can throw and how fast you can run.

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4 hours ago, LadyG said:

This was noted in the RYA members magazine. I will post their answer later, but I wonder what you would have answered?

Q why should diesel tanks be kept reasonably topped up?

Clue, two reasons.

 

They shouldn't be kept reasonably topped up 

A full tank of diesel  in an unused boat will result in greater volume of fuel to deal with if diesel bug occurs

Also bio diesel in the fuel has a shorter shelf life 

Therefore only add fuel if you intend to consume it promptly 

 

By the way the oxygen reason you quoted  is rubbish . For example  in a rectangular tank  the surface area of fuel in contact with the air is the same at any tank level unless the tank is full to the brim.

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2 hours ago, boots said:

With aircraft, the drain is to remove the water directly as this could cause engine failure - never heard a pilot worry about microbial growth

 

Remember every time a jet airliner flies, the fuel tanks are exposed to extremely low temperatures. Typical air temperature at 35,000 ft is -56°C and the fuel typically cools to -30°C on long flights. This would seriously inhibit any bug growth. It also means any water in the fuel could cause serious problems (2008 British Airways 777 crash landing at Heathrow) even though the fuel passes through a heated filter system.  

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