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What is the optimum capacity for fresh water,fuel tank for engine/heating,fuel tank for a stove and a holding tank for a pump out toilet . It is for a 58 feet narrow boat for 2 people and a dog ,residential use with visitors .

Asked by: costas  | 5.12pm, Sunday 19 June


WW says:

If you are planning to live on the boat, you obviously don't want to be filling up the water tank every day or two which suggests as large a tank as possible. However, if the tank is too large - and situated at the front of the front of the boat where most of them are - the amount of water in it will affect the trim of the boat. The best solution may be to have a large tank but top it up fairly regularly so that you don't reduce the weight too much between fills. This way, you will have some emergency capacity to call on if, for any reason, you are not able to fill up as often as normal. Giving a precise volume is not easy but something around 250 to 300 gallons comes to mind. With a large tank like this, it is particularly important to have a good water filter that will remove any 'nasties' - and not just the smell - before they reach the tap.
On the face of it, the same argument might be applied to the fuel tank but, these days, you have to think about the diesel bug. If the fuel is left in the tank for too long, it can become contaminated with water which provides an ideal breeding ground for microbes that feed on the fuel and eventually clog the pipes. You therefore need a modestly sized tank so that you fill it fairly frequently with fresh fuel. Again, it is difficult to give a figure but, since you are running an oil fired boiler as well, I would suggest about 80 to 100 gallons.
The same basic considerations apply to the tank for the stove but I have no direct experience of oil-fired stoves on boats.
Many residential boaters avoid the question of holding tanks by opting for a cassette toilet. These are far more civilised than the old 'bucket and chuck-it' types and have the advantage that they can be emptied free of charge. They also mean that you will not have the problem of being iced in and miles from a pump-out point. However, I appreciate that the choice of loo type is a personal one and, if you are determined to have a pump-out, something around 100 gallons should give you a reasonable range. A tank of this size should be located as near to the centre line of the boat as possible to avoid it listing to one side as the tank fills. Finally, dogs find pump-out toilets very difficult to use so make sure you have a good supply of poop bags.

Graham Booth  | 11.45AM, Monday 27 June

I would edge to a smaller diesel tank as you can get away with. If you have an 80 gallon tank, you might find that you don't get through this in a year- and with hot diesel being recirculated from the engine, the fuel can degrade. Ideally, a fuel tank would not be integral with the hull- especially at the stern- as heating of the fuel happens with sunlight on the stern. This can also exacerbate air flow in and out of the tank as the gas inside the tank expandes and contracts- which increase moisture transfer. The greater the moisture, the more liable fuels are to both diesel bug and decay.
A smaller, seperate tank, filled more often would be ideal; however this is not currently the norm. Smaller tanks are easier to clean of debris as well...
You can use a larger tank for heating systems, as hot fuel is not returned to the tank- and they make good sense as it is easier to seperate heating fuel from propulsion fuel. However, they do need water-fuel seperators fitted in the supply line, as with propulsion engines, to avoid damage to the burner unit.

Mark Langley  | 1.53PM, Tuesday 28 June


Readers say:

Thank you Graham for your speedy reply. These were the sizes I was thinking of but I just thought to check before ordering the boat.

costas  | 6.55PM, Monday 27 June

Thank you Mark I was thinking to have separate fuel tanks. I read forum after forum but I think I made my mind up after your answer.

costas  | 10.27AM, Thursday 30 June

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