how big a hot water tank

A little goes a long way. I have a 22 litre calorifer, the size really determined by what would fit (wooden boat and all that). But 22 litres in the tank converts to more at the tap because it's temperature is hotter than you can handle. So you have a thermostatic mixer valve at the tank to blend in cold water to an acceptable temperature. I don't have a shower but I guess 22 litres would not go far enough for showers for 4 but it's more than enough for 4 people washing and washing crockery. the water warms up v quickly as well - 30 minutes is ample.
 
pottyYachtie said:
How big a hot water tank would you put into a 30 ft boat built for 4 people?
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Fit as big a calorifier as you have space for.

Work on the principle that you can never have too much hot water.

Even if you don't use it today, if it's well insulated it'll stay warm for a couple of days and will save you having to run the engine unnecessarily just to get hot water.

It'll also leave some for a wash & shave the following morning, and the washing up after breakfast.

You can never have too much hot water.
 
Mine was changed to 55ltr by the previous owner. His rationale was that he had also increased the overall water capacity. I think this is a good idea, as long as it doesn't upset the balance of the boat.
He also fitted a small device to the shower plumbing which keeps the maximum temperature safe at all times by bleeding in some cold water if necessary.
Allan
 
Allan said:
Mine was changed to 55ltr by the previous owner. His rationale was that he had also increased the overall water capacity. I think this is a good idea, as long as it doesn't upset the balance of the boat.
He also fitted a small device to the shower plumbing which keeps the maximum temperature safe at all times by bleeding in some cold water if necessary.
Allan
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How does that work? On our system it is a pain to get the calorifier empty for frost protection in winter as the pump only works while there is water in the cold tanks. (I use a syphon to ground level on the drain cock and disconnect the inlet pipe to get the water out, but it is a pain to do). Is there a safe and easy way to alter the plumbing so that the calorifier can be drained by the pump after the main tanks are empty.
20 litres works for us on a sailing boat where the engine is not used all the time and we are seldom on shore power, as it heats up reasonably rapidly, though we shower ashore as much as possible. Usually where shorepower is available there is a shower available not too far away.

When commenting on calorifiers on here I like to take the opportunity to warn against choosing the shiny Italian made Isotemp ones, but you do need good insulation.
 
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I've never drained the water from my tank but I imagine it would be as difficult as yours. The cold water is pumped into the tank so would stop when the cold water tank is empty.
The temperature control is a simple device which fits between the hot and cold supplies for the shower mixer. I understand it is the type of thing fitted in old peoples homes to stop scalding. It is purely mechanical and works perfectly.
I agree with what you say about insulation, it make all the difference and is more important than increase the volume of water if space is a problem. Better to have 30ltr of hot water than 55ltr which goes cold overnight.
Another thing to look out for is the length of the heating pipe inside the tank. some just go in and come out. mine has a long coil going right down the centre. It makes all the difference in the time it takes to heat the full tank.
Allan
 
Fit the largest one you can squeeze into the space available, when mine failed 18ltr replaced it with a 50ltr sure cal one they do lots of different sizes and designs good insulation and advice.
Have lots of hot water mixes with cold at outlet with thermostat for showers and safety and stays hot for over 24 hrs. Also have electircal element for 240v when required.
 
Quandary said:
How does that work? On our system it is a pain to get the calorifier empty for frost protection in winter as the pump only works while there is water in the cold tanks. (I use a syphon to ground level on the drain cock and discopnnect the inlet pipe to get the water out, but it is a pain to do). Is there a safe and easy way to alter the plumbing so that the calorifier can be drained by the pump after the main tanks are empty.
20 litres works for us on a sailing boat where the engine is not used all the time and we are seldom on shore power, as it heats up reasonably rapidly, though we shower ashore as much as possible. Usually where shorepower is available there is a shower available not too far away.

When commenting on calorifiers on here I like to take the opportunity to warn against choosing the shiny Italian made Isotemp ones, but you do need good insulation.
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just have the pump before the hotwater tank, the hot water tank has a drain on the bottom to empty it. most pumps can run dry now so no problem.
 
ukmctc said:
just have the pump before the hotwater tank, the hot water tank has a drain on the bottom to empty it. most pumps can run dry now so no problem.
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I am afraid I do not understand, can you elaborate? My pump, like most others is before the hot water tank, it uses cold water to displace the hot. When the cold water is finished it tries to pump air which does not displace the water effectively. I would not be prepared to allow the pump to run on air for the length of time it would take to displace the contents of the cylinder even only 20l. as it would only come out at a dribble. I usually ease the straps and rotate the tank to ensure the pick up pipe internal end is as low as possible when syphoning it to ground level. the higher head increases the speed a bit, with a saildrive you normally have dry dusty bilge cavities so I like to keep water out of them.
 
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