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Tash and Bex

"outside the box" thinkers only please!!!

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Hi,

 

A little one for outside the box thinkers please.

 

I realise a bath on a boat is a ridiculously indulgent waste of water.

 

I also realise the folly of putting a bath on a boat in terms of the space it consumes.

 

I am installing a full sized corner bath with a capacity of around 200L on Helena during a major refit. 

 

I am trying to think of ways to reliably, safely and "legally"(in terms of the BSS) produce enough hot water to fill the bath. Currently I am considering fitting an auxiliary water tank of around the same capacity of the bath to extend our tank capacity enough to allow for it without affecting our bunkering routine too much. and I am considering ways of heating this "buffer" tank before using it to bathe.

 

A few little boaty tech facts about Helena...

 

I have a large (around 700L) water tank, my hot water cylinder is a standard horizontal calorifier, can't remember the capacity, not much! It is currently heated either by a 1kw immersion heater (rarely), the webasto water heater (usually) or the engine. Fairly conventional stuff with exception to the cold storage tank.

 

If i were to sneak in a 250L plastic tank under the new wardrobe floor I could theoretically heat the water that is in it and specifically use it exclusively for our bath.

I would obviously have to have it open vented, but I think I could easily add a balance pipe to the main tank to fill it when we bunker, and gravity would refill it as we use it. I am considering a second hand second webasto to this end.

My calculations seem to suggest a 5kw heater will take approximately an hour to produce a 30c rise in that kinda volume of water. 

Other things I have considered are of course an instantaneous gas heater (an 11L morco would only take 20m to fill the bath directly fed with "cold"water, but at what cost in terms of gas) which is certainly still an option. If I choose to heat the tank of water rather than the instantaneous option of course the tank would be insulated and in order to stop convection mixing the water into the main tank a one way valve could be fitted on the fill (necessary?)

I have also considered the bonus that, if the webasto/tank option is viable I can install some evacuated tube solar hot water on the roof of the boat and pre-warm the tank or even heat it in summer, via a plate heat exchanger. I realise if I do either of these things there will have to be a way of getting the tank to above 65c weekly to remove the risk of legionnaires.

 

Please understand that I am well aware of the folly of the above, please keep the discussion based expanding on my thoughts and let me know your thoughts on where I would stand with the BSS compliance.

 

Thanks in advance, Bex

 

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How much cruising do you do?

A bigger/second calorifier would give "free" heat if you cruise enough

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3 minutes ago, smiler said:

How much cruising do you do?

A bigger/second calorifier would give "free" heat if you cruise enough

very little, we have a permanent city centre mooring now. I have been trying to work space in for a larger domestic unvented calorifier, but I just can't, unless I were to use it horizontally and even this would be a push

 

Edited by Tash and Bex

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I think the sensible thing to do would be to double- or triple- up on components, eg have 3 calorifiers and 3 water heaters. You'd need to do the sums on sizes, heat input etc to size things properly and/or make sure the temperature is okay. The reason for doing so, is that when its NOT needed to heat up water for the bath, there isn't a large calorifier/heater running at very low setting, instead you could manually shut off the other leaving one "normal" duty bunch of components operating. Obviously you'd need to consider hot water expansion/(cold contraction) when designing how things are shut off etc.

 

 

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Just now, Paul C said:

I think the sensible thing to do would be to double- or triple- up on components, eg have 3 calorifiers and 3 water heaters. You'd need to do the sums on sizes, heat input etc to size things properly and/or make sure the temperature is okay. The reason for doing so, is that when its NOT needed to heat up water for the bath, there isn't a large calorifier/heater running at very low setting, instead you could manually shut off the other leaving one "normal" duty bunch of components operating. Obviously you'd need to consider hot water expansion/(cold contraction) when designing how things are shut off etc.

 

 

the open vented auxiliary tank becomes this extended calorifier, if it is connected exclusively (obviously via a pump), to the bath tap it will be effectively excluded when it is not needed. The shower will continue to be connected to the existing system.

 

the large, insulated, plastic tank can quite easily have a small header tank to allow for expansion and this tank can be open vented

 

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20 minutes ago, Tash and Bex said:

My calculations seem to suggest a 5kw heater will take approximately an hour to produce a 30c rise in that kinda volume of water. 

Where will you get a 5Kw supply ?

 

If you are heating 'cold' water which is probably at around canal temperature heating by 30* will only give you a luke-warm (40*C) bath. You would be better heating it to a higher temperature (and killing the bugs) and then adding cold water to suit.

 

Most moorings offer a 16 amp supply - 5Kw would be approx. 22 amps, even without running the fridge, freezer, etc etc etc the heater would 'pop' the trip every time you switched it on.

 

Even a 1kw immersion heater is a no-no when cruising and trying to run it from the batteries.

 

 

 

 

 

 

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another consideration would be to utilise the webasto to directly heat the bath, the principal being, fill the bath with cold water, switch on the webasto, go find something to do while the webasto circulates and obviously warms the water!

3 minutes ago, Alan de Enfield said:

Where will you get a 5Kw supply ?

 

If you are heating 'cold' water which is probably at around canal temperature heating by 30* will only give you a luke-warm (40*C) bath. You would be better heating it to a higher temperature (and killing the bugs) and then adding cold water to suit.

 

Most moorings offer a 16 amp supply - 5Kw would be approx. 22 amps, even without running the fridge, freezer, etc etc etc the heater would 'pop' the trip every time you switched it on.

 

Even a 1kw immersion heater is a no-no when cruising and trying to run it from the batteries.

 

 

 

 

 

 

A webasto water heater is rated at 5kw (or 9kw)

 

we do not have shore supply at our mooring

 

40c water is fairly warm, recommended maximum temp for a bath is 39c

Edited by Tash and Bex

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4 minutes ago, Tash and Bex said:

another consideration would be to utilise the webasto to directly heat the bath, the principal being, fill the bath with cold water, switch on the webasto, go find something to do while the webasto circulates and obviously warms the water!

A webasto water heater is rated at 5kw (or 9kw)

 

we do not have shore supply at our mooring

Apologies - just shows the error of making assumptions.

 

18 minutes ago, Tash and Bex said:

............we have a permanent city centre mooring now.

 

One assumes that a mooring has utilities.

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Just now, Alan de Enfield said:

Apologies - just shows the error of making assumptions.

 

 

One assumes that a mooring has utilities.

lol, nope, zero facilities unless you count a wonky mooring ring and a bollard!

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One of my boats had a bath fitted so I had a 100 litre horizontal calorifier with 2 immersion heaters. Depending on the shore supply availability and what I was running at the time, I could use one or if in a hurry use both immersions and ensure I don't exceed the shore supply rating. Just added cold water to get the desired water temp in the bath. Is the 200 litre capacity of your bath allowing for displacement when you get in? Sorry, just realised you have no shore supply.

Edited by Edders
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24 minutes ago, Tash and Bex said:

very little, we have a permanent city centre mooring now. I have been trying to work space in for a larger domestic unvented calorifier, but I just can't, unless I were to use it horizontally and even this would be a push

 

I dont think that would work very well

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11 minutes ago, Tash and Bex said:

the open vented auxiliary tank becomes this extended calorifier, if it is connected exclusively (obviously via a pump), to the bath tap it will be effectively excluded when it is not needed. The shower will continue to be connected to the existing system.

 

the large, insulated, plastic tank can quite easily have a small header tank to allow for expansion and this tank can be open vented

 

Without delving too deeply into the effectiveness of insulation or the type (well.....heat handling capability) of the plastic tank, I'd have thought a purpose-designed calorifier would be better performing. Also, I had in mind you'd heat (a smaller amount of water) to what you might consider normal domestic hot water temperature, then mix during filling the bath to comfort. Of course, the energy demand would be the same.

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1 minute ago, Edders said:

One of my boats had a bath fitted so I had a 100 litre horizontal calorifier with 2 immersion heaters. Depending on the shore supply availability and what I was running at the time, I could use one or if in a hurry use both immersions and ensure I don't exceed the shore supply rating. Just added cold water to get the desired water temp in the bath. Is the 200 litre capacity of your bath allowing for displacement when you get in?

I've just looked at the capacity, which it clams is 210l, so no allowance for displacement, but I think working on worst case will give me suitable headroom in the specs

3 minutes ago, ditchcrawler said:

I dont think that would work very well

 presumably a horizontal one would? even given the rubbish stratification issues

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If running costs is an issue, then I think that solar thermal would provide an abundance of piping hot water. The downside is that this option is only viable from April to Sept!!

We have solar thermal at home and it is fantastic. Many, many deep baths provided courtesy of the sunshine. Cheap to install evacuated tubes and pumping station - just need a coil to run it through a storage cylinder to heat the water. Simples.

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7 minutes ago, musicman said:

If running costs is an issue, then I think that solar thermal would provide an abundance of piping hot water. The downside is that this option is only viable from April to Sept!!

We have solar thermal at home and it is fantastic. Many, many deep baths provided courtesy of the sunshine. Cheap to install evacuated tubes and pumping station - just need a coil to run it through a storage cylinder to heat the water. Simples.

Yes it would definitely be a bonus, and an external heat exchanger in combination with a circulation pump on the tank would replace an internal coil. In your experience, even on fairly short and cool days outside of april to september, do you get a "pre-heating" effect from the solar water system.

 

Running costs are not a huge issue, the bath would certainly be seen as a weekly "treat" with showers being taken the vast majority of the time

 

 

Edited by Tash and Bex
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53 minutes ago, Tash and Bex said:

I've just looked at the capacity, which it clams is 210l, so no allowance for displacement,

Bath with a friend and double the displacement 🙂

 

210 L is a lot of water in a bath unless you want to swim lengths. I reckon we use less than 100 L in a corner bath at home.

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To keep it relatively simple I would use a second twin coil calorifier calorifier fitted with an immersion heater.

 

Whan moored use a small petrol genny to supply the immersion heater to heat the hot water for the bath and when cruising the engine will heat the second calorifier.

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Just now, Onewheeler said:

Bath with a friend and double the displacement 🙂

 

210 L is a lot of water in a bath unless you want to swim lengths. I reckon we use less than 100 L in a corner bath at home.

Brilliant, so allowing for a full bath of hot water will give me a considerable overhead, perhaps I can reduce the capacity of my auxiliary tank to 150L

 

3 minutes ago, cuthound said:

To keep it relatively simple I would use a second twin coil calorifier calorifier fitted with an immersion heater.

 

Whan moored use a small petrol genny to supply the immersion heater to heat the hot water for the bath and when cruising the engine will heat the second calorifier.

it's an ideal solution, my only issue would be sizing the second calorifier, what capacity would I need to fill a full size bath with nice hot water assuming the cold water I mix in is at what, 10 degrees?

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I would give further consideration to using a Morco or similar. I'd imagine you'd use a fair amount of gas but if that's an issue you could invest £300 or so on 2 refillable bottles, and pay roughly half for the gas. That's if you have transport of course, and somewhere fairly local that allows self fill on lpg.

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Heating a plastic tank is fraught with problems. Heating an open tank, or more correctly a cistern inside a boat will lead to uncontrollable condensation.

Heat water in a calorifier to a higher than normal temperature, say 90 degrees and dilute with cold.

If you are permanently moored consider a roof calorifier with a solar water heater, you can then use gravity circulation, no pump, no electricity consumption. As long as the solar array is under the calorifier it will circulate. Then you could always empty it to take it off the roof when cruising.

It worked for Tom Rolt!

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where is the new bath going to be located and the tank as potentially you are adding 400  kilo's of water to the boat, if not on the centreline you will get a substantial heel, my off-centre 200 litre waste tank produces a noticeable list at 50% and I have never had more than 80% as things start sliding a little bit. Even a 1 or 2 degrees list is noticeable when in bed.

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18 minutes ago, Detling said:

where is the new bath going to be located and the tank as potentially you are adding 400  kilo's of water to the boat, if not on the centreline you will get a substantial heel, my off-centre 200 litre waste tank produces a noticeable list at 50% and I have never had more than 80% as things start sliding a little bit. Even a 1 or 2 degrees list is noticeable when in bed.

it won't be on the centreline, which i agree could cause an issue, however if i further explore the "auxiliary" tank option either the bath or the tank will be full so they can be ballasted for. my waste tank is quite another issue!

 

we have a cross bed arrangement, ballasting and list don't seem to affect sleep as much in a cross bed

22 minutes ago, Boater Sam said:

Heating a plastic tank is fraught with problems. Heating an open tank, or more correctly a cistern inside a boat will lead to uncontrollable condensation.

Heat water in a calorifier to a higher than normal temperature, say 90 degrees and dilute with cold.

If you are permanently moored consider a roof calorifier with a solar water heater, you can then use gravity circulation, no pump, no electricity consumption. As long as the solar array is under the calorifier it will circulate. Then you could always empty it to take it off the roof when cruising.

It worked for Tom Rolt!

but an open vented tank doesn't necessarily mean an open tank, just an unpressurised one, if i have a similarly closed expansion tank which is then vented I could vent through the deck head.

 

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A simple back of the envelope calculation:

 

2x 75l calorifiers

they can happily operate up to 85 deg C

mixed with water at 10 deg C, this would mean 200l @ 66 deg C

 

1x 75l calorifier

operating at 85 deg C

mixed with water at 10 deg C, this would mean 200l @ 38 deg C

 

 

So it shows its definitely possible, if you part-filled the bath to less than 200l and was happy with ~40 deg C (I think I'd prefer a touch more) then you don't even need to worry about a second calorifier. But it may be inefficient if its a horizontal, and for "normal" use on a boat given that you'd need a gas or diesel (or immersion) heater which you'd pay for the energy, rather than using the available excess heat from cruising and running the engine.

 

 

9 minutes ago, Tash and Bex said:

 

but an open vented tank doesn't necessarily mean an open tank, just an unpressurised one, if i have a similarly closed expansion tank which is then vented I could vent through the deck head.

 

A calorifier isn't "really" pressurised either, at least not to a great amount. Its only pressurised to the normal pressure the water pump operates at, to physically be able to flow the water out of the taps at a given flowrate. Its not, say, 10 bars or so, the pressure rise due to heating of water is relieved and vented by the PRV.

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7 minutes ago, Paul C said:

A simple back of the envelope calculation:

 

2x 75l calorifiers

they can happily operate up to 85 deg C

mixed with water at 10 deg C, this would mean 200l @ 66 deg C

 

1x 75l calorifier

operating at 85 deg C

mixed with water at 10 deg C, this would mean 200l @ 38 deg C

 

 

So it shows its definitely possible, if you part-filled the bath to less than 200l and was happy with ~40 deg C (I think I'd prefer a touch more) then you don't even need to worry about a second calorifier. But it may be inefficient if its a horizontal, and for "normal" use on a boat given that you'd need a gas or diesel (or immersion) heater which you'd pay for the energy, rather than using the available excess heat from cruising and running the engine.

 

 

A calorifier isn't "really" pressurised either, at least not to a great amount. Its only pressurised to the normal pressure the water pump operates at, to physically be able to flow the water out of the taps at a given flowrate. Its not, say, 10 bars or so, the pressure rise due to heating of water is relieved and vented by the PRV.

a calorifier is running at 25psi in most cases, which is around the same pressure as a non vented domestic system. the issue really comes if the prv fails, they don't half go boom if they boil up....

 

However assuming that doesn't happen then this is a definite possibility should it not prove possible to implement my "plastic" tank idea.

incidentally, a plastic tank would have the same capacity as the bath and therefore wouldn't need to be heated past 40 degrees and diluted, however I would have to heat it past i think, 65c regularly to destroy legionnaires bacteria 

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1 minute ago, Tash and Bex said:

a calorifier is running at 25psi in most cases, which is around the same pressure as a non vented domestic system. the issue really comes if the prv fails, they don't half go boom if they boil up....

 

However assuming that doesn't happen then this is a definite possibility should it not prove possible to implement my "plastic" tank idea.

incidentally, a plastic tank would have the same capacity as the bath and therefore wouldn't need to be heated past 40 degrees and diluted, however I would have to heat it past i think, 65c regularly to destroy legionnaires bacteria 

I think you would be sailing very close to the wind with a lot of faith th a pressure switch and a pressure relief valve at 21 psi max pressure.

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