Hot Water System

[Simi 60]

New boat has a perfectly adequate HWS on board for when attached to a marina berth.
A Rheem household 140 litre with 240v supply
As we plan on actually using the boat and unattached we need an alternative.

The boat will mainly be used in warmer climates mainly with two people on board.
We have had boats before so are used to short showers so not much hot water required for showering, some months even cold showers will be the norm.
Main water usage will be hot water for washing up.

One thought was to use the existing tank as storage and try and set up a recirculating water supply getting heat from the primary engine when running and then kept warm by the genset when running for an hour a day while supplementing solar charging.
I think in reality this will not work.

On demand gas is considered, but laws in Australia mean that only certain systems meet approval so that will be a $1000 PLUS installation plus gas is not always readily available

That leaves small 240v and off engine systems.

I was looking at this would appear to be the simplest install once I remove the existing electric HWS as power and water are already there.
Duoetto 12Volt-240Volt Electric 10Litre Hot Water Heater
https://www.keoghsmarine.com.au/HOT...torhomes-RVs-Camper-trailer-Power-Motor-Yacht

Next was this unit and while it has some advantages it will be a more difficult install.
Kuuma / Force 10 24 Litre Water Heater
https://www.whitworths.com.au/main_itemdetail.asp?cat=133&item=93079&intAbsolutePage=

Any thoughts or is there something better I am missing?

 

[ksanders]

we have a standard marine water heater. it gets geat from the engine while cruising. otherwise it heats the water using 120 V from either the generator or shore power.

we just came back from a weeklong cruise and never wanted for hot water. I can't imagine things would be different as A full-time cruiser, or live aboard.

 

[caltexflanc]

When we were living aboard and cruising full time we had a set up identical in size and configuration as the OP. We found the water heater kept water hot for at least a day without power. An hour or two a day from the genset was enough to keep it just fine. My advice would be to do nothing, go for a cruise and see how it works for you.

 

[Simi 60]

My advice would be to do nothing, go for a cruise and see how it works for you.

Sounds like fair advice, thanks

 

[Bay Pelican]

Quality marine water heaters (ours is Isotherm) will keep water hot for 24 hrs. Their insulation is designed for storage. Isotherm sells 240v 50 hertz units.

We anchor out for months and find that a 25 liter unit provides all the hot water we need. The water is heated whenever the generator or main engine is on which is usually once or twice a day.

Choosing the wattage for a six gallon unit is an important decision. Using a 120v US based system we have had both a 1,500 watt unit and now a 750 watt unit. The time required to heat the water has changed from approximately 15 minutes of generator run time to approximately 30 minutes of generator run time with the 750 watt unit.

It was our preference to drop to the 750 watt unit to reduce the load on our generator during the first 15 minutes when both chargers are at full output. Ours is a 8kw generator. With a larger generator or only one charger this would not be an issue.

 

[angus99]

We have an Isotemp Spa 30 (about 8 gallons). It has multiple mounting options--ours is fixed to a bulkhead--and it can be mounted horizontally or vetically. A mixing valve prevents scalding while extending the volume of hot water, which otherwise would be overheated by the engine coolant loop. It has a polypropylene case so it's a little less pricey than the stainless shells. The tank is 316 stainless. They also make a Spa 40--about 11 gallons--if you have the space.

 

[FF]

The solar shower (a plastic bag) works fine , and can be carried below easily if your shy on deck showering.

Just for dish washing using the stove to heat a quart is fast and simple.

No need for hot to rinse soap off.

Underway boats can feed some of the sea water coolant to an always on sink spout.

Great for checking the engine cooling underway and does well at rinsing , or even washing and showering .

 

[DeniseO30]

Simi, you can keep the larger tank and use a typical engine heated WH that will heat all the water via thermo-siphon (gravity flow, one to the other) I would take longer to heat it all but if the engine is running.... and running....

You could use designated external engine heat exchanger but that is what is inside a marine water and would cost about the same.

 

[sunchaser]

When we were living aboard and cruising full time we had a set up identical in size and configuration as the OP. We found the water heater kept water hot for at least a day without power. An hour or two a day from the genset was enough to keep it just fine. My advice would be to do nothing, go for a cruise and see how it works for you.

 

[Trundlebug]

When we first bought our boat it had a 25litre hot water tank with engine heated coil calorifier and 240v immersion heater (2kw).

After using the boat for a while we discovered that the 25 litre hot water tank wasn't really big enough. 2 people could have a shower, with just enough left over to wash up with, but that was about it.

So I decided to add another 35 litre calorifier next to the existing one in the engine bay (there was plenty of room at the aft end), and plumb it in series with the existing one. So the HW take off is from the original tank, and that tank gets heated first, the new (second) tank is connected in series so starts to heat up when the first tank has nearly equalised.

It's been fantastic. We have what seems like unlimited hot water for 36 hours after a decent run of 2-4 hours. It means we don't have to worry about running out of hot water when having a shower. There's now enough to shower 4 people in succession and still have enough to wash up and have a shave the next morning.

In your position I would advise doing exactly the same, but wire it so you can heat it up by immersion from the generator on the first tank if you need it. We don't have a generator so I can't do that. But it would be the easiest solution instead of a complete re-installation.

 

[DeniseO30]

When we first bought our boat it had a 25litre hot water tank with engine heated coil calorifier and 240v immersion heater (2kw).

After using the boat for a while we discovered that the 25 litre hot water tank wasn't really big enough. 2 people could have a shower, with just enough left over to wash up with, but that was about it.

So I decided to add another 35 litre calorifier next to the existing one in the engine bay (there was plenty of room at the aft end), and plumb it in series with the existing one. So the HW take off is from the original tank, and that tank gets heated first, the new (second) tank is connected in series so starts to heat up when the first tank has nearly equalised.

It's been fantastic. We have what seems like unlimited hot water for 36 hours after a decent run of 2-4 hours. It means we don't have to worry about running out of hot water when having a shower. There's now enough to shower 4 people in succession and still have enough to wash up and have a shave the next morning.

In your position I would advise doing exactly the same, but wire it so you can heat it up by immersion from the generator on the first tank if you need it. We don't have a generator so I can't do that. But it would be the easiest solution instead of a complete re-installation.

Funny how we said the same thing with so many different words.

 

[Lepke]

I have a house hw 50 gal tank and surrounded it with 2" foam along with good insulation applied to all pipes (even cold) so heat isn't drawn out. I can keep water warm enough for a comfortable shower for 4 days if I'm not using much hw for other things.
With a heat exchanger you can heat with engine water. With some valves you can use either main or generator.

 

[Tidahapah]

Simi,
I used to have instant gas hot water but upon failure of the unit a replacement could not be used due to the new regs. ( could have but had to be installed outside)
I have chosen to go with a Force 40 lt unit and not connected to main engine cooling water, strictly 240 V.
So far I am happy but probably with your boat would go at least 90 lts. Even with my solar panels i still run my gen set an hour or so a day which is enough time to heat water and a bit longer sometimes to make water.
have just spent 2 weeks out on the Swains with 4 of us free diving a couple of times a day and heavy use on frig and freezers (freezing fish and crays and lots of fresh water washing) and still happy with the set up.

 

[Simi 60]

I have chosen to go with a Force 40 lt unit and not connected to main engine cooling water, strictly 240 V.
So far I am happy but probably with your boat would go at least 90 lts.

Good to hear and the price is right on the 40's.
Why do you think I will need 90?
There'll only 2 of us on board 99% of the time

 

[Peter B]

Good to hear and the price is right on the 40's.
Why do you think I will need 90?
There'll only 2 of us on board 99% of the time

Can you refresh our memories as to why you want another cylinder at all, when you have a 140L one heated off 240v already. I agree with those who said just use what you've got heating from the genny/house bank/inverter, until you see how well it copes. If you leave the dock with it heated right up, with good insulation and that volume, topping up the heat via genny or house bank would not take all that much I would think.

FWIW, we have no 240v on our boat when away from the dock, but a quick 30 min preheat off 240v while getting ready is sufficient to get it quite hot, then engine heat keeps it that way, but it stays hot at anchor wth no heat input for at least 48 hours. (Isotherm 42L with engine heat exchanger)

 

[Simi 60]

Can you refresh our memories as to why you want another cylinder at all, when you have a 140L one heated off 240v already.

I dont want "another" one, but as the existing unit is 10 years old it may not have much life left anyway

I agree with those who said just use what you've got heating from the genny/house bank/inverter, until you see how well it copes.

As did I.
I wont be replacing it unless the batteries cant cope or the system dies.
I certainly wont be running the genny for several hours a day just for hot water.

If you leave the dock with it heated right up, with good insulation and that volume, topping up the heat via genny or house bank would not take all that much I would think
FWIW, we have no 240v on our boat when away from the dock, but a quick 30 min preheat off 240v while getting ready is sufficient to get it quite hot, then engine heat keeps it that way, but it stays hot at anchor wth no heat input for at least 48 hours. (Isotherm 42L with engine heat exchanger).

Once I leave the dock I dont plan to be back on one for at least a year.
That means once it goes back in the water next month thats it, no more shore power.

 

[BruceK]

Marine HWS are often 10gal/40L. Is your issue you want engine heat as well as 240v input?
You can run the existing 240v water heater when the genny is doing other things, eg batts, eutectic fridge, etc, they like a good load. But if you aim to use solar more and genset less, maybe a new HWS both tapping engine heat, and using 240v, is better.
You could see how it goes. Or hold off replacement until the Rheem dies. The PO must have managed ok,a domestic Rheem is a less common system, maybe some thought went into it. You might find it works for you too.
PS. In view of your new post about prolonged cruising, what`s your water capacity, do you have a desalinator?

 

[Tidahapah]

Simi,
My rational behind the 90 lts is just more holding capacity and hot water for longer when shut down.
Not using engine is just a personal thing of mine , it is really just another water connection that can fail either causing hot water heater problems or engine problems.
Look I have been at sea as a Chief Engineer for over 40 years and still like to keep things simple and have less problems , I can make enough of these myself with the places I go.

 

[Simi 60]

The PO must have managed ok,a domestic Rheem is a less common system, maybe some thought went into it. You might find it works for you too.

The PO only used her on weekends and even then may not have left the dock, so he had plenty of power.

PS. In view of your new post about prolonged cruising, what`s your water capacity, do you have a desalinator?

No desal but 4500L worth of water tankage and 7000L of fuel

 

[Simi 60]

Simi,
My rational behind the 90 lts is just more holding capacity and hot water for longer when shut down.
Not using engine is just a personal thing of mine , it is really just another water connection that can fail either causing hot water heater problems or engine problems.
Look I have been at sea as a Chief Engineer for over 40 years and still like to keep things simple and have less problems , I can make enough of these myself with the places I go.

Same here, would rather not use engine heater and will only be motoring for several hours a week anyway.

But I do have a good deal on 2300W of solar going on the roof to keep 800ah of 24v batts charged and hopefully not needing the genset as much.
There should be enough power to run a smaller HWS system as often as it needs when the time arrives .

 

[BruceK]

Advice is predicated on information supplied. 2300 watts of solar is new information > different advice.

 

[Tidahapah]

Simi,
from what you have said with no water maker you will have to go in and get water at some stage.
The best investment for any long term cruiser who carries plenty of fuel is a water maker and a no frills 60 lt / hr model can be purchased for 5k or 6 k for 120 lt/hr.
Then run the gen set, heat water and make water at the same time, you will be so glad you did.

 

[Simi 60]

Simi,
from what you have said with no water maker you will have to go in and get water at some stage.

I will also need to go in and get fuel as well.
Once a month pull into a fuel dock tip in a few hundred litres of fuel and top off the water while there was my way of thinking.

We lived aboard our previous boat for several months at a time and only had 200L water tanks and never needed a desal.
4500 litres of water on this one should seem quite luxurious and will keep us going for quite some time I imagine.

But, we'll see how it goes.

 

[Bay Pelican]

Bay Pelican has a water maker and 1200 liter tanks. We use our washing machine daily using perhaps 50 liters for the wash. At that we seldom go through more than 200 liters a day. A 4500 liter capacity would be more than sufficient for extended anchoring.

The only difficulty I see is that to refill 4,500 liters would require you to take a slip for the night or at least a few hours. A fuel dock would not be happy with you tying up the dock for the time it would take to refill the tanks with a normal water hose. In North America and the Caribbean the water hoses have 1/4 or less of the flow rate of the fuel hoses.

 

[FF]

"Once a month pull into a fuel dock tip in a few hundred litres of fuel and top off the water while there was my way of thinking."

Where do you store to dump a months worth of garbage?

***

If you have an abundance of solar , with a safe switching setup you can use any excess DC fed directly to the HW heater element.

Sure its slow , but if there is juice to burn , might as well use it.

Underway the marine style heat exchanger with either the propulsion engine or noisemaker works fine.

The solar folks sell heat exchangers that install in the over pressure relief setup on a std home style heater .

Using the waste heat from a small noisemaker is a good way to reduce its load so shorter run times can be had.

 

[Simi 60]

Where do you store to dump a months worth of garbage?

Reality is, if near civilisation, every time you go ashore in the dinghy you take some rubbish.

On the last boat we got rid of most packaging before storing stuff on board.
We could go a month at a time in remote locations and still only have a small amount of rubbish to get rid of.

Fresh fruit and veg, rice, fresh fish, bugger all rubbish there.

 

[Simi 60]

We use our washing machine daily using perhaps 50 liters for the wash.

Really?
We only use ours once a week when on land.
Same size machine on the boat.

The only difficulty I see is that to refill 4,500 liters would require you to take a slip for the night or at least a few hours.

Good point.
Apparently 20 litres/minute is average for a tap here making 50 minutes/1000l.

Maybe if we are the last fill of the day or a quiet day midweek they'll let us stay a bit longer.
Midweek in the past has worked before for an hour or two with no issue.

I can certainly see how it could be an issue on the weekends

 

[FF]

With a large boat , there is the ability to have space for a pure solar HW heater.

These are very simple to create m a box painted black inside with 50 ft of soft 3/4 refrigeration copper tubing .

A glass cover works, but if sized to use a replacement double glass sliding door insert , the efficiency goes up.

Solar HW gets really expensive and complex IF they must be used in climates that freeze overnight.

But for a southern warm lifestyle , the only purchase is an aquastat that senses the water temp in the tubing , and a tiny DC pump to circ it into the existing on board HW tank.

The circ pump has a very long life as its sealed , the drive from motor to pump is magnetic , no shaft seals.

IF you have the room this would be a cheap simple way to make unlimited HW that is basically seamless.

Till it freezes.

 

[Simi 60]

With a large boat , there is the ability to have space for a pure solar HW heater.

.

Space yes
Extra weight wanted aloft no.

Its either 180kg of water and system Vs same weight for 9 x 250w panels
I cant really have both.

 

[Phil Fill]

We have two water heaters, 8 gallon marine electric, and a Wabosto diesel which is part of heating system. The Wabosto can heat the water only, during the warm months. However in the warmer months the electric is used and is on a timer that heats one hour twice a day. The domestic water pump is a low psi so water is saved conserved. We very seldom use the on board washer, so land is used.

Water tanks hold 400 gallons that can last 2+ weeks. We have a microphor sanitation that is like a small septic tank that uses no chemical or electric. When at the dock we use the holding tank and get pumped out once a week. When away from the dock and when can not get pumped the Microphore is used. So we could go 2+ weeks away from a dock.