Run the water heater from the inverter?

[BrianSmith]

We often run the boat for 4-5 hours at a time, and it's not unusual to run it for 8 or more. But in the next 30 days or so, we may be looking at running it non-stop for about 140 hours, to cover the distance from the USVI to FL. (If the Bahamas don't loosen their restrictions, we have to go around them.)

I don't want to run the generator more than I have to, and everything that we'll need for a long passage like that is either DC, or runs off the inverter. Except the watermaker and the water heater. I expect to run the generator and watermaker for about an hour every other day, which will heat up some water, but in between, with the main engine running and charging the house bank, what about running the water heater from the inverter?

I would turn it on only once the house bank is fully charged, but then just leave it on all the time, so as it draws power from the house bank, the alternator will keep the house bank topped up.

Inverter: Magnum 3000 watt model.
Water heater: Seaward S1900E - 1500 watts, 120 volts.
ME alternator: Balmar 205 amp
House bank - 760 amp hours (8 GC batteries, not yet 3 years old)

The amp calculators I find online refer to something called the Power Factor that's necessary to calculate amps, and from what I can tell, a resistive load like a water heater is 1.0, or very close to it. Assuming 0.9 for the Power Factor, the water heater will draw about 14A AC, or 140A DC.

Thanks for any input. (Except for any input like "just go through the Bahamas - they'll never know!". Not doing that.)

 

[Pau Hana]

Is your water heater plumbed into the engine's cooling system? It's an easy way to heat the water in the tank while underway...

 

[BrianSmith]

Is your water heater plumbed into the engine's cooling system? It's an easy way to heat the water in the tank while underway...

Nope. It used to be, but somewhere along the line, a PO replaced the water heater with one that's electric-only.

 

[Comodave]

That’s too bad. Waste all that excess heat and then have to use electricity to heat it.

 

[Larry M]

You can but watch your alternator output. If you leave with a battery deficit, your alternator may not be able to charge the bank and support the water heater.

 

[menzies]

Might be safer to have cold showers for the six days. One every other day, just three cold showers.

 

[Pau Hana]

Nope. It used to be, but somewhere along the line, a PO replaced the water heater with one that's electric-only.

To me, the simplest workaround would be to replace the Seaward with an equivalent unit that has the heat exchanger. Much more peace of mind than worrying about load sharing and potentially flat batteries...

 

[DavidM]

140 amps DC or more with efficiency losses is a lot to draw even from a 205 amp Balmar alternator.

How about replacing, even temporarily for this trip, the heater element with a lower wattage one, either a 500 watt element like this one: https://www.amazon.com/dp/B074K98XR...jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

or this 300 watt element: https://www.amazon.com/dp/B0176DVBR...9Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

These will drop the load on your alternator to 1/3 or less.

David

 

[BrianSmith]

To me, the simplest workaround would be to replace the Seaward with an equivalent unit that has the heat exchanger. Much more peace of mind than worrying about load sharing and potentially flat batteries...

Except for the fact that we're living on the boat full time, and we're currently in the USVI, which is under lockdown, and I couldn't get a new water heater here in time for us to depart for the US.

BUT... what is the potential for "flat batteries" in my scenario? The main engine (and hence the ME alternator) won't stop running the entire time we're making this trip.

 

[Larry M]

I’d run the boat till the batteries are topped off. Switch on the water heater and watch your SOC meter. You’ll know fairly quickly if the alternator will keep up with it. Keep monitoring it. Your voltage regulator may throttle back the alternator as it gets warmer/too hot (if your voltage regulator has that function). We’ve run our 1.5 hp water maker from the inverter while underway with no problems as long as the house bank is full first.

At the end of the day, if your concerned, I’d just run the generator as needed. It would be too bad if your alternator failed for the trip your planning.

 

[Comodave]

I think for a one time trip that I would just go ahead and run the genset to heat the water. I wouldn’t want to burn up the alternator halfway through the trip, where would you get a replacement? What will the genset burn in fuel for the few extra hours? Not nearly as much as a new alternator will cost to say nothing of the PITA that would be.

 

[BrianSmith]

140 amps DC or more with efficiency losses is a lot to draw even from a 205 amp Balmar alternator.

How about replacing, even temporarily for this trip, the heater element with a lower wattage one, either a 500 watt element like this one: https://www.amazon.com/dp/B074K98XR...jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

or this 300 watt element: https://www.amazon.com/dp/B0176DVBR...9Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

These will drop the load on your alternator to 1/3 or less.

David

That's a VERY interesting idea! And maybe not just temporarily. 500W might be enough to heat the water satisfactorily all the time. And there are 1000W elements that should also do the trick. Thanks for the suggestion!

 

[BrianSmith]

I think for a one time trip that I would just go ahead and run the genset to heat the water. I wouldn’t want to burn up the alternator halfway through the trip, where would you get a replacement? What will the genset burn in fuel for the few extra hours? Not nearly as much as a new alternator will cost to say nothing of the PITA that would be.

'Tis a valid point. But it sure would be nice to be able to heat water whenever we're underway, even for just a few hours. Maybe the suggestion to replace the heater element with a lower watt unit, making it safe to run off the inverter any time, is my best bet.

 

[DDW]

I'd run the genset, and I hate running the genset. If you try it with the inverter, make sure your alternator frame temp is monitored. A few hours on the genset would be far preferable to burning up the alternator mid-voyage.

 

[Flatswing]

Why The concern with the genset if you are motoring anyway? Fuel shortage? Once hot, my hot water says warm for 24+ hrs. Shower every other day after water maker run.

 

[twistedtree]

I think it will be just fine, especially for an occasional long run like this.

Once heated, it will turn off, so won’t be running all the time.

Just keep an eye on the alternator temperature, and the battery charge state. If either starts getting into trouble, turn off the water heater for a while.

 

[STB]

Personally, I run the genset any time I am underway. I've got bigger noisemakers while motoring, anyway.

And, more importantly, when the generator is running and keeping the exhaust pressurized, there is no chance of it getting washer pushed back into it by backing down and/or following seas.

And, yes, my exhaust is designed correctly with proper elevation and angle. I paid a professional, full-time marine genset shop to do that when I first bought the boat. I just feel safer with a belt and suspenders.

Also, I find hot water stays hot for a long while
Sometimes it is hot enough in the morning from the night before.

My new boat only has a 6 gal heater vs the 11 in my old boat, but I actually like it better. It is plenty for a couple of showers, at the least. And, when needed, it heats up really fast -- it is the same 1500W heater as the 11gal was.

At any rate, I know people boat differently. You can run the 1500W heater off of a sufficiently powerful inverter or alternator.

But, keep in mind that 1500W is 125A @ 12V which is more like 140-150A after inverter inefficiency (Yes, power factor is 1.0 for resistive heater loads).

So, the water heater represents a bigger, most of the capacity of your 205A alternator, full output.

If running off batteries after the engines are off, and you are willing to run them half way down, and don't have any major loads, you can get that 5 hrs from 760Ah @ 12V. Of course, you'll have to motor or genset to charge those batteries back up.

Also remember that if you deeply discharge batteries they'll end up with a high charge acceptance rate which can also be a heavy load on the alternator during the initial charging phase until their voltage comes up and acceptance goes down.

These things are all personal. Totally up to your needs and preferences.

 

[menzies]

Might be safer to have cold showers for the six days. One every other day, just three cold showers.

I want to know why this wasn't answered buddy?

 

[Moonfish]

On our sailboat we used to have a couple of those solar shower bags. Just lay them in the sun for a couple hours and they heat up real good. And we live in the Pacific NW!

Much less expensive and far less labor intensive option for just this one trip. Other than that, I'd go with running the genny to heat water.

 

[hollywood8118]

'Tis a valid point. But it sure would be nice to be able to heat water whenever we're underway, even for just a few hours. Maybe the suggestion to replace the heater element with a lower watt unit, making it safe to run off the inverter any time, is my best bet.

Just my take, doing long offshore passages i always try to shower just before sleeping on my first off watch at night. Having a good shower ( hot and of moderate length) really helps me sleep better and gives me something to look forward to. Running the genset for a hour to make some hot water and run the water maker is good for all the systems and uses very little fuel. I never understand a power boater that worries about a little fuel use by the genset. Your going to burn around 600 gallons of fuel for the trip.. whats 15 more?.
Great boat by the way, Have a friend that used to have the Kristin
trawler" Aruna". have a great trip.

HOLLYWOOD

 

[OldDan1943]

1. you have gas cooking?
2. your fridge and freezer, 12 volt?

IMO, your voyage is a good reason to have a 12 vt water maker. When I had my WM installed, I opted for a 12 volt system.

First thing I would do when back is to replace that HW heater with one with engine coolant coils. In the process of replacing the HW heater, put a couple of valves on the water line to and from the engine cooling system.
IF for some reason the tank coil fails (highly unlikely) you can isolate the HW heater from the engine coolant system.
I know my N46's JD had a coil on the engine and I just ran the hoses to and from the engine cooling system and put isolation valves in line.

Personally, I would be more concerned about burning up the engine alternator. Yes, I have for a spare alternator but, after running for a few hours, that engine and engine room will be way too hot to work in ER while bobbing around in the ocean.

Push come to shove, I vote for running the generator while running the water maker at least. We have a generator for a purpose so why not use the generator. I doubt the generator uses a gallon of fuel per hour. Sounds like, in a manner of speaking, you want to go camping again.

If you are worried about fuel, a couple of small fuel bladders will resolve that problem.

Are you transiting during the hurricane season? If so, this presents even more problems.

God's speed and have a safe voyage.

 

[FF]

There are 12 and 24V heating elements for off grid folks, so if you do not need multiple showers or dish washing its an easy swap.

These are usually low amps as they are usually a diversion load for wind machines.

Even simpler is to simply power your existing 120v heating element with 12V .

A switch would do to make the change easily, it will be slow to heat , but with 8-12 hour days , no big deal.

A 300W DC element,there are many others.


https://www.amazon.com/Watt-Submersible-Water-Heater-Element/dp/B00KLKGJ1I

 

[OldDan1943]

There are 12 and 24V heating elements for off grid folks, so if you do not need multiple showers or dish washing its an easy swap.

These are usually low amps as they are usually a diversion load for wind machines.

Even simpler is to simply power your existing 120v heating element with 12V .

A switch would do to make the change easily, it will be slow to heat , but with 8-12 hour days , no big deal.

A 300W DC element,there are many others.


https://www.amazon.com/Watt-Submersible-Water-Heater-Element/dp/B00KLKGJ1I

That is a viable alternative but, I think he mentioned because of the lock down, there is there maybe a problem shipping into him. I'd give it a try. SMILE

 

[FF]

OF course the simplest low cost system is either a solar shower or an insulated tank exposed to the sun.

A Jumbo version of the solar shower.

These can produce enough hot water for a dishwasher or washing machine, even while anchored.

 

[Simi 60]

Is your water heater plumbed into the engine's cooling system? It's an easy way to heat the water in the tank while underway...

But does nothing if anchored spending several days between legs.

 

[OldDan1943]

But does nothing if anchored spending several days between legs.

If you think you can make hot water even with low wattage heater element from your batteries, for days, you are wrong.
So you basically have 4
1. Run generator and run the HW heater the normal way
2. Use a low wattage element in the HW heater which I think will disappoint you with its recovery time
3. Capture the ME heat to the HW heater
4. Take cold showers.

Those black plastic bags? You are in survival mode.

Are you afraid to use the generator?
Are you saving your generator for some special reason?
Generators generally use less than 1 g/h. If you cant afford that, sell the boat.
Penny wise, pound foolish
The generator will use even less if you only run it to heat the water..... Maybe one hour a day, maybe less

 

[sunchaser]

First thing I would do when back is to replace that HW heater with one with engine coolant coils. In the process of replacing the HW heater, put a couple of valves on the water line to and from the engine cooling system. .

Brian

Good advice IMHO.

My Seaward lasted about 10 years before Al tank rotted out. Other Seaward owners have reported similar luck. If your tank is approaching that age suggest you change it out on a preemptive basis with a glass lined tank from Torrid, Raritan etc.

 

[wkearney99]

First thing I would do when back is to replace that HW heater with one with engine coolant coils. In the process of replacing the HW heater, put a couple of valves on the water line to and from the engine cooling system.

IF for some reason the tank coil fails (highly unlikely) you can isolate the HW heater from the engine coolant system.

My Seaward lasted about 10 years before Al tank rotted out. Other Seaward owners have reported similar luck. If your tank is approaching that age suggest you change it out on a preemptive basis with a glass lined tank from Torrid, Raritan etc.

+1 on proactively addressing the tank if/when you can get one.

But the engine coolant loop is not a simple 'set and forget'. Our EB47 had that setup and over time the weight of a hose on a fitting eventually lead to the elbow snapping off. This puked $240 worth of coolant out of the starboard engine. Fortunately it was just as we were pulling into a marina for a fueling stop. Though this was during the initial delivery run from RI to MD, so we 'got acquainted' with the boat's systems pretty darn fast. Thankfully we caught it just as it happened and shut that engine down before it took any damage. And +1 to having the fancier CAT engine monitoring displays to help immediately diagnose the situation. We were fortunate that the marina chandlery was open and had suitably-sized threaded fittings to allow blocking off the port from the engine. That and just enough of the $20/gallon CAT concentrated coolant!

Our was a valve directly mounted to an elbow off the engine, and the hose was left with too much unsupported length. This resulting in a bobbing/vibrating action that eventually caused the hard elbow to fail. We've not re-connected it. But it's on the to-do list. If just to have the option to use the heat for longer journeys. When it does get reconnected I'm looking to have a bracket made that hard-mounts the valve in such a way to not put the fittings under stress.

Anyway, if/when you get the chance to set it up, take extra care that you don't set up connections that will be put under undue stress under normal operating conditions.

As I recall from another boat that had a loop setup like this it doesn't take long to heat up the contents of the tank. Might be a good plan keep the valves closed until you know you want to make some hot water. Better that inconvenience rather than suddenly losing all your coolant, especially in a situation where it might not be convenient to get more.

 

[ghost]

I upgraded my boat to try to run without a generator for a few years. Eventually I went back to a generator with a super quiet sound shield. My insight is that there is a high chance keeping your water hot with the inverter will be a non issue. But you will need to monitor your system, as with all electrical “systems” it is less about any single component, but the dynamic system of how and when your loads come together at single points of time.

Once your water is hot, you won’t spend terribly much energy keeping it hot. The heater has a thermostat and will occasionally cycle for short periods of a few minutes. Your batteries will buffer much of this load, so your alternator won’t necessarily spike. What will matter is other high amp loads at the same time.

I’ve even heated water from cold in the morning without the engine running when I had amp hour capacity, and while that would likely only use 50 amp hours of energy, it’s a constant load. I’d more likely suggest you use your generator until batteries are fully charged, water fully hot and then shut the Genny down and see how your system works when simply “keeping up” with the load. I think you will be surprised, but it will depend on the system overall.

Long term I’d replace that water heater and put the loop back.

 

[FF]

No question a HW loop from the engine is the great long term solution,
But tossing one of these , painted black, in the cabin top might be quick and cheap.


Product description Nuova rade Flexible Water Tank Rectangular

Water Tank Rectangular 55 / 75 / 100 / 120 / 150 / 200 Liters.