Hot Water Heater Trouble For Your Main Engine Or Am I Over Reacting?

I have gone from a sailboat with a 54 hp Yanmar to a Nordic Tug with a 330 hp Cummins. Looking at the hot water heater for the fresh water system I can see some blue color residue around the hot water heater connections. Is it a good idea to plumb yoUr main engine cooling system into your domestic water heater? If it fails you just fried your main engine, a couple of huge boat bucks. It is nice to have hot water when you get to the dock. But after twenty minutes you could have it via the power cord. So my concern is, is it a good idea have the engine cooling system ran into the domestic water heater or should I plug it off at the engine?

As with anything, there's a risk. There are a huge number of boats with domestic hot water off the engine. IMO, think rhe risk is pretty low. If the heat exchanger in the water tank fails, you probably aren't going to have a quick engine failure as the domestic water pressure is higher than the coolant loop pressure. So the engine isn't going to be without fluid in the coolant loop.

Ted

My Catalina 400 has the Yanmar 4JH4 engine, likely the same a you had on your sailboat. My hot water tank, like yours now, is heated with a heat exchanger off the engine. I have never worried about it at all. I don't think you should have a problem. As near as I can tell, many boats, not just the NT, use a similar system.

BTW, I am looking at the NT-37 myself. So far how have you found the switch from sail to power?

dhays said:

My Catalina 400 has the Yanmar 4JH4 engine, likely the same a you had on your sailboat. My hot water tank, like yours now, is heated with a heat exchanger off the engine. I have never worried about it at all. I don't think you should have a problem. As near as I can tell, many boats, not just the NT, use a similar system.

BTW, I am looking at the NT-37 myself. So far how have you found the switch from sail to power?

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You spend a lot more time checking, learning and maintaining your mechanical systems. But I am really glad we made the switch. The comfort level for the captain is up 1000%. No more standing in the cockpit getting drenched, hot or cold. We loved our Hunter 41 Deck Salon, but Traveling up the east coast from Florida to New York area each year we had problems with too high of water the past two trips. Our mast was 63 and we got stuck due to the 65 foot Bridges and the high water levels. With the 37 we seldom open a bridge with our 15' clearance.

When we purchased IRENE, we discovered the coolant loop for the water heater and cabin heater had no valves installed. We installed valves at the engine, just in case we catch a problem and need to secure that loop.

Good Luck

My 1977 boat has had it since new. In about 2008, my water heater started leaking freshwater into the bilge so I replaced it. Once removed, I could read the date stamp that read 1976. Apparently it withstood 31 years of operation without failure. The failure was totally unrelated to the heat exchanger.

YMMV but I think the risk of failure is low.

If the water is already hot, why do you need to heat it???

Sorry...I couldn't resist!!!! As you were!!!

Pgitug

If not so equipped and as suggested by Irene too, install water loop circulating valves on your engine. That way you can choose when coolant is going through the water heater. We commonly run with valves closed. That way we have more electric load needs to keep the genset loaded for its roughly 2 hour per day run time.

sunchaser said:

If not so equipped and as suggested by Irene too, install water loop circulating valves on your engine. That way you can choose when coolant is going through the water heater. We commonly run with valves closed. That way we have more electric load needs to keep the genset loaded for its roughly 2 hour per day run time.

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Time for me to demonstrate my ignorance again... I have never had a boat with a genset.

Am I to assume that if you have to run the genset, you want it to run with a certain minimal load for its own long term health? Doesn't charging the batteries provide enough of that load? But if you are running the engines going somewhere, the alternators would be charging the batteries (and heating the water in the hot water tank) so why would you need to be running the genset? Do you have an all electric galley so you run the genset anyway during dinner prep? How much of that can be taken care of with the inverter off a fully charged house bank?

Likely stupid questions, but I really don't know....

It only takes 1 hour to heat the hot water and the water will stay hot warm for hours. Our hot water is on a timer that heats the water for one hour twice a day. The webasto also heats the hot water. Anyway does not take long to heat the hot water.

dhays said:

Time for me to demonstrate my ignorance again... I have never had a boat with a genset. Likely stupid questions, but I really don't know....

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We are very much off the genset when cruising. But it is a managed part of our longer trips when we're not at a dock somewhere.

There is a general rule of thumb that running a genset above 40 to 50% load is healthy for the generator (armature and windings) end and likewise keeps the constant RPM diesel properly heated. Our 12.5KW unit has a max capacity of 50 amps per leg at 110 V or 50 total at 240 volts.

The hot water tank will not electrically heat unless genset running. But a genset run for 45 minutes or so brings it right up to temperature for the day.It is a 15 amp unit and too big for the on engine alternators. So with battery chargers running at about 20 amps and water heater on, the genset has a good base load. With spot electric heaters or AC heat pump on even more load. Then an all electric galley, washer and dryer, TVs, hair dryers etc the load can approach 12.5KW.

I have no desire to be genset free, after 10 years of owning the vessel the genset is approaching only 500 hours of use (1/4 of engine hours) so hardly an imposition to use it.

if you have shutoff valve for the loop right at the engine block and leave them off when not heating water...hardly a risk at all...


But many commercial boats up north have bus heaters in them and I have yet to hear of someone cooking an engine because of that loop. Yes leaks can occur...but regular checking of the hoses and connections make it an extraordinarily rare possibility.


Take a poll of when the last time anyone on here had a decent engine hose fail during operation either on a boat or a car...and which hose? Main coolant or heater loop? May give you warm and fuzzies or a good scare...but I'll bet reduced concern.

Thanks for the information. I can see that managing a genset and inverter is another area that I am going to have to educate myself on.

Currently I only have AC available when on shore power. The rest of the time it is all DC. A heat exchanger from the engine heats our hot water tank quickly when under way. This means we can sail/motorsail to anchorage, have hot water for dishes that night, and enough hot water for showers the next morning, but then we have cold showers from then on if don't move on to another location. It also means that when on the hook we have no microwave or coffee maker. My wife misses her Keurig in the morning.

dhays said:

Thanks for the information. I can see that managing a genset and inverter is another area that I am going to have to educate myself on.

Currently I only have AC available when on shore power. The rest of the time it is all DC. A heat exchanger from the engine heats our hot water tank quickly when under way. This means we can sail/motorsail to anchorage, have hot water for dishes that night, and enough hot water for showers the next morning, but then we have cold showers from then on if don't move on to another location. It also means that when on the hook we have no microwave or coffee maker. My wife misses her Keurig in the morning.

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My Californian was probably similar to your sailboat when I purchased her. No genset, no inverter, small alternators, small house bank, propane stove, no need for air conditioning here in Northern California.

My small Keurig requires 1500W to heat the water, my highest draw item on the boat. Since my 1000W inverter can't handle this load, I need shore power or my Honda eu2000i generator to power the Keurig. I carry a spare Mr. Coffee style coffeemaker as a backup. When I replace this inverter, it'll be with a 1500-2000W unit.

Egad. Keurig determining what genset needs are!
While I like the reduced time between "I would like a cup" and "ready", surely making coffee the old way, by putting a pot on the stove is still a great backup. Propane stove, that is.

FlyWright said:

My Californian was probably similar to your sailboat when I purchased her. No genset, no inverter, small alternators, small house bank, propane stove, no need for air conditioning here in Northern California.

My small Keurig requires 1500W to heat the water, my highest draw item on the boat. Since my 1000W inverter can't handle this load, I need shore power or my Honda eu2000i generator to power the Keurig. I carry a spare Mr. Coffee style coffeemaker as a backup. When I replace this inverter, it'll be with a 1500-2000W unit.

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Good to know. I am thinking that as I look at boats, I should be looking for about a 2000W or more inverter or be looking to upgrade it.

The Keurig is a huge "quality of life" issue for us and I would like to be able to run it with just an inverter on the house bank. I don't mind making drip coffee with a filter and hot water (do it all the time on our current boat) but my wife likes the Keurig and it really pays to be able to have the small things which make her happy.

Another AC draw for us will be a CPAP machine for my wife. She just started to use one a couple months ago and it makes a huge difference for her. Currently, we can't use it on our boat without shore power. We will need to be able to run it nightly while at anchor. It doesn't draw much, but is something that would take continual AC power throughout the night unless I can figure out a 12v solution.

My Mr. Coffee runs off my 1kW inverter!!!

No solar Dave? It would help replenish batts, allow more use of an inverter, especially for low demand appliances like the CPAP, and in daytime feed your fridge.
"Keurig" is not a brand sold here, I`m guessing it`s an espresso machine, I would not be without one. Big demand items are hard to run for long from batteries lacking any form of replenishment. Can you find space for the Honda genset Flywright mentioned? Compact, fuel economical, relatively quiet, highly regarded, store it below and use it on deck as required.
Diesel genset owners often go looking for things to turn on to give the genset enough work to remove the risks of underloading(glazed bores etc), by multitasking it. Typically, charging batts is not enough.

Pgitug said:

I have gone from a sailboat with a 54 hp Yanmar to a Nordic Tug with a 330 hp Cummins. Looking at the hot water heater for the fresh water system I can see some blue color residue around the hot water heater connections. Is it a good idea to plumb yoUr main engine cooling system into your domestic water heater? If it fails you just fried your main engine, a couple of huge boat bucks. It is nice to have hot water when you get to the dock. But after twenty minutes you could have it via the power cord. So my concern is, is it a good idea have the engine cooling system ran into the domestic water heater or should I plug it off at the engine?

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It's a very common system with few failures. I think you are worrying too much.

BruceK said:

No solar Dave? It would help replenish batts, allow more use of an inverter, especially for low demand appliances like the CPAP, and in daytime feed your fridge.
"Keurig" is not a brand sold here, I`m guessing it`s an espresso machine, I would not be without one. Big demand items are hard to run for long from batteries lacking any form of replenishment. Can you find space for the Honda genset Flywright mentioned? Compact, fuel economical, relatively quiet, highly regarded, store it below and use it on deck as required.
Diesel genset owners often go looking for things to turn on to give the genset enough work to remove the risks of underloading(glazed bores etc), by multitasking it. Typically, charging batts is not enough.

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Thread drift I am afraid, but I have not considered solar for my current sailboat. I want to move away from the sailboat for several reasons; 1) my back can't take the constant bending over, 2) I am getting tired of being out in the cold and rain all the time, 3) I am under power most of the time anyway. Even if I was to stick with the sailboat, I don't like most of the solar mounting options I have.

For the type of power boat that I am considering, I have wondered about solar. It seems to me that there is a lot of flat, unused, exposed real estate on the top of many pilot houses.....

"It also means that when on the hook we have no microwave or coffee maker. My wife misses her Keurig in the morning."

Usually a $100-$150 inverter will take care of the lifestyle , with no increase in battery capacity , as the operation is short.

A 1000W inverter will use 100Amps for a min reheating a cup.Not much in amp hours.

"Another AC draw for us will be a CPAP machine for my wife. She just started to use one a couple months ago and it makes a huge difference for her. Currently, we can't use it on our boat without shore power. "


We cruise often with two different folks that use the CPAP machines. They have them configured with stand alone batteries that are good for about 25 hours a piece. They always have two batteries available and never rely on shore power even if we are at docks. Recharge times seem to be about 3 hours per battery so they can do that while underway or with a genset running - this is what they use when camping and one when they went on a cruise.

FF said:

"It also means that when on the hook we have no microwave or coffee maker. My wife misses her Keurig in the morning."

Usually a $100-$150 inverter will take care of the lifestyle , with no increase in battery capacity , as the operation is short.

A 1000W inverter will use 100Amps for a min reheating a cup.Not much in amp hours.

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It's not much in amp hours but it's quite a bit in amps. You need battery capacity (and heavy cables) to provide that much current without a voltage drop.

Also, a 1000 watt inverter draws significantly more than 1000 watts of power from the inverter. The "1000 watts" is "cooking power" not power consumption. Look at the label on the back for actual power consumption and the amount of power needed from the inverter.

dhays said:

......... It also means that when on the hook we have no microwave or coffee maker. .

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I installed a 2000 watt inverter in our boat (four group 31 AGM batteries for a house bank) and we make significant use of the microwave and coffee maker (not at the same time) on our boat. I don't regret doing this.

For this to work, it's important to do the job right. Good batteries, good wiring and good inverter, not something from Harbor Freight. Mine has a built in transfer switch so there's no need to move plugs around or do anything else.

2 theories on inverters...use several small cheap ($100 or so) ones that can be easily replaced or use one or more big, nice expensive one(s) that when it doesn't work...you are back to the genset or without till fixed/replaced (time and $$$).


I too like the concept of two really nice, powerful inverters dealing with AC on my boat...but when they start costing 1/10 the total cost of my vessel...I tend to look for reasonable alternatives.


If I ever get to the point where solar replaces my genset....I may buy into the nice inverter setup and skip the genset.


On many boats the genset is just too integral and thus the big inverter setup to me is a bit too much redundancy unless I spent a load of time in remote places and they were needed as backup for a genset.

"On many boats the genset is just to integral and thus the big inverter setup to me is a bit too much redundancy unless I spent a load of time in remote places and they were needed as backup for a genset."


I definitely agree with this - once you are heating or cooling anything you are in the area where a genset will be running and then you can charge/run everything else. Cooking, icemaker, reefer, A/C , heat etc are not really suited to an inverter as I learned on a past boat.
For the really remote trips I would bring along my portable genset to get by until the main unit were to be repaired.
YMMV

smitty477 said:

I definitely agree with this - once you are heating or cooling anything you are in the area where a genset will be running and then you can charge/run everything else. Cooking, icemaker, reefer, A/C , heat etc are not really suited to an inverter as I learned on a past boat.

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All depends on size. We have a 12v refrigerator, 12v diesel furnace, and propane stove. No icemaker or AC. 12v adaptors take care of charging the electronic gadgets. Our battery bank is only about 850amp hours yet is plenty.

Granted, we don't get the experience of kicking back in an AC cooled saloon, sipping an iced drink while watching TV. Barbaric I know.

"All depends on size. We have a 12v refrigerator, 12v diesel furnace, and propane stove. No icemaker or AC. 12v adaptors take care of charging the electronic gadgets. Our battery bank is only about 850amp hours yet is plenty.

Granted, we don't get the experience of kicking back in an AC cooled saloon, sipping an iced drink while watching TV. Barbaric I know."


And that works really fine I am sure for certain boating spots and durations. So if it works then that is all that matters.
FWIW - we also have 12 reefer, and can cook without electric and make hot water off of an engine. But when we are on longer trips or if someone wanted to do the great loop you may find that the environment and/or the duration does not fit well by adding batteries and/or doing without.
Choosing your needs careful first is always the best route when deciding on boating needs/wants.

CPAP will run off a small 300 watt pure sine wave inverter, less then 150 bucks.

koliver said:

Egad. Keurig determining what genset needs are!
While I like the reduced time between "I would like a cup" and "ready", surely making coffee the old way, by putting a pot on the stove is still a great backup. Propane stove, that is.

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LOL....Yeah. I'll forgo all the complexity of running an electric Coffee maker. Remember Percolators? They do a great job with little energy draw when I heat with my Alchohol/Electric Origo...
I've had one for 20 years for use on the boats. Once you get the technique and timing down, the coffee is as good as anything else..