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Old 02-20-2016, 09:15 PM   #1
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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?
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Old 02-20-2016, 09:26 PM   #2
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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.

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Old 02-20-2016, 09:47 PM   #3
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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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Old 02-20-2016, 10:39 PM   #4
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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?

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.
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Old 02-20-2016, 10:53 PM   #5
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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.

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Old 02-20-2016, 11:03 PM   #6
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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.
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Old 02-21-2016, 01:42 AM   #7
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If the water is already hot, why do you need to heat it???

Sorry...I couldn't resist!!!! As you were!!!
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Old 02-21-2016, 04:39 AM   #8
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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.
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Old 02-21-2016, 12:01 PM   #9
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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.
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....
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Old 02-21-2016, 12:22 PM   #10
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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.
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Old 02-21-2016, 12:24 PM   #11
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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....
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.
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Old 02-21-2016, 12:32 PM   #12
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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.
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Old 02-21-2016, 12:35 PM   #13
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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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Old 02-21-2016, 01:11 PM   #14
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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.
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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Old 02-21-2016, 04:26 PM   #15
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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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Old 02-21-2016, 04:27 PM   #16
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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.
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.
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Old 02-21-2016, 04:55 PM   #17
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My Mr. Coffee runs off my 1kW inverter!!!
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Old 02-21-2016, 05:33 PM   #18
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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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Old 02-21-2016, 06:23 PM   #19
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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?
It's a very common system with few failures. I think you are worrying too much.
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Old 02-21-2016, 07:20 PM   #20
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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.
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.....
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