Cabin heat from engine

[a64pilot]

I think you can do it, I think it can be made to work to a limited extent.
But I think you will be happier, gain less weight, less complexity and spend less money if you buy a Diesel heater to supply heat. I don't think there is nearly as much heat as your thinking, I'm not arguing the math, I'm terrible in math, just a sailboat doesn't seem to retain heat very well, to stay warm, it seems you have to continually dump quite a lot of heat into one and 5 mins after the heat stops, it's cold inside. I'd assume the R value of a sailboat is some low number, or maybe its the humidity or both, I don't know. But they are hard to heat.

But sometime people enjoy tinkering with "stuff" and often build quite complex machines to do things that are more simply done by just purchasing something already made.
But they learn a lot, have had a hobby of sorts, and heck there is pride in doing something yourself

[Tomaz473]

All math aside: You have a sailboat. So I would think you use sails. Light use of the engine confirms this.
So, after a nice day of sailing you sail into the anchorage.
You start the engine, drop the anchor and than? You run the engine for several hours to heat the boat ?
So from practical aspect it is not the very best concept.

You like the anchorage so much that you decide to stay another night. But your water is cold, so you need ti run the engine . . . I hate to run my engine on idle...

Cost aspect: Such tank with heat exchangers and proper insulation - all marine grade materials probably costs more then a separate diesel heater. Add all the valves, hoses and complexity...

Space aspect: large water tank is bulky and after you insulate it it is even bigger.
space is at premium on a small boat. A diesel heater takes much less space then a tank.

[Dockhead]

Originally Posted by Pizzazz

That is the idea, to expand hot water storage from 6 to 46 gallons and circulate the water from the bigger tank through the smaller tank heat exchanger. I could even install a valve to separate the two tanks once warmed up so that I get hot water from the smaller tank and heat from the larger tank (avoiding the cold/hot mixing as long as possible).

Regarding the raw water bypass, I will just bypass the engine heat exchanger and will feed the raw water from the pump into the mixing elbow to allow the cooling of the exhaust.

I see now the complication of having to operate two valves to charge the system but I still like the concept of capturing excess engine heat vs. producing new heat in a separate heater or stove. Next, I will do a test run with the raw water bypass to see how long it takes to warm up the 6 gallon tank on idle speed before going ahead.

It is truly maddening to freeze inside a boat that dumps megawatt/hours of waste heat into the cold ocean.

If there were some good way to store some of that heat, it would be golden.

I have thought about something like what you propose, but it did not seem practical considering the volume of water needed to store a reasonable amount of heat, and the cost of all of the components required.

What you propose to do would cost more, I'm sure, than a simple Webasto Air Top heater, or a nice pot heater like someone suggested above. And unlike a bit of hot water tankage, the heat storage capacity of those is limited only by your diesel tanks. I'm not even mentioning the amount of time you would have to spend futzing with it.

I wish there were some good way to store waste heat, a lot of it. BMW used to have these melting salt devices to store heat for car cooling systems, to avoid cold starts. Maybe that technology could be used somehow.

[Juho]

My engine heats the hot water (very quickly). It would be very straight forward to add another hot water container (with or without isolation, with or without AC) in the engine cooling loop. That would add some weight to the boat, but you could keep the second tank empty when it is not needed.

[JPA Cate]

A little Webasto forced air system would head the boat much faster, and might enhance the value of the boat when the OP is ready to sell it, and it's engine would be in better shape at that time. What I mean is that I think the OP's plan will turn out to be extraordinarily costly, and not do a very good job of warming the boat.

High quality thermal underwear would cost a heck of a lot less (even if the whole family need them). And, of course, there are the inexpensive cotton ones, as well......and they function well as pajamas.

In CA [where I grew up and started sailing] a kerosene burning trawler lamp will not only put out enough light to read by, but heat the saloon quite well, as it did on the 36 footer we had. Now, they don't do too well where it is really cold, because they also put out water (from burning the fuel, and you need to trim the wicks). The water goes out the flue with the diesel heater, so the latter gives you dry heat.

In short, I think there are less expensive and simpler ways of making cold people warm.

My two cents.

Ann

[Juho]

Originally Posted by Pizzazz

All I am doing is making the water heater 7x bigger.

After scanning through the thread, I note that you already covered what I wrote. This looks like a simple and quite safe approach.

I sometimes played also with the idea of using paraffin wax to store the heat (not much better than water, and it would be more difficult to empty the tank when you want to make the boat light).

[Pete7]

Originally Posted by 1affiah

Another consideration is weight. How will your boat handle with another 350++ pounds of water, plumbing, etc? Maybe list to one side, or "heavy in the butt"?

My thoughts too, 150kg on one side of a 31 foot yacht will cause it to lean to one side permanently.

You want instant heat occasionally in that climate so either a drip feed diesel heater or a hot air blown heater which we have. Actually our ST2000 came from a vehicle supplier so avoided the "marine" price tag. Probably one of the best things we have added to the yacht, instant heat in minutes and 2kw ideal for 31 feet, needing to be turned down to half way after an hour or so.

Pete

[Cheechako]

Instead of a big Rube Goldberg project of dubious result, work some OT and buy a good heater! :>)

[Pizzazz]

I spoke to a Yanmar technician today. The raw water bypass is not worth it. The fresh water cooled engine runs at 175F which is more than enough for rapid water heating. A bypass would give an extra 15-20F but I would rather not keep the water that hot.

So this project boils down to installing a 40 gallon tank and connecting it in series with the Raritan heater. Some valves and a radiator. A piece of cake. We estimated about 1.5 hours at idle to warm up 40 gallons, less than an hour at full load. I can live with that.

Re: oil lamps, I like them very much but no way the wife would allow an oxygen depriving burner around the kids.

Re: diesel heaters, just the idea of drilling a 4" hole in the deck puts me off. One of the spec sheets suggested 6' of chimney, where do I fit that. Not worth it for me and my needs.

Re: additional weight, I have a slight list to port now because of the 4 golf cart batteries, the tank on starboard will fix that. Also, soon or later I would have installed additional tankage anyway - 80 gallons of water is much better at anchorages than 40, even if half of it is hot.

Sent from my MotoE2(4G-LTE) using Tapatalk

[Stu Jackson]

Originally Posted by Pizzazz

1. A bypass would give an extra 15-20F but I would rather not keep the water that hot.

2. So this project boils down to installing a 40 gallon tank and connecting it in series with the Raritan heater. Some valves and a radiator. A piece of cake.

3. We estimated about 1.5 hours at idle to warm up 40 gallons, less than an hour at full load. I can live with that.

4. Re: oil lamps, I like them very much but no way the wife would allow an oxygen depriving burner around the kids.

So glad to hear.

1. You might want to investigate "thermostatic mixing valves" for your hot water. While faucets work great for us grown ups, with little kids, they are a blessing. Johnson makes one.

2. Seaward makes a 28 gallon one. Have you found a larger one?

3. I doubt it, but the proof is in the pudding. Good luck at idle, mine takes at least an hour to heat 6 gallons. 1/2 an hour at cruising revs. I define idle as 1000 rpm. I run my engine at 1800 for the hour I use to recharge when at anchor. Maybe we have to define "idle" since I'm so idle so often.

4. Wait! You mean you can't have romantic candles either? Usually the trawler lamps are way high in the saloon, but I guess the kids could stand on the table.

Good luck, glad we've been able to help. Please let us know what you buy and how it turns out.

Thanks for an enjoyable day.

All the best,

Stu

[Stu Jackson]

Try this:

Water heater thermostatic mixing valve | SailboatOwners.com Forums

[nicholson31]

Every point has been made here for both sides, so I will just add from my experience ,



I have a 31ft with both an engine heater and a bulk head Force 10 propane heater, both have worked extremely well. The engine heater we have used often when motoring and gives unbelievable heat for such a small unit however, to use it when moored and continually starting the engine would be a nuisance and annoyance to you and anyone around you. It is not installed on the Raw water side, personally i would never compromise that system with added plumbing and/or valves.

The force 10 worked great, looks traditional and cozy many comments on it and really takes up little space. I would prefer the Dickerson though for the fan option.

I said worked because I just installed an Espar D4 diesel heater and removed the force 10. Gets pretty cold, not chilly, up here so we went with something that can really supply even heat everywhere in the boat.
Stu was blunt but to the point!!

Sell you a good Force 10 bulk head heater!!

[sailorchic34]

What an interesting Idea. From an engineering standpoint, it would sort of work.... BUT... It's not really very efficient. Yes a 13 hp engine running under full load will produce some heat. But your not running it anywhere near full load at anchor.

At a fast idle with little load, it's going to produce maybe 18,000 btu's per hour... maybe. Of that amount, some of the heat radiates off the walls of the engine. Some goes to the heat exchanger and some is used to move the pistons around and around.

So your looking at capturing roughly maybe 6000 btu per hour while burning 18,000 btu's of diesel per hour, at fast idle. For a thermal efficiency of 33% Not very good.

Then your going to store that heat in a 40 gallon tank. The tank even insulated will loose about 5% of the heat per hour. So you end up with 5500 btu's an hour going to the tank. That's enough to heat 6 gallons 100 degrees F. So your running the engine about 6 hours to heat the water in the 40 gallon tank.

With Diesel at about 139000 btu's per gallon and ~ $3 ish a gallon, $2 dollars of that goes right out the window.

The thing to remember is an engine is design to convert energy to rotational motion, It also heats water as a byproduct. While it's great to do capturing waste heat, when your moving, it is a very poor choice from an efficiency standpoint to do so while at anchor.

So while the idea will work, it will not work well, even with capturing 100% of engine coolant flow. Which from an engineering standpoint is overly complicated and prone to failure. Which would be bad.

The typical diesel or propane heater will be roughly 80% efficient or twice what heating water via engine is.

Buy a diesel heater and two CO detectors. You'll be way ahead of the game then.

Note: in northern California it takes about 4000 btu per hour to keep my 34' boat (old and small cabin) warm enough in winter (45 degree water temp).

I also use an oil lamp to take the chill off on cool nites. Works well.

[Pizzazz]

Originally Posted by sailorchic34

What an interesting Idea. From an engineering standpoint, it would sort of work.... BUT... It's not really very efficient. Yes a 13 hp engine running under full load will produce some heat. But your not running it anywhere near full load at anchor.

At a fast idle with little load, it's going to produce maybe 18,000 btu's per hour... maybe. Of that amount, some of the heat radiates off the walls of the engine. Some goes to the heat exchanger and some is used to move the pistons around and around.

So your looking at capturing roughly maybe 6000 btu per hour while burning 18,000 btu's of diesel per hour, at fast idle. For a thermal efficiency of 33% Not very good.

Then your going to store that heat in a 40 gallon tank. The tank even insulated will loose about 5% of the heat per hour. So you end up with 5500 btu's an hour going to the tank. That's enough to heat 6 gallons 100 degrees F. So your running the engine about 6 hours to heat the water in the 40 gallon tank.

With Diesel at about 139000 btu's per gallon and ~ $3 ish a gallon, $2 dollars of that goes right out the window.

The thing to remember is an engine is design to convert energy to rotational motion, It also heats water as a byproduct. While it's great to do capturing waste heat, when your moving, it is a very poor choice from an efficiency standpoint to do so while at anchor.

So while the idea will work, it will not work well, even with capturing 100% of engine coolant flow. Which from an engineering standpoint is overly complicated and prone to failure. Which would be bad.

The typical diesel or propane heater will be roughly 80% efficient or twice what heating water via engine is.

Buy a diesel heater and two CO detectors. You'll be way ahead of the game then.

Note: in northern California it takes about 4000 btu per hour to keep my 34' boat (old and small cabin) warm enough in winter (45 degree water temp).

I also use an oil lamp to take the chill off on cool nites. Works well.

Great input. I believe you may be a little conservative with the heat output. The 2GMF engine uses 220 grams of diesel per hp. Say the engine is running at 1,400 rpms fast idle, producing 4 hp that is used to drive the alternator, pumps, pistons, etc. It uses 0.3 gallons per hour with an energy content of 40,000 BTUs. Four hp of mechanical energy is equivalent to 10,000 BTUs or 25% efficiency. Thus, 30,000 BTUs is converted to heat. Some of it heats the engine (which also heats the cabin) but the majority is taken away from the cooling circuit (otherwise the engine compartment will overheat). If we can capture half of the cooling circuit heat, this will give me 20,000 BTUs, which is enough to heat 40 gallons of water by 60-65F. This is for one hour at fast idle. Imagine I run the engine at full load for half an hour before anchoring (taking down the sails, etc.) and the heat output is there.

I agree that marine propulsion engines convert a greater proportion of the heat into mechanical energy (the calculated figure above is 25%, literature says up to 45% is more likely) and there are many studies where truckers can save on diesel by using a diesel heater vs. idling. Point taken. However, for occasional use and especially if one can heat the water while underway, I think the stored energy system is not that inefficient.

[Cheechako]

Originally Posted by sailorchic34

What an interesting Idea. From an engineering standpoint, it would sort of work.... BUT... It's not really very efficient. Yes a 13 hp engine running under full load will produce some heat. But your not running it anywhere near full load at anchor.

At a fast idle with little load, it's going to produce maybe 18,000 btu's per hour... maybe. Of that amount, some of the heat radiates off the walls of the engine. Some goes to the heat exchanger and some is used to move the pistons around and around.

So your looking at capturing roughly maybe 6000 btu per hour while burning 18,000 btu's of diesel per hour, at fast idle. For a thermal efficiency of 33% Not very good.

Then your going to store that heat in a 40 gallon tank. The tank even insulated will loose about 5% of the heat per hour. So you end up with 5500 btu's an hour going to the tank. That's enough to heat 6 gallons 100 degrees F. So your running the engine about 6 hours to heat the water in the 40 gallon tank.

With Diesel at about 139000 btu's per gallon and ~ $3 ish a gallon, $2 dollars of that goes right out the window.

The thing to remember is an engine is design to convert energy to rotational motion, It also heats water as a byproduct. While it's great to do capturing waste heat, when your moving, it is a very poor choice from an efficiency standpoint to do so while at anchor.

So while the idea will work, it will not work well, even with capturing 100% of engine coolant flow. Which from an engineering standpoint is overly complicated and prone to failure. Which would be bad.

The typical diesel or propane heater will be roughly 80% efficient or twice what heating water via engine is.

Buy a diesel heater and two CO detectors. You'll be way ahead of the game then.

Note: in northern California it takes about 4000 btu per hour to keep my 34' boat (old and small cabin) warm enough in winter (45 degree water temp).

I also use an oil lamp to take the chill off on cool nites. Works well.

and... as a side benefit he gets to carry around 400# of water and stuff!