Running engine at anchor for hot water - load

[FlyingScot]

Originally Posted by dan104

Guess I must be lucky, my boat although only 36' has a nice standup shower and a 6 gal water heater that uses both exhaust heat but also AC heater. I have found on passage any time we run the motor (Beta 43) we are making water, heating it, and topping up batteries. One thing to worry about at idle speed is that if you are charging LiPo4 batteries they will draw more power that the fan on the alternator can cool for it's needs and it can over heat and burn.


BTW: Coming back from Islands to Chesapeake we had 4 on board and every body took hot showers each day, of course we used 60g for a 1600NM trip.

Trying not to nitpick, but I've never seen exhaust being used for water heating. I suspect you mean it uses waste heat from the engine fresh water cooling loop to heat the water heater fresh water. This is a normal boat configuration.

[jackrabbit59]

You can't change the laws of physics. Electricity to heat is 100 percent efficient. Best you can get from diesel or gas is around 30 percent. I have an 11 gallon water heater and it draws 10 amps. I heat my water from the batteries and solar around lunchtime for 30 minutes. Batteries top off again in the afternoon and water stays hot enough for showers for 12 to 18 hours. Ocean temp is around 60 degrees.
Anyway physics says running an engine for hot water production is very inefficient. Invest in another solar panel and lithium battery and save the fuel.

[MVDarlin]

Recomnend you look at propane flash heater for large hot water supply. Endless hot water. Easy to operate. Portable. Hang in cockpit when in use. Check Camplux on Amazon.

[FlyingScot]

Originally Posted by jackrabbit59

You can't change the laws of physics. Electricity to heat is 100 percent efficient. Best you can get from diesel or gas is around 30 percent. I have an 11 gallon water heater and it draws 10 amps. I heat my water from the batteries and solar around lunchtime for 30 minutes. Batteries top off again in the afternoon and water stays hot enough for showers for 12 to 18 hours. Ocean temp is around 60 degrees.
Anyway physics says running an engine for hot water production is very inefficient. Invest in another solar panel and lithium battery and save the fuel.

I love love love solar, but it seems wrong and unfair to state that gas/diesel engine only convert 30% of the energy from the fuel.

So you can't change the laws of physics but you can surely make a more thermally efficient engine. The latest Prius has about 40% thermal efficiency from the gasoline/petrol engine. My 2020 Toyota Hilux 2.5D (3rd world model achieves near 44% IIRC).

But this overlooks what Thermal Efficiency is. The waste is heat, which is excellent for heating water.

Now let's talk Solar. The very best panels on the market have less than 25% panel efficiency. You lose at least 1% for Lithium and as much as 10-15% from LA. Then you have wiring losses (3-15%). Another 6-15% inverter losses.

We heat water with solar for years and we love it. But we also installed 2 new 25L water heaters and still take advantage of the 'free' heat when the engines run.

[s/v Jedi]

Originally Posted by FlyingScot

I love love love solar, but it seems wrong and unfair to state that gas/diesel engine only convert 30% of the energy from the fuel.

So you can't change the laws of physics but you can surely make a more thermally efficient engine. The latest Prius has about 40% thermal efficiency from the gasoline/petrol engine. My 2020 Toyota Hilux 2.5D (3rd world model achieves near 44% IIRC).

But this overlooks what Thermal Efficiency is. The waste is heat, which is excellent for heating water.

Now let's talk Solar. The very best panels on the market have less than 25% panel efficiency. You lose at least 1% for Lithium and as much as 10-15% from LA. Then you have wiring losses (3-15%). Another 6-15% inverter losses.

We heat water with solar for years and we love it. But we also installed 2 new 25L water heaters and still take advantage of the 'free' heat when the engines run.

Well it isn’t exactly free. Having the water heater plumbed in the engine coolant loop, means that the engine takes much longer to reach it’s operating temperature which reduces lifespan significantly.

[CaptTom]

Originally Posted by s/v Jedi

Well it isn’t exactly free. Having the water heater plumbed in the engine coolant loop, means that the engine takes much longer to reach it’s operating temperature which reduces lifespan significantly.

"Much" longer? Care to quantify? I would have guessed that, once the engine is under load, it heats up pretty quickly. At least with twin engines, I've never noticed a difference between the engine with the loop and the one without. I'd have guessed the difference in the lifespan of the engine wouldn't be significant at all.

[s/v Jedi]

Originally Posted by CaptTom

"Much" longer? Care to quantify? I would have guessed that, once the engine is under load, it heats up pretty quickly. At least with twin engines, I've never noticed a difference between the engine with the loop and the one without. I'd have guessed the difference in the lifespan of the engine wouldn't be significant at all.

You can do the math. But with two engines it would be simpler to just measure it.

If you have minster size engines in a motorboat you could burn so much that it’s not measurable; my comments are for sailboats with a small auxiliary engine as always.

[malbert73]

Originally Posted by s/v Jedi

You can do the math. But with two engines it would be simpler to just measure it.



If you have minster size engines in a motorboat you could burn so much that it’s not measurable; my comments are for sailboats with a small auxiliary engine as always.

I’m sure the increased time to heat up coolant can be measured. Every boat I’ve ever owned or cruised has the coolant go through the water heater. I’m sure the added time is measured in minutes on each. Perhaps significant.
This is the first assertion ever that I’ve read that there is a “significant” decrease in engine life that can be measured due to this. Care to substantiate?

[wsmurdoch]

Originally Posted by s/v Jedi

Well it isn’t exactly free. Having the water heater plumbed in the engine coolant loop, means that the engine takes much longer to reach it’s operating temperature which reduces lifespan significantly.

I don't think that is the case with my system (Yanmar 3HM35F). The engine coolant supply to my bus heater and to my water heater branch off the engine at the same spot as the coolant supply to the jacketed exhaust manifold and raw water heat exchanger. There is no appreciable coolant flow to any of them until the engine coolant thermostat opens.

[s/v Jedi]

Originally Posted by wsmurdoch

I don't think that is the case with my system (Yanmar 3HM35F). The engine coolant supply to my bus heater and to my water heater branch off the engine at the same spot as the coolant supply to the jacketed exhaust manifold and raw water heat exchanger. There is no appreciable coolant flow to any of them until the engine coolant thermostat opens.

No, I don’t think the water heater loop is regulated by the thermostat, that would fix the problem. All the connections I have seen have the coolant connection close to the water pump to get positive pressure at all times the engine is running.

[wsmurdoch]

Jedi, I have to apologize. You are correct. I just took a second look at the piping on my engine, and the coolant pump outlet to my water heater and bus heater is below the thermostat not above the thermostat with the heat exchanger outlet. That is also confirmed by the system drawing in the service manual. I was wrong.

[s/v Jedi]

Originally Posted by wsmurdoch

Jedi, I have to apologize. You are correct. I just took a second look at the piping on my engine, and the coolant pump outlet to my water heater and bus heater is below the thermostat not above the thermostat with the heat exchanger outlet. That is also confirmed by the system drawing in the service manual. I was wrong.

No problem, the only reason I know is because I don’t agree with the way it’s done and I put a valve in the circuit to disable it unless motoring for a long period. That happened so rarely that I completely removed it, but I have no heating other than a heat pump. I recently looked into this again and still don’t like it. It would be best to have a valve that is opened and closed by a thermostat.

To those who think it doesn’t matter: you have the thermostat for the same reason. If you remove the thermostat you also run below operating temperature longer with reduced lifespan. If it wouldn’t matter, they wouldn’t put thermostats in.

[FlyingScot]

Originally Posted by s/v Jedi

No problem, the only reason I know is because I don’t agree with the way it’s done and I put a valve in the circuit to disable it unless motoring for a long period. That happened so rarely that I completely removed it, but I have no heating other than a heat pump. I recently looked into this again and still don’t like it. It would be best to have a valve that is opened and closed by a thermostat.

To those who think it doesn’t matter: you have the thermostat for the same reason. If you remove the thermostat you also run below operating temperature longer with reduced lifespan. If it wouldn’t matter, they wouldn’t put thermostats in.

I've heard and read about engine efficiency and lowest emissions from a fully up to temperature engine, but I have never heard of reducing longevity by taking longer to heat up.

If this was a significant problem I presume every manufacturer would limit how big of a boiler you could install or disallow them entirely. Or solve the problem by having an additonal thermostat on the boiler cooling loop.

Can you provide some additional information how lifespan is negatively affected by slower warm up?

[skipperpete]

I share your interest FlyingScot and remain unconvinced by the previous arguments. Road tankers that carry chemicals such as Palm oil, tallow and stearate have a system called “heat in transit” where the engine coolant circuit is plumbed into the tanker heating coils to keep the product at a pumpable viscosity and you can rest assured that Caterpillar,Mack and Cummins would be on the warpath if this very common system damaged their engines. The thermostat simply sidelines the radiator and runs the coolant through the tanker coils. Even then, the cooling system easily reaches operating temp and the thermostats open to allow the radiator to maintain that temp despite the 30,000 liters of product.
The calorifier on our boats only adds about 5 litres to the coolant volume and the thermostat directs the coolant flow away from the heat exchanger almost completely via the bypass circuit .......which raises the problem of what happens if the thermostat is ever removed completely. On some engines this causes overheating due to the coolant having dual pathways once the ability to automatically blank off the bypass is removed, and the coolant will always take the path of least resistance.... the constantly open bypass. Even worse is that it’s a sneaky overheat, often not seen by the temp sender depending on where it’s located in the circuit.

[pbdayger]

Did not see any comments ref: propane on demand water heater. Have been thinking about rigging in my head, remove the propane tank when not in use… on Ontario I could utilize t lake water adding a small pump… on our 31 Dufour I think it would work well. Why wouldn’t it Wouk well on any size boat….???? Pros/cons????
PeterB