Replumbing an Outboard for Heat

Discussion in 'Outboards' started by DogCavalry, Nov 24, 2021.

  1. DogCavalry
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    DogCavalry Senior Member

    I get your concern @Mr Efficiency . The big danger would be back pressure from too much system restriction, or making too much demand on the impellor, so it fails prematurely. Allowing enough bypass water to cool the exhaust shouldn't be too hard.
     
  2. Barry
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    Barry Senior Member

    As Mr E has mentioned but is probably the most important part of this plan, is to capture the hot water after it has done the cooling of the block. As the water jacket after the thermostat is open, is open to atmosphere, or at least open to whatever pressure "a" is at the exhaust to ocean water interface. The cool water then should be coming up from the leg and flooding the water jacket and the hot water is then pushed by the water pump into the exhaust "water jacket" or piping back down the leg to the prop hub, AT THE TOP OF THE BLOCK. Assuming a prop hub exhaust

    So if you capture this hot water after cooling the block, I do not see how this could impact the engine. Pretty much all freshwater and closed systems work this way that have a heat exchanger with a tap to a water circulation heating system

    A possible weak link might be the water pump whose only purpose in life was to be able to create enough water pressure and volume to get the water to the top of the block and past any back pressure due to "pipe" losses, head and hub back pressure.

    Depending on the height of your heat exchanger and the additional friction losses, the water pump, impellor will more than likely have to produce a bit more work to over come the downstream resistance.

    Perhaps you might have to provide an additional circulation pump, like a bilge pump before the heat exchanger to over come this if you find that the original flow rate is impacted.

    As there is a market trend these days to hang outboards on bigger and bigger boats with cabins, DC, you may be breaking new ground and if we see in the future outboard manufacturers produce a factory installed water tap in the block to attach
    to a heating system, we will remember that DC started a trend.

    DC, you are a little late completing your Ark, as you may have missed the great flood in Vancouver. Those not from the Pacific Northwest may not have heard about the extreme flooding with maybe billions of dollars of flood damage taking place
    and possible more to come, in DC's area.

    Do you need a few more umbrellas?
     
    Last edited: Dec 1, 2021
    alan craig and DogCavalry like this.
  3. DogCavalry
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    DogCavalry Senior Member

    I never use umbrellas @Barry , I prefer to get wet, and complain about it like an old hound dog laying on a nail. My thoughts exactly re engineering. Gravity flow down into the heat exchanger, with a take-off at the bottom that overflows out through the transom. That box could be expoxy glass on plywood. A heat conducting interface,maybe just tempered glass, because it's corrosion proof, and a manifold on the other side carrying clean heated water through pex lines. Maybe under the sole, to a couple heater cores from scrapped astro vans (I have 3) delivering hot air to driver, window defoggers, etc.
    Since the side of the system in the cabin is separate from the sea water, even a catastrophic leak is only annoying, since that side will only carry a few liters of water. And I can repair pex with couplers and crimpers. Anne was telling me a heated floor in winter will improve my romantic prospects. I've certainly done enough underfloor heating for less motivation.

    The temperature we set the holding tank water at is 125f, or 52c, in our passive houses. The heat comes from a Sanden heat pump. That's enough to provide under floor heating for a 4 bedroom 3 bathroom house. The waste heat from a pair of 150s would be enough to heat a neighborhood. Consider the fuel consumption, and that they are 40% efficient at best. 60% of that fuel burn leaves as hot water. Imagine burning fuel that fast in a heater. The thermal gradient is favorable too, with water coming out of the engine at 160f, and water in the heater side only needing to be 125 to heat the cabin.
     
  4. DogCavalry
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    DogCavalry Senior Member

    20211126_104319.jpg This heat pump heats the house.
     
  5. Barry
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    Barry Senior Member

    If it is similar to a standard heat exchanger you want any water inlet to flood the exchanger from the bottom to ensure that the chamber is completely full. If you "sprinkle" the heat exchanger from the top with a direct access to a gravity transom drain, you may lose a lot of available heat. With a pump up from the bottom process, the box/chamber will be guaranteed, (pretty much) to be filled with the hot water.
     
  6. fallguy
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    fallguy Senior Member

    No way would I mess with the ob water flow. Too many easier ways to make heat.
     
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  7. Mr Efficiency
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    Mr Efficiency Senior Member

    I wouldn't be doing it, and no doubt any such contrivance would instantly void any engine warranty, which admittedly is not a factor with this motor.
     
  8. DogCavalry
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    DogCavalry Senior Member

    I'm with @Barry . Understanding how it works is pretty good insurance. And it's totally worth trying. That's an incredible amount of heat to dump in the water.
     
    Last edited: Nov 27, 2021
  9. Scuff
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    Scuff Senior Member

    I'm with Barry, if you pickup the water after the engine it shouldn't hurt anything. You may need to block the flow between your pickup and return locations to be sure you don't affect the cooling flow through the engine especially if you use a booster pump. I don't see why it wouldn't work.
     
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  10. fallguy
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    fallguy Senior Member

    In order to use the engine heat, you'll need muffin fans and radiators.

    The most common time to need heat is sleeping on the boat at nite or, of course on a cold transit.

    Do you plan a cooktop? Those can throw enough btus to heat a small cabin. Propane is not good here because it creates lots of dampness, but I have been on a few houseboats where the old man I went with used the propane cooker to heat the place up when it got chilly or left a pot of water under the boiler which made quite a watery mess on the windows, but achieved his goals of taking the chill off.

    There are so many cheap chinese heaters; it hardly makes sense to mess with the ob.

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  11. Mr Efficiency
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    Mr Efficiency Senior Member

    "After the engine" is in the exhaust passages, I can't see this being practicable. Some sort of heat exchange might work, but plumbing into the water passages, will end in tears, quite likely.
     
  12. fallguy
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    fallguy Senior Member

    I once had batteries failing in my boat. About two or three. It got so bad, I'd bring an extra new battery on a trip. I called the dealer and decided to swap out the old voltage regulator (vr). It turns out the old vr was too close to the exhaust manifold(em) and all new vrs were sold with new ems which were redesigned to hold the vr further away from the em to reduce the failure rate. Why do I mention? Well, probably hecause so many things impact an outboard. A few degrees of increase in heat might be really problematic. Or vice versa, what if your engine runs a bit cooler than design?
     
  13. trip the light fandango
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    trip the light fandango Senior Member

    The least invasive way is to use the engine cowling/ exhaust manifold as a hot air collector and duct it to the cabin, the tube would need to be well insulated with say little computer fans pushing the warm air. Checking for fumes would be sensible , a thermometer in the cowling would show whether its worth the effort or not . Or slightly whackier little wind turbines that turn the energy into heat as you travel, alternator /electricity, ,..or more sensibly using the outboards alternator..
    12v electric heater.
     
  14. DogCavalry
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    DogCavalry Senior Member

    Thing about the aftermarket heaters is
    1 they don't do diddly if it's cold.
    2 they are expensive
    3 they require a separate fuel system
    4 they are a bloody insult to my intelligence, and that of competent engineers everywhere.

    The heat being dumped away like it's worthless should offend anyone, except aftermarket heater salesmen.
     

  15. DogCavalry
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    DogCavalry Senior Member

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