Fin keel heat exchanger

Discussion in 'Boat Design' started by sighmoon, Jun 18, 2013.

  1. sighmoon
    Joined: Oct 2007
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    sighmoon Junior Member

    Would it be viable to use a fin keel with internal fresh water pipes as a heat exchanger for cooling the engine?

    The object would be to save having to pump in sea water - no broken impellors, no debris blocking anything, one less hole in the hull, etc = cheaper maintenance and more reliable.

    Looking at (as opposed to calculating) the amount of water coming out the exhaust of a typical marine diesel, it doesn't look like that much. When the boat's motoring, the area of water passing over the surface would probably be greater than a normally cooled engine. At rest, with the engine idling, convection would ensure a flow proportional to the engine temperature.

    Would it work?
  2. tunnels

    tunnels Previous Member

    What do you stand to gain from doing this ??

    Some where some one will have a way to calculation for the right size of pipe to get the right surface area of the pipe to transfer the heat that a specific size engine produces when it is under load at specific rpms , so how do you feel about plumbing your keel with lengths of pipe and where would you place then and how would you secure them so they are in a main water flow so the water is moving past all 360degrees of the total length of all of the pipe outside of the boat ?? the system still has to have a circulation water pump
    would it be easier to go buy a heat exchanger the right size for your motor mount it plumb it and be done with it end of story !! in reality you will end up with a exhaust that still needs o be cooled so the pump stays and another 2 holes through the hull for the plumbing to pass though!!and a second pump to circulate the water !!!
    For me its going to cause drag !!
    its going to have to have 2 holes through the hull !!
    the pipes will have to be really secured some how
    the whole lot will have to be antifoul painted
    and as it gets caked with sea growth so becomes inefficient to the point of the motor could over heat its self !!
    then what ??
    over the side with snorkel and flippers and wire brush and clean it !! .
    cant really see any advantages what so ever just a heap of hassles !!
    but people do have them and they do work !!.
    pluses very few, :(
    minuses heaps !!:confused

    Water pump impellers need to be changed once a year and you always carry a spare always !! its usually lack of use is why they break !! and of you having problems with rubbish why don't you fit a see into water filter with a removable top ?? they work a treat and filter all the crap out of the water before it gets to the pump !!!
  3. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    Yes but fin keel is supposed to be heavier than a radiator..
    A rudder on the other hand.. :)
  4. sighmoon
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    sighmoon Junior Member

    The idea is that the pipes are inside the keel, as part of the casting, so no extra drag, and not an intricate engineering masterpiece. The keel, being metal, would conduct the heat away at a calculable rate.

    Cracked paint and fouling isn't an issue I'd considered. Freshly cooked seafood, anyone?
  5. sighmoon
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    sighmoon Junior Member

    In the case of my boat, the bilge is too shallow.
  6. tunnels

    tunnels Previous Member

    What ???

    The idea is that the pipes are inside the keel, as part of the casting,
    The how will the pipes dissipate the heat ?? so as the keel gets warm then hot then the cooling is not taking place and you have one cooked motor !!
    where and how can the heat get away if its inside the keel ?? and if the keel gets hot what's it going to do but expand and could cause other problems!!
    It will needs a free flow of water completely round the total length of all of the pipes to transfer the heat out and away and cool the water inside !!. :confused:
  7. Mark Cat
    Joined: Jun 2011
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    Mark Cat Senior Member

    In my experience, the keel cooler name has expanded to include any method of cooling the engine(s) using a hull (or hull mounted) or keel heat exchanger. Although, I must admit I can not recall one that was actually a part of the keel.

    To gain the maximum benefit, Keel cooling is usually paired with a dry exhaust.

    The idea is to not use raw sea water to cool the engines (or engine mounted heat exchangers) or exhaust, thus avoiding the potential galvanic corrosion problems. Even static sea water in a heat exchanger or wet exhaust manifold can form a galvanic cell (especially when the water level falls below a protection zinc).

    And as already said, when you go beyond the off-the-shelf keel coolers (Easily sized by the manufacturer), the sizing can be a challenge to model.

    All for now,

    Mark Cat
  8. tunnels

    tunnels Previous Member

    I understand what you saying and the problems of creating a cooler is growing bigger by the minute . fitting ,mounting ,and making a dry exhaust inside a boat ,and totally insulating the kit and caboodle is a major issue !!!! and we haven't even touched on the sound insulation bit yet
    to me if its just a issue with the water pump and getting clogged id be concentrating on that and that's alone making sure it is easy to maintain and virtually fool proof in its operation .
  9. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    I don't see how the keel would get hot when its sitting in water. The heat transfers from water through the pipe to the mass of the keel which is cooled by water flow. I don't see any issues with cooling capacity.

    I do see issues with maintenance - if for any reason there is a problem, corrosion, blockage etc. Its going to be a major head ache.

    Naturally the dry stack issues exist but they are teh same with any kind of keel cooler.
  10. TeddyDiver
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    TeddyDiver Gollywobbler

    Actually there will be some issues. There are two water/metal layers and the thickness of the keel from the inner tubing to surface where thermal conduction happens.
    The capacity of the first one depends of the surface areas which has to be quite generous. I don't have the formulas at hand now but they are here in the BDNet also. From my memory 70hp engine in a displacement boat should have about 1.6sqm. Needs a lot of tubing inside the keel.
    The thickness factor in a cast keel doesn't help either. What ever the material excess material thicness acts like an isolation and reduces conduction capacity. Not too hard to calculate either..
    BR Teddy
  11. tunnels

    tunnels Previous Member

    YES you are seeing what I saw immediately it was stated the tubes be case as part of the keel .
    Personally this excise is a total waste of time and will go no where so im out of here !! :confused:
  12. Village_Idiot
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    Village_Idiot Senior Member

    Actually, I would like to see an implementation of this in a flat-bottom jon boat hull. Hull gauge would be 0.10" - a "double-hull" of sorts could be fashioned, where the inner chamber is watertight, but contains freshwater that is plumbed to the inboard heat exchanger, which is in turn plumbed to an outboard engine. No pipes in the hull, water is free-flowing, hot water goes to one end of the boat, cooled water is drawn from the other end.

    Why? Because there are places where outboard engines are the preferred propulsion for a myriad of reasons, but they must also run through occasional sand that tends to plug water passages, or, more commonly, jam the thermostat so that the engine overheats. A water-to-water heat exchanger with a discrete volume of water would be ideal in this situation.

  13. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    I don't see why it wouldn't work. It's just a matter of dissipating heat.

    TeddyDiver pointed out the lessened weight of the keel and the area needed. The rudder is an idea, if the plumbing could be figured out to be reliable. I'm not sure if relying on convection would be a good way to go no matter how you did the cooler.

    But the OP hasn't said anything about the size of the boat or engine or what the boats made of or if it's a new build or what. The size and shape of the fin would be something handy to know. The temperature of the water it would also be in would be handy to know. How long the engine would be used for might matter too. If only for an hour or so at a time, the fin might be able to absorb the heat like a heat sink and then be able to dissipate the heat over the space of hours, until the engine could be run again for awhile. All those things would matter, but in theory, why wouldn't it work?

    Then again, keel coolers don't have to be a bunch of pipes stuck on the outside of the boat, about as hydrodynamic as an old time heat radiator in a house. I've read about steel boats using the internal frames and stringers as an internal keel cooler so there is no outside the hull apparatus. Even outside the hull stuff can be streamlined.

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