water cooled exhausts, why ?

Discussion in 'Propulsion' started by saeble, Dec 20, 2005.

  1. saeble
    Joined: Mar 2005
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    saeble Junior Member

    after being mortified over the costs of water cooled exhaust manifolds... my inventive mind kicked in and asked the big question, "Why do I need these mainfolds?"

    Much to my amusement. I discovered I have no actual clue as to exactly why water cooled manifolds are basically standard on many small powerplants.

    Having said that, I've done some research and it seems that chiefly, water cooled manifolds are mostly about keeping the engine space cool/fire free than anything else. Is this the case ?

    I want to use two V6 Chev motors in two seperate hulls/engine spaces. If I make my own extractor/headers and have them ceramic coated, then wrapped in good thermal insulation, I should be able to get away with it shouldn't I ? In addition I will probably run some largish thermofans to pump air through the enginespaces.

    cheers !
     
  2. FAST FRED
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    FAST FRED Senior Member

    Dry exhaust are no problem and are used on most comercial vessels.

    BUT the ex gas temp of gasolene is much higher than diesel and you will need to be very carefull of not lighting the fiberglass boat on fire. Once lit it is almost impossable to get out.

    You will also need a keel cooler to keep the engine operating , and a good low drag set of keel coolers may make the exhaust manifolds look cheap!

    FAST FRED
     
  3. saeble
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    saeble Junior Member

    cool !

    my hull design will be steel, so no problem with hull fires.

    I have my own ideas for a keel cooler, I think I have this covered, I have found some very good aluminium extrusions which I can build keel coolers which could potentially run the entire length of the boat. Thankyou all the same for the adivice.
     
  4. Jango
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    Jango Senior Enthusiast

    Why can't he use a standard Inboard cooling system - small scoop on the bottom, w. a hose to an external pump, thru the engine or closed cooler and hot water overboard thru a fitting above waterline?
    Seems fairly simple with little or NO drag.
     
  5. rxcomposite
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    rxcomposite Senior Member

    Water cooling makes the engine room cooler especially if the engine bay is small. It also reduces noice.

    But if this is not a priority, a dry exhaust wrapped in ceramic is the simplest and most practical way.
     
  6. saeble
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    saeble Junior Member

    my engine space will be basically below deck with a top hatch so hopefully I'm not going to have any issues
     
  7. silverback
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    silverback Junior Member

    Just a few comments for your review:
    If your engine compartments are going to be hot, review your plans for intake/combustion air. You may have to run ducting to the air cleaners.
    Regarding your keel coolers: I question your choice of aluminum. Aluminum alloys for the extrusion process are usually not suitable for sea water. I'm not familiar with the alloys in Australia. In the US, alloys of the 6000 and 5000 series have been used to build boats. 5000 series better for hulls. One can weld aluminum channel or half-pipe to these hulls for coolers. Do not use aluminum with a steel hull.
    If you weld steel channel/half-pipe and or mechanically attach a cooling arrangement to your hull, keep in mind that you will have high spots and low spots. It is very easy to airlock these coolers. You will have to think about vents for the high spots, and drains for the low spots. You want drains for repairs, and coolant changes. Do not simply drill and tap into your cooler material. Weld fittings into the coolers for threaded plugs.Your engine compartments are small? With a single 'stem' cooler and circuitous runs, the stem HAS to be the high point. There are ways to have vents inside the hull if the runs are long and it's not possible to vent completely at the 'stem'.
     
  8. saeble
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    saeble Junior Member

    Air is coming in from way up, probably through a duct running up through either the centre console or the overhead framing. Suffice to say my air should be nicely dry and cool.

    Haven't really looked into the engine cooling yet to any great depth. I appreciate the advice. Nice to know there's some people here whom can be helpful without being derisive and looking down thier noses at you.

    I'm hoping I can get cunning with the inner faces of the hulls as far as a mounting point/s goes. Failing all this, theres always the automotive and silly method I've seen work to great effect on a home made paddle wheeler... yeah.. paddle wheeler... big paddles which where attached to standard truck diff, trans and engine, just like one would bolt up a set of rims... This guy ran a humungus truck radiator and a nest of theromfans and it ran as cool as the proverbial cucumber.

    So many ways to skin the proverbial cat... :)
     
  9. silverback
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    silverback Junior Member

    Tell us more about this boat project.Has the hull been built yet? You have several hundred horsepower/kW pushing a steel, displacement hull and it has a center(centre) console.How long and wide? What is the water temperature? Will live in salt water? Trailerable? How will it be removed from the water; Travel lift with slings, marine railway, dry dock??? Will it operate in shallow water with risk of impacting the bottom/debris from the beach? Is the water silty?
    Now is the time for you to research engine cooling.
     
  10. silverback
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    silverback Junior Member

    About radiators. Radiators are used for industrial engine cooling also. Examine a portable gen-set that is built into a shipping container. A notable amount of horsepower/kW is consumed by the fan and they work well. Many vessels/barges use radiator cooled engines. Usually, they are gen-sets.Work boats that operate in shoal areas and dry up as part of their routine have gen-sets with radiators and have 100%: hotel power, refrigeration, and hydraulics. Radiators are an additional option for cooling, but not for everyone. You mentioned the term "nest of thermofans". I'm not quite sure how many fans are in a 'nest', but I'm guessing it's equivalent to the Montana term "herd of thermofans".
     
  11. gonzo
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    gonzo Senior Member

    How about a coil wrapped around your dry exhaust with water for cooling?
     

  12. saeble
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    saeble Junior Member

    I'm a bit preoccupied with the hull right now guys, I'm messing about with some different bow profiles and a much more diver friendly stern. My thanks to you for the encouragement and the good lines of thought and questioning.

    I'm thinking I will probably 'go with what I know' in terms of cooling. The radiator/heat exchanger thing is becoming more and more attractive. I like the idea of being able to see if and when I have a coolant problem... not when I hear something is being scraped off my hull. Working in and around reefs is going to mean its more than likely I'll be doing some unplanned hull integrity testing at some point. Mangling a keel cooler or even mashing a vented space in which one rests isnt my idea of fun.
     
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