Wet exhaust setup

Discussion in 'Boat Design' started by LopiTech, May 14, 2014.

  1. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    How about some more information on the vessel? Exhaust systems can be very application specific.
    Very generally, the dry portion of the exhaust is raised as high as practical, so that there can be plenty of fall from the introduction of cooling water to the exhaust exit.
    Boatdiesel.com has plenty of info on the subject, as well as Seaboard Marine website.
    I wold hazard to guess that more marine engines die as a result of poor exhaust engineering than from any other cause.
     
  2. tom kane
    Joined: Nov 2003
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    Because hot water rises (as in thermo siphon) you would need to keep all of your cooling jacket and coils full at all times even when you input pump fails so your water outlet needs to pass the highest point in the system to achieve that. Even if you use one-way valves you need to make sure that if the system boils there is plenty of relief outlet.
     
  3. LopiTech
    Joined: May 2014
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    Location: Alberta

    LopiTech Junior Member

    For more vessel information, I don't know what all I can help with. I do not know what year or type it is, other than a guess of early 1960's maybe late 50's. I converted it to a jet drive using a Yamaha jet drive, powered by a zx10r sport bike engine. Here is a overall pic of it when I first bought it.

    167.JPG

    Tom, if I were to have the exhaust exit the hull higher than the header, would the engine not flood quite quickly if the motor stalled or something else of that nature and the pump stayed running? That is why I thought the exit should be as low as possible, to be sure it could never fill higher than the waterline. You seem very knowledgeable and I obviously do not want to wreck a very expensive engine so I am just looking for all types of input and options. If I kept it low in the waterline and ensured the pump rate did not exceed the hydro-static pressure needed to allow natural drain, the pump could remain on and continue to cool the system while the engine is not running. If this would not work I am eager to learn why, so please help me understand.
     
  4. tom kane
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    I am not clear now exactly on what you are doing but the photo looks the same as I tried on a GT 4 cylinder high lift cam motor. Cooling coils on the headers (exhaust extractors) then injecting the water into the headers. I found that injecting water into the exhaust resulted in the water getting into the motor to the extent it shorted the spark plugs making rough running and I even lost a valve insert doing damage to the motor.

    I changed the water injection point into the headers further away from the motor (about 2 feet) that did help but the exhaust valves still rusted and stuck. I am not a fan for water in any exhaust system better to have a water jacket system and a good muffler and perhaps a little more exhaust noise.

    I have added this image with my version of what I tried.
     

    Attached Files:

    Last edited: May 19, 2014
  5. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    I didn't notice it earlier.
    This is asking for trouble, both if the pump stops running while the engine is on and the other way around.

    I can imagine an electronic circuit that controls the pump through an ignition or alternator signal, or even a pump powered directly by the alternator output, so it cannot flood the engine.

    Far more reliable is a simple belt driven impeller pump.
     
  6. LopiTech
    Joined: May 2014
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    Location: Alberta

    LopiTech Junior Member

    I have been trying to find a way to have the pump run only while the engine is running but it is difficult. Injector wires seem to just have a ground signal sent to then, and the alternator has a very high output voltage. A belt or chain pump would be ideal, but I do not know of any that would self prime a hose about 5 feet.
     
  7. LopiTech
    Joined: May 2014
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    Location: Alberta

    LopiTech Junior Member

    I think I may be able to use the oil pressure switch to trigger a relay to turn on and off the pump. I have to do some testing to make sure, but it seems like it is possible to use a negative trigger wire for a relay.
     

  8. LopiTech
    Joined: May 2014
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    Location: Alberta

    LopiTech Junior Member

    After a lot of research and thinking I have decided I need some type of anti siphon valve or anti vacuum check valve at the top of my headers. Without it, the hot air inside will cause a vacuum inside which will draw water up inside the headers to the engine. I can either try to find 4 small units or even just drill tiny holes in it, if I can't find something that will work. Does anyone know of a small stainless valve like that? Something that just threads right in to a 1/8" collar that would hold pressure in the pipe, but on vacuum would open?
     
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