In gear or N when sailing?

Discussion in 'Diesel Engines' started by DennisRB, Nov 15, 2010.

  1. DennisRB
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    DennisRB Senior Member

    Not arguing about what causes the most drag. But it seems like our volvo 40 gets a hydraulic lock and wont turn over. This caused the starter motor to smoke. I was told I need to run it in N when sailing. If I leave it in gear something will allow water to be pumped into the exhaust valves? But I cant see how this could happen?
     
  2. Landlubber
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    Landlubber Senior Member

    "hydraulic lock"...you mean water got into the head?......I doubt that the prop can turn the engine over via the reduction box to pump water through the system (my old Yanmar TE series could roll start)...that would be easy to know anyhow.

    What type of box do you have.....a shaft brake may be needed here. Easy to make one if you do need it.
     
  3. CDK
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    CDK retired engineer

    The torque generated by the prop cannot turn the diesel through its compression stroke, but once the compressing has leaked away, the next 1 1/2 turns go easy.
    So the prop slowly turns the crankshaft and the water pump; with no exhaust gas to expel the water, the exhaust manifold fills up and it flows into the cylinder.

    Your starter motor it unable to compress water, so it smokes.
    If you do not act quickly now, the valve stems and piston rings will rust solidly to the surrounding iron and your engine is ready for the scrapyard.
     
  4. michael pierzga
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    michael pierzga Senior Member

    Never heard anything like this. You seem to indicate that you must keep the engine running to prevent water from entering the engine ????

    If you're talking about prop shaft free wheeling the transmission while sailing, then perhaps the transmission in over heating. No engine,no oil pressure, no cooling. Dont know your trans. . At any rate virtually every yacht Ive ever sailed had a prop shaft lock to stop free wheeling prop shafts from wearing the transmission. This yacht has a spring closed , hydraulic transmission pressure opened, disc brake system. The old classic, keep it simple stupid, shaft stopper is a wooden pencil jambed into the coupling to stop freewheeling ...start engine in a hurry..snap the wood pencil...no damage.
     
  5. DennisRB
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    DennisRB Senior Member

    All I can say is the starter motor had plenty of power and the engine would not turn over. Smoke came out of it when it could not turn the engine over, as if it was locked. So I assumed it was full of water or diesel.

    Thanks CDK. So although it does not appear to turn over, it might actually be happening very slowly. When you say, take action before it rusts up. Is running it for a few hours OK? Or is more required?

    Micheal, I am not talking about an overheating trans from free wheeling.
     
  6. michael pierzga
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    michael pierzga Senior Member

    Something is wrong with your installation. post a photo of provide a basic sketch. It is inpossible for water to enter an engine if the installation of the exhaust system is correct. Impossible. Forward, nautral engine on off..impossible.
     
  7. DennisRB
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    DennisRB Senior Member

    I have no pics but the exhaust exits the boat at the stern well above the water line too.
     
  8. michael pierzga
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    michael pierzga Senior Member

    The only way for seawater to enter the engine is thru the exhaust. Typical mis installation is at the engine side , not the over board side. The water injection jacket on the exhaust and the Aqua lift muffler arrangement. Get any of these details wrong and sea water can enter the engine.....your engine would be destroyed in days. It would be impossible for any competent mechanic not to immediately spot a mistake and not alert you...something sounds fishy.
     
  9. TeddyDiver
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    TeddyDiver Gollywobbler

    There's a possibility that a worn impeller allows water to flood the system. Depends thou what's the hight of waterline vs engine (exhaust injection)...
     
  10. Bglad
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    Bglad Senior Member

    It doesn't make sense the water in the engine is related to the prop shaft turning or not turning. Sounds like a plumbing problem. Check your raw water system for a vented loop. Your installation may be fine without one at rest but your heel angle while sailing might cause the raw water plumbing to become submerged allowing water to siphon into the exhaust. As CDK pointed out water can't exit the exhaust unless the engine is running. In case you don't know a vented loop is a U-shape piece of plumbing that mounts above the waterline and has a vent at the top. When the raw water system is under pressure the vent closes. When at rest it opens and allows the piping to drain. Goes somewhere in the line after the raw water pump usually just before the exhaust elbow. If one is installed check and make sure it is functioning properly.
     
  11. daiquiri
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    daiquiri Engineering and Design

    I agree with what Bglad, CDK and Pierzga. You should check out your raw water plumbing. Here is a simple illustration of a vented loop (for a bilge pump in this case), in case you don't know what does it look like and why is it necessary: http://www.boatdesign.net/forums/fi...-loop-dirrect-discharge-26049.html#post255257
    In that pic, imagine the raw water intake as a through-hull opening at the left side and the engine exhaust instead of the pump at the right side of the pic. If the engine exhaust is placed below the heeled waterline and there's no vented loop, the water rises up and fills the cylinder. However, a vented loop is an ABC of through-hull fittings. I would be very surprised if it wasn't installed on your boat.

    P.S.:
    This page probably shows and treats it more clearly: http://www.yanmarhelp.com/i_exhaust.htm
     
    Last edited: Nov 16, 2010
  12. michael pierzga
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    michael pierzga Senior Member

    As is always the case when talking long distance, a picture of your exhaust system geometry would be very helpful. What is the position of the water injected exhaust water jacket ? Does your system have a syphon break ? Is the aqua lift mounted below or above the engine exhaust level ? Does the exhaust exit from the aqua lift arc way above the waterline before exiting the boat at the waterline. ? All will be visible in a picture. All these details will also be obvious to any local marine engineer. They should be able to spot any defect with a simple examination.
     
  13. kenJ
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    kenJ Senior Member

    The reason for sailing with the transmission in gear is to prevent transmission damage caused by a freewheeling prop. Unlike car transmissions, most marine trans use friction plates rather than gears to connect the engine to the shaft, over a long period of time a freewheeling shaft will damage the friction plates.

    I agree with everyone else, it is not the transmission that is causing water in your engine. If you can talk to the boat's builder, get a diagram of the correct raw water and exhaust hose routing to ensure your plumbing is correct or if in doubt consult a reputable marine mechanic.
     
  14. CDK
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    CDK retired engineer

    Dennis you wrote in past tense, so you got the engine running again.
    If not, make sure the exhaust manifold is empty, remove the valve cover, press down the exhaust valve with a wedge made from aluminum or copper (to prevent damage to the cam) and turn the engine with a wrench.

    Once the engine blockage is gone, start the thing and let it run for a few hours at idle rpm. Check the engine oil: there may some water in it, soon to disappear once the temperature rises.
     

  15. michael pierzga
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    michael pierzga Senior Member

    Starter motor with smoke poring out can mean many things. As far as ... ". Mr. CDK... if water is in the oil it will soon disappear "" statement ...HOLY MACKEREL !!!!!!!!!!!!!!! your whole engine will soon disappear. If you sense any water in the oil...STOP NOW...I repeat STOP NOW, and immediately have an engineer investigate.
    Mr CDK's explanation that water will soon disappear is foolhardy and simple minded. Disregard Mr CDK's Pedantic criticism of your grammar and his thought process ...don't run the engine if you have fears of future salt water intrusion.
     
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