If the engine doesn't start, it drowns?

Discussion in 'Inboards' started by CaptainAB, May 8, 2010.

  1. tunnels

    tunnels Previous Member

    The whole system was covered by large manual or electricly operated valves so there was not back pressure going anywhere to either of motors .plus when at idle there was a smaller dia pipe out each side . Was quite a complicated set up when it was all finished , but in use under way it was amazingly quiet .:D
  2. apex1

    apex1 Guest

    Ahh, the designer and the builder enjoy daily three meals for free now?

    A exhaust through the hull bottom is really insane! It produces such a back pressure*, that would cut the engine power dramatically, no one in the entire marine world would even think about such setup.

    You must have missed something there.

    *not the one formerly mentioned blow back! You know the difference?

  3. tunnels

    tunnels Previous Member

    Ahh but it had two big scoop arangements on the bottom of the hull that created a vortex and sucked all the exhausts and had no back pressure at all even at a slow speed .
    Have fitted these to a few boats over the years ,bit like what the modern out boards have to suck the exhaust through the centre of the prop ! same principle! .
    I was waiting for some one to think about this and ask !!. :D
  4. apex1

    apex1 Guest

    A vortex? Strong enough to work against about 2m water column, or 20kPa ? And what about the resistance? And how would you start the engines?

    Such arrangement btw. would be much different from a outboard system.

    Hmm, I have my doubts tunnels...:confused:
  5. tunnels

    tunnels Previous Member

    I had the responsability of making everything that was made of glass for the boat , i was handed plans signed and stamped with approval by 3 people and given all the info supplied by the designer . So if things didnt work they were his responsability not mine .
    The boat was 147 ft long and the exhaust were no where near 2mtrs under the water lucky to be .8 to a metre at most ,like i said it was a complicated set up !
    I have a photo of the boat on the transporter before it went in the water some where just cant find it at the moment .

    The vortex system is also used by Salthouse on there range of boats . The columb that went through the hull was a part of a wing section standing on a 5 degree angle with an angle cut off the rear section so it to produced a suction when the hull moved through the water .
    I would say there would be more than 100 of there boats on the water and they all have this system .This makes the boat very quiet and the exhaust gases surface way behind the boat as its traveling along . Just like your outboad does !:D

    The thing of resistance , as long as anything is designed in a friendly shape the resistance is minimal and could even be benificial ! .
  6. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    ......many boat are being built with underwater exhaust systems, there is a bleed port that comes out the side/rear of the boat for when it is at idle, if the main exhaust is, say 8 inches, the bleed port is only about 3 inches. It allows idle pressures to be basically neutral and when the boat gets going the main exhausts are extracted by the shape of the hull and the exhaust system....we even did this in China......
  7. powerabout
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    powerabout Senior Member

    Yes its true very common on megayachts the bleed port would be more like 200mm for 700 ish horepower and the underwater outlet would be less them a meter under as tunnels says.
    Works well as the only the gas comes out the bled port and the water goes underneath till you close the port of course.

    I just dont get that other fitting showing a gen set and a main engine in the same unit???
  8. tunnels

    tunnels Previous Member

    Yeah at last some one that understands things !! welcome !Thought i was going this one alone till now . A simular system was used for quiet running with the old MTBS & MGBS during WW2 !. I see even Mercruser now has a box arrangement that can be installed on the transom to turn the exhaust down at water level . The Volvo Penta IPS system uses the simular set up !!
    Its nothing new !!
    There is very little thats new in reality , everything we see today is just a modification of some older principle from the 1920s /30s/ 40s , its been the advances in better materials that has made some of these old principles work better and more efficently .
    To understand better what im talking about go visit a maritime museum or read the book "FROM DHOWS TO DELTAS". That book has a wealth of stuff in it if you read it carefully and absorb all thats written and study some of the pictures . :D
  9. apex1

    apex1 Guest

    There was no bleed port mentioned in tunnels statements! But a vortex instead.

    And 6000hp is quite a lot of gas to be blown through the exh. pipe. (8in. will not handle that, as you know)

    Handling less than 100cm of water column, and having a bleeder, makes another picture, sure.

  10. powerabout
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    powerabout Senior Member

    Yes Apex the bleed through the side is ony designed to allow idle engine power to have an easy exit other wise the exhaust would be fighting the water column as you correctly stated ( unless your moving so the fairing can take effect)
    And you need to close it after you start moving as there's a good change the extra volume of gas will drag water out and leave a black stain
  11. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    We should mention to Captain AB that this thread drifted off to megayachts where 99% will have a dry riser to the muffler then all downhill to water injector and out the 2 outlets we mentioned so you cannot have the problem mentioned by pumping water without a running engine.
    The gen sets would also be done the a similar way but as they are expected to run at full load with a stationary vessel they will have a water stripper after the water injector and drop the water out under the water and the cooled, dry, clean exhaust above the water.
    In the last 15 years or so this has also become a norm on small boat gen sets as well ( for any builder that has its act together that is)

    PS Mind you on a small boat you will not have the vertical height so there will probably be a water lift between the water injector and the stripper so back to the problem of possibly drowning your engne
  12. apex1

    apex1 Guest

    Thanks pa,

    I know what we are talking....................

    .....for 4 decades now.:p

    And I concur on the water separator issue on modern systems.


  13. tunnels

    tunnels Previous Member

    Theres 3000hp in each system and the vortex is under the boat and yes there was a bleed off pipe for when at idle and for starting purposses and a series of shut off valves for when the boat was underway. :D
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