Is a marinized diesel necessary if....

Discussion in 'Diesel Engines' started by pha7env, Mar 26, 2012.

  1. CDK
    Joined: Aug 2007
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    CDK retired engineer

    My experience with stainless flexible tube is limited to a piece I took from a scrapped army vehicle. I wanted to use it between a diesel generator on rubber mounts and a fixed muffler, but it developed cracks after just a few engine hours because it resonated wildly.
    I later found out that what I used was just the inner lining of an exhaust hose. There originally was a braided layer around it with asbestos fiber in between, but people in some sort of space suits had already removed the dangerous stuff.

    Regarding flex engine mounts: I use real silent blocs that allow my little diesel engines to move considerably, especially during starting and stopping. If the engine/gearbox has to take the prop thrust, much larger and stiffer mounts are used, but they still call them flexible.
     
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  2. Frosty

    Frosty Previous Member

    This is piddle talk . Of course you can use flex mounts but of course you use an exhaust flex geez I thought I was talking to engineers.
     
  3. pha7env
    Joined: Aug 2011
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    pha7env Junior Member

    My experience is with the insulated, stainless braided flex created for diesel engines. Also, the boat of i'm "pre-designing" will have engine room at the boats center and use a constant velocity joints (probably 2) in flex mounts that will absorb some of the prop thrust as is travels toward the transmission. I will probably use a indirect and cushioned shaft system just aft of the transmission thrust bearing that will not only allow disconnect for sail, with the backup rig, but allow prop free-wheel under tow. Understand that there will be only around 100 hp that we are dealing with. An example of the flex coupling can be found at http://www.flexible-coupling.com/r-and-d-flexible-shaft-coupling.html.There are a number of different types, but i have used them extensively on dry land and trust them. There are a number of things on the market allowing flexible engine. exhaust and drive shaft mounting. Some get expensive. Which to use and which to pass up are among the things i am trying to learn. I just hear of so much trouble in the ocean with wet exhaust, and i love the smell and sound. rj
     
  4. keysdisease
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    keysdisease Senior Member

    Below: Flexible engine mount, dry stack exhaust bellows, flexible exhaust support.

    There are also some really excellent thermal insulating lagging products now available, ceramic hard coat and traditional looking lagging but with ceramic fill that work much better to reduce radiated heat than traditional lagging.

    Also, re wet exhaust, there are wet exhaust systems that remove the water from the exhaust and discharge the water seperately below the waterline eliminating any splashing noise. These are especially popular for generator systems, but are also used in propulsion applications.

    Steve
     

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  5. pha7env
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    pha7env Junior Member

    That's the type of stuff i am looking for. Awesome. Thanks!! Any links to products like this will surely be appreciated. I have a lot of planning to go, including whether i want to build a hull or adapt an existing vessel and it's components.
     
  6. CDK
    Joined: Aug 2007
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    CDK retired engineer

  7. dinoa
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    dinoa Senior Member

    Lingering wet exhaust fumes like to enter open port holes at berth. Dry stacks don't.

    Dino
     
  8. keysdisease
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    keysdisease Senior Member

    Each system has its very valid pro's and con's, many of which have been mentioned.

    It's up to the vessel owner / operator to decide which system is best for the given type and use of vessel.

    I don't believe either is better for ALL vessels, or for that matter in all circumstances. In fact many large yachts have the options to either go up the stack dry or out the hull wet because in different circumstances on the same vessel either system may be better than the other.

    As important as vibration reduction, if not more so, the bellows I pictured in previous post allow for expansion and contraction of the exhaust system, something that should really be allowed for. I caution anyone not familiar with marine exhaust systems to not just start welding, but to seek advice from someone that knows how they go together.


    Steve



     
  9. CatBuilder

    CatBuilder Previous Member

    Now I have certainly seen flexible exhaust couplings used before. No problem there. If the engine is bouncing around on soft mounts, you fix the exhaust soon after the engine and for the rest of the run out of the hull. The couplings seem to last quite a while, but do seem to have a finite life.

    The big question is... would it be possible to make a dry stack as quiet running as a wet exhaust?
     
  10. keysdisease
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    keysdisease Senior Member

    Yes... but you would have to give up a LOT of space for dry mufflers, isolate the dry exhaust run through the trunk and insulate the dry stack truck from airborne noise as it passes through any accomodation spaces. You will also have a lot of radiated heat in the engine room you would not have with a wet exhaust.

    Steve

     
  11. pha7env
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    pha7env Junior Member

    I am sure that the finite life of the expansion joint(flex joint) will be finite. As are impellers, salt manifolds, ect. on a wet system. If we do get this thing rolling and get to the crossing stage, it must be "all oceans" certified. The dry stack will present through the decks in day head room, between the pilot house and the salon. The stack will present topside on the flybridge and continue inside the mast and exhaust out of the top of the mast. We will carry a short stack to intall when running mast down. If the engine to muffler does not do the job we will install a secondary muffler in the "stack house" which will be the mast base and inlet for the forced air out and possibly into the engine room to maintain the room temp. Will also have the option to open to flow cabin air into the engine room and positively expel it up the air exit running parallel to the exhaust. Love all the comment, especially the ones that warn of problems. I LOVE to address problems. Thanks for the links CDK. Please remember, our first boat will surely be wet exhaust because most boats in our "great loop", shallow draft, price range will carry them. There are a few reasons other than draft to buy an inexpensive boat first. 1. it will get my wife and i on the boat sooner(hopefully by fall), and 2. our kids will actually get to go to college 3. Knowing that there will be many likes and dislikes i don't want to sink a bundle in a boat that we won't like. Need to learn what is wanted, needed and just plain necessary. Once again in humble thanks, I am only and will remain, Robert Jones
     
  12. pha7env
    Joined: Aug 2011
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    pha7env Junior Member

    Steve(Key disease), do you know the manufacturer of the flex coupling you attached? Or have a link other than to the picture? Thanks!
     
  13. CatBuilder

    CatBuilder Previous Member

    Sorry, sometimes my thoughts are clouded by catamarans. In my personal case, I was picturing the engine rooms of my own boat which are all the way aft behind a water/air tight bulkhead with no accommodations between the engine and the exhaust outlet.

    I'm putting a small diesel in one of the engine rooms with a huge alternator on it to charge batteries from time to time. Propulsion is outboard. So, I was just thinking a little bit about a dry exhaust for a moment from a personal perspective...
     
  14. pha7env
    Joined: Aug 2011
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    pha7env Junior Member

    The boat i would like to build, or refurbish will kindof be a cross between Bruce Roberts, Tad Roberts and the larger diesel ducks ofGeorge Buehler. The engine will will be just aft of loser midship. The pilot house will be mid and raised. The Salon will be flush deck, with an aft master and passageway forward, beside the engine room. The engine room will be the longest room, but not full width because of the passageway. Or so it stands in my head as of this moment. The idea melds as i learn. i really would like the master to be midship and the ER to be aft, but i'm not sure we could work out the weight distribution. hopefully some of the fuel supply will be integral with the hull. who knows, may build the bed onto main fuel tanks an build the secondary and tertiary under the storage port and starboard in the bedroom. If i build the master midship, i could bulkhead it also and completely if i made the airducts sealable. hmmm??? Anyone else have the "slow boat to China" mentality, or are you all young enough to still want to stay home and go fast on the weekends??? Been there, been fast. Now it is time to see the "ends of the earth" (in a few years...)
     

  15. keysdisease
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    keysdisease Senior Member

    Robert, I sent you an e-mail.

    Cat, I can't imagine anything for your setup except a wet lift / seperator system like for a genset. A good one will have the exhaust gas discharging cool and dry and sounding about as loud as a dryer vent in a house. Water will discharge below the waterline, you wont't even know the thing is running.

    Which reminds me of my McGregor 36 with the twin Yamaha 9.9 4 cycle hi thrust motors. My usual prep for getting underway was to fire them up after loading but before untying from the dock. This was to get them warmed up a little. For the first dozen times I did this I would grind the starter trying to start a running engine when getting ready to pull away. Damn things were next to silent at idle, I got used to looking for the pee hole stream before turning the key.

    Steve
     
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