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46' Post SF Sinks

Discussion in 'Post Yacht' started by Jimbo1959, Sep 1, 2014.

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  1. Jimbo1959

    Jimbo1959 Member

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    Hi all, Last week at the shop a Post went down a few days after launch. It went down in less than 2 minutes. The cause was that the port muffler exploded. The hole was 2 as large as the outlet through the transom 8".
    The owner stats they were getting ready for sea trial. The generator was running, they started the port engine (DDA 6-71TA) within in seconds they heard a loud bang, saw smoke. The boat started down immediately, they got everbody off.
    My thought is since the exhaust goes through the transom at 8", the muffler is approx. 24" long by 24" diameter. Maybe the muffler was full of water and when the started, the pressure created to push the water out the 8" hole was too great and the muffler gave way. Only problem with this thought is that a lot of boats are rigged this way and don't sink. Any thoughts?

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  2. Marmot

    Marmot Senior Member

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    I'd like to see a diagram of the exhaust system showing diameters, height above water line, and a photo of the failure point.

    Something sounds odd about this whole thing.
  3. Capt J

    Capt J Senior Member

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    I have seen SF in certain marina slips like that. The Exhausts would fill up with TONS of floating debris everytime you started them......like a 5 gallon bucket would come out of debris between both exhausts.......I would think it would be entirely possibly for something like the right size coconut to float in there and get wedged and block it. Up North Beavers and such have been known to build nests in boat exhaust.
  4. P46-Curaçao

    P46-Curaçao Senior Member

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    Not a great picture, but it shows the muffler...

    IMG01066-20140812-1124.jpg
  5. Jimbo1959

    Jimbo1959 Member

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    Post # 4 is exactly what it looks like. I'll try and get some dimensions tomorrow, but I can tell at least a 1/3 of it is blown out. Whats odd is they had ran the engines a few times earlier in the week. They got the boat up and out of the water. We pickled both engines and gears. Both engine lit right off, so I think that much is salvaged. The interior is destroyed oil everywhere. The only saving grace is that it went down in fresh water and here in CA it is very dry, low humidity.
  6. PacBlue

    PacBlue Senior Member

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    I remember seeing Black Cloud at Avalon a few times, sad to see here go down. We purchased a 46 Post sistership out of San Fran quite a few years ago, not too many of them running out west.

    Very few production boats are capable of blown exhaust openings of 8" plus, takes some very quick thinking too stuff life jackets or whatever to stop the sinking.

    I do recall that at full load our 46 Post's swim step was just a few inches above the waterline, and we did not have a tower.
  7. RT46

    RT46 Senior Member

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    I will be carrying a football or something that I can plug up the exhaust in an emergency.

    It would be tough to react quickly enough in the event of a total failure of the system, I would imagine that the boat would be beyond recovery very quickly.

    I recall that a multi-million dollar French owned mega yacht when down very quickly in rough seas and it was believed that the exhaust system caused extensive flooding. Somewhere on YF is a thread.
  8. chesapeake46

    chesapeake46 Senior Member

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    Many years ago I had a similar problem.
    Fortunately I was in the bilge when it happened, heard the water, told my wife to get some blankets, jumped overboard and stuffed them into the exhaust.
    Luckily for me, I was in the slip and the yard manager was immediately at my side.

    The blanket was sufficient to slow the water until we got her in the lift.
    In fact, I ran her to the lift on the other engine.

    After that I now have a piece of lumber, cut into the correct size that can be pushed into the exhaust hose and clamped if it should ever happen again.
    But you'd still need a blanket or something to slow the flow.
  9. chesapeake46

    chesapeake46 Senior Member

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    I agree with the fishy statement.

    If it's like my 46, the exhaust is 8 inch and sits about 1/2 to 2/3's submerged all the time.
    The original exhaust tube does not pass to far into the bilge from the transom.
    Then there is exhaust hose to the muffler. Then hose from the muffler to a metal offset tube. ( in my case it was an 8 inch aluminum offset ) then hose again but now elevated by way of the offset tube, up to the exhaust mixing elbow.

    The muffler is not elevated, but is on the same center line as the exhaust tube at the transom if that makes sense. I want to say "level" but nothing ever seems level in a boat.

    Attached Files:

  10. Capt J

    Capt J Senior Member

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    I wouldn't say fishy, a 2 year old Luhrs went down like that here offshore while the guys were fishing a tournament. They went to start the engines, blew the transom exhaust tube off, 6-8" is A LOT of water pouring into the stern of the boat, 2-3" later the scuppers are underwater and pouring in the cockpit and into the bilge through any deck hatches etc.......and if you have the lazzarette open trying to stop if from inside or even inspect it, down she goes. Not only do you have water pouring into the open exhaust, but you also have the engine pumping water into the boat as well.

    Think about it, if you have a loud explosion at the dock, it might take you a few minutes to figure out what just happened. I would think a Basketball (rubber) and an airpump would be a good choice to pump up in the exhaust to block the water flow.....
  11. chesapeake46

    chesapeake46 Senior Member

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    In the situation above, I can see where the skipper might not even realize there was a problem until it was too late. Assuming the exhaust hose " popped" off, not exploded off.


    [/QUOTE] ..Think about it, if you have a loud explosion at the dock, it might take you a few minutes to figure out what just happened. I would think a Basketball (rubber) and an airpump would be a good choice to pump up in the exhaust to block the water flow.....[/QUOTE]

    Now this situation, someone heard an " explosion" of some sort. What else would you do but look in the bilge as fast as humanly possible ? How the heck could any skipper or captain NOT look into a "BOOM" ?

    You're right, 8 inches is alot of water but if the crew thought quick enough, that boat woulda been saved. Once you slow the water, the bilge pumps would eventually get it and I think, well before it even got over the forward floor boards.

    As for the bicycle pump, well, I've got 8 inch plumbing test plugs in my exhausts now. I fill them with a portable can of compressed air. They have a schrader valve like a bike.
    It is hard enough to fill the plugs on a calm day, in the slip, with your wits about you. It'd be much worse if the boat was pitching and rolling, the waves were pushing and pulling the plug and your trying to get a fitting to hold and then pump it.
    Even if you were inboard, you'd still have a time of it.
    It's not a bad idea, but pretty hard to pull off.
    A heavy blanket is the first line of defense for me .... after maintenance inspections, I mean. ;)
  12. Capt Ralph

    Capt Ralph Senior Member

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    Boat fenders

    As a practice, I always plug the exhaust when working on any exhaust system. I found you can use different sized fenders with a towel and wedge them in.
    I can also let air out and pump back up. but if you have a 8" fender, practice fit/pressure and your ready if it ever happens.
  13. Beau

    Beau Senior Member

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    Sad to see any boat go down. I have heard of muskrats eating thru exhaust tubes in the Hudson River? If it was an "explosion" - was it back pressure related? Be interesting to read how the facts develop. Any YF members on site?
  14. Capt J

    Capt J Senior Member

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    If you heard a boom upon startup is I'd check the engine room, that could take a few minutes......really and that's all she wrote, I could honestly see how it happened and sank.
  15. Marmot

    Marmot Senior Member

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    Yeah, if the outlet was submerged one foot it would flow just under 1300 gallons per minute ... 12,200 pounds of freshwater per minute.

    But, that is assuming there is an 8 inch hole ... did a large chunk of the muffler leave the building or did it just split?
  16. Jimbo1959

    Jimbo1959 Member

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    There is a 1/3 of the muffler missing from the side of the muffler. The pieces were in the lazz bilge after it got raised and pumped out.
  17. Beau

    Beau Senior Member

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    Wow, that's a big piece of the muffler. Any analysis of the cause yet?
  18. Capt J

    Capt J Senior Member

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    Then once the scuppers get underwater you have even more water flowing in.....she's on the bottom in 2 minutes.....maybe less......not enough time to react to it and contain it in most situations.
  19. RT46

    RT46 Senior Member

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    I had a good friend loose the mains approaching a bridge.

    Both engines stalled and would not restart.

    Alarms were going off.

    He was trying to restart.

    Trying to deploy the anchor.

    Then bam he drifted hard into the bridge and damaged the boat.

    When all was said and done it was a loose wire in the halon shut down.

    All he would have to have done was hit the bypass and restart, but that was not in his emergency restart check list when there was no fire. The restart bypass is now in my muscle memory on an emergency restart.

    Threads like this are helpful because not only do they help dx and prevent this type of failure but the incident ends up in your mental muscle memory and "stuff the exhaust" becomes an emergency reaction to a loud bang and sudden flooding.
  20. P46-Curaçao

    P46-Curaçao Senior Member

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    I agree for 100% and already stored some fenders within reach and will also instruct my wife next weekend!

    I'm interested in better solutions to close the holes...

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