OFFICIAL 390/40 Motor Yacht Thread

Discussion in 'Sport Yachts/Yachts' started by Robf, May 4, 2016.

  1. Joel_MD

    Joel_MD Member

    210
    Jun 20, 2016
    Chesapeake Bay
    390 Motor Yacht, 2005
    Cummins 480 CE
    That's a good point too. I don't know how heavy the big-block V-8s are, but I know the marine version of the C-Series Cummins weighs around 1,950 lbs with all the cooling apparatus. Probably at least 50% heavier than the gas engines. Do you have a problem like me, with water pooling in that area and not flowing aft to the scuppers?
     
  2. alnav

    alnav Member

    795
    Sep 16, 2009
    West River, MD
    40 MY
    QSB 425
    At least on mine, the void is open except for a piece of plywood running down the middle. You can see this in the picture I posted.

    FWIW, the QSB-425s are aft of the horizontal center of gravity but they are probably lighter than the 480CE engines.
     
  3. alnav

    alnav Member

    795
    Sep 16, 2009
    West River, MD
    40 MY
    QSB 425
    Just noticed this post. Did you get it fixed? I had this problem early on and it turned out to be the bleed valve on the bottom of the accumulator tank had worked loose. Tightening that down fixed my problem.
     
  4. Jmwarren

    Jmwarren Member

    417
    Jul 14, 2011
    Ontario
    390 Motor Yacht
    Cummins - 480CEs
    Yeah,

    On mine water actually ran down the rear and INTO the scuppers.

    I pulled the aft seats and sealed the scuppers. The rear door is well enough protected that we don't get water coming in there.

    The wing doors can lead to wet carpet too if you get a driving rain, so we pull the carpet back when we're away. We also put towels at the bottom of the doors to reduce the number of bugs in the cockpit.
     
  5. Joel_MD

    Joel_MD Member

    210
    Jun 20, 2016
    Chesapeake Bay
    390 Motor Yacht, 2005
    Cummins 480 CE
    I never thought about water coming in from the scuppers, but that could be happening to me as well. Like I said in the previous post, the previous owner fabricated teak thresholds for both of the wing doors that tends to keep most of the water out. Maybe the pooling is coming from the scuppers, and perhaps the real cause of all this is the weight of those big Cummins 480s. Maybe a I could rig up a flapper valve on those scuppers that would allow water to exit only.
     
  6. alnav

    alnav Member

    795
    Sep 16, 2009
    West River, MD
    40 MY
    QSB 425
    I talked to the shop foreman at Prince William Marine today. He has seen a lot of these boats over the years as they are pretty popular on the Potomac. He said, in addition to this void being full of water he has seen even more instances of the void in the forward end of the engine room bilge being filled. He also said the most frequent reason for both is leaking at the rub rail. He said the rub rail needs to be pulled and the deck to hull joint re-sealed on all our boats at their age.
     
  7. Jmwarren

    Jmwarren Member

    417
    Jul 14, 2011
    Ontario
    390 Motor Yacht
    Cummins - 480CEs
    I can't think of a void in the front of the engine room? Unless he's talking about the voids under the genset and vacufluah I'm stumped!

    I verified this weekend that there's no trapped water in the front void but am still glad the hull and stringers are uncored, solid fibreglass on these boats!
     
  8. alnav

    alnav Member

    795
    Sep 16, 2009
    West River, MD
    40 MY
    QSB 425
    I think he was talking about the platform right under the engine room hatch.
     
  9. Jmwarren

    Jmwarren Member

    417
    Jul 14, 2011
    Ontario
    390 Motor Yacht
    Cummins - 480CEs
    On mine that's a platform (plywood, suspended between the stringers). It sits on top of the black water tank.
     
  10. Joel_MD

    Joel_MD Member

    210
    Jun 20, 2016
    Chesapeake Bay
    390 Motor Yacht, 2005
    Cummins 480 CE
    On my 390 MY the hinged step that allows access to the central vacuum seems to have a design flaw. It has a piano hinge that ends up taking a lot of weight and flexing considerably every time someone steps on it. This arrangement may have been adequate the first few years, but all that flexing is damaging the area where the hinge is connected. I've been brainstorming to come up with a way to add support so the hinge doesn't carry all the weight. Has anyone else seen this problem? Any ideas for fixing it? I've thought about fabricating some aluminum supports for the sides of the step, which would take some of the weight off the hinge.
     
  11. alnav

    alnav Member

    795
    Sep 16, 2009
    West River, MD
    40 MY
    QSB 425
    Joel, on the 40MY, one of the few changes that was made was to move the vacuum into the forward bilge, essentially right under the galley fridge and replace the hinged step with something more substantial that doesn't need a hinge. Not sure this is at all helpful but thought I would pass it along.
     
  12. Joel_MD

    Joel_MD Member

    210
    Jun 20, 2016
    Chesapeake Bay
    390 Motor Yacht, 2005
    Cummins 480 CE
    That sounds like a good change. There's plenty of space below the galley fridge. I keep laundry detergent and other stuff in that area.

    I wouldn't mind relocating the vacuum, but the previous owner built a sliding drawer for tools that sits above the vacuum. After pulling up the hinged step, the drawer can slide out and it's big enough for a screwdriver set, flashlight, and other stuff.
     
  13. mkistner

    mkistner New Member

    4
    Jun 28, 2017
    Jacksonville, FL
    2006 Sea Ray 40 Motor Yacht
    480 Cummins Diesels
    My wife and I purchased a 2006 40MY in June of this year with 480 Cummins and have been enjoying it since. We purchased the boat from BE Marine on Lake Michigan and had the upper station disassembled and shipped to Jacksonville, FL where it was reassembled and now resides.

    We are finding the carpet in the aft cabin on the port side of the bed getting wet and I cannot locate the source. We opened the rear window to clean when we first got it here and it leaked when we put it back in but after tightening the clamps the leak is now sealed (tested with a water hose). I am fairly confident the carpet issue is non-related to the rear window. Visually, all the porthole windows do not show any signs of leaking nor does the ceiling. I have pulled the drawer next to the bed and opened the access panel in the hanging locker and cannot find any evidence of moisture (bone dry on the fiberglass shell)..

    Has anyone had a similar issue and any suggestions as to where this water could be coming from would be appreciated.
     
  14. alnav

    alnav Member

    795
    Sep 16, 2009
    West River, MD
    40 MY
    QSB 425
    I had this exact same issue arise twice in the same year after we bought our 40MY. In the first case, the leak was caused by the shore water connection failing. This fitting is barely visible through the hanging locker access panel but I would think you should have seen it leaking when you pulled the panel as long as the shore water connection was on or the potable water system was otherwise under pressure (if it is bad I think it will leak in either case). That fixed the first instance...
    I got the problem again later that year and it was more difficult to find. The problem turned out to be the seam that runs up from the port side of the swim platform to the rub rail. I only found it when it happened to be raining so recommend you take a hose to that area and see if it is leaking. Re-caulking that seam fixed the problem.
    I did ask Sea Ray about the problem while I was searching for the cause of the second leak. The advice I got was "one area we have seen is the stainless thresholds under the plex doors between the cockpit and the catwalks can leak through the screw holes, run underneath and over and down the hull inside in the areas you are referring to. You can simply remove the threshold clean up any existing silicone and reinstall with new silicone/bedding material including in the screw holes. Other than the portlights and windows the only other areas to check would be the rubrail, and also possibly the aft cockpit deck seating. You may want to remove the attachment screws and reinstall with silicone. You may want to pull up and reseal the thresholds on both sides under the cockpit plex doors just for good measure, that area tends to see a lot of water from water running down on top and water running aft down the catwalks. At a minimum you might want to pull the screws out fill the hole with caulk and reinstall the screws." None of these were part of my problem but perhaps this info could help you.
     
    Last edited: Sep 13, 2017
  15. mkistner

    mkistner New Member

    4
    Jun 28, 2017
    Jacksonville, FL
    2006 Sea Ray 40 Motor Yacht
    480 Cummins Diesels
    Alnav,

    That is all good advise that I will follow. I did seal an area on the rub rail that looked suspect. The cockpit bench seating was removed at transport and would be an area that could likely be the culprit. I will also pull and reseal the thresholds and see if that does the trick.

    The problem is that looking in the access panel and behind the drawer I just can't find a route that makes sense for water to get to the carpet. I will update once I seal these areas and hopefully seal the leak. Thanks for taking the time to answer my post.

    Mike
     
  16. mkistner

    mkistner New Member

    4
    Jun 28, 2017
    Jacksonville, FL
    2006 Sea Ray 40 Motor Yacht
    480 Cummins Diesels
    One more quick question, would you seal with 3M 5200, 4200 or something else?
     
  17. alnav

    alnav Member

    795
    Sep 16, 2009
    West River, MD
    40 MY
    QSB 425
    I think the area where you see the water is a low spot such that any water that is in nearby voids is going to show up on the carpet. The boat tends be stern-down in general, more so I understand with the 480 engines. It's even more pronounced while underway.
     
  18. alnav

    alnav Member

    795
    Sep 16, 2009
    West River, MD
    40 MY
    QSB 425
    You should only ever use 5200 if you never ever expect to have to remove it while 4200 is less permanent. I believe Sea Ray uses Sikaflex 291 for the original exterior caulking and I have used that in the past. I am also a fan of BoatLIFE Life Caulk and I think that is what I used for the transom seams that were leaking I mentioned earlier.
     
  19. mkistner

    mkistner New Member

    4
    Jun 28, 2017
    Jacksonville, FL
    2006 Sea Ray 40 Motor Yacht
    480 Cummins Diesels
    Thanks for the advise.
     
  20. Fin

    Fin Member

    33
    Sep 14, 2017
    Nininger, Minnesota
    2004 Sea Ray 390 Motor Yacht
    Twin Mercruiser
    Hi everyone. Took possession of my new (to me) 2004 390 Motor Yacht last week! First time owner with definite "deer in the headlights " looks but a SMILE that has yet to leave my mug. Great purchase experience with the previous owners and a very helpful group at the Marina. I'm having close friends with years of boating teach me the ins and outs.

    Primary use this season is on the Mississippi River with shorter trips as I get up to speed on the boats functions and capabilities. This is a great forum with tons of information. Thank you guys!
     
    Terryk likes this.

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