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Bilge pump confusion...

Discussion in 'Technical Discussion' started by NEO56, May 5, 2014.

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  1. NEO56, May 5, 2014
    #1
    NEO56

    NEO56 Member

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    New to Yacht Forums, have been around boats my whole life and owned more boats than cars (truth) but was reading some stories from Passagemaker (can I say that?) and came across a story about a woman (nurse) coming home from graveyard shift only to find she and her husbands trawler listing badly to starboard and with the bow pulpit resting on the dock box. It was winter time and snow was on the boat....with everyone at the marina who was woken up to help in the marina, came to the conclusion that a through hull fitting had broken in the extreme cold. Here is what really happened. Having spent 100% of my time in tropical waters, I don't understand how this happened. Maybe someone smarter than I am can offer an explanation.

    Read below:

    By the middle of that freezing cold day, it was determined that the problem was caused when our bilge pump decided to siphon water into our boat instead of the other way around. The other automatic pump was not working at the moment—it was on the list of things to fix this winter.

    Apparently, with our stern water tanks empty and snow on the bow, and perhaps with the right motion from the bubbler system, a siphon started in the wee hours. In retrospect, Scott thinks he might have run the pump before going to bed, which probably set up the siphon flow. Scott awoke to find our Ford Lehman covered in water up to the injectors. Our electrical system was out. The water heater, a new water pump still in the box, our Westerbeke genset, both banks of batteries, all our winter projects (including a Raritan Lectra/San and a new water heater) were soaked.

    How is this possible? It is (or was) my contention that bilge pumps had a check valve that would only allow one way flow....apparently I need to get better informed. Any way this scenario would freak me out! Can't wait for your responses. I'm actually going to start writing checks and signing contracts for a new build this Fall or Winter, and something like this requires a complete understanding on my part.
  2. AMG, May 5, 2014
    #2
    AMG

    AMG YF Moderator

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    If it is not a RIB-boat you have the through hull fitting high above the waterline, and the hose even higher if it is a small boat. Then it can not happen. So if you are building a boat, it will take no extra cost, only an experienced builder.
  3. Pascal, May 5, 2014
    #3
    Pascal

    Pascal Senior Member

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    Check valves are a bad idea on Bilge pumps as sooner or later they will fail, either open or worst closed. It s a band aid for poorly installed pumps, but something many builders do frequently. A vented loop is better solution than check valves if needed

    Bilge pump discharge lines should be run high and set up to prevent syphoning.
  4. Capt Bill11, May 5, 2014
    #4
    Capt Bill11

    Capt Bill11 Senior Member

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    Bilge pumps do not normally have check valves. Check valves fail and restrict flow. But bilge pumps should have vented loops that can prevent just such
    thing from happening. That plus if that boat had a proper high water alarm and a large capacity emergency pump that never would have happened.

    If you don't mind me asking, what brand and size boat are you having built?
  5. Caltexflanc, May 5, 2014
    #5
    Caltexflanc

    Caltexflanc Senior Member

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    Indeed, another case where bad design and bad seamanship inevitably led to a bad result.
  6. Lawrenc, May 5, 2014
    #6
    Lawrenc

    Lawrenc New Member

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    Most bilge pump on recreational craft are centrifugal pumps- these do not have any sort of integral check valve.

    They are very efficient for pumping a high volume at low pressure with minimal power consumption- all good things.

    as noted above by others, the possibility of such an installation back-syphoning can be avoided by proper installation design.

    I've also seen heavy snow make a boat go down on her lines to the point that cockpit scuppers back flowed water into the cockpit, and causing flooding through a cockpit hatch.
  7. david_japp, May 5, 2014
    #7
    david_japp

    david_japp Senior Member

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    Bilge pumps

    I'm a 2 belts and braces kinda guy.... On my 62 ft steel motoryacht Tiky, we have a heavy duty automatic bilge bump in each of the 3 isolated bilge areas. We also have a high water flood alarm audible everywhere inc the helm and linked to a strobe on the mast (not strictly legal, I know) and I'm considering fitting a WIFI alert system that will call my mobile if there. Is a flood while I'm not aboard. We also have a heavy duty Bilge pump driven by one of our 2 Gardner diesels operated via a manual clutch. All these pumps have fireproof hose, are double clipped and looped to just under the main deck. We also have a portable 30GPH double acting hand-pump with enough house to reach down to the bilge while being operated from on deck. Hopefully we'll never need any of this kit.
  8. NEO56, May 5, 2014
    #8
    NEO56

    NEO56 Member

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    Actually this episode took place aboard a 35 ft. Marine Trader.
  9. NEO56, May 5, 2014
    #9
    NEO56

    NEO56 Member

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    Hi Capt. Bill,
    I wasn't sure about posting this due to Forum rules? I'll let the moderator decide. I'm going with Outer Reef Yachts and using their 105 mold, so it's going to be a 95 ft. with a 10 foot cockpit. I was going to go smaller until my Rep told me that the 105 had a 24 ft. beam. That kind of sold me on the larger boat. You see, I have a tendency to become claustrophobic. And will not only live aboard full time but will be entertaining Clients as well from time to time.
    OR Yachts are basically a custom yard and are very accommodating. Contracts have yet to be signed, and I'm doing my level best to get everything done "right" prior to signing. As you know, once production starts, "changes" become very expensive and costs overruns come out of my pocket! Having just started a new Oil company, I have no idea how severe my workload is going to be, but I should be ready by the end of this year to pull the trigger. I want to be able to travel to the yard every quarter or so, as this is my first.... and last build. And yes, I know all about deprecation and costs associated with a boat this size. Hopefully I will be able to write off some of those costs to offset "new build shock". I am going to start a website to document the joys and headaches of such an undertaking.
  10. Capt Bill11, May 5, 2014
    #10
    Capt Bill11

    Capt Bill11 Senior Member

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    Well it sounds like a very exciting project and I wish you well with it. I think it's a great idea to start a web site where people can follow along with you on the build. It could be very helpful to any one contemplating doing the same thing.

    It will be a lot of work no doubt. But as I'm sure you know, you have a great resource here to tap into to help guide you along with your build should you need it. The combined years of building, selling, managing, maintaining and running boats of the members of this forum is staggering. And the quality of the vast majority of the advice found here is first class.

    So while I can only speak for myself, but I'm pretty sure the other members would agree, feel free to ask any and all questions you may have here no matter how large or small.
  11. dsharp, May 5, 2014
    #11
    dsharp

    dsharp Senior Member

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    To answer your question how it's possible, most builders tend to put thru hulls in the waterline where they will be less noticeable. The pump discharge hose should loop up as high as possible before going through the hull. For forward bilge pumps with low floorboards make a high loop difficult. Also floating docks don't usually have any tall pilings for the boats rub rail to ride against. A snow load or slack lines could let the thru hull ride against the dock or a bilge thru hull under water will easily let water siphon back in. I have seen very few high water alarms on pleasure craft. I have seen a lot of poor maintenance and float switches that need replaced or have severely corroded wiring which allows unexpected sinking.