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Gen water pick up type

Discussion in 'Generators' started by Pascal, Jan 19, 2022.

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  1. Pascal

    Pascal Senior Member

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    We ve been on the hook about almost a whole month now and I ve been having an issue with both our Onan 45s.

    after 12 to 24 hours running, sometimes a little more, they gradually get significantly louder. They never overheat, never run over 180, but eventually produce a little steam. I can tell visually that they don’t get enough water flow.

    If I switch generator, it s all good for another day or two...

    Fairly New pumps and impellers, clean strainers, clean HE intakes etc.

    I went under boat a couple of weeks ago and it turns out that weed and grass gets sucked tight against the thru hull. Turn off the gen and the stuff floats away

    We have shower head style thru hulls which I ve had on a number of generators without any issues but I m wondering if another type would solve the issue. on the positive side, nothing makes it thru so I never have to clean the strainers.

    I know you can’t have scoops on gens... South Bay strainers with relief holes in the back maybe ?

    Or are ohnos typically loud? The raw water pump on these 45 doesn’t seem much bigger than the ones I had on the previous 27.5s

    yes they were pretty dirty in this picture but they are clean now... all the holes open

    Attached Files:

  2. Capt J

    Capt J Senior Member

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    You can have a scoop as long as it has holes in the rear of it. Be careful, as when they get clogged and louder, you'll end up eating raw water pumps (they'll leak at the shaft as the seal gets sucked in) due to the really high head pressure. I have a 66' Sunseeker that does the same thing except everything ends up in the strainer and clogs it (bronze tube you can't inspect without shutting the gen down and opening the lid). I have a feeling the stabilizers kick all of the grass under there near the gen pickup.
  3. rtrafford

    rtrafford Senior Member

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    Pascal, I've approached this issue both on generators and HVAC with the theory that oversizing the thru-hull pick ups actually slows the flow of water at the point of entry, making it (in theory) less attractive to passing debris. I've oversized by doubling the size of the through hull in comparison to the feed hose for the system. Equally I've oversized the strainers to provide more volume to handle debris and growth clogs. So far it's worked fairly well.
  4. Pascal

    Pascal Senior Member

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    I had the issue once when a diver didn’t clean the holes in the back but I caught it just in time. I think that was with a 20KW NL. Not sure.

    interesting comment about the stabs. I have noticed some Cloudiness in the water when we re swinging hard even if not using the zero speed. I also suspect the anchor chain I getting stuff loose on the bottom.

    especially considering the amount of chain I have to use to get the toy anchor to hold :(
  5. Slimshady

    Slimshady Senior Member

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    Can you connect both thru hulls together with valve. Can shut off clogged one and let genny get water from other side until grass floats away.
  6. Pascal

    Pascal Senior Member

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    Yea I was thinking about that, sort of a cross over feed, hooked up just past the strainer.
  7. Slimshady

    Slimshady Senior Member

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    Yes exactly
  8. Capt Ralph

    Capt Ralph Senior Member

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    On a Hatt we managed, There was an extra 1 1/4" thru hull available. That thru hull was Tee'd into the gen-sets raw water supply and joined right before the common strainer.
    WOW!!!, Lowering the velocities at the thru hull, in half made a great difference. Near zero grass held in place against the skin strainer like yours. Impeller loss drastically reduced.
    Sadly, that gen set was replaced with twin NLs.
    Fixing to tie those inlets together this summer.
  9. Pascal

    Pascal Senior Member

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    Interesting idea. I wish they d set up a sea chest instead. Even better.
  10. Capt Ralph

    Capt Ralph Senior Member

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    I have mixed thoughts on Sea Chest; I remember when I started delivering to the Abacos. These sea grass spines (like pine needles), kept filling the sea chest on an ole 44 Striker like a lawn bag catcher. What troubles and PIA to clean.
    Later, on a Great Harbor 47, the same thing.
    And this was just trying to move thru the water. I recall is was less of an issue at anchor.
    Naw, I do not wish for sea chest. It is a great idea, but just a larger vacuum cleaner.