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A/C raw water pick up

Discussion in 'Technical Discussion' started by Capt Ralph, Jul 7, 2018.

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  1. Capt Ralph

    Capt Ralph Senior Member

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    Two of the three raw water inlets for our A C pumps are outboard, P & S, 2 feet inside the chines, mid ship.
    Problem is, sometimes in slop or at speed, the pumps pick up air and loose prime while under way.
    My third A C pick up is way down close to the port keel mid ship. It services the forward cabins. Rarely used while under way. Always figure it wont pick up mud or silt when I mess up sense mostly never used while under way.
    I've often thought the water would be cooler, the deeper and away from the sun.
    I'm planning on updating the A C pumps and plumbing to them.

    The question; Is the water really cooler 2 feet deeper?
    Any advice welcome?
  2. Pascal

    Pascal Senior Member

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    I don’t think a couple of feet makes a difference temperature wise.
  3. rpontual

    rpontual Member

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    This make me wonder if it isn’t a good time for you to install a “closed system”. One pump with one scoop, one sea strainer, one seacock, etc to a heat exchanger and one pump to circulate a closed system to the a/c units.
  4. Capt Ralph

    Capt Ralph Senior Member

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    I'll be reducing the pump count.
    But don't see adding a closed loop condenser water, HE isolation system. Thank you for your thoughts.
  5. Pascal

    Pascal Senior Member

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    Having the TH lower reduce the risks of loosing prime underway, along with using scoops.
  6. rpontual

    rpontual Member

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    My boat has four a/c units (2x 12kBTU + 2x 8kBTU). One cooling water pump. I have an oversized strainer, which is for me a major benefit .
  7. Capt Ralph

    Capt Ralph Senior Member

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    We have 7 currently. One day when I win the Lotto, another one or two at the helm.
  8. Pascal

    Pascal Senior Member

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    I don’t see the point either. If anything having multiple pumps increase reliability as you don’t loose the whole system.
  9. f3504x4ps

    f3504x4ps Member

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    Two feet the temp is about the same, 7' and the temp is cooler.
  10. Capt Ralph

    Capt Ralph Senior Member

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    Yes but running, the bottom does not pick up air and air lock up. (Not Pump issue).
    So, I'm going to combine the salon and forward A Cs on the lower pick up near the keel. I do have a good pump for over 48+Kbtu and should do fine cooling the 4 units involved.
    The stb chine pick up services the galley and second M stateroom. Not sure what to do here. Lightly used.
    It's interesting these inside chine pick ups catch air but I would think the grated / scoop design would keep water charged to the pump.
    Port is a high volume March pump, Stb is a high volume Little Giant. Low port (near keel) is a bronze Obendorfer, All on similar grated scoop T H pick ups.

    I'll pour some more cheap hooch over this.

    BTW; anybody need some good 7Kbtu, 230Vac, 60hz condensing stations?
    Upgraded 3 x 7Kbtu systems to 12Kbtu. Now have dust collecting , good 7Kbtu, 230Vac condensing units in my shop.
    Pay shipping and a tip and their yours.
  11. Boomer

    Boomer Member

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    I can't run my ac under way as it picks up air like you said and the pump loses prime
  12. Capt J

    Capt J Senior Member

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    What good is that? Have you tried a clam shell on it to direct water up there?
  13. rpontual

    rpontual Member

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    One thru-hull located at optimum place, one large strainer, one oversized pump. I find it reliable because is much simpler to inspect and perform routine checks.
  14. Pascal

    Pascal Senior Member

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    One pump is fine and indeed better than a bunch of them all over the boat, what I was questioning is the complexity of a heat exchanger and running a closed loop with self contained.

    With chillers it s great but why bother with self contained or split. Just set up a manifold and send raw water to the units.

    I used to have 5 remote condensers (3 16k and 2 9k) fed by one raw water pump. No need to set up a closed loop. Now I have two 36k chillers also on one pump. I have a spare and can change it in 15’ but for those not mechanically inclined having two pumps increase redundancy
  15. rpontual

    rpontual Member

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    Pascal, my boat has four a/c units cooled through a raw water pump. I mentioned the closed loop because it seems to be getting momentum in the industry.

    The benefits I see from a closed system are:
    - always clean pipes and clean a/c units
    - less risk of sinking due to seawater intrusion because seawater circuit would be short and simple, possibly 100% visible in the engine room.
  16. PacBlue

    PacBlue Senior Member

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    The ideal configuration would be a centerline pick-up / mini-sea chest with a manifold to direct raw water to your users, sized for the necessary flow of water. Vee - hulls with pick-ups 2 feet inboard are less than ideal as you have found out and Bertram or the installer took the easy way out on this one.
  17. Pascal

    Pascal Senior Member

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    If you re going to use a closed loop then you receive better off using a keel cooler.

    I have never seen a closed loop on any boat except of course chillers. But never a closed loop for self contained units
  18. Scallywag

    Scallywag Member

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    I ran a closed system for about 6 years. My boat is a 70' aluminum motoryacht. Pascal will remember my boat as he did the delivery (rodeo!) when I bought her. She had an interesting keel cooled closed loop system, which was excellent in theory. The problem is in the Florida Keys (bayside) the water is constantly 90 degrees during the summer months, much warmer than the 60 or 70 degree cool great lakes. The amount of surface area the current closed system had was too low and loop temperatures would often approach 115 degrees causing the system to be inefficient.

    So, trying to keep the benefits of a closed loop system, I added a Sen-Dure 180,000BTU heat exchanger and decommissioned the keel cooler. The heat exchanger was designed by Flagship Marine https://www.flagshipmarine.com/heatexchanger.html One pump pushing seawater through the heat exchanger in the engine room and another pump circulating fresh water through the loop. This was more efficient, but I was still dealing with 105+ degree loop temperatures.

    I'm unsure if it was due to constant use 24 hours a day 365 days a year (live aboard and air conditioning running is pretty much all year for us) or an undetected bonding issue (you'd think my aluminum hull would take the brunt of it... not the CuNi core), but the heat exhangers proved to be less than durable. I dealt with the manufacturer and had a mechanic check for a stray current, but everything was fine. Leaks would develop at the end cap of the core bundles on the raw water side. I would check the zincs monthly and they always were in tact and no more than 50% done. I went through 3 heat exchangers in 3 years. At $2,800 each I just decided to decommission the heat exhanger and pump raw water through the boat to my 7 stand alone systems.

    I should have done this a long time ago! My air con is much more efficient and I'm consuming less electricity. A closed system is a great idea if you are sitting on sea water that is 70 degrees or cooler, but in the tropics it is inefficient. You are still pumping seawater into your boat, but it is nice to have it isolated to one area. I could have chased down the issue with the heat exchanger getting chewed up, but it just made more sense to keep it simple.
  19. Pascal

    Pascal Senior Member

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    Do I remember that trip :). I was wondering how the keel cooler had worked out...

    Odd about the corrosion on the HE. I installed two Flagship Chillers and 5 air handlers a little over a year ago,very well built.
  20. Scallywag

    Scallywag Member

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    Yeah Flagship makes quality stuff. Sen-dure actually made the heat exchangers. They make quality stuff too. The reason for repeated failure remains a mystery, but I'm over it when it comes to a fresh water loop system.

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