Spin on a Stainless Ball Valve?

Discussion in 'Metal Boat Building' started by AdamFrench, Dec 21, 2007.

  1. AdamFrench
    Joined: May 2007
    Posts: 4
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    Location: San Francisco

    AdamFrench New Member

    Here's what I know:
    1) Galvanic corrosion between dissimilar metals in sea water occurs when the potential difference between the two metals is greater than 200 millivolts.

    2) The potential of 316 stainless as compared to a Ag/AgCl electrode is -390mV.

    3) The potential of low alloy steel is -580mV

    4) The potential of steel/cast iron is -630mV

    5) My boat is out of the water, the to do list is long, and I've got two through hulls to replace and a third to add. They're both 1.5" threaded steel pipe. I've seen descriptions of isolating bronze through hulls with plastic sleeves, nylon washers, paint, etc. What I really want to do is order up a treo of 316 1.5" ball valves, spin them on, and tick another item of the list so I can get this little vessel back in the water.

    6) I'll get a response telling me I'm crazy to do anything but follow the holly path and spend the next 6 week hand building unobtanium valves.

    How about a real-world strategy for a salty old boat? Spin on a few 316 valves and move on? or sit around building steel flanges and plastic spacers? I know there's never an easy way. But sometimes there is.


    R/V Magnet
  2. Frosty

    Frosty Previous Member

    Sounds as though you are talking steel hull here?

    Insulating the cocks from the hull is not possible the water inside will be a conductor.

    I had a steel boat that had stand pipes that brought the cock up to just above the water line. If the cock failed the boat would not sink.

    This seems to be general practice now. Im thinking of doing it with my fibre glass boat.
  3. kmorin
    Joined: Apr 2005
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    Location: Alaska

    kmorin Senior Member

    Threaded Risers?


    I don't see any headache with the small amount of 361L on some A-53 or A-106 threads. With the added dialectic of TFE-Gel or pipe dope that would further reduce the galvanic cell's activity, the two metals won't have the exposed area to promote much interaction.

    I'd be more concerned with the idea of threads on a through-hull than the galvanic issue. The notches (thread grooves) in the side of the risers go almost half through in sched. 40 wall pipe. I think the time for flanges is worth the security for the connection type alone.

    If time is important, then see if you can find a dealer/distributor of Lokring in your area. These hydraulically installed mechanical connections will install a flange on your riser in about ten seconds and allow you to use flanged valves. (regardless if you install isolation kits) Lokring beats a butt weld in most cases and there's no arc or spark, if you don't have AC power or air to drive the install tool you can use a hand powered 'porta-power' type pump to set the fittings; but it takes longer than 10seconds.


    [FULL DISCLOSURE: I do sell Lokring but only in Alaska, on the other hand, I've used it on boats, barges, and offshore platforms for years and it works incredibly well.]

    Good luck with the haul-out.

  4. lazeyjack

    lazeyjack Guest

    How about a real-world strategy for a salty old boat? Spin on a few 316 valves and move on? or sit around building steel flanges and plastic spacers? I know there's never an easy way. But sometimes there is.


    R/V Magnet[/QUOTE]

    that'll work , done same thing lots, put lanacoat on your threads with the tape or the hemp, they work ok together your steel pipe(which could be any grade or wall thickness) your zincs will take care of the rest
    go do it then take a rest
  5. Rusty Bucket
    Joined: Feb 2007
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    Location: florida

    Rusty Bucket Junior Member

    Why not consider plastic?

    Hey Adam, I understand your comments about "holy" orthodoxy of boat building and repair. If you really want to open up a pandoras box of opinion just ask a question about electrolysis or galvanic corrosion. My experience has been that properly sized bronze thru hulls work just fine if inspected during your annual haulout. I don't have any first hand experience with stainless through hull fittings but I personally would avoid them. Stainless is wonderful when used in an oxygen rich environment like salt air or salt water but when deprived of oxygen it can fail rather dramatically and real fast. I have a 1" aquamet shaft that I use as a come-along handle that failed inside the hub of a prop, it also has severe pitting where it went through the cutlass bearing. A couple of issues back of Passagemaker magazine shows a large ss bolt that was consumed almost completely through do to lake of oxygen. I suggest that you consider a "nylon" type through hull. I personally can't see the downside and have used them before with no problems. What was there before and was there an issue? Good luck. Regards, rusty

  6. Brent Swain
    Joined: Mar 2002
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    Location: British Columbia

    Brent Swain Member

    Weld on stainless nipples for thru hulls. I've been using stainless type 316 ball valves on stainless nipples for over 30 years, and dozens of boats . No problems. They get plenty of well oxygenated water. There can be some tiny pinhead sized paint blisters around them, but not enough to worry about. (Compared to the worries with other alternatives.)
    The beauty of such thru hulls is they don't have to be 90 degrees to the hull, and can be welded in parallel to bulkheads , letting the plumbing take up far less room.
    Plastic thru hulls break off if a heavy piece of equipment shifts against them or if you have a fire aboard, leaving a huge hole in your hull( Or several.)
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