My bottom cleaning diver was changing the doughnut zinc on my CD36 yesterday and received a jolt when he touched the propshaft zinc - no harm done, but was surprised! Anyone ever seen this before, how can I check for stray current safely, and what fixes are recommended. My zinc was gone - not sure if it fell off or corroded off - was on for 10 months.
My shorepower was plugged in and the Heart INterface 2000 charger/inverter was on (floating the house batteries), the shorepower polarity seems OK (the boat's polarity light is functional but not lite), but I will check the polarity at the shorepower box. I believe the charger is grounded OK, but will have to check this out to make sure. Any ideas from this intelligent crowd before I see what Nigel Caulder has to say?
igassn@aol.com
Diver zapped while changing zinc - any suggestions?
Moderator: Jim Walsh
-
John Sill
Re: Diver zapped while changing zinc - any suggestions?
Was your inverter output connected at the time? Frequently an inverter will put half voltage on the ground system, i.e. about 60 volts. Gets real dangerous if you're hooked into the boat's electrical system! Small inverters should only be fed into isolated loads, not grounded systems; but I don't know your system. Good luck!
jesill@erols.com
jesill@erols.com
-
Ken Coit
Re: Diver zapped while changing zinc - any suggestions?
That probably explains where the zinc went. You might consider a "Perry" nut for your prop once you get the shaft cooled off. West Marine lists them a prop nut zincs. That way you won't block the water flowing to your cutless bearing. I posted the details several weeks ago.
Ken Coit
parfait@nc.rr.com
Ken Coit
Tim wrote: My bottom cleaning diver was changing the doughnut zinc on my CD36 yesterday and received a jolt when he touched the propshaft zinc - no harm done, but was surprised! Anyone ever seen this before, how can I check for stray current safely, and what fixes are recommended. My zinc was gone - not sure if it fell off or corroded off - was on for 10 months.
My shorepower was plugged in and the Heart INterface 2000 charger/inverter was on (floating the house batteries), the shorepower polarity seems OK (the boat's polarity light is functional but not lite), but I will check the polarity at the shorepower box. I believe the charger is grounded OK, but will have to check this out to make sure. Any ideas from this intelligent crowd before I see what Nigel Caulder has to say?
parfait@nc.rr.com
-
Joe Sankey
Re: Diver zapped while changing zinc - any suggestions?
Tim:
I think its possible the problem may not be your boat. It is not uncommon in our area for neighboring boats to have stray current which can affect your boat. In fact, at one marina the stray current was so bad my son got shocked touching the shrouds of our CD22 OUTSIDE the marina basin while he in the water to wash the bottom. Friends in the marine supply business even tell stories of large bronze props disappearing due to someone else's problem.
Joe
sankey@gulftel.com
I think its possible the problem may not be your boat. It is not uncommon in our area for neighboring boats to have stray current which can affect your boat. In fact, at one marina the stray current was so bad my son got shocked touching the shrouds of our CD22 OUTSIDE the marina basin while he in the water to wash the bottom. Friends in the marine supply business even tell stories of large bronze props disappearing due to someone else's problem.
Joe
Tim wrote: My bottom cleaning diver was changing the doughnut zinc on my CD36 yesterday and received a jolt when he touched the propshaft zinc - no harm done, but was surprised! Anyone ever seen this before, how can I check for stray current safely, and what fixes are recommended. My zinc was gone - not sure if it fell off or corroded off - was on for 10 months.
My shorepower was plugged in and the Heart INterface 2000 charger/inverter was on (floating the house batteries), the shorepower polarity seems OK (the boat's polarity light is functional but not lite), but I will check the polarity at the shorepower box. I believe the charger is grounded OK, but will have to check this out to make sure. Any ideas from this intelligent crowd before I see what Nigel Caulder has to say?
sankey@gulftel.com
-
Matt Cawthorne
Re: Diver zapped while changing zinc - any suggestions?
Tim, The fact that your zinc is gone is a safety issue in terms of the boat potentially sinking and the AC zap is obviously a hazzard to your crew. I recommend that you invest $50 in a digital multi-meter. One lead can be dropped overboard and the other attached to the prop shaft from inside the hull. Set it on AC-Volts and see if you have anything more than a very miniscule amount. If so start turning things on and off to see what is the offending piece of gear. You may actually have to unwire some pieces of gear to get it to go away. If after all of your AC gear is un-wired you still have an AC current then try plugging in at another marina. It could be that the fault is in someone elses boat and the marina ground does not properly handle it.
About a year ago there was a thread about whether on not to bond the through hulls to the prop and zinc. I tried getting a copy of the ABYC standards on this and found out that they cost something like $600 to buy. The person at the ABYC office suggested a book by Larry Wing on marine electrical wiring. He uses diagrams from the ABYC standards and gives good explanations. I liked the book and recommend it. He states in his book that the ABYC does not take a strong stand on whether or not to bond. It has its advantages and disadvantages. You are experiencing the disadvantages.
My CD-36 was originally bonded, but I do not keep it so any more for just this reason. I purchased an expensive silver/silver-chloride half cell to use in sorting our the DC galvanic issues, but believe that a zinc works just as well....just a different reference voltage.
It might be worth your time to track down that other thread using the search feature on the top of the web page.
Matt
mcawthor@bellatlntic.net
About a year ago there was a thread about whether on not to bond the through hulls to the prop and zinc. I tried getting a copy of the ABYC standards on this and found out that they cost something like $600 to buy. The person at the ABYC office suggested a book by Larry Wing on marine electrical wiring. He uses diagrams from the ABYC standards and gives good explanations. I liked the book and recommend it. He states in his book that the ABYC does not take a strong stand on whether or not to bond. It has its advantages and disadvantages. You are experiencing the disadvantages.
My CD-36 was originally bonded, but I do not keep it so any more for just this reason. I purchased an expensive silver/silver-chloride half cell to use in sorting our the DC galvanic issues, but believe that a zinc works just as well....just a different reference voltage.
It might be worth your time to track down that other thread using the search feature on the top of the web page.
Matt
Tim wrote: My bottom cleaning diver was changing the doughnut zinc on my CD36 yesterday and received a jolt when he touched the propshaft zinc - no harm done, but was surprised! Anyone ever seen this before, how can I check for stray current safely, and what fixes are recommended. My zinc was gone - not sure if it fell off or corroded off - was on for 10 months.
My shorepower was plugged in and the Heart INterface 2000 charger/inverter was on (floating the house batteries), the shorepower polarity seems OK (the boat's polarity light is functional but not lite), but I will check the polarity at the shorepower box. I believe the charger is grounded OK, but will have to check this out to make sure. Any ideas from this intelligent crowd before I see what Nigel Caulder has to say?
mcawthor@bellatlntic.net
-
Dana
Re: Diver zapped while changing zinc - any suggestions?
All the previous comments are correct...the most important is to isolate the source, i.e. your boat/marina/neighbors boat.
1. Power should never be on or even connected to shore power (connecting a ground path) when a diver is in the water working on the boat...just too risky. Too many conditions beyond your control...i.e. marina/neighbors boat.
2. With your boat disconnected from shore power, a digital volt meter, measuring between the rough water location of your stern and the power ground terminal of your shore power receptacle. If there is a voltage then the problem is a neighbors boat or the marina and the marina should be notified to find the cause asap.
3. If there is no voltage, you must consider that some electrical gear on your boat or marina is faulty. A test could be repeated with power connected to your boat, if the voltage is now present between the water and the ground of the dock side receptacles, then you or the marina have the problem....i.e. the neutral and ground wires in the receptacle are reversed or your equipment has a fault....
darenius@aol.com
1. Power should never be on or even connected to shore power (connecting a ground path) when a diver is in the water working on the boat...just too risky. Too many conditions beyond your control...i.e. marina/neighbors boat.
2. With your boat disconnected from shore power, a digital volt meter, measuring between the rough water location of your stern and the power ground terminal of your shore power receptacle. If there is a voltage then the problem is a neighbors boat or the marina and the marina should be notified to find the cause asap.
3. If there is no voltage, you must consider that some electrical gear on your boat or marina is faulty. A test could be repeated with power connected to your boat, if the voltage is now present between the water and the ground of the dock side receptacles, then you or the marina have the problem....i.e. the neutral and ground wires in the receptacle are reversed or your equipment has a fault....
Tim wrote: My bottom cleaning diver was changing the doughnut zinc on my CD36 yesterday and received a jolt when he touched the propshaft zinc - no harm done, but was surprised! Anyone ever seen this before, how can I check for stray current safely, and what fixes are recommended. My zinc was gone - not sure if it fell off or corroded off - was on for 10 months.
My shorepower was plugged in and the Heart INterface 2000 charger/inverter was on (floating the house batteries), the shorepower polarity seems OK (the boat's polarity light is functional but not lite), but I will check the polarity at the shorepower box. I believe the charger is grounded OK, but will have to check this out to make sure. Any ideas from this intelligent crowd before I see what Nigel Caulder has to say?
darenius@aol.com
-
John R.
Re: Diver zapped while changing zinc - any suggestions?
I would be highly suspect of failed equipment or a circuit on board the vessel. I would pay particular attention to the reverse polarity indicator light that is wired into the common (white) side of your AC system. If it doesn't already have a momentary switch installed in that circuit you should install one. My next check would definately be the isolated charger circuitry in the Heart.Tim wrote: My bottom cleaning diver was changing the doughnut zinc on my CD36 yesterday and received a jolt when he touched the propshaft zinc - no harm done, but was surprised! Anyone ever seen this before, how can I check for stray current safely, and what fixes are recommended. My zinc was gone - not sure if it fell off or corroded off - was on for 10 months.
My shorepower was plugged in and the Heart INterface 2000 charger/inverter was on (floating the house batteries), the shorepower polarity seems OK (the boat's polarity light is functional but not lite), but I will check the polarity at the shorepower box. I believe the charger is grounded OK, but will have to check this out to make sure. Any ideas from this intelligent crowd before I see what Nigel Caulder has to say?
Dana's advice regarding having all AC disconnected from the vessel when a diver is in the water is a very prudent safety precaution.
Last I knew, ABYC most certainly did advocate the grounding of the AC system to the vessel common ground point. SAFETY FIRST was their primary concern in their comments. Nigel Calder whom you mention and whose advice is obtained from many experts also recommends a grounded AC system to the vessel common ground point for safety reasons.