Bottom Cleaning

[jibes138]

Just thinking about the comments recently about swimming in marinas including one death reported. How many of you clean your boat bottoms or change zincs in the water in the marina? I know a lot of diving services offer monthly cleaning service in the marinas. I scuba dive and often change my zincs if I'm not hauling over the winter. Just wondering how much risk this is. Since I'm in salt water probably not a big deal with the conductivity of the water, but how about up near Oriental where it is more brackish? Any thoughts?

 

[Steve Dion]

I think you will find that you are at more risk of electrocution in salt water than in fresh water.

We have our boat in fresh water and zincs last for years. Our brothers/sisters that have their boats in salt water usually change them on a quarterly basis.

http://www.hometrainingtools.com/saltwater-circuit-project/a/1344/

 

[RichH]

Why even take the risk of changing the zincs in a marina .... mal-wired, frayed, bimbo drop a hair dryer overboard, etc. etc. etc.

Why not go up to near Oriental, etc. where there is little tide, run your bow up on a mud flat, etc. .... dunno if there are electric fish/eels/alligators in the Pamlico though, I do know they have lots funny black snakes with white mouths.

 

[jibes138]

More info please

If this is such a risk how come if I am sitting on the dock dangling my feet in the water I wouldn't get a life threatening shock? Or dropping a wet dock line in the water wouldn't immediately cause electrocution? I'm trying to understand the risk from a technical perspective, I've heard of one electrocution but it certainly doesn't seem very common or we'd be reading about it in the paper a lot.
Previous posts have suggested fresh water is much more dangerous since salt water will conduct to ground with less impedence, yet Steve is suggesting salt water is more dangerous. Any electrical geniuses out there that want to jump in?
Rich, plenty of places to anchor up and do the work, South River is a good choice as it is usually very calm, no current, and quiet away from any electrical sources. I have seen alligators near Oriental in Pierce creek, they have a picture in the marina there of one. You just have to be tougher than the alligator like the old Tarzan movies.

 

[Steve Dion]

Dave: I suppose that this reinforces your case about fresh vs salt water.

http://www.sail-world.com/Cruising/Dock-tragedy-shows-danger-of-fresh-water-marinas/62455

 

[Bad Obsession]

I always do my cleaning and zinc change away from a marina. In my area if you leave Colonial Beach and head down river the water clarity gets much better. I usually dive in the Coan River, St. Mary's River, Canoe Neck Creek, or another place like them.

I don't scuba dive but I am able to do my zincs by myself.

I never thought about the electric risk...I always did it because I would NEVER want to swim in Monroe Bay. I know what used to get dumped in those waters! LOL

 

[RichH]

Fresh water has less electrolyte than salt water
The human body has more electrolyte than fresh water and less electrolyte than salwater

So, a body in fresh water will more readily conduct any electricity relative to the fresh water (body is better conductor than fresh water, therefore more electricity will go through the body).
Conversely A body in sea water will less readily conduct electricity than the seawater.
(body now less of a conductor than the seawater)

...... and in any electrocution the electricity will probably travel preferentially through and along the veins and arteries and nerves due to their relative higher salinity / conductivity.

 

[Joe]

Gee....... I've never heard of such a thing. We have divers cleaning boats, changing zincs, blowing out outdrives with compressed air all the time in our marinas. They all wear wetsuits though.... maybe their insulated... hardy, har, har.

I have dived on my boat occassionally and I'm more concerned about the old paint residue that's rubbed off during cleaning than being electrocuted. It's nasty.

Now.. I do know that electrolysis is an issue in some marinas... but not electrocution. Hey... wouldn't that kill the fish if it were strong enough to kill a human?

 

[Snotter]

Niger Calder in his Mechanical and Electrical Systems book stated that a lethal electrical gradiant can be such that a swimmer could swim into a lethal gradiant and not be able to stop in time to save his life. He also stated that he believes that many drowning deaths could be attributable to electricution. This stuff was on my mind after jumping into the water to clear my prop after rapping a line in the marina.

 

[Joe]

Yikes, Snotter...... so, how do you recommend checking for this phenomenon before going in the water to check the bottom, or clear a prop? Some kind of continuity tester, maybe? Wouldn't a marina power line have a circuit breaker to protect against this type of accident?

 

[Bad Obsession]

Just do your cleaning away from other boats while on the hook. Problem solved!

 

[Brian D]

I propose an experiment. Since I am not in the states right now (else I would do it myself) I will hope that someone will muster up.

Go to HD and get a copper ground stake, or any copper pipe. Also, pick up some AWG12 insulated wire. You should already have a length of rope on the boat or dock.

1. Connect the copper wire to the copper ground stake/copper pipe.
2. Lay the pipe on the dock.
3. With a digital multimeter, measure the current between the pipe and the dock ground (any metal fitting on the dock electrical, even the ground plug). There should be zero volts AC measured.
4. Drop the pipe in the water a few feet (rope will hold it). Do the same measurement.
5. Drop the pipe to the bottom. Do the same measurement.
6a. Only if you are brave enough, hold the bare wire from the pipe in one hand and the meters probe in the other hand (with the other probe to the ground point on the dock electrical outlet) and measure the voltage flowing through your body.
6b. OR... hold one probe and put you feet in the water.

If you get any voltage readings then you have what is called a ground loop. This means that electric current is flowing in the water. How much is determined by your readings. There should be zero volts AC, or very little. If you want to measure the current (amps) you will need a current meter or clamp meter.

So, if someone does this, post the results. Should be interesting.

 

[Snotter]

Yikes, Snotter...... so, how do you recommend checking for this phenomenon before going in the water to check the bottom, or clear a prop? Some kind of continuity tester, maybe? Wouldn't a marina power line have a circuit breaker to protect against this type of accident?

When checking my boat's AC wiring I discovered that the white and green wires were swapped on one of the power connectors used to connect the shore power to the boat. If there was some kind of fault in one of my appliances or the hot water heater I am guessing that it wouldn't trip the breaker unless it exceeded the breaker's trip current.

I am just parroting Calder's book--he suggested sticking a voltage meter between the green ground wire and the water while looking for wiring issues.