Electrically Isolated Prop

[Bill Roosa]

The ground is a safety device!!!

It has been said that we are all safe in our cars and they have common floating grounds to the frame.
I ask you, have you ever been around a 24 volt vehicle system. You can indeed get shocked quite a bit when things are not securely grounded. A loose ground cable at the engine can be quite annoying. Annoying, because it is only 24 volts. Take your circuits up to 110 or worse 220 and let Mr. Corrosion take out your neutral (working return for AC) and see how annoying it is. It can be positively deadly. You just think you are safe in a car because you can't feel the 12 volt "leaks". You are passing current just not very much because it is only 12 volts. So trying to compare the two can be misleading. You can get away with working on live 12 volt with no ill effects. 24 volts is detectable but you will not get "bit". 50 volts produces a bite and 110 is deadly.
When at the dock the dock (hopefully) provides a ground to earth. What provides your "earth" when you fire up the genset/inverter when away from the dock? Note that your body is connected to the earth and is at 0 volts with respect to it any time you touch water or anything that is connected to water and conducts current even badly. Fiberglass and wood are good examples of bad conductors. If your floating AC ground is at something above/below 50 volts relative to earth you WILL notice it. Your body has all day to come to ground potential and unless you touch a energized circuit should stay (sans the static electricity issue which I am going to ignore but it does provide illustration to what is going on) at 0 volts. So if you let your AC ground "float" while away from the dock you can get into the situation where the AC ground is significantly above or below earth that you can get shocked.

Floating grounds are a safety hazard!!!!
Dedicated grounds are a pain from the maintaince standpoint.
Take your pick.

I've worked around 24 volt vehicles and portable 110/220 generators most of my adult life and I'm telling you you will eventually see it my way. Mr. Corrosion will insure you get a wire with high resistance eventually. I pray it does not electrocute someone.

 

[Bill Roosa]

Back to Hermit's questions

The real reason you want to tie all the circuits is because they are a system. When you design it to account for all the variables you realize that there are situations (safety rearing it's ugly head again) where even if you isolate everything perfectly they are still connected and interact and the only way to maximize the safety of people in the boat is to tie the circuits together. This causes maintenance issues alas.

Lightning WILL induce voltages in ALL the boat metal. The wires running down the mast being the most likely source and wires running parallel to the lightning current being less likely. The engine is such a large piece of metal it is assumed that it will get involved.


So run all your DC and AC wires horizontally and avoid vertical runs or runs that parallel the lightning wires.
Run all your lightning wiring vertically and avoid horizontal runs.
Move as much electrical stuff off the mast as possable. Those things that do remain on the mast should have inductors at approprite locations to discourage lightning from entering them.
Tie AC, DC, Lightning, and RF (with appropriate isolation capacitors and inductors and in the appropriate location) together at the keel.

AC can also kill (here I go with safety again) so insure that you don't float the ground and get into a situation where you are at 0 volts and the boat ground is significantly different.

So tie the AC ground to the common ground point with an appropriate capacitor.
Install an isolation transformer (best) or isolation diode in the AC shore power ground line.
Keep up on the maintenance and bug the marina and other owners if you notice a problem with their side of dock.

DC can cause your metal to corrode (finally getting off my safety soap box) so isolate all the thru hulls and anything that is not an electrical device. Any electrical device should have a dedicated (don't tie the anchor light ground and the steaming light ground together until they get back to the panel) return to eliminate stray currents. The engine is a great place for the DC ground because of the alternator/starter/instrument senders all being "frame grounded" to the engine. Attach the engine ground to the common ground point with a single "lightning sized" wire with inductor to discourage lightning from entering.
I would disconnect my prop and shaft if possible and use a zinc to protect them from themselves.

RF circuits can provide a path for lightning into your DC system (antenna remounted to the pushpit rail is an alternative) so be sure they are protected with either lightning arrestors or are disconnected during storms and when away from the boat. VHF does not need a good ground unless you use some odd sort of antenna which only a ham would use. HF/SSB radio does need a good counter-poise (big word for RF ground) and that can be treated as AC so use a capacitor to keep those nasty DC electrons out of the circuit.

Again, it is a system. There are safety and maintenance issues to be resolved and it ain't cheap or easy.

 

[Stu Jackson]

Grounding

Hermit, in your #40 you said you didn't understand grounding in homes. You might want to do some reading on that, first, like here: http://www.epanorama.net/documents/groundloop/why_grounding.html I Googled for this, try wikipedia, too. My "Sunset Book of Home Wiring" does a good job, too. Once you "get" this idea, then you'll be better be able to differentiate between the A.C. ground for the 120 Volt 3-wire system and the D.C. ground for the 12 volt 2-wire system. I haven't read Casey's Simplified Book, but for more reading, I recommend Calder's or more internet research.

Some more info on marine electrolysis that I picked up from searching for bonding information: http://www.yandina.com/electrolysis.htm They also make galvanic isolators. Pretty good website reference material.

The more I've read about your original question, the answer is as someone, above, said: the zinc on your shaft will protect your shaft and prop, so your flexible coupler is NOT an issue for you, the rest of your question is just D.C. and A.C. wiring, which Stan Honey's article pretty well covered.

There have been years of disagreement by boaters and electricians on connecting the A.C. ground to the D.C. ground, hence, your PO's (the "good" electrician) possible disinclination to do so. Calder discusses it at length on the page opposite the one of the wiring diagrams I posted earlier. I recall discussions years ago as to whether Catalina did it or not. I'll do some digging and see if I can find some of that material.

Your boat, your choice.

 

[Hermit Scott]

This is definitely the kind of things I wanted to know; the reasons why some people choose one way and why some choose another.
I read all the links that were provided and I thank all of you for that information.
From what I can ascertain, the shore power cable already has a default ground. In a house there is only one default ground. I think it is overkill to have extra grounds on a boat, unless a generator is providing power, then there is no other ground that is definitely at the potential of the water, even if a default ground were added and attached to the frame of the generator, the generator is not in contact with the earth. That makes me have my doubts that it would protect just like one in contact with the earth. I seem to recall from my military experience that the generators were to have a spike drove into the ground attached to the frame for an earth ground. I suppose a cable with a plate dangling into the water from the generator would provide the same protection.

The only real issue for having all wiring grounded to the water would be that lightning could induce currents in the wiring. This seems more of a danger to equipment than to people. And probably wouldn't save your electronics anyway.
For the coastal cruising I am going to be doing, I am not concerned with that. If I was making an Atlantic crossing, maybe.
I am very aprehensive about having any possible currents running through metal parts going through the hull, be it from my boats electrical system or stray currents.

 

[Stu Jackson]

Glad to hear we helped

Only thing I would suggest (being an engineer!) is to use the appropriate terminology. Nowhere in the links could I find a term called "default" ground. It's either the A.C. ground or the D.C. ground. Also, as far as generators go, the photo from Calder that I posted and other links explained the onboard generator ground and showed its wiring. Yup, ya canna drive a stake into the earth when you're on a boot, matey! Good luck and fair winds, Hermit. Happy Holidays, too.

 

[Hermit Scott]

I don't know where I got that term. (default ground)
So we have AC positive, AC negative, and AC ground?
I didn't see the wiring diagram for the generators but the part about making your own hookah from an air compressor from Lowe's was VERY interesting.

 

[Stu Jackson]

Wires

AC positive is black
AC neutral is white (not negative) It's different than DC
AC ground is green

Wiring diagrams are on page 2, post #26 on this thread in the thumbnail.

Since you're into this stuff so much, I recommend you beg, borrow or library Calder's Boatowner's Manual for Mechanical and Electrical Systems. I've found the 2nd Edition easier to read than the new 3rd edition. It's right up your alley, and has more information than the Casey book you have that started this thread.

Happy Wiring!

 

[Franklin]

Try reading this (http://amasci.com/amateur/whygnd.html). It will explain why there is a need for a 3rd wire. It doesn't state it clearly, but it states that the reason is to protect the circuit from thunderstorms. "Thunderstorms pump negative charge downwards, and the charge filters upwards everywhere else on earth. "

So, if you have a negative DC charge on one end of your wire and positive charge on the other end of your wire, you have problems.

The thing is, my boat is only 37 feet long. There is not going to be negative on one side and positive on another. So I don't need to ground my generator to earth to protect it from mothernature. But big electrical systems do have to worry about that and that is why there is a Green (ground) wire.

The other ground, the one for the system to work correctly, is the generator itself.

Why do we not have to worry about this with DC systems? Because DC current looses a lot of current when traveling, so DC systems don't span miles (that's the whole reason for AC).

 

[jimq26]

Hermit - do you have to make comments about drug use etc. on this site?

I didn't see the wiring diagram for the generators but the part about making your own hookah from an air compressor from Lowe's was VERY interesting.

You have done this more than once on this site, and it is not very impressive IMHO.

 

[Maine Sail]

Re: Hermit - do you have to make comments about drug use etc. on this site?

You have done this more than once on this site, and it is not very impressive IMHO.

Ummm Jim you might want to Google a bit before talking of other members drug use or accusing them of such talk..

A hookah is a scuba diving device not a bong!!!!!

Hookah (LINK)

 

[Hermit Scott]

Well...just smoking drugs at ambient pressure is not working for me anymore. Now I use a compressor from Lowe's. Jimq26, you have to try it at 135 p.s.i. before you can appriciate what I am saying.

 

[Hermit Scott]

Seriously though Jim, I do not do drugs nor do I advocate drug use. Not terrestrially or sub-aquatic.

 

[jimq26]

Great - glad to hear that.

Seriously though Jim, I do not do drugs nor do I advocate drug use. Not terrestrially or sub-aquatic.

There have been a few references over the past number of months that were misleading then. As we all well know, there is no room for such nonsense on a sailboat.
Just shows how old fashioned I am when I think of what a hookah pipe is for eh?

 

[Hermit Scott]

Jimq26, I think I know what you are talking about. Someone on here has the screen name Steve420. (name has been changed to protect the innocent)
420 is a reference to people who partake of canabis. So I had a private conversation with this 'Steve420'. I asked him if his name was a reference to pot and he said he owns a 42' sailboat. I was mistaken about what his name meant. Bob Marley was born on 4-20-19whatever. OR a million other urban legends to it's origin.

 

[Stu Jackson]

Uh.......

Can we just get back to wired?

 

[sailaway78]

Hermit

I have to give it to you. You post up some interesting subjects, that get lots of different opinions, and tons of replys. Glad you found this board. And by the way, I remember you posting that you talked to TonyB some time back. Did he mention heading out for an extended cruise. Seems like I remember him saying he was planning on leaving in Oct. or Nov. And he hasn't been on the board for a while.

 

[Franklin]

Na....he's just been working his butt off offshore and on his boat. He drove into town for Thanksgiving to pick up his woman and head to Austin. He has christmas off but I think he is heading out of town again.

I know all this because I asked if he wanted to join me on a sail to Mexico. He wanted to go but I plan on returning the 4th and he needs to be at work on the 2nd.

 

[Hermit Scott]

I'm glad I found this site also. I have reaped alot of technical advice and opinions and learned things that may save my life one day.

I think Tony is just tired of the internet for now. Like Franklin said, he's working alot.

Franklin, the reason I bought a sailboat was to sail to the Bahamas one day. Tony recommended I go the other way down to Mexico first. Where do you go when you go down there, how far past Padre do you go? Also I was wondering how far out into the Gulf do you sail?

 

[Franklin]

Franklin, the reason I bought a sailboat was to sail to the Bahamas one day. Tony recommended I go the other way down to Mexico first. Where do you go when you go down there, how far past Padre do you go? Also I was wondering how far out into the Gulf do you sail?

So far I've only been to Vera-cruz....soon to be Tuxpan (100 miles up the coast from Vera-cruz). There isn't a lot to see on the Gulf side. I plan on seeing all of the Caribbean this time next year (staring of a 4 month cruise) and so far I' still shooting on hiting Key West, then Bahamas, then heading east for 3 days and then south for 3-4 days to hit the Caribbean. Once there it's just a days sail to the next Island.

I have to admit though, I've been thinking about Galveston to Cosomel, to PR to Grenada.