RF drain, grounding question

goldenstate

Member III
Blogs Author
Seeking assistance:
Several of the Raymarine electronic gadgets I am installing have 3 wires, positive, negative, and RF drain which is a ground wire.

I do not believe I have a grounding plate in the bottom of my boat. In contact with my propellor shaft I found a metal lever attached to a green wire (green wire associated with grounding, I presume)
391E77D2-3FB9-49A8-AE8A-8268574628C3.jpeg
The other end of this wire is coiled and taped and in my engine compartment, terminated at a bolt holding my Racor primary filter to the compartment wall.
CEA22179-3A7F-4277-BF48-B732CB5D0F55.jpeg
1. Does it make sense that this wire is more or less insulated from the rest of the boat? Is it preventing electrolysis or keeping me or the boat safe? Is it just wired incorrectly?

2. Would connecting the Raymarine RF ground lines to this wire be the right thing to do? It does seem like it would be a good ground assuming the contact between the metal lever and the prop shaft is clean. If so, should I shorten that long coil of wire? The Raymarine manuals highlight the importance of the ground wire being large diameter and short length.

Thank you in advance for suggestions.
 

Tin Kicker

Member III
E for effort, not for effect.

Get the green wire off of the RACOR before anything. If you get a hot battery short or lightning strike, that is about the very LAST place in the world you want to have energy pass thru or by. The coil is totally unnecessary too. btw - Black is the ground color for DC, green is for AC. My guess is that it just happened to be what the last person had in his tool box.


Then just bring your grounds to the battery or engine block. There are arguments + and - for both sides and both will work as long as the cable is thick enough between the engine and battery. (Generally 1/0 or greater for this size engine and alternator)
My preference for grounding electronics is to the battery because (1) these are sailboats and the engine is normally off and (2) the connection from the battery to the engine is an extra item/resistance/failure point/etc in the circuit.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Informational trivia (perhaps lacking 'wisdom') but the factory DC ground point in our '88 boat was a bolt on the engine bell housing. I did move those wires to a separate DC ground buss bar installed in the engine compartment. I maintained that buss for the new Betamarine, as well.
Being concerned about resistance, I used to remove those big cables every few years, sand paper them clean, and reattach.
 

Tin Kicker

Member III
Informational trivia (perhaps lacking 'wisdom') but the factory DC ground point in our '88 boat was a bolt on the engine bell housing. I did move those wires to a DC ground buss bar. I kept that for the new Betamarine, as well.
Being concerned about resistance, I used to remove those big cables every few years, sand paper them clean, and reattach.
Totally normal and how the ABYC discusses grounding, obviously originating in the powerboat world. On a work boat I'd leave it because the engine is normally running and the alternator is the source of electric power. It's all about what works best for the situation.

btw - In re-doing my electric system, I found one of the heavy grounds slightly loose and with very small arc marks on the lug. As Loren wrote, occasionally checking connections is a really important part of preventive maintenance.
 

goldenstate

Member III
Blogs Author
Thank you @Tin Kicker for the guidance.

That the ground would wind up on the fuel filter did not make sense to me, but my electrical knowledge is more about pattern matching and following examples than theory and design. Back at home at the computer I read more about the propeller shaft lever ground thing I found, and apparently it is a "shaft brush." I think its role is to prevent the propeller from corroding and I should shorten that wire and attach it to the grounding point for the engine.

For the Raymarine RF drain I am essentially creating a third wire ground network (In addition to the positive and negative wires everything already has) where none existed before. I'm not entirely sure why this should be necessary now in 2020 when it wasn't before, but I'm trying to dutifully follow the instructions.

On the color of the wires, in an AC system I expect:

Black = Hot/Positive
White = Neutral/Negative/Common Ground
Green = Earth Ground

In a DC system, I expect
Red = Hot/Positive
Black = Neutral / Negative (From what I have gathered new-school thinking here is to make this a YELLOW wire to avoid AC-hot confusion, but nearly all my new gadgets have black (not yellow) negative small gauge wires from the factory)
[What color wire to buy?] = Earth Ground / RF Drain

I found this chart that implies green or green w/yellow is the right color for the ground for ABYC, but I would be curious if others think there is a better choice.
 

Tin Kicker

Member III
I've seen that list and have a more extensive version in pdf on the iPad, but the only place I've seen it used is in brand new boats.

Will fess up to you that in re-wiring my boat, the DC circuits are red, white, or black with red to anything normally powered, white to switched items, and black for wires always grounded. More important than that is using a Demo label maker with water proof 1/4" lettering at each end of each wire, sometimes mid-run too, and covering each of the labels with heat shrink sleeves.
 

goldenstate

Member III
Blogs Author
Doing a little more research on my propeller shaft brush (the lever pressing against my shaft, connected to the green wire).

This Cruising World article says that:

The purpose of the shaft brush "centers around bonding of the shaft to the hull for the purpose of mitigating corrosion."

Sounds good. Will that work properly? "Usually not too well frankly. Most of us that deal with matters of marine corrosion don't actually recommend them. The failure rate for these brushes, and especially something as jury rigged as the one in the photo above is just too high. I've checked many of these over the years for electrical continuity and found an open circuit between the shaft and the brush."

Okay, so what should I do instead? "Simply provide adequate shaft anodes to protect the shaft and propeller for a reasonable amount of service time and treat any other underwater metal you wish to protect separately with additional anodes as needed. Most of these shaft brushes are just going for a ride on the boat they're installed on and really not contributing much to help in the corrosion protection area."

Here's a video of a grounding brush on a smallish boat:


Here's another video about shaft earthing/grounding on a much larger boat:


I guess the concept is that the spinning shaft can become isolated from the grounding system of the boat (because of lubrication and because a transmission in neutral is not connected to the shaft (?) and in this circumstance the corrosion of the propeller will accelerate.

So, the shaft brush makes a connection to the shaft while turning, and the wire which is connected to the brush should be led back to the grounding point on the boat (which is of course what Tin Kicker said I should do). All that said, the brush may not be making a very good connection to the shaft in terms of continuity, so the sacrificial anodes are the best line of defense.

Just making all of the notes for myself and anyone else who may come across a similar brush installation in his/her boat.
 

Frank Langer

1984 Ericson 30+, Nanaimo, BC
Tin Kicker, in post #2 above, you mention your preference to attach ground wires directly to the battery rather than to the engine, because the engine doesn't run while sailing. With all due respect, and my lack of knowledge, if the ground wires go to the engine stud, and a large wire from that same stud to the negative terminal of the battery, doesn't that ground the wires regardless of whether the engine is running? It also seems to me that even if there wasn't a ground wire to the negative battery terminal, the ground wires attached to the engine should be enough as engine is grounded through its connection to the tranny, tranny coupler, prop shaft going into the water. Am I missing something here? Thanks for any clarification you, or others, can provide.
Frank
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Tin Kicker, in post #2 above, you mention your preference to attach ground wires directly to the battery rather than to the engine, because the engine doesn't run while sailing. With all due respect, and my lack of knowledge, if the ground wires go to the engine stud, and a large wire from that same stud to the negative terminal of the battery, doesn't that ground the wires regardless of whether the engine is running? It also seems to me that even if there wasn't a ground wire to the negative battery terminal, the ground wires attached to the engine should be enough as engine is grounded through its connection to the tranny, tranny coupler, prop shaft going into the water. Am I missing something here? Thanks for any clarification you, or others, can provide.
Frank
Our engine installation had several grounds tied to the engine bell housing, and I only moved them (with a connecting ground cable) to a ground buss just to tidy up the engine compartment cable runs.
 
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Christian Williams

E381 - Los Angeles
Moderator
Blogs Author
Stan Honey gives the overview:

 

Frank Langer

1984 Ericson 30+, Nanaimo, BC
Stan Honey gives the overview:

Thanks Christian! That's an article one should save, read carefully a few times, and then put into practice.
Frank
 

Tin Kicker

Member III
Tin Kicker, in post #2 above, you mention your preference to attach ground wires directly to the battery rather than to the engine, because the engine doesn't run while sailing. With all due respect, and my lack of knowledge, if the ground wires go to the engine stud, and a large wire from that same stud to the negative terminal of the battery, doesn't that ground the wires regardless of whether the engine is running? It also seems to me that even if there wasn't a ground wire to the negative battery terminal, the ground wires attached to the engine should be enough as engine is grounded through its connection to the tranny, tranny coupler, prop shaft going into the water. Am I missing something here? Thanks for any clarification you, or others, can provide.
Frank
As the saying goes, there's more than one way to skin a cat. Everything said here till Christian's [excellent] article have been about the "ground everything together" approach, which is common in small boats like ours. What I wrote is essentially like what is in this image from that article, it's just that my ground bus bar is in the battery compartment, rather than at the engine. While it's pretty common for a boat to have at least several cables attached to the engine bell housing, the point is to have one path and not a ground loop with multiple paths. It doesn't matter how heavy the cable used, multiple paths will create all sorts of problems, especially when you start tying in radios and other electronics.


Below are the current states (continually changing as I work on the boat) of what I've found in the OEM wiring and what mine is migrating to and you can see that both show only one connection to the engine.

OEM as found on my 32-3:


What my boat is migrating to is below WHICH IS CONSTANTLY CHANGING as I put things in. Note that I've added an electrical sub-panel at the top forward corner fo the quarter berth access panel. The ground bus in mine (shown to the lower left of the voltmeter) is a 1.5" wide bar of copper in the battery box, only inches from the two batteries. The bar was tapped for a combination of 3/8", 1/4", and 10-32 stainless bolts & nuts which has really cleaned up the installation a lot.



Now Christian's article has me thinking that it will be good to install some capacitors to protect the radio and chart plotter. hmmm
 
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Christian Williams

E381 - Los Angeles
Moderator
Blogs Author
As an aside, it is well known here that when it comes to electricity I do everything by rote and with the forum holding my hand.

But even I could marvel at the way the cable TV installer grounded his cable box at a hidden corner of my house.

cable ground MG_5853.JPG

Yep. The pipe is PVC.
 

goldenstate

Member III
Blogs Author
This is sort of a separate question, (and I have googled for an answer, but not found any satisfactory explanation) but why do we use the engine block as a ground (how does it function as a ground)?

I had sort of thought that the engine was connected to the big metal shaft of the propeller which is in the water, and that's the best we can do with a sailboat. If this is the case, why don't people make a bigger deal out of ensuring the propeller shaft has continuity with the engine block (why doesn't everyone have a propeller shaft brush like I found?) Why would anyone put in a shaft isolator (like the one @Kenneth K suggested in this post?)

Should I have a separate fat wire from my engine block to something metal other than my propeller outside the boat? (I thought this is what a 'bonding plate' is? But I don't think I have one...

Or is it that the block is just a big hunk of metal into which negative electrons disappear?

I'm not being facetious, I'm just hoping that by understanding what is going on with the engine block I can better understand the grounding process.
 

Kenneth K

Sustaining Member
Blogs Author
The nylon shaft isolator or drivesaver is used to correct minor misalignments between the transmission and the propeller shaft. It's also supposed to cut down on engine vibrations.

To make up for the fact that it electrically isolates the shaft from the engine, you're supposed to connect a bonding strap, or wire, for metal-to-metal metal connection between the two sides of the shaft coupling.

This was my point in my previous post: Either many people don't realize the strap is required for grounding, or they do realize it, but leave it off because they know it has the potential to make galvanic corrosion on the shaft worse.
 

goldenstate

Member III
Blogs Author
The nylon shaft isolator or drivesaver is used to correct minor misalignments between the transmission and the propeller shaft. It's also supposed to cut down on engine vibrations.

To make up for the fact that it electrically isolates the shaft from the engine, you're supposed to connect a bonding strap, or wire, for metal-to-metal metal connection between the two sides of the shaft coupling.

This was my point in my previous post: Either many people don't realize the strap is required for grounding, or they do realize it, but leave it off because they know it has the potential to make galvanic corrosion on the shaft worse.
I see - I had not understood that the principal function of the drivesaver was alignment.

I guess this supports the idea that the engine block is a useful ground because it is connected to the big stick (propeller shaft) in the water. (But doesn't that linkage promote the galvanic corrosion of the propeller?)
 

Kenneth K

Sustaining Member
Blogs Author
I'm no electrician, but here is my way of looking at it:

When talking about DC: Although the connection "to the big stick (propeller shaft) in the water" seems to be recommended (for reasons of safety, I assume), it's not required. Hook up any device between the positive and negative battery posts and it will operate--that's all it needs. It's somewhat like your car--your car doesn't need to be (and isn't) grounded to the earth.

When you talk AC, in a boat, it's trickier: You could technically say the same thing, about disregarding the earth ground, but, hopefully, no one would be reckless enough to say so. If you don't have an actual ground to earth (water), your body may become that ground in certain situations, which would hurt like hell, right up to point where it kills you.
 

goldenstate

Member III
Blogs Author
I'm no electrician, but here is my way of looking at it:

When talking about DC: Although the connection "to the big stick (propeller shaft) in the water" seems to be recommended (for reasons of safety, I assume), it's not required. Hook up any device between the positive and negative battery posts and it will operate--that's all it needs. It's somewhat like your car--your car doesn't need to be (and isn't) grounded to the earth.

When you talk AC, in a boat, it's trickier: You could technically say the same thing, about disregarding the earth ground, but, hopefully, no one would be reckless enough to say so. If you don't have an actual ground to earth (water), your body may become that ground in certain situations, which would hurt like hell, right up to point where it kills you.
I'm comfortable with those concepts and agree. But why then, aren't our DC systems a "closed loop" between the batteries and the gadgets/load that use power? Couldn't we only have the the AC system grounded to the water via the engine block? The shore power battery charger would be the only AC/DC crossover point.

The more nuanced issues are:

The grounding for the AC shouldn't matter except in a system failure, because you are supposed to be grounded to your shore power line at every outlet. But I don't want my boat to kill me, so the supplemental engine-block-ground-wire makes sense.

The Radio Frequency Isolation (RF drain wire) issue remains mysterious to me. Some of the Raymarine stuff requires it, but the Standard Horizon VHF radio does not? I know there is some need to isolate radio frequencies if one is trying to achieve long-range radio transmission via Single Side Band radio at sea. Something about dragging a long ground in the water behind you?

Maybe it's overkill and Raymarine is just trying to cover themselves so as not to interfere with SSB systems?

I find my black DC ground wires connected to a common post connection, and then I run my new green "RF drain earth ground" wires to the same common connection, isn't this just redundancy? Maybe that's the whole point.
 

Kenneth K

Sustaining Member
Blogs Author
But why then, aren't our DC systems a "closed loop" between the batteries and the gadgets/load that use power?
I'm guessing it's this. If the DC system were a "closed loop," your positive battery cable could chafe against, and make contact with the engine block, and..... nothing would happen. Your engine block is now a "hot battery post," but you don't know it, until you rest your hand on it while the other hand is resting on something else in the system. And then you start to get that tingly feeling......

Good luck on your more nuanced questions.... way above my pay grade.
 
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