Aluminum boat: bonding, ground plane, isolating

[Mark_VTfisherman]

I have some questions for Silvertip and any others that may chime in. I'm a little long winded so bear with me LOL

I was reading this: http://forums.iboats.com/forum/boat-...ring-or-ground along with a number of other threads, and developed some questions.

Years ago, I was instructed by an ancient boat shop owner that everything in a boat should be individually grounded, and that aluminum boats should be bonded with a perimeter tinned copper wire connected at bow, stern, and transom - separate from the electrical 'grounds' (negatives) and that bond wire was then to be connected to the battery negative. He said fiberglas and wooden boats didn't need this. Duh.

I no longer believe part 'B' of that to be fully correct. I've learned over the years a bonding should be separate from the electrical negative. Also, my own boats since the first one have been fiberglass which leads me to my questions since I now have a (currently gutted, fixing rivets) 19' Starcraft Holiday which is of course aluminum.

I know electrics on a boat are important to do correctly because of galvanic potentials of metals within the boat and other electrical forces/potentials created when in the water. My boat electrical 'awakening' happened about 2002 when I refit and restored my 1964 14' MFG Niagara I got about 1992. When I first got the thing I had made a ground post under the dash above the helm. The fiberglass at the helm was backed with a piece of 3/4" plywood, the ground post mounted to that. Good intentions; when taking everything apart in 2002ish I discovered there were metallic tracings between the helm- 8-10" away from the ground post- and the ground post. After some thought I suddenly realized these were actually either aluminum or tin residue that had travelled along the grain of the wood which was apparently an adequate conductor in its damp environment. This amazed me! I had electroplated wood!

Now, fast forward to today: working on the Starcraft tinny, I intend to plastic sleeve my transom/motor through-bolts, use plastic isolator washers, and do my best to NOT make the hull connect in any fashion to the battery -negative (or +positive LOL). I intend to also isolate the 22-gal aluminum belly fuel tank I scavenged from a bayliner and maybe create a single hull ground plane point for a bond that I can use for both protecting the boat and provide an actual ground plane for the vhf antenna that's not incidental. (I know there's a simple capacitor fitting to remove/isolate the shielding electrical 'ground' at the antenna which is usually a path to the battery -negative and plan on obtaining one)

In the past, I strove to actually use the electrical potential of boats in the water and added zincs specifically to achieve a potential 'voltage' as is described by this manufacturer who sells "black boxes" for attracting fish https://www.protroll.com/black-box-technology. However, I don't believe a boat's electrical 'field' is the end-all of catching fish: though it 'seems' to help 'sometimes,' certainly doesn't hurt fishing success, and the 'preferred volts' are often achievable simply by correcting wiring problems. Correcting wiring problems on plastic boats many times yields a neutral 'field' which imho is nearly or as effective as having the 'preferred volts' present.

I don't want an electrical field emanating from my aluminum boat.

How would you suggest creating an isolated bonding and ground plane for my boat? Is it necessary (goal is to protect boat)? Do agree battery negative should NOT be connected to the boat? (Boat may see salt or briny water maybe once every two years) I am pretty sure I'm correct in assuming that I should bond the fuel tank, and use a two-wire fuel gauge sender, OR is it sufficient to simply electrically isolate the fuel tank (from the hull) and connect the tank's ground strap to the battery -negative? The helm: it seems this is an overlooked place where the motor could gain electrical contact with the hull. I've not seen this ever addressed: your thoughts?
I have ideas, I've read things, but face-to-face conversations with boat techs and builder shop folks here locally have made me conclude that I know much more at this point about boat wiring than they do - and I KNOW I don't know nearly enough! I've always believed that a competent builder/mechanic/carpenter/fabricator has to, "know enough to know what he doesn't know" and that's where I'm coming from here. I know enough enough to know I don't know...

 

[roscoe]

Ok, I'll chime in.

I think you are over thinking this.
I have 2 50+ year old Starcrafts, and an Alumacraft, with no special grounds, and so far, the aliens have not used my boats as a homing beckon. 2 of them are in great condition with no corrosion, while the 3rd is a file or carp with no corrosion.

 

[Mark_VTfisherman]

My intent here is to learn more about doing things 'correctly' as I'm often called upon to work on other's boats and there's plenty of discussion around various topics I've raised, and I wanted to expand these discussions without posting on old threads which is frowned upon. At 52, I'm just not going to go get a gopher job at a boatbuilder or go back to college for marine electrician certification, but I can certainly learn from the experts when they chime in.

Overthinking is often an accusation hailed my way, but having dealt with building code issues and 'following' tradesman who don't overthink -if they think at all- in repairing simple deviations from code to major safety concerns, I think my questions are valid. A margin of error is often acceptable but knowing what is 'correct' is important.

 

[Silvertip]

Maybe you need to visit a ship builder who builds large aluminum yachts. In the Midwest that would be a trip to Sturgeon Bay, WI in Door County on the Great Lakes. Since their craft would likely see both fresh and salt water and are routinely tied to powered slips at marinas they would describe this for you (perhaps for a fee). On the other hand, some ship building web sites/forums may have more detailed answers than I gave in the article you referenced. If you try to isolate the engine using non-conductive fasteners you risk hull/transom damage from vibration that progressively loosens the hardware. Besides, you then need to look at virtually every electrical device on the vessel to see if it could present an electrical path to the hull. A bilge pump with an automatic switch sitting in water in the hull is just the beginning. Boats get wet (inside and out) so water sitting against anything electrical can be an issue. I contend that if you simply bolt up the engine and attach the negative battery terminal to the engine block you now take care of all things powered through the engine harness. You feed the helm and other accessories through a "boat" harness and fuse/breaker panel from the battery via a separate pair of #8 or 10 wires. Use as few negative buss points as possible. Yes -- a single point ground (battery terminal) is best but it is not catastrophic to have a couple. Even a daisy chain ground such as used on the instruments on many boats is ok but if the ground opens on the first gauge they all go down. If you have AC on the vessel than that's a whole 'nuther issue and you need to follow strict marine AC practices.

 

[Mark_VTfisherman]

Thank you for the response. I'm using a Blue Sea Systems 12-fuse block with the integral ground buss. I've used this for other's boats a few times and finally my own boat will get one. It's so compact, clean, and safe!

No AC. Way to much to think about on a small boat 16-25 feetish and a cooler works. IMHO there's not really reason to have 120VAC on anything under 28/30' and of everyone I know I think the longest is 24'. My 'circle' is fishermen. Although I can see that both refrigerators and air conditioning on larger boats is desirable and 12VDC doesn't do that well, these days nearly every electrical 'need' is pretty inexpensive and easy to achieve with 12V. A tiny refrigerator and an electric coffee maker would be desirable luxuries for staying on the water all weekend. But I digress.

VHF transmit and receive issues that I believe are due to ground plane issues are of interest to me. Cleaning up crazy wiring and isolating grounds, and making home runs to a single-wire battery positive+ to fusebox has let me 'fix' most of these transmit/receive issues. Recently learned about isolating the antenna shielding with capacitors or using a capacitive fitting and I think that may have been the answer to the couple I couldn't fix.

Again, thanks for your input.

 

[Bondo]

Ayuh,.... I've got an antique tinbarge,.... I discovered so long as everything, lights radios, fish finders, everything is grounded to a buss bar, to the battery ground,...
Everything works fine, 'n the hull is fine,....

I once grounded marker lights as cockpit lighting to the gunwales,....
In weeks, I had pitting all over the hull,...
Ran dedicated grounds, 'n no problems,...

 

[Fed]

I remember reading in an official Mercury document (could have been a manual) the recommendation was to make sure the outboard was well grounded to the alloy hull as this offered the hull protection by the motor anodes.
Then there's the school of thought that says to also run a dedicated ground from the battery negative to the hull which I believe may be a US requirement but I see it as opening the door for full on 12 Volt hull electrolysis.
Many years ago I temporarily wired a bait pump with 2 BP connectors below the water line, they lasted an hour or so & on inspection one of the connectors was simply 'gone', eaten away completely.

 

[Mark_VTfisherman]

Thanks Bondo and Fed.

I've not seen any damage from what 'I've done' even in the past when I was using the 'ground motor to the hull to use motor's zinc' which I don't like anymore. I feel now that adding a hull zinc is not only better but is correct. Nevertheless, all these boats are, were, freshwater and not slipped or moored.

I'm going to check further, but it seems a contact over on Maine coast or something or a ham guy locally might be needed to find a person that doesn't say, when I mention 'ground plane,' 'What do you mean by 'plane'?"

 

[Doh]

I remember reading in an official Mercury document (could have been a manual) the recommendation was to make sure the outboard was well grounded to the alloy hull as this offered the hull protection by the motor anodes.
Then there's the school of thought that says to also run a dedicated ground from the battery negative to the hull which I believe may be a US requirement but I see it as opening the door for full on 12 Volt hull electrolysis.
Many years ago I temporarily wired a bait pump with 2 BP connectors below the water line, they lasted an hour or so & on inspection one of the connectors was simply 'gone', eaten away completely.

An Outboard also has Sacrificial Anodes, your Anchor Winch/Stereo does not. Ground everything but the Outboard to the Neg. post on the Battery.

 

[Fed]

If you don't ground your outboard it to the battery negative won't turn over.