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Old 23-02-2010, 17:56   #1
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SSB Grounding on an Aluminum Boat

Perhaps I missed a section on this elsewhere but I am interested in anyone's experience with the grounding of an SSB radio on an aluminum (or steel?) boat.

The antenna tuner for our ICOM M-802 is connected to the hull of our boat (Dudley Dix 43). The boat's 12 volt dc electrical system is grounded to the hull via the engine alternator and starter but the propshaft is electrically insulated from the engine and the hull is painted with epoxy and antifouling so there "should" be no large underwater surface electrically exposed to the water. I know on fiberglass boats, people fit copper plates to give the radio a ground plane. On our boat, I suppose the zincs are filling this function.

Is there the possibility of electrolysis or crevice corrosion from the radio?
Will the antenna be less effective without another connection to the seawater?


Any comments or suggestions very much appreciated.

Thanks,
Ian
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Old 24-02-2010, 00:16   #2
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Ian,

You SSB doesn't need a metal-to-seawater contact for ground. It will create a capacitive coupling. I wouldn't worry about crevice corrosion unless you talk on the SSB all day, every day. I would worry about your battery negative connected to the hull. How did that happen at the engine? If your prop-shaft is isolated from the hull, the rubber engine mounts should isolate the rest.

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Old 24-02-2010, 00:47   #3
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Thanks Nick. I will check this (the engine electrical connection to hull) out with my voltmeter when I get back aboard later his week. With regard to the RF "ground", if I understand correctly, you are saying that the metal hull of the boat will act as a giant capacitor so antenna power should be OK. If I was paraniod about the RF ground, I could install the KISS-SSB counterpoise that I see discussed on this site to the tuner ground as a $150 solution.
Ian

Ian

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Old 24-02-2010, 00:55   #4
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The antenna tuner should be grounded to the hull through an isolating diode. This prevents DC currents entering the hull. as others have said the hull is an excellent ground plane and no adittional plates are needed.
Sorry don’t have a link how to do this, but a google search should show up something (my internet is very slow on the boat)
For an aluminium boat you should also have the engine earth isolated . It is not difficult to do. I will describe how you can do it if you want to make the change.
Cheers John
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Old 24-02-2010, 08:38   #5
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Erhmmm, no, there should not be a diode in the SSB ground. If you want galvanic isolation between SSB ground and the hull you have to use capacitors. You can search this forum or Google to find the info incl. examples and even photo's on how to do it. I think it's overkill when the radio isn't used much but it can't hurt and the capacitors are transparent for HF and a total block for DC.

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Old 24-02-2010, 08:43   #6
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Erhmmm, no, there should not be a diode in the SSB ground. If you want galvanic isolation between SSB ground and the hull you have to use capacitors. You can search this forum or Google to find the info incl. examples and even photo's on how to do it. I think it's overkill when the radio isn't used much but it can't hurt and the capacitors are transparent for HF and a total block for DC.

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Sorry you are correct. I was working from memory, but capacitors make more sense
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Old 24-02-2010, 09:11   #7
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I agree with Jedi. Ground the tuner to the hull. Don't worry about isolating capacitors unless you're REALLY paranoid. If you are, search for Stan Honey's excellent primer on boat grounds...he did it for West Marine I think. A Google search for "Honey boat grounds" will find it fast. It includes pics and explanation of how to make a simple DC-blocking capacitor bridge.

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Old 24-02-2010, 09:13   #8
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Folks used to pay me to do this stuff. :-) To get the best performance, the ground strap from the ATU should be as short as possible, straight to the hull of your metal boat. Thick tinned copper braid is best, I won't recommend a copper strap as it is more difficult to work with, even though it may work a bit better. We used to dip the braid in plastic to stop it corroding, and solder big terminals to the end, but that's for military application, and soaking the while thing in silicone grease is probably adequate for us. Inspect it now and then, make sure the braid is not rotten, and the grounds are good. Certainly do not use a diode. You do not need a capacitor, the addition of one would need proper selection in any case, you have size, voltage rating, and self resonant frequency to consider.

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Old 24-02-2010, 09:13   #9
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Thanks again to all of you for your suggestions. The capacitor solution was also recommended by Dockside Radio in Florida from whom I bought a Pactor modem yesterday.
Ian
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Old 24-02-2010, 09:19   #10
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What did they recommend as a capacitor Ian?

Bill
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Old 24-02-2010, 09:40   #11
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What did they recommend as a capacitor Ian?

Bill
They didn't specify and perhaps recommend is too strong a word, more of a "you should look into capacitors" suggestion. Ian
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Old 24-02-2010, 09:49   #12
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Here ya go. Scroll down to Figure 1.

Grounding

Honey recommends "several 0.15uF ceramic capacitors

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Old 24-02-2010, 09:54   #13
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Ceramic are a good choice. Half a microfarad will give a capacitive reactance of about 0.1 Ohm at 3 MHz, lower than that at higher frequencies, and that's good.

You really do not need a capacitor though, we never use them on naval vessels.
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Old 24-02-2010, 10:15   #14
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If you connect your Icom tuner ground stud directly to the hull, then you have just connected your battery negative to the hull via the SSB wiring. No big deal IF your hull is already part of your ground system. As to whether an aluminum hull boat should be part of the ground system is highly debatable. The big problem with ground/bonding systems is that many don't get installed correctly in the first place and most rarely get the required regular maintenance afterward.

Eric
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Old 24-02-2010, 10:18   #15
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How about the copper strap? Especially if connected to am aluminum boat? Can aluminum be used instead?
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