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Old 24-02-2010, 10:44   #16
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ho wait... if the tuner ground post is indeed connected to DC negative than I would certainly add capacitors. Also, no copper must contact aluminium. Use a very short AWG #8 with tinned lugs and stainless steel fasteners... keeping a stainless washer between the hull and the lug. If you can attach it to the hull right next to the tuner you could just use the capacitors to bridge the gap. Just solder lugs on each end. If you use ceramic capacitors you must mechanically protect them against damage plus spray them with something to protect them against the environment (or even pot them in epoxy).

I agree with fairbank that the aluminium hull should never be used for any DC nor AC ground. This is easy to check. But I wouldn't hesitate to use it for SSB ground as long as you don't start a winlink node or other funny 24/7 stuff (yes, some do that ;-)

cheers,
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Old 24-02-2010, 11:11   #17
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Eric, good point, capacitors remove that issue. Bill's link to Honey looks good, though I would suggest a stronger mechanical arrangement to prevent the capacitors from breaking under flexture. There is a safety issue here as well. Capacitors will dissapear in a puff of smoke should you get a lightening strike. At this point your SSB is sitting at about 8 million volts with respect to yourself.......

Conrad, The best document I know of for determining galvanic compatibility is MIL-HDBK-1250A. It is available for free download here. https://assist.daps.dla.mil/quicksea...t_number=36168

For a marine environment, we like to see less than 0.25V between metals when immersed in Brine. Copper and T6061 Aluminium gives about a volt, which is VERY bad. T6061 and Tin (Tinned Copper braid) gives 0.25V, which is fine.

I recommend tinned copper braid, thick and short. Cover it in silicone grease. Use capacitors if you are more worried about corrosion than life. :-)
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Old 24-02-2010, 12:34   #18
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Originally Posted by btrayfors View Post
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.

Bill
WA6CCA
Aluminium hulls IMHO are fantastic they do not suffer the problems associated with other materials particularly fiberglass such as
core rot / delamination
hull ,deck joint problems
osmosis
fuel or water tank corrosion
In addition they are much less likely to leak and sink if you hit a submerged object
I could go on, but this post is about SSB installation.

The only price you pay for these advantages is that you need to be "REALLY paranoid" about electrical problems. Follow the absolute best practice, overkill, what ever you like to call it when it comes to electrical installation.
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Old 01-03-2010, 12:57   #19
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Thanks for all the suggestions regarding RF grounding - the consensus answer seems to be to insert a capacitor into the grounding circuit if one is concerned.

On the related topic of grounding anything to the hull, I asked the boat's designer for his comments and he replied:

Whether or not to bond is a controversial issue. The safest to prevent electrolysis is to keep all electrical stuff isolated from the hull. However, this can be very dangerous if there is an electrical short in a piece of equipment. If the casing is live and someone touches the casing and the boat structure at the same time then their body will be the conductor and that can be deadly. ABYC standards call for bonding to keep everything at the same electrical potential. One of the reasons is for the safety of the crew. The following is an extract from the ABYC standards book (mine is very old and the wording may have changed since).

PURPOSE
This standard establishes requirements and recommended methods for bonding direct-current electrical systems:
- to provide a low resistance electrical path, within the confines of the hull, between otherwise isolated metallic objects, particularly those in common contact with sea water and potentially subject to electrolytic corrosion due to stray currents;
- to prevent the possible existence of an electrical potential on exposed metallic enclosures of electrical equipment;
- to provide a low resistance path to ground for voltages that may be considerably in excess of those for which the system is designed, as might occur when lightning strikes, and
- to minimize radio interference.

Ian
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Old 01-03-2010, 13:41   #20
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Sounds good.

Ground it. All military vehicles I know of use a thick tinned copper braid. We try to keep the length to breadth less that 5:1, but that is not always possible. Sometimes we double up, use two lengths in parallel.
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Old 01-03-2010, 14:04   #21
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Actually, the subject of killing yourself with electricity is quite interesting. You need to get 10 - 100 mA travelling through your chest cavity to get the heart fibrilating, and in a salt water environment, this is fairly easy to do. 110 VAC will drive this current very easily. If you are really unlucky, you can kill yourself with 10 watts.
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Old 01-03-2010, 16:52   #22
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Originally Posted by Namoian View Post
ABYC standards call for bonding to keep everything at the same electrical potential. One of the reasons is for the safety of the crew. The following is an extract from the ABYC standards book (mine is very old and the wording may have changed since).
Yes, they have changed. ABYC does not recommend a bonding system. They merely provide installation guidelines if you decide to install one. People think ABYC is the law but it is not. Each one of their standards states that use of their rules is entirely voluntary and only serve as a guide to achieve a specific level of design or performance. There are two entirely different schools of thoughts on the subject of bonding.

Eric
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Old 02-03-2010, 00:27   #23
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As mentioned above, there are two theories about aluminum hulls - grounded and ungrounded. Either seems to work OK so long as they are done properly.

Typically the bigger boats are grounded. I was just up at one of the best Dutch yards and happened to ask how they do this. They said that #1 the hull should only be grounded in one place. If you have multiple connections to the hull you can get current loops that will eat the hull. For that one connection they use a bi-metal flat bar - this is a bar with aluminum and steel exploded together which then bond at a molecular level. The weld the aluminum end to the hull and bolt the ground lug to the steel end.

On my own boat the hull is insulated (not connected in any way to the electrical system). The thing to watch out with this is when you are bolting equipment like electrical windless, the casing is usually grounded so you need to quite carefully insulate the mounting bolts so they don't contact the hull. The same is true with many VHF antennae.

As to the SSB, I would use the capacitors. They are cheap and easy, and no matter which theory you are using about hull grounding you don't want to create a new (dc) ground connection wherever the antenna tuner is mounted, and the caps allow you to avoid that.
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Old 02-03-2010, 03:12   #24
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just a short strap to the hull & I would bet the tuner has isolation on the earth connection internally by design.

regards Bill Goodward
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Old 02-03-2010, 04:23   #25
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just a short strap to the hull & I would bet the tuner has isolation on the earth connection internally by design.
Icom tuners do not have isolation nor does SEA. SGC tuner's do but they have a 220k resistor in parallel with the three .033 microfarad capacitors.

Eric
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Old 14-04-2010, 07:26   #26
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As mentioned above, there are two theories about aluminum hulls - grounded and ungrounded. Either seems to work OK so long as they are done properly.

Typically the bigger boats are grounded. I was just up at one of the best Dutch yards and happened to ask how they do this. They said that #1 the hull should only be grounded in one place. If you have multiple connections to the hull you can get current loops that will eat the hull. For that one connection they use a bi-metal flat bar - this is a bar with aluminum and steel exploded together which then bond at a molecular level. The weld the aluminum end to the hull and bolt the ground lug to the steel end.

On my own boat the hull is insulated (not connected in any way to the electrical system). The thing to watch out with this is when you are bolting equipment like electrical windless, the casing is usually grounded so you need to quite carefully insulate the mounting bolts so they don't contact the hull. The same is true with many VHF antennae.

As to the SSB, I would use the capacitors. They are cheap and easy, and no matter which theory you are using about hull grounding you don't want to create a new (dc) ground connection wherever the antenna tuner is mounted, and the caps allow you to avoid that.
Hi Evans,
this topic of grounding the Aluminium hull is such a debated point, but the way it was explained to me was:
1) It is almost impossible in real situations to keep the hull insulated from the battery. Just a touch of dirt on the engine mounts, graphite brush dirt from the alternators, temperature or pressure senders can connect the hull to the battery negative.
2) So you might as well connect the negative to the hull anyway, and then make sure that you do it in a place where it's dry (on a stringer out of the bilge) and easily looked at. If its dry, it actually can't form a battery anyway.
3) Using this point, one can easily monitor if there is current flowing through the hull from the negative then.
4) This also means that if a positive wire should touch the hull, this should trip the fuse (if it is a direct short) rather than just causing undetected corrosion.
5) Corrosion only occurs on the positivly charged side of a circuit, so the negative side can actually only cause plating onto the Aluminium.

I can't unnderstand why big boats would do this and not smaller vessels.
Alcan Marine have a recommendation to ground the hull here:

http://www.alcan-marine.com/Internet...%20chap.08.pdf

I'm having my Aluminium hull wired at the moment and I am having endless debated with my sparkie about these exact points!!!
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Old 14-04-2010, 07:58   #27
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I can't unnderstand why big boats would do this and not smaller vessels.
Alcan Marine have a recommendation to ground the hull here:
I asked Royal Huisman this question (Top Dutch builder of 100' aluminum sailboats). They said on small boats it was possible to properly flexible mount and isolate the small engines and motors. But on bigger boats (+100') it had proven practically impossible to maintain isolated mounts #1 because of the larger loads on this bigger gear and #2 because there is just simply so much stuff mounted on these boats that a mistake always got made somewhere.

On the even bigger boats (+300'), there is an 'active cathodic protection system' often used that monitors and actively maintains the hull potential.

This is all a matter of practical trade-offs. Either system is fine if done properly.
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Old 14-04-2010, 09:10   #28
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[QUOTE=estarzinger;436934]I asked Royal Huisman this question (Top Dutch builder of 100' aluminum sailboats). They said on small boats it was possible to properly flexible mount and isolate the small engines and motors. But on bigger boats (+100') it had proven practically impossible to maintain isolated mounts #1 because of the larger loads on this bigger gear and #2 because there is just simply so much stuff mounted on these boats that a mistake always got made somewhere.

On the even bigger boats (+300'), there is an 'active cathodic protection system' often used that monitors and actively maintains the hull potential.

This is all a matter of practical trade-offs. Either system is fine if done properly.[/QUOTE

Evans,
Have you ever tested to see if you actually have isolation between the negative and your hull?
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Old 14-04-2010, 09:49   #29
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I can only speak for steel navy vessels, but these are all grounded. Except for the batteries, power is all AC on these of course, and we do design the EMC filters in naval equipment to have low leakage currents to ground, (i.e., the ship hull).

Bill
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Old 16-04-2010, 16:41   #30
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[QUOTE=espresso;436982]
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Evans,
Have you ever tested to see if you actually have isolation between the negative and your hull?
Yes, I test every couple of months and whenever I install new equipment. There is no significant electrical connection. I had some trouble getting the windless instalation isolated - needed some G10 sleeves and pads - but finally got it.

But with dirt and salt around its impossible to achieve 'absolute isolation'. I clean the tops of the batteries and the bus bars when a 'leakage path' builds up.
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