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Old 21-06-2015, 18:58   #16
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Re: Steel boat ground

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Pelagic, when you say to a common ground frame, I presume you mean a frame that is also connected to the hull?
)
Yes a structural transverse frame that has been drilled to tightly take a long bolt that captures all the bonding cables. If I remember correctly there are about 6 cables connected to this ground point making all potentials common.
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Old 21-06-2015, 19:05   #17
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Re: Steel boat ground

He is a pic of the old engine mount rail. Well, the top of the angle anyway.

You can see the small holes for the "hanger " bolts, where the mounts were suspended down through the angle. The rubber bit had the normal two mounting bolts, and it sat in a round "cup". There was no play, the engine sat hard on the cups. Adjustment was by the "hanger" bolts.

What I find amazing is the engine was rebuilt at a reputable yard just befor I bought the boat. Why this was never addressed is beyond me.
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Old 21-06-2015, 19:07   #18
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Re: Steel boat ground

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Originally Posted by Pelagic View Post
Yes a structural transverse frame that has been drilled to tightly take a long bolt that captures all the bonding cables. If I remember correctly there are about 6 cables connected to this ground point making all potentials common.
Thanks.
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Old 22-06-2015, 01:42   #19
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Re: Steel boat ground

If galvanic or electrolytic corrosion in metal hulls is caused by inappropriate current flows then isolating all current sources from the hull would appear to be an effective counter to the corrosion problem.

I would certainly want to know the reason why you have low ohms readings between potential current sources and the hull.

Apparently having excess anodes on a steel hull will cause problems with the coatings.

If your underwater coatings were perfectly waterproof and isolated the hull metal from the water your anodes would last a long time, rapid depletion is indicative of relatively high current flows somewhere either from a large amount of exposed anode surface area and poor hull immersion fluid isolation or from some other current source.
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Old 22-06-2015, 04:34   #20
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Re: Steel boat ground

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If your underwater coatings were perfectly waterproof and isolated the hull metal from the water your anodes would last a long time, rapid depletion is indicative of relatively high current flows somewhere either from a large amount of exposed anode surface area and poor hull immersion fluid isolation or from some other current source.
That is why they are called 'sacrificial anodes' and it is important that they are well-grounded to the steel hull where bolted on to work properly.

Many yards mistakenly bottom paint over the studs rather than taping them to stay clean.

Stray currents are often more from poor marina wiring than anything else
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Old 22-06-2015, 05:40   #21
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Re: Steel boat ground

I think,if one is trying to keep the engine isolated from the hull,one has to remember the control cables [speed and shift] as they connect the engine to the binnacle and that to the steering cables and they to the rudder etc, I once had a steel boat and insulated the cable connections with plastic bushings.
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Old 22-06-2015, 06:13   #22
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Re: Steel boat ground

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I think,if one is trying to keep the engine isolated from the hull,one has to remember the control cables [speed and shift] as they connect the engine to the binnacle and that to the steering cables and they to the rudder etc, I once had a steel boat and insulated the cable connections with plastic bushings.
The idea is not to keep the engine isolated from the hull. Rather to keep the engines DC ground isolated from the hull.

A typical engine only has a few DC connections:

1. The alternator. Many marine alternators are isolated anyway, so simply removing the ground strap and connecting this to the battery negative fixes the problem.

2. Oil and water senders. Isolated 2 pole senders are not expensive and a simple screw in replacement.

3. Starter motor. This is harder. Isolated starters are rare. The simple solution is to ground the engine to the DC negative for the few seconds the starter is operating. This can be done simply and automatically.

With these steps the DC negative is no longer connected to the engine block and therefore DC negative is not connected to the hull or to seawater. There is no need isolate the control cables unless you want to reduce the local contact of dissimilar metals.
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Old 22-06-2015, 12:49   #23
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Re: Steel boat ground

I also have a steel boat where the whole vessel is Isolated ground or negative floating DC supply (e.g. the negative is not connected to sea water). Luckily the engine (Perkins 4236M) was designed to be isolated from the ground

I have a simple test circuit in place to tell me if things are not correct.

If you want a copy of the circuit diagram, PM me with your email address as the only electronic copy I have is in WORD and it is too big to attach to this forum

I have found things like the ICOM 802 SSB grounds itself to the hull even with the head set switched off (not mentioned in the manual) and that some USA VHF aerials ground to the mast and a piece of metal swarf got into a coax connector
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Old 22-06-2015, 16:05   #24
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Re: Steel boat ground

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I have a simple test circuit in place to tell me if things are not correct.

If you want a copy of the circuit diagram, PM me with your email address as the only electronic copy I have is in WORD and it is too big to attach to this forum

See attached document, I worked out how to shrink it

Page 1 Notes on the circuit diagram
Page 2 Bad picture of the diagram which was drawn in in a Pub in the UK

Hope it makes sense
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File Type: doc EARTH FAULT TEST CIRCUIT v1.0.doc (196.0 KB, 50 views)
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Old 27-06-2015, 17:51   #25
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Re: Steel boat ground

I found the low ohmic ground connection. It's the radio antenna. The ground passes right through the radios, remove the coax, the ground goes away.

That antenna has been there a loooong time.

Don't know what to do about it. Put a capacitor across the shield connection on the back of the radio?

Went to a large local ham outlet, they were no help. "Go to West Marine or build it yourself."

Looks like I'll just tolerate it for now.

I'll be putting in the proper hull ground if the current deluge ever stops.
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Old 28-06-2015, 00:23   #26
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Re: Steel boat ground

I'm going to go out on a limb and say if there is no current flowing to the hull through the coax cable you don't have to worry about it being grounded.


Most of the VHF marine antennas I know of do not need to be grounded to the hull to work. The reason for grounding them is for lightning protection. If you wanted to make sure remove the antenna from the hull. Keep it vertical and measure the SWR if they are under 2:1 you're OK.
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Old 28-06-2015, 01:59   #27
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Re: Steel boat ground

Icom makes an accessory capacitor set for their HF radios which just connects to the earth terminal on the radio or tuner with a flying lead for connection to the hull. This provides a signal earth for the HF without providing a current path for DC. All other earths are disconnected.
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Old 28-06-2015, 04:56   #28
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Re: Steel boat ground

Greetings and welcome aboard the CF, Doodlebug.
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Old 28-06-2015, 08:54   #29
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Re: Steel boat ground

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Icom makes an accessory capacitor set for their HF radios which just connects to the earth terminal on the radio or tuner with a flying lead for connection to the hull. This provides a signal earth for the HF without providing a current path for DC. All other earths are disconnected.
Looking for stray grounds on a steel boat

I have found things like the ICOM 802 SSB grounds itself to the hull (not mentioned in the manual) . Be aware that the set is powered UP even when the switch on the head set is off.

The ground wire sends RF and 12V dc to the grounding point so I have fitted a double throw, double pole switch to stop this happening when the headset is switched off and also I bought, whilst I was in the UK, a grounding isolation bridge which fits between the ATU ground connection and the ground on the hull which stops 12V going to the hull.

The grounding isolation bridge is, I suspect, the same as the Icom capacitor mentioned above

I have also found some USA VHF aerials ground to the mast and that a Wirie will also ground through the connection bracket
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Old 03-07-2015, 20:03   #30
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Re: Steel boat ground

The small boat has a VHF only.

Our big boat, which I haven't looked at yet, has a ICOM VHF, SSB, and I just installed a Wirie.

Lots of fun.
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