martinpayne
New Member
Shipping August Sun to New Zealand from the US
Posts: 5
Jeanneau Model: Sun Odyssey
Yacht Name: August Sun
Home Port: Kemah
Country: USA
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Post by martinpayne on Jun 16, 2014 18:48:43 GMT
Hi We have a 2000 SO 40’ and are currently in the Sea of Abaco in the Bahamas. We had a SSB (ICOM M802 + ST 140 auto tuner) installed before we left Florida, but have had very poor transmission of signals. We used a KISS, but without much success and I have now been advised that I now need to install 3” copper strap back to the auto tuner.
My question is:
On the aft end of the keel attachment to the hull, there is a plate with 4 bolts (also, there are 6 bolts/studs which are evident as the primary keel attachment). Can I drill and tap into this plate and attach the copper strap? Also – what is the purpose of the plate? Martin & Kathy
‘August Sun’ Marsh Harbour Bahamas
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Post by so40gtb on Jun 17, 2014 0:19:19 GMT
I believe that the bolts and plate you refer to are the aft attachment of the keel to the hull. Other than the usual issues with drilling into thick steel, I would expect that you could attach the copper strap there. Two cautions, though. The concept is to attach the strap to a large metal surface which always lies underwater. First, if the keel is encapsulated in epoxy paint, you will not have conductivity between the sea and the keel and this may not work (the internal grounding on the 2000 SO40 uses the propeller skeg as the sea ground point) [however, the area of the keel and the thin coat of epoxy are effectively a large capacitor, so it might well work]. Second, since the plate and copper strap both lie in the bilge, corrosion is likely and that will limit the effective conductivity between them, unless the attachment is sealed to make it waterproof.
--Karl
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Post by Xlnt on Jun 17, 2014 8:33:05 GMT
In my boat, the copperplate is attached to a separate groundplate mounted aft of the keel. Similar to this one: GroundplateRgds XLNT
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Post by Trevor on Jun 17, 2014 10:19:06 GMT
Hello martinpayne,
What a great subject but it does get a little involved. An RF ground is a slightly different thing to a DC ground and when using HF that is the ground we are concerned with. If you don't have an earth plate the keel can be used.
Let me explain after a few calculations. Let's assume the keel has 4 square meters of surface area. That would be about right I think for my boat by the time the bulb at the bottom of the keel is taken into account. Let's assume the antifoul thickness is 0.25mm. That gives a capacitance of about 0.15 microfarad. If we work out the capacitive reactance (AC resistance) at the lowest frequency ( say 2524 kHz) it is about 0.4 ohm. So the RF resistance to earth for the keel when it is totally insulated at the lowest frequency is about half an ohm.
If you connect that directly to the earth on your radio, you are begging for DC leakage current to flow. DC leakage currents mean corrosion. To stop that DC current you need a capacitor (or several in parallel) between the earth of the radio to the connection point on the keel. Lets say we use a few 1 microfard capacitors soldered across an air gap in the copper strap. The copper strap is used because the RF signal travels on the outside of the conductor so a wide copper strap has greater surface area equaling lower Rf resistance. I would simply connect that to the keel bolt nut with a stainless hose clip.
So now we have a good RF earth and no DC connection to the keel. Perfect.
I hope this helps.
Regards,
Trevor
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Post by windward54 on Jun 17, 2014 15:13:24 GMT
And I'd check the system a little more. I use the KISS on my 49DS and it does a really great job. I've used foil to a thru hull on my last boat, and had good sucess with that as well. My signal reports were as good on these two grounding ways as those boats that used a dynaplate. The tuner should see the KISS as they are connected together. I've heard of people being told to install a copper strip to the transceiver unit, but that isn't an issue as the two units are connected via the control cable.
You could try running a copper strip from the tuner to a thru hull that is always under water to see if the signal improves. Also check the GTO-15 feed line, as they can wick moisture easily if not covered.
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Post by On y va on Jun 17, 2014 16:33:29 GMT
NEVER EVER connect any grounding to your keel or keel bolts.
The plate at the back of the keel you are referring too (with the 4 bolts), is nothing more than a large washer. It devides the pressures of the loads on the keel and bolts.
Just install a correctly sized grounding plate as suggested by XLNT. Larger better than smaller.
Marco
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Post by chuckr on Jun 23, 2014 6:56:24 GMT
i can only tell you what worked for us on a 2000 Jeanneau DS40 - same rig - icom 802 and at140 -- we ran the copper stripping from the tuner at the back of the boat along the bottom of the boat to the keel boats and used stainless steel hose clamps and attached it to the keel bolts - no drilling - then we ran the same stripping to the radio from the keel boats
we have a gam electronics antenna and we have been told many times we had one of the best radios in the caribbean -- in our atlantic crossing we had good reception for gribs ect almost all the way to horta from halifx or montreal or a station in fla --
it is simple and some experts say it does not work but we beg to differ
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Post by Xantia on Aug 30, 2014 21:34:39 GMT
I have used the keel as a RF ground on our 42DS and can confirm that it does work. The heads of the keel bolts are never wet and show no signs of corrosion, even though I just used a hose clamp around the head of the bolt to attach the strap. But I have had even better performance by HF radio on 7 MHz using a wire dipole made from electrical flex and hauled up the mast as an inverted V using the spinnaker halyard. It is especially useful for single hop short skip of a few hundred kilometres and has the huge advantage of keeping induced currents out of the boat electrics, so the LED lights don't flash and the battery low voltage warning isn't triggered. On top of that the antenna is well away from people.
It is not a convenient antenna though, taking a few minutes to raise. Low cost and no holes in the boat are its virtues.
Cheers Ian
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Post by Trevor on Aug 30, 2014 23:09:35 GMT
Hello Xantia, Sounds like a good solution using the "inverted v". I am imagining the centre of the "V" (where the halyard attaches) has the coaxial feed line attached so assume that is simply fed through a hatch or companionway. I guess you could get the length right for 7Mhz which would be about 66ft for the entire length so that would be quite efficient and not make the ATU work too hard. I am a little concerned at the direct connection to the keel however so please stick with me while I make an attempt (probably very badly) to explain. Imagine two pieces of dissimilar metal in a glass of salt water. Let's imagine the two metals are brass and iron and they are in the glass of water with their ends sticking up above the water level. Each metal has an electrochemical property called an electrode potential and that can be researched by looking at a table called the Anodic Index. Those two pieces of metal can sit there indefinitely and not have any current flow between them. As soon as I connect the top of them with a piece of copper wire, a current flows through the wire and an identical current flows through the salt water. We have just made a crude form of battery because that is exactly how a battery works. One of those pieces of metal will be regarded as an "anode" and one as a "cathode". The anode piece will be eaten away and parts of it deposited on the cathodic piece. In a vessel that has all of the below water parts "bonded" the connecting wire goes back to a purposely placed anode. That zinc anode is the metal at the lowest end of the Anodic index and is always eaten first, hence protecting the expensive metal bits at the higher end of the anodic index. Jeanneau do not "bond" their below water fittings so I am happy that my metal bits are simply sitting in salt water not connected to anything. The corrosion that could occur by directly connecting DC or AC ground to the keel may not happen anywhere near the keel. It may happen underwater somewhere completely different to the keel. That is why in a previous post, I suggested capacitors (they pass AC current but block DC current) be used in series with the copper strap to eliminate the dissimilar metal corrosion currents that could occur if they were simply connected together. I am not suggesting this is definitely happening but I am suggesting it could be happening. By putting capacitors in series with the ground connection to the keel that possibility is eliminated but the Radio Frequency ground is still maintained. Sorry for the long post but thought it was worth discussing. Regards, Trevor
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