There are a number of resources available with information on grounding for sailboats, unfortunately, not all of it is consistent or useful. You will find in talking to people about their own grounding systems that there are many possible solutions and some common elements, but no single solution works best for all boats.
SGC’s book "HF User’s Guide", has an overview of the issues related to HF installation and operation and includes a section on grounds for boats. You can download a copy from our publications page.
The thing to be careful of with ANY RF ground advice you get, no matter who you get it from, is to be skeptical and be ready to test carefully to be sure that it really works ON YOUR BOAT. There are some accepted principles that are the basis for all successful installations:
Get as much metal into your RF ground as you can. On some boats the engine, keel, thru-hulls, and even copper plates are connected together into the RF ground.
Keep ground straps as short as possible. Connecting to your RF ground can be tricky. Often people will use a Volt-Ohmmeter to check their ground straps and declare them good because there is little or no resistance. However, the ground strap is not for DC current. An RF ground is carrying RF energy and a DC resistance to ground will not show if there is an impedance to ground at RF frequencies.
Be aware that RF conductivity is not the same as DC conductivity. Don’t confuse your safety ground (equipment chassis, reefer, etc) with your RF ground. The RF ground is required for the ANTENNA and is an RF circuit. Your safety ground on the DC circuits is NOT intended to handle RF. While many boats connect these together successfully, it can cause interference. RF energy carried through the DC ground may get into instrumentation or other equipment. It is normally best to have the RF and DC grounds be separate.
Dynaplates and other external devices meant to connect your RF ground to seawater can be very effective, but they will only be so if you maintain them properly. If you connect your RF ground to Dynaplates, thru-hulls, and other fittings, then you must inspect them regularly and CLEAN them regularly. Dynaplates should not be left more than 3 months without inspection and cleaning.
Inspect your connections regularly. A salt water environment is hard on any sort of electrical connections. Your RF ground and your antenna need to be inspected regularly because the Smartuner will hide slow changes in your antenna or ground system until it can no longer compensate for them. You may operate for a long time as your fittings corrode and then find that you can’t operate at all. It will seem sudden, but the problem grows gradually.
A useful test of the quality of your ground is to lay out several long wires on deck connected to the RF ground connection on your Smartuner. You might also throw a wire over the side to connect to seawater as well. When you remove these temporary wires, reconnect to your boat’s grounding system. The signal should get better. If it gets worse, your RF grounding system needs work.
Bonding a lot of metal in your boat together with short, direct copper straps can create a very suitable grounding system. The engine, fuel and water tanks, the keel, and any other piece of metal of significant size can be bonded together effectively. Copper foil or wire is usually best here.
Some boat owners install a large area of copper foil on the inside surface or their fiberglass hull and use this as an RF ground. It capacitively couples to the seawater and makes a generally excellent grounding system.
A leaded keel also makes an excellent RF ground. Depending on the construction of the hull, you may or may not be able to make a good connection to the keel bolts.
Overall, there are probably as many different ways to create a good RF ground as there are people giving advice about them. What works in one boat may or may not work well in another. Be prepared to adjust your RF grounding as you test it and remember that it will degrade over time, so you also need to be ready to maintain it.
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