The Dynaplate is nothing new, they've been around for years. In the days of LORAN C the Dynaplate was a staple as part of any complete installation to ensure a good solid ground for the system and keep RFI noise at a minimum. Today many people still have a Dynaplate installed for grounding purposes, but the truth is not that many people really understand the design premise surrounding this seemingly simple little plate. I think its safe to say that the majority of boat owners just see the plate, think nothing of it and surely don't consider it as an item that requires periodic maintenance. In the photo below you see a new Dynaplate:


The Dynaplate is made of what is known as sintered bronze, think of the plate as a metallic 'sponge". Looked at under a microscope it will look like thousands of bronze colored BB's all contected together. When new the sintered bronze is extremely porous and will absorb water, which is the exact premise for its function. You see grounding requires a specified surface area of conducting metal to the ground, whether it be on land under your lawn, or in the water attached to your boat specified values are given for effective ground surface area. To that end, the manufacturer, Guest, recommends three different sized Dynaplates for three different uses. The basic model is 6"X2"X1/2" and is suggested for basic electrical bonding purposes, whereby all of your underwater metals are tied together via a bonding system on your boat. Bonding is a topic for another entry here and i'll certainly get to it at a later date.


The second size Guest offers is 12"X3"X1/2" and is recommended for LORAN C use and to serve as a radio frequency ground. The largest plate is 18"X6"X1/2" and is recommended as a suffieient ground plane for SSB or Ham radio use.


The simple idea here is that since the plate is absorbing water it is actually exposing a much larger surface area to the ground than the plate's actual physical dimensions imply. For example, with the largest plate mentioned above, the manufacturer claims it provides the equivalent of 12 square feet of ground surface area.


In theory this is logical, sound thinking, but marine life realities kick in here and that's where the maintenance side of the Dynaplate comes into play. You can clearly see the DO NOT PAINT labeling on the above plate, yet we see many that end up with a nice liberal coat of anti-fouling bottom paint smeared all over them. Once that's been done, the plate is effectively useless. The sintered bronze will do just what it's supposed to in that event, absorb the paint, blocking all of the pores in the metal and reducing the exposed surface area. I've seen some where the boat owner realized the error in their ways and tried to get all the bottom paint off the plate with acetone or similar solvent. Trust me, its too late, all you do when you try to clean the plate at this point is drive the paint a little further below the surface. The pores in the metal are forever blocked. You need a new plate. In the photo below, you see a plate that has had more usual treatment over the years, as in no maintenance.



The plate above can be saved. Its going to need some scraping to get the barnacles off and then a good scrubbing with a wire brush and some bleach. Scrub until you get it back to its original bronze color. This should be done annually if you are going to rely on a Dynaplate to provide adequate grounding surface area under your boat.

Written by: Ed Sherman
Ed Sherman is a regular contributor to boats.com, as well as to Professional Boatbuilder and Cruising World, where he previously was electronics editor. He also is the curriculum director for the American Boat and Yacht Council. Previously, Ed was chairman of the Marine Technology Department at the New England Institute of Technology. Ed’s blog posts appear courtesy of his website, EdsBoatTips.