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Old 06-05-2019, 01:36 PM   #1
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Dynaplate issues

The photos attached to this post show the Dynaplate installation. The exterior photos were taken after the hull had been pressure washed during the first haul out since purchasing the vessel. White gelcoat is visible in places around the Dynaplate. The vessel is not equipped with a SSB or HAM radio. There are no lighting rods installed on the vessel. The vessel has a galvanic isolator installed. There is a large anode installed on the hull near the transom with an attached green ground wire from the rudder post. The green ground wires attached to the Dynaplate connect four thru hull fittings and then to the engine block. There is no wire connecting the Dynaplate to the negative post of the battery.
I have the following questions:
1. What caused the loss of bottom paint around the Dynaplate?
2. Why was the Dynaplate installed instead of connecting all of the green grounding wires to the transom anode?
3. Is the Dynaplate wired correctly?
4. What should be done to prevent a repeat of the bottom paint loss around the Dynaplate?
Thanks
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Old 06-05-2019, 01:54 PM   #2
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I would ditch the Dynaplate. I think that the paint loss is due to "over zincing". Dynaplates are used as an SSB ground or a lightning dissipation ground, but there is a lot of skepticism about the latter.

Looks like you may not have a prop shaft zinc unless there is one on the end of the prop that I can't see in the pic. With or without the Dynaplate you need to protect the prop. That rudder zinc might help but most boats use both rudder and prop shaft or end of prop zincs. And you need continuity between the prop and any zincs.

So if there is no way to get a zinc on it, make sure that the prop shaft continuity with the engine block is good and depend on the transom and rudder zinc to protect it. If no continuity then add a shaft brush and a bonding wire to the system. Make sure that the bonding system is continuous with connections to the engine block, thruhulls, rudder and prop shaft.

David
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Old 06-05-2019, 02:23 PM   #3
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Prop shaft anode

Quote:
Originally Posted by djmarchand View Post
I would ditch the Dynaplate. I think that the paint loss is due to "over zincing". Dynaplates are used as an SSB ground or a lightning dissipation ground, but there is a lot of skepticism about the latter.

Looks like you may not have a prop shaft zinc unless there is one on the end of the prop that I can't see in the pic. With or without the Dynaplate you need to protect the prop. That rudder zinc might help but most boats use both rudder and prop shaft or end of prop zincs. And you need continuity between the prop and any zincs.

So if there is no way to get a zinc on it, make sure that the prop shaft continuity with the engine block is good and depend on the transom and rudder zinc to protect it. If no continuity then add a shaft brush and a bonding wire to the system. Make sure that the bonding system is continuous with connections to the engine block, thruhulls, rudder and prop shaft.

David
David:
The attached photo shows an aluminum collar anode on the prop shaft which is difficult to see on the other photo.
Does your recommendation to "... ditch the Dynaplate" mean just disconnect the green grounding wires or to remove the Dynaplate from the hull?
Thanks
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Old 06-05-2019, 02:38 PM   #4
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Well for now, remove the bonding wires. Then with the next haul out, consider converting it to a thru hull if that will be useful or filling and glassing it over.


When you remove the wires, keep them connected inside for continuity.

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Old 06-05-2019, 02:40 PM   #5
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Generally the Dynaplate was used for SSBs and Loran that are all but rare. If you still have an SSB...it's debatable to keep it. if not I would get rid of it and patch the hole(s).



Grounding wires should not be from item to item...but have more centralized buss bars or a main strap.
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Old 06-07-2019, 12:26 PM   #6
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Ditto what psneeld said about centralizing the ground wires.



If you disconnect all connections to the Dynaplate then it will no longer have any effect into any other part of the system. You could then defer any decision on what to do with it.


Considering you only have the one hull anode and one shaft anode, I'm not convinced that the bottom paint loss is due to over-zincing. There are a few other possible causes, one is galvanic corrosion caused at a marina through the shared ground. Of course the galvanic isolator should prevent this. Another possible cause is stray current corrosion within the sphere of your own boat. One other thing to check is to make sure you have very low resistance (Like 1 ohm or less) between ALL underwater metals AND the transom zinc.



Unless you have shaft brushes, the prop, propshaft and its zinc can be considered an isolated assembly. (Because electrically it probably is)


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Old 06-07-2019, 12:37 PM   #7
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I also noticed the way the ground wires are attached to what looks like an engine bracket. One wire is under the bracket and 2 wires are on top - on the same bolt. Another wire is in a different location on the same bracket. This is a sure recipe to have poor conductivity between one or more wires. These wires should either come together on one stud, or be installed on a purpose made buss bar which then needs a very good connection to the engine block or centralized boat ground.



I just realized you said there is a green wire from the transom anode to the rudder post, but you didn't mention any other wires there? Both of these items MUST connect to all of your other underwater metal grounds and the total measured resistance between any 2 of those points should be 1 ohm max.


Ken
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Old 06-07-2019, 01:17 PM   #8
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Quote:
Originally Posted by kchace View Post
Ditto what psneeld said about centralizing the ground wires.



If you disconnect all connections to the Dynaplate then it will no longer have any effect into any other part of the system. You could then defer any decision on what to do with it.


Considering you only have the one hull anode and one shaft anode, I'm not convinced that the bottom paint loss is due to over-zincing. There are a few other possible causes, one is galvanic corrosion caused at a marina through the shared ground. Of course the galvanic isolator should prevent this. Another possible cause is stray current corrosion within the sphere of your own boat. One other thing to check is to make sure you have very low resistance (Like 1 ohm or less) between ALL underwater metals AND the transom zinc.



Unless you have shaft brushes, the prop, propshaft and its zinc can be considered an isolated assembly. (Because electrically it probably is)


Ken
Ken:
I am considering the following causes for the loss of bottom paint around the Dynaplate:
1. Internal DC stray current corrosion
2. External DC stray current corrosion
3. Galvanic corrosion from faulty installation and/or failed connections of the bonding system
4. Failure of the galvanic isolator
5. Failure of the gel coat barrier coat
Am I correct to assume that failure of the galvanic isolator would expose the vessel to external DC stray current corrosion? I have decided to disconnect all the bonding wires from the Dynaplate. There is a prop shaft brush connected to the engine block but it is not connected to the Dynaplate or the transom anode. The engine block is connected to the Dynaplate.
Thanks
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Old 06-07-2019, 01:28 PM   #9
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Quote:
Originally Posted by kchace View Post
I also noticed the way the ground wires are attached to what looks like an engine bracket. One wire is under the bracket and 2 wires are on top - on the same bolt. Another wire is in a different location on the same bracket. This is a sure recipe to have poor conductivity between one or more wires. These wires should either come together on one stud, or be installed on a purpose made buss bar which then needs a very good connection to the engine block or centralized boat ground.



I just realized you said there is a green wire from the transom anode to the rudder post, but you didn't mention any other wires there? Both of these items MUST connect to all of your other underwater metal grounds and the total measured resistance between any 2 of those points should be 1 ohm max.


Ken
Ken:
I have noticed the same issue with the bonding wires on the engine block. Correcting the wires going to the engine block is on my "To do" list.
There are no other bonding wires connected to the transom anode. My current plan is to disconnect the bonding wires from the Dynaplate and connect all of the bonding wires to the transom anode.
Thanks
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Old 06-07-2019, 06:44 PM   #10
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Sounds good as long as there is also a connection to the main boat ground.
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Old 06-07-2019, 06:49 PM   #11
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Quote:
Originally Posted by DLETF View Post
Ken:
I am considering the following causes for the loss of bottom paint around the Dynaplate:
1. Internal DC stray current corrosion
2. External DC stray current corrosion
3. Galvanic corrosion from faulty installation and/or failed connections of the bonding system
4. Failure of the galvanic isolator
5. Failure of the gel coat barrier coat
Am I correct to assume that failure of the galvanic isolator would expose the vessel to external DC stray current corrosion? I have decided to disconnect all the bonding wires from the Dynaplate. There is a prop shaft brush connected to the engine block but it is not connected to the Dynaplate or the transom anode. The engine block is connected to the Dynaplate.
Thanks
Yes. There are 2 ways a galvanic isolator can fail - open or shorted. If it fails open, you lose your safety ground connection to the dock. If it fails shorted, it's like there is just a piece of wire there and you would not be protected from adjacent boats or wiring causing galvanic currents through your shore power connection. If you have a meter with a diode function you can easily test it. If you get to that point, ask and I'd be happy to detail it.

Oh, and just for fun, it's possible for half of it to fail. This would also show up with a meter test.

Ken
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Old 06-07-2019, 06:58 PM   #12
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I believe the dynaplate is copper or bronze or such. If it was the only thing connected to your transom zinc that may explain the paint loss around the plate.
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Old 06-07-2019, 07:22 PM   #13
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Quote:
Originally Posted by kchace View Post
I believe the dynaplate is copper or bronze or such. If it was the only thing connected to your transom zinc that may explain the paint loss around the plate.
Ken:
You are correct that the Dynaplate is made of bronze; tiny bronze spheres bonded together by heat & pressure into a porous plate. However, there is no connection between the Dynaplate & the transom anode.
Thanks
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