Galvanic Isolation?

Hello everyone,
my wife Karin and I are new to this forum and would love to participate in this great way of sharing knowledge and experience.
Our IP 485 is presently on the hard in San Carles de la Rapita/Spain after a 6 month trip from Portugal along the coastline which was beautiful.
Technically, there is always something new...
Two months back our bowthruster failed with quite an audible bang and thus also blew it's 500A fuse.
After liftout we discovered that the bowthruster's gearbox had been completely eaten away by galvanic corrosion. Just like
swiss cheese... The anodes however were still in good shape ( more than 60% left) and the timespan of only six months during which that happened leeds me to believe that we must have a shorepower problem. Also our jib's boom as well as the housing of our windlass show paint flaking and blistering.The bowthruster gearbox has really been completely destroyed. I have added some pictures to show the extent. Our prop, a Variprop, however seems undamaged. I also have the impression, that all the bad vibes are happening towards the bow of our boat.
My question is: Is a galvanic isolator installed on all the 485's as a standard, and if so, where would that be? In my documentation, there is no mention of such an installation. Or could there be a completely different problem I have to deal with?
Thanks all for a response and best wishes from Germany,

Thomas,

You indeed have serious problems. I will share my thoughts.

First per your question, your boat does not have a galvanic isolator, instead it has an isolation transformer which I view as a better solution. With the isolation transformer the AC onboard the boat is independent from any issues with shore power, there are no direct electrical connections between onboard boat systems with energy transferred through magnetic fields between shore power and AC on the boat. This is covered in the owners manual from IP. For boats such as our IPs where a bonding system connects underwater metals (green wires) there is only one connection of the bonding system to the boats DC negative system at the bus bar in the engine compartment. This is also discussed in the owners manual.

Now, it is possible that an installer other than IP has added electronics, air conditioning, or other things not done at the IP factory and added new return paths defeating the bonding system or similarly made connections defeating the independence of the isolation transformer. Other owners have found such problems.

Looking at the bow thruster destruction and with you saying the the thruster anodes are "60% good", I would suspect that the bow thruster anodes did not have a good electrical bond to the metal they protect in the tunnel. This can happen by someone removing the thruster anodes and props, cleaning up the drive mechanism of all the barnacles/growth and then bottom painting the tunnel and the drive mechanism without carefully taping the thruster shafts and the area where the thruster anodes seat. If this area is painted the anodes become ineffective. Finally, the bow thruster is not supposed to have green wire connection to the bonding systems.

With the boat out of the water it is also a good time to perform a bonding test of all green wire connections. There is a process using a simple ohm meter to do this. I believe I have written about this here and it is documented in many places beyond just IPs. Out of time tonight.

good luck,

Harry Burns
IP 370-24 Two for the Roads.

Hello dear Harry,
thank you very much for your reply and thoughts.
Dismantling the gearbox and thereby also the adjoined props I had the impression that the anodes were a very tight fit to the shaft with no paint/antifouling in between. It also seems improbable that only by lack of good contact to the shaft (there are two anodes, so both would need to have had a poor contact) the erosion would be so quick and intense.
BUT two seasons ago, I had new installations made by a company in the Netherlands with whom I had a bagful of bad experiences...
- Two aircon sets and a solar panel array with charger were installed new. So I now have a feeling that I need to investigate the quality of that installation.
Would it not be wise to install a galvanic isolator in addition to the isolation transformer to protect our boat from stray currents originating from a "dirty" marina shore power environment?
Thanks again for your thoughts and all the best,

Thomas Hehz
IP 485 "Calypso"

Tom,

To answer your question, I do not believe that installing a galvanic isolator adds benefits for your boat. The IP installed isolation transformer provides all the protections of a galvanic isolator and more. Let me include one reference for isolation transformers that summarizes their benefits, they are not on our smaller IPs based upon weight and cost I expect - www.boatus.com/seaworthy/magazine/2015/j...ion-transformers.asp

It is possible when you had air conditioning installs done that the contractor was not familiar with boats with isolation transformers since you do not generally see them on boats less than 45 feet. Thus, they could have connected around the transformer, possibly the AC ground which would defeat the isolation provided by the transformer leading to susceptibility to corrosion issues.

Harry Burns
IP370-24 Two for the Roads

Hello dear Harry,
Thanks a bunch for your help. I read about the benefits of the magnetic transformation. Calypso is in Spain and we are presently at home in Germany. Will be on board in January and check out the A/C installation. Lots of repairs because of this...
Best regards and thanks again,
Tom

As a 485 owner, a very comprehensive analysis here. I would only comment to add that the O/P asks where the isolator is located. On mine (and I think most) it is located under the panel to the right of the chart table as you face forward (in other words starboard side). I think most are Charleston isolators BUT I think some 485s did not have these factory installed and so possibly have nothing.

I am in the UK so good to hear of another 485 this side of the Pond. So sorry to hear of your experience.