Greenline 48 Stern Thruster Galvanic Corrosion

I have more to write about the 're-power' of the Greenline 48, but that's in another thread and happened years ago - so have to dig deep. However, the most recent 'excitment' is near to mind, and was just resolved - so I figure I would post about it in case anyone wants to check their stern thruster (for any boat I suppose!)

We purchased the boat used in 2018, and it's a 2016 Greenline 48. It came with Bow + Stern thrusters, which I have greatly enjoyed using. I came from a boat without any thrusters, and although I can run the boat without them (and had to, recently) there is nothing like going perfectly sideways or counteracting a strong wind or current with a smash of the button. Whatever the case, however you captain - this isn't about the use of the thrusters.

Anyway, after moving the boat up to San Juan Is. WA in 2021, we had more rain on the boat than it's ever seen. We had some minor leaks - likely screws through the teak into the fiberglass, or sealant failing around the window - but we had water in the bow cavity, which would make it's way back when cruising. Even with the bilge pumps, some water would make it back to the engine compartment, and then back to below the Lazerette where it filled a small area below the thruster motor inside the boat (the propulsion parts being outside the stern below water). This standing water contacted the positive because the Stern Thruster was installed upside down, such that the positive terminal was at the bottom.. we found this out after the Stern thruster failed. That's when we began to worry that the problems were bigger (they were) because the water was energized if the thruster had power and electricity was contacting the bolts connected through the hull to the external part of the thruster.. and escaping the boat.

The terminal bolt was powdered rust (it just broke when touched) and the through hull bolts were also completely corroded.



The bigger problem was the Shafts + Props. They were extensively damaged (the Zincs were fine!)

here is a picture of a piece of the shaft after extraction:

So..this was a slow then fast process. We never noticed because the stern thrusters are so rarely in operation AND we had to have some water in the area of concern. But once it happened, the amount of voltage must have been high (thrusters thrusting) and the damage was extensive. I'll post more pics and the fix in a followup post later.

Check your stern thruster!

cheers

Chris

A sundowner tug recently sunk at a marina here due to stern thruster galvanic failure , open hole into boat.

I have learned something today, after calling this Galvanic corrosion , it is actually “ stray current “ corrosion. Thanks to @boatpoker for that. More photos!

Thank you so much for sharing so much information about your experiences with your Greenline. I have am considering a barely used 2022 40 Hybrid that has had its stern thruster replaced already. After reading this thread and others about exploding LiPo batteries, I am going to walk away and/or do a lot more due diligence. I am too old for a project boat!

@KWSeawolf First I don't know what stories you have read about exploding batteries but most of the Lithium batteries used on boats are of a different composition and don't blow up and are extremely difficult to burn. Plenty of threads and research on "LFP" batteries.

I have recently purchased a GL33. I have owned a dozen boats and have found the Greenline construction to be sound.

Any boat can have issues but I would just engage a qualified surveyor and/or an electrician to inspect the boat.

LiPo's can catch fire if they begin to collapse. And I think it's when water (as in fire hose or sinking) hits the burning LiPo an explosion can occur. This is why I think it's so important to have a full-featured battery monitor on your LiPo BMS. By "full-featured", I mean one that is mounted at the helm and shows the voltage and resistance of each individual cell. Such a monitor also highlights any improperly large discrepancies between the charge levels of the cells. If a single cell begins to fail, it can be the source of a fire, if you continue to place demands on it. The early Greenlines were not delivered with such a monitor. I had to add mine. I saw in later years that a monitor was being delivered with Greenlines. Not sure about today. Regardless, I think Greenline is a fine boat (am biased, of course) and that any LiPo risk can be mitigated through proper use, care and monitoring.

Good feedback Scott. I don't think the 2013 Victron batteries im my new to me GL33 even have the ability to output cell details. That is one of several reasons I plan to replace them. More options are available now for batteries that provide the details on each cell.

READY said:

Good feedback Scott. I don't think the 2013 Victron batteries im my new to me GL33 even have the ability to output cell details. That is one of several reasons I plan to replace them. More options are available now for batteries that provide the details on each cell.

Click to expand...

It's usually the BMS (Battery Management System) that's outputting this cell status info. But then the BMS has to be able to get the info from the battery's cells. I don't know enough about how this is done by various manufacturers to even comment on this aspect.

No expert either but generally all off the shelf LFP batteries have an internal BMS to manage its cells. Some of the higher end batteries now output the cell data via Bluetooth or CANBUS. This will probably become standard in a year or two.

In a multi-battery situation there can be a second BMS that monitors and controls all the batteries. Example would be in my case the Victron Lynx Smart BMS. It is networked to the batteries, mppt solar controller and the inverter/charger. It is essentially a high level manager for the system. Until I replace my victron batteries I have no way to see the individual cell data. But the BMS in each battery is using that to balance the cells and is designed to prevent any issues as described.
Having a separate BMS to manage the bank is not necessarily a requirement but certainly is another level of protection. If nothing else it may extend the life of your batteries.

KWSeawolf said:

Thank you so much for sharing so much information about your experiences with your Greenline. I have am considering a barely used 2022 40 Hybrid that has had its stern thruster replaced already. After reading this thread and others about exploding LiPo batteries, I am going to walk away and/or do a lot more due diligence. I am too old for a project boat!

Click to expand...

To be clear, I love the layout and fit and finish - but I am disappointed by some of the issues I have found. Of course I have a relatively new house (2020) and there are dozens of things that were not correctly installed, completed, connected, or to code - so I think it's just the shape of things unfortunately.

As for doing diligence, we had a licenses surveyor and a very detailed report - but the issues with the stern thruster (as an example) were not discovered until much much later - and even though they existed in 2016, it took until 2023 (!) for it to really become an obvious problem. I think things like this can happen in a variety of of boat manufacturers.