Greenline 48 Stern Thruster Galvanic Corrosion

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WhippetGood

Member
Joined
May 9, 2024
Messages
7
Location
Roche Harbor, WA
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.

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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:
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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!
 

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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.
 
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