Bow thruster is eating zincs, one per month.

[LN-RTP]

Something is going on. Not sure what.
Had the boat 7 months. Did not pay attention to the small thruster sinc under the foot of my 4 HP Vetus thruster until I hauled the boat for a bottom job.
Copper based paint on the bronze foot during the haul out February 2018.
6 weeks later I dove on the boat in the Keys, zinc gone, the SS screw still there.
Installed new zinc then and there.
Checked it 5 weeks later, almost gone, installed another one yet again.
Prop and rudder zincs ok, no stray electricity on the canal. (Other boats have no zinc problem)
Have a surveyer friend come by later this week. Hopefully he has some ideas.
Have to look at other things to, stray power to thruster? Pull main breaker rather than just the On-Off button? All battery switches off? No shore power?
Anybody else had a similar problem with a Vetus thruster?
(Previous owner had the boat on a lift for 16 years, zinc was no factor then)

 

[Last Tango]

You say there is no stray power in your Canal.

Then you have stray power / ground fault / open circuit on your thruster

 

[LN-RTP]

You say there is no stray power in your Canal.

Then you have stray power / ground fault / open circuit on your thruster

Yeah, must be.
Will start to take things apart, measure etc.
First thing to check will probably be the on-off button next to the joy stick.
Any better ideas?

 

[gaston]

Yeah, must be.
Will start to take things apart, measure etc.
First thing to check will probably be the on-off button next to the joy stick.
Any better ideas?

Have a look at leakage at the solenoid close to the thruster

 

[LN-RTP]

Have a look at leakage at the solenoid close to the thruster

Yeah, that is a good one.
Wishing for easy fix.

 

[kchace]

I think you're on the right track. It WILL be an easy fix once the cause is found.

Ken

 

[Nopistn]

If you can't find anything try disconnecting power to the thruster for a month and see if there are any changes.

 

[LN-RTP]

If you can't find anything try disconnecting power to the thruster for a month and see if there are any changes.

Yeah, good idea but I use the tub as much as I can, every few days or every few weeks.
Opened the main breaker today, in case that will make a difference, but will come back with my expert electrician buddy and measure every contact and every terminal shortly.

 

[Delta Tango]

Hi
put your multi meter on the thruster - your looking for current on the outside of the electric motor. Connect to the main positive and use the negative of your meter to touch various parts of the thruster to see if you have voltage; find voltage and you have found your problem. Bow Thrusters are insulated on both the positive and negative side of things so if you have stray current you have a problem. If you have bonded your thruster to the ships negative I would disconnect it, its not needed and a stray current will always seek the easiest path out - possibly your thruster and not the other anodes on the vessel.

 

[LN-RTP]

Hi
put your multi meter on the thruster - your looking for current on the outside of the electric motor. Connect to the main positive and use the negative of your meter to touch various parts of the thruster to see if you have voltage; find voltage and you have found your problem. Bow Thrusters are insulated on both the positive and negative side of things so if you have stray current you have a problem. If you have bonded your thruster to the ships negative I would disconnect it, its not needed and a stray current will always seek the easiest path out - possibly your thruster and not the other anodes on the vessel.

Ok, that sounds like good advice.
Tried something similar 2 days ago, but realized it is a 2-man job: 1 to bend the protective plastic panel to the side and away from the contacts, then another to operate the multi meter.
In the meantime I disconnected shore power, turned the thruster breaker to OFF and both battery switches to OFF.
Should be a dead boat now and when I measure the thruster contacts as you suggested, will turn one switch on at a time. Will also look for a bonding wire while I am down in the hole anyways. Air Condition compressor is almost on top of the thruster so it is a bit tight there. (Will check if the AC is touching the thruster housing or contacts. )

 

[CharlieJ]

I do not believe you have a stray current problem. Stray current would have taken out your thruster anodes and then taken out the propeller, shaft and anything else metal. And very quickly.

If the thruster is bonded to the rest of the boat's underwater metal components then the thruster anode is being challenged to produce more cathodic protection current than it was designed for.

1. If there is bonding between your underwater metal components and the thruster, break that connection.
2. If there is no bonding, check for continuity between the motor housing and the B- terminal. If there is continuity than you have a motor insulation problem.

 

[LN-RTP]

I do not believe you have a stray current problem. Stray current would have taken out your thruster anodes and then taken out the propeller, shaft and anything else metal. And very quickly.

If the thruster is bonded to the rest of the boat's underwater metal components then the thruster anode is being challenged to produce more cathodic protection current than it was designed for.

1. If there is bonding between your underwater metal components and the thruster, break that connection.
2. If there is no bonding, check for continuity between the motor housing and the B- terminal. If there is continuity than you have a motor insulation problem.

Thanks Charlie:
Will do that in a day or two.
Been sidetracked with other stuff. (Had an insurance survey yesterday, then today fixing stuff the surveyor found, etc)

Thanks for all comments and ideas. My first boat with a bow thruster. The prop on this one is plastic by the way, the anode is under the tail, rather small: Vetus BF 50 I believe is the model number, 4 HP.
Boat is an Albin 28TE, they all came with the same bow thruster, nobody on the Albin forum has experienced what I have, just lucky I guess..

 

[LN-RTP]

Now measured for current on the bow thruster:
Found a few micro Volts when the power is on: Between the main positive contact and metal pieces on the thruster, but very little. Get 10 times as much measuring between my thumbs.
Also found a green bonding wire on the thruster and it seems to lead aft while also bonding the thru hulls and ending at the metal rudder stock.
Yes, there is a 2 big zinc anodes on the rudder and they seem to last forever.
Sooo, that there seems to be the problem. I should disconnect the thruster from the bonding circuit and let it work as an independent contractor...?
Any potential negatives to that plan?

 

[bglad]

The thruster and metal parts between should be connected to the bar zincs at the stern. if that connection is broken somewhere the thruster zinc may be protecting strainers and thru-hulls too. If you have a long wire check continuity between the thruster and bar zincs. If it is poor solving that problem should get the bar zincs doing the work again instead of the little one on the thruster.

This may be easier said than done afloat since sitting in water will give some connection result. Best done on the hard. You could also track down the green wire and make sure the chain is not broken somewhere.

 

[LN-RTP]

The thruster and metal parts between should be connected to the bar zincs at the stern. if that connection is broken somewhere the thruster zinc may be protecting strainers and thru-hulls too. If you have a long wire check continuity between the thruster and bar zincs. If it is poor solving that problem should get the bar zincs doing the work again instead of the little one on the thruster.

This may be easier said than done afloat since sitting in water will give some connection result. Best done on the hard. You could also track down the green wire and make sure the chain is not broken somewhere.

Not sure this boat has a bar sink, but rather 2 noon shaped zincs on the rudder.
Yes, will be tracing the green wires and look for a break or a bad connection.
Found 2 green wires in the transom that is cut clean off, but they seem to be in addition or parallel to the regular green bonding wire.
Thx.