Bow/Stern Thruster Warning

Yesterday our bow thruster started acting up as we were leaving a side tie on a tight dock with some wind (with multiple boats rafted behind us, and very shallow water in front). As I was moving the bow out with the thruster and stern with propwalk, the thruster kept running after I let go of the joystick. I tried to shut it off with the button at the helm and also tried switching direction with the joystick, but continued to run at full speed. I made a quick dash to the forward berth to shut off the main thruster switch/breaker. All turned out fine, although i had to do a ton of back and fill to get us turned around (we were facing shore and it was very shallow in front of us). I've spoken with the company (Imtra for our Sidepower unit) and they gave me some very good troubleshooting advice. It will likely be either the main switch at the helm, the control box on the motor or the solenoid (welded contact). I will find out when I'm back at the boat next weekend.

Moral of the story is make certain you have a seperate shutdown/breaker for the thruster and know where it is located. In doing some internet troubleshooting before calling the company, I was supprised to find examples of this happening where there was no seperate shutdown. In one instance, the owner had to shutdown the entire electric system at the main breaker, which meant his engine also shutdown. Talking with some friends later in the day, I was surprised to find that the ones with thrusters had no idea where the the main switch is located on their boats. If I hadn't been able to shut it down right away, it would have probably spun us into the dock or another boat.

Got back to the marina and resorted back to the way we got our old sailboat into the slip - spring line on the end piling. Anyway, just a reminder to make sure you have a main shutoff for your thruster and know where it is located. Probably also a good idea to practice docking without it, particularly at your home slip (something I do on a regular basis).

I have a dedicated battery switch for the windlass and thruster, do you have a dedicated battery?

Carolena said:

Moral of the story is make certain you have a seperate shutdown/breaker for the thruster and know where it is located. .

Click to expand...

I agree. While I've never had an issue, I do appreciate the Master shut-off switch at the helm. As you've discovered, you never know when you may need it...

thanks! Good info!

Carolena said:

Anyway, just a reminder to make sure you have a main shutoff for your thruster and know where it is located.

Click to expand...

Good reminder. I realize that I don't know exactly how mine is wired. On the overhead in my pilothouse I have a bank of switches. These are for engine, house, nav instruments, trim tabs, and bow and stern thrusters. Switching on the bow and stern thruster switches give power to the Vetus switches in the PH and on the flybridge. I assume that there is also a solenoid somewhere that connects the main breaker for the thruster batteries, but I honestly don't know and don't know where it is.

I spend a good part of the weekend crawling around in the boat learning more about different systems over the weekend. I still have much to learn.

No way. everyone says thustlers are never a problem.....

Glad things turned out OK. Must have suprised the shi* out of you...

I have no clue where a breaker for the thruster is. Never seen it.

My thruster runs off the house bank. Guess I could shut off the main house bank at the big rotary switch? Isn't there a chance you can ruin the alternator doing that if the engine is running?

Have a breaker at the helm for mine.

Thank you for your warning!


In my Nordic tugs main switch is at the bow of the bed inside and stelrn truster main switch in the engine room star board side. Bow-stern trusters have separate batteries.

Could also use a motorized battery switch for the thruster battery (located close to battery) with a remote switch for operating it at the helm; that's my set-up

OK, but why did the thruster keep running? That is the question.


My boat has a toggle switch on the same panel as the two directional buttons, but I suspect it just controls power to the buttons and wouldn't help if the problem was a mechanically stuck thruster relay.


The thruster circuit and wiring is protected by a fuse that would take a few minutes to get to but it is also controlled by the hose bank main switch so I could turn that off. The problem of course, is leaving the helm to run down the ladder to turn it off.

cardude01 said:

I have no clue where a breaker for the thruster is. Never seen it.

My thruster runs off the house bank. Guess I could shut off the main house bank at the big rotary switch? Isn't there a chance you can ruin the alternator doing that if the engine is running?

Click to expand...

Probably not if you have separate house and starting batteries but each boat is unique. If your thruster continues running and is about to run your boat into other boats or rocks, it may still be the best choice.

Sometimes solenoid welding closed and the only way is to disconnect power from your trusters main swits, if you have one installed. Joy stick switch is not enough ...

I had the exact same thing happen except I was using the remote around my neck on the bridge since I don't have a joystick there. I knew where the main breaker was for the thruster so I had to make a mad dash down the ladder to trip it. Turned out a button on the fob had stuck. Sure is a pucker moment!! My guess would be your joystick or a couple wires shorting. Good luck!

A shunt trip breaker is perfect for this scenario.


Shunt Trip Safety Switch

Designed to enhance personnel safety and protect equipment in commercial and industrial applications, Eaton’s new safety switches with shunt trip technology can be operated electrically and remotely – expanding the range of applications where safety switches can be applied. Building on Eaton’s extensive portfolio of safety switch solutions, the new shunt trip incorporates a side-handle operation mechanism and visible blade indication that have decades of successful installation and operation.

• Features
• Documentation

• Can be used with emergency stop pushbuttons or other remote signaling means to quickly disconnect power from equipment
• Solution for oil and gas, industrial plants, solar installations, utilities, commercial construction and water and wastewater treatment
• Available in two-, three- and four-pole configurations for maximum system voltages of 600Vac and 1000Vdc with fusible and non-fusible protection options
• Meets Underwriters Laboratories (UL) standards and is listed to the UL98 standard for AC configurations and UL98B for DC configurations
• Variety of coil voltages available
• Visible means of disconnect
• Standard heavy duty safety switch with integrated shunt trip module
• Passes Class 1 ground fault testing (1200% opening)

with this mounted on/near helm.Across the line control at thruster,low voltage control from remote.

Blue Seas makes a remote battery disconnect switch which would do the job as well. I believe it would be possible to connect two (or more) remote switches so one would be available at each helm.


I have to wonder though, how common is this problem? Is it common enough to install special systems to deal with this possibility? More or less common than a stuck windlass motor? A runaway starter motor?


Is being able to disconnect the bow thruster with the normal battery switch enough to cover this possibility even though we might have to leave the helm to do it?

cardude01 said:

I have no clue where a breaker for the thruster is. Never seen it.

My thruster runs off the house bank. Guess I could shut off the main house bank at the big rotary switch? Isn't there a chance you can ruin the alternator doing that if the engine is running?

Click to expand...

Shutting off the main could blow the diodes in the alternator, but if it is still connected to the engine start (assuming that is a seperate bank), you should be OK. As for this working in our senerio, it didn't. Our thruster runs off the house bank, but it has a seperate breaker/shut off from the main house disconnect. Once we were back in the slip, with the engine off, I turned off both the engine and house breakers then turned on the main thruster breaker, which caused the thruster to keep running. It is a direct wire from the house bank to the thruster breaker/main switch.

psneeld said:

Must have suprised the shi* out of you...

Click to expand...

Yep, to put it mildly. Luckily it is only a few steps from the pilot house to the berth and the switch is readily accessible.

WesK said:

OK, but why did the thruster keep running? That is the question.

Click to expand...

I'll figure that out this weekend. Imtra customer support, which was great, by the way, said it is either the joystick switch at the helm, the control unit on the thruster motor, or the solenoid on the thruster. They explained what I need to do to troubleshoot. I initially assumed that the solenoid contacts had welded shut, but they think the control unit is more likely. That would be great, as the control is the least expensive of the three parts, followed by the solenoid then the joystick control. I was going to order the solenoid before talking with them, but after the conversation I decided to wait and troubleshoot so I'm not just throwing parts at it. Only downside is no thruster for this comming weekend. I'll report back once I have it figured out.

I think the important thing here is for everyone to know that something like this could possibly happen and be familiar enough with their boat that they can take an appropriate action quickly and without having to stop and think about it.

While I agree that it might not be necessary,And not necessarily cheap at that,it seems that a lot of boaters are chosing fail safe systems backups(think redundancy).This should actually be something that is an option from the thruster installers.Or the alternative might be a lot of fiberglass repair.Just an option.IMHO

The more I think about this, my thruster has an overload circuit that has opened on me before when I've laid on the thruster too long. Wouldn't that kick in?

I believe that is only on thermal overload,which most likely would have occurred if the thrusters were electric,not hydraulic. The question would be if they overloaded before the boat struck another boat,dock ,rocks,etc.

cardude01 said:

The more I think about this, my thruster has an overload circuit that has opened on me before when I've laid on the thruster too long. Wouldn't that kick in?

Click to expand...

Wouldn't it depend on how the overload works? If the overload protection works by opening the switch or solenoid that is faulty and stuck shut, then it likely wouldn't work.

dhays said:

Wouldn't it depend on how the overload works? If the overload protection works by opening the switch or solenoid that is faulty and stuck shut, then it likely wouldn't work.

Click to expand...

usually in series with the contacts,installed as a motor protection,so as a safety,it will disconnect the power to motor,regardless of any issues with the contacts.

They are known as thermal overloads,or street name "heaters".They are sized for the normal running load of a motor,and the thermal contacts will open if the motor starts to exceed the rated current draw.When they cool down,they will reset.

Thanks tinped. So the overload protection is independent of any of the other switches or contacts. Yet another thing I learned from TF.

The on thruster solinoid for my Vetus bow thruster is such that the contacts can stick (welded actually) and the thruster is locked on. When this happened I was saved by a battery switch that cuts off power to thruster. Fast moving and the Admiral taking the helm were necessary.