Sidepower Bow (and Stern) Thruster Troubleshooting

American Tugs have Sidepower bow thrusters installed as standard equipment, and some also have optional stern thrusters. On the AT34, the bow thruster is a model SP75T, mounted upright under the berth. I believe the stern thruster is a similar motor, but mated to a different gear case, and mounted on its side in the stern lazarette. Most of this document should apply to them also, but I don’t have one on my boat.

Picture 1: Bow Thruster under the berth of an AT34.

The black plastic solenoid cover has been removed. Note the grey dust from the worn brushes….

After about 3 and a half years, 1400 engine hours, and about 200 locks, my bow thruster began to malfunction. The performance seemed a little down (although that’s a gradual process and hard to estimate), and it would occasionally (maybe 10% of the time) fail to operate. That *is* easy to quantify, and adds a little excitement to the docking or locking experience… The control panel turned on, but the motor would not run. This gradually got worse, until it was pretty unreliable – failing to run close to 50% of the time. I called the nice people at IMTRA (the Importers) in MA (508-995-7000  sidepower@imtra.com) and talked to Phil, who does tech support for Sidepower. They’re ready to help, and emailed me a troubleshooting guide, which I followed. That guide, and the owners manual (if you don’t have a hardcopy) are available on their website:  www.imtra.com

Be aware that two models of thrusters have been installed: pre-2005 and post-2005 (with IPC, Intelligent Power Control). The troubleshooting is slightly different. Dive under the bunk and compare your thruster with the photos in the guide: after you remove the black plastic solenoid cover, the post-2005 thruster has 3 wires on the starboard side, and the older one has only 2.

The troubleshooting steps are designed to isolate the problem to: the joystick, wiring, solenoids, electronic control box, or the motor.  Once you know where the problem is, you can replace the bad component. Of course when it came time to run through the troubleshooting steps at the dock, the thruster would happily run.  I did eventually get it to fail and was able to run through the steps, which, in my case, showed that the motor was bad. It turned-out that the brushes in the motor were worn out.

Troubleshooting steps:

1.  Measure the voltage between the Red and Yellow wires at the thruster. It should be at least 12V at rest. Then measure it when the thruster is run (if it runs). If it drops below 10.5V the thruster is not designed to operate, and it indicates that the engine start battery is probably failing.

2.  Download both the Troubleshooting guides from this site, and the User Manual if you don’t already have a hardcopy.

3.  Figure out which version you have, and run thru the troubleshooting guide to isolate the problem. You’ll need a good voltmeter to do the testing specified in the guide.

4. You’ll probably need the serial number for ordering parts. It’s a 6 or 7 digit number on a silver plate on the motor. On mine, it was towards the front of the boat, in (of course..) the hardest place to read (especially hanging upside-down…). We needed to use a mirror to read ours.

Removing the Motor:

If the motor or brushes are bad, it has to come out. This can be done quite safely in the water, without leaving a big hole in the bottom of the boat - which is never a good idea…

1.  You’ll need an 8mm hex wrench for this. Invest in one from Sears that attaches to a socket drive to make it easiest. A torque wrench is handy, too.

2.  Turn the Engine Start Battery switch (under the helm seat) OFF.

3.  Check that the thick red and yellow wires are no longer ‘live’ with a voltmeter. Remove them (there are 2 thick wires on each post, and insulate the red ones, just to be sure…

4.  Pull the white plastic ‘low-current’ connector apart.

5.  Remove the 4  8mm hex-head screws that hold the motor in place. Do this like a cylinder head – loosen gradually them in sequence.

6.  Pull the motor straight upwards. It weighs 25-30 lbs, so have your wife do that. There is a rubber ‘Lovejoy’ coupling underneath – don’t lose it. That’s a black rubber donut-shaped thing that absorbs any shocks between the thruster motor and the propellers.

Replacing the Brushes:

When I removed the motor from my boat, the problem was obvious: chunks of graphite from the brushes fell everywhere. They should wear-out eventually, but not (I think) as fast as they did.

Picture 2: Old brushes (top) and new ones (bottom)

There are 4 brushes, held in place by coil springs. Be very careful not to let those springs unwind and come off their mounting post – if you do you’ll hear “Ping…Bugger !”. You’ll need a helper for this part probably (unless you’re lucky enough to have 3 hands).

Important: This motor is basically an up-rated, continuous-duty, starter motor. If you’re not comfortable with the following steps, take it to any automotive alternator/starter repair shop, and they’ll be able to overhaul it for you.

1.  Remove the screw and washer that holds the brush lead wire.

2.  Put a finger on the side of the spring to hold it onto its mounting stud, then pry the end of the spring upwards, whilst your helper gently pull the brush upwards out of the holder.

3.  Carefully allow the spring to reseat back on the holder.

4.  Repeat steps 1-3 for the other 3 brushes.

5.  Blow all loose crud away from the motor, then carefully clean the commutator (the segmented brass cylinder that is under the brushes.

6.  Carefully clean the gaps between the segments, and blow out any crud.

7.  Repeat step 2 to pull the spring back, while your trusty helper carefully slides the spring into position.

8.  Attach the brush lead screw. I used a drop of Loctite Blue on each.

9.  Repeat steps 7-8 for the other 3 brushes.

10.Clip the brush shield back in place.

Picture 3: Cleaning the gap between the commutator segments. The tool is being shoved down the (empty) brush holder. The models oh-so-elegant finger at the bottom is holding the coil spring in place.

Replacing the Motor:

1.  This is the reverse of the ‘removal’ procedure, except you say ‘bugger!’ in different places.

2.  The 4 bolts I removed had traces of dried ‘Loctite’ on them, but that is not covered in the User Manual instructions. Since there were no lock-washers used, I cleaned the bolts and used ‘Loctite Blue’ on them. That’s the mildest of the threadlocking compounds.

3.  Ensure the Lovejoy rubber fitting is in place, and then carefully lower the motor. If the metal flanges mate up tight, and the holes align, then it’s in place correctly.

4.  Torque the 8mm hex bolts to the specified 24ft-lbs (or just ‘very tight’ if you don’t have a torque wrench), and do so like a cylinder head: progressively tightening in sequence.

5.  Connect the thick red and yellow wires (there are 2 thick wires on each post) and put a smear of silicon grease on them.

6.  Connect the white plastic ‘low-current’ connector.

7.  Turn on the engine battery switch, try the thruster, and enjoy that ‘coffee-grinder’ noise….

8.  While you’re hanging upside down by your heels in the thruster compartment, it’s a good time to check the oil reservoir level, You know, you’ve been meaning to do it for years now…It takes EP90 (extreme pressure) gear oil - probably the same oil used in your dinghy outboard gearcase.

9.  Replace the black plastic cover over the solenoids. Incidentally, those 2 little metal pins on the outside of the cover are spare shear pins for the thruster propellers.

Jeremy Bell.     AT 34 #48 “Tardis”