ABT Bow Thruster Seal Replacement

My ABT Bow Thruster (Model 10-Trac, 24VDc, 10-HP) is an important piece of gear for helping me safely dock & undock Ophelia during high wind or situations with cross-current.  Ophelia has both an ABT bow thruster and a Side-Power stern thruster.  We modified the older ABT thruster around 2018, to match the newer Side-power thruster, so that they are both “proportional.” The main advantage of electric proportional thrusters over non-proportional thrusters is primarily much longer run times at lower power settings.  The last thing I want is for either thruster to “time-out” in the middle of a stressful docking situation.  As such, preventative maintenance is key to keeping the system functioning well.

Although thrusters, in general, are typically only used for a few short bursts to assist moving the bow or stern in the desired direction, they can provide great confidence during what can often be extremely nerve-wracking moments. For example, when entering a new marina, one may find themselves carefully making way down a narrow fairway, with big expensive boats on either side. Any gusts of high wind or unexpected current can quickly cause the boat to fall off course!  It’s crucial to be able to control the boat and maintain a standing position, against wind or any cross – current.  Bow & stern thrusters serve to do just that.  They assist with control of the boat, when in tight quarters.

That being said, I tend to make every attempt to not rely on either of my thrusters, unless absolutely necessary. Thrusters have a tendency to be a bit finicky, from an electrical & mechanical standpoint and, in-line with Murphy ’s Law, they will probably decide to not work, just as you go to use them!  So having strong single engine skills at the helm is the best solution to avoid a problem.

After talking with the kind folks at ABT TRAC about my specific 18 Year-Old Bow Thruster (Original Order Number 7905), I learned what sort if preventative maintenance I should be undertaking. Specifically, I learned that the prop seals are a 6-year replacement item.  My bow thruster does not have any zincs, as it is connected the boats bonding system.  With Ophelia out of the water for winter, I decided to try to change the prop seals myself, to better learn about the system, & because I had no knowledge of when this job was last done.  There is also a Pinion Seal that I did not replace. At the advice of ABT Trac, the Pinion seal can be replaced at any time, with the boat in the water and should really only be done when there IS a problem, as it involves removing the electric motor.  However, the Prop Seals have to be done with the boat out of the water, since they are well below the water line.

ABT emailed me the Service Manual for my review. After a few clarifying phone calls, I successfully made a 2 hours project take 6 hours (3 per side). Clearly much room for improvement.  With the proper tools, I am confident I can shave off 2 hours per side. Here are the basic steps that I followed, to change out the prop seals on Ophelia.

  • Purchased from ABT, the following two Items
    1. ABT-Trac Seal Kit – Part #32275 (Contains both Prop Seals & Pinion Seal (unused))
    2. Cap Screw Monel – Part # 10233 (16- pieces needed; 8 Per side)
    3. Prop Seals have a 6 Year replacement interval
  • Tools to Bring
    1. Cordless Drill with Long Extension
    2. Hex Allen Bits for Drill to speed up removal of Cap Screws
    3. My 24-Inch Long, Half Inch Socket Driver for Leverage
    4. “Steering Wheel Puller” that I bought on Amazon
    5. Two empty Quart-sized Containers of Oil, for draining the Gear Oil (Cut Side Open)
    6. Blue Shop Towels for Oil Over-Spill
    7. Red Loctite
    8. RTV Sealant
    9. Extra Long Bolts (need to measure distance from Seal Housing to Outside of Thruster Tube) for Steering Wheel Puller, to assist with breaking Free, the Seal Housing (after all 8 Cap Screws have been removed)
  • Remove Nose Cone (Allen Hex) (Nose Cone are ¼-20 threads)
  • Remove Cotter Pin (new one is in Spares Kit)
  • Remove Prop Mounting Nut (24 Inch Socket Driver makes this simple)
  • Use the Steering Wheel Puller & Threaded Jacking Holes, to pop the Prop free (Paint & marine growth and RTV sealant make this a little hard, but puller handles the job in minutes)
  • Safely locate the Shaft Key and don’t misplace it
  • Using Drill and HEX Extension, remove all 8 of the Cap Screws from the Seal Housing
  • PRIOR to removing Seal Housing, gently score/mark the outside, so that you can be replace the seal housing to exact same side & location, including same screw hole mapping. These are machined together and we do NOT want to alter, scratch or replace them to a different location.
  • Lay Down Blue Shop towels under Gear Housing
  • Place your single Oil Catch below the Gear Housing, in anticipation of removing Seal Housing (oil will flow)
  • Using the Steering Wheel Puller, locate two Long Bolts (long enough to get leverage outside of the tunnel) to fit into two of the 8 holes. Per the ABT Tech, twist left to right, to break the Seal Housing Free and wiggle it off.  This was the hardest part. Resist the urge to pry it off with some other tool, because you do NOT want to damage the back face of the Seal Housing.
  • Allow all the OIL to drain out. Could Take 2 or 3 hours, so may want to work on the other side, while first side is draining oil out. (helps to loosen the Header Tank Cap in forward head, under the sink)

Side Note:  The Gear Box Oil is presumably supposed to be drained from a nut, inside the bulbous bow, but seemed way too difficult.  Not much room to work.  Gravity seemed to work great.  Simply plan ahead and have 2 1-Quart Oil bottles, cut-open at the side, to allow the old Gear oil to drain into roughly 28 ounces.  Lay Down in TUBE, blue shop towels; when the seal housing comes off, oil will begin to gently, yet consistently, flow out of Gear Housing!  We will Refill the Oil at end of job, using Header Tank under Master Sink.


  • With the Seal Housing removed, we are ready to replace the Seals, using the Kit we bought from ABT. The two Seals we are replacing are all located IN the Seal Housing you just removed.
    1. In this Seal Housing, you will be change out a total of 4 parts:
      1. 1 O-Ring,
      2. 2 seals with metal springs (back to Back, with metal facing outwards from each other,
  • 1 Excluder Ring (The Larger / Harder rubber Disc)
  • Put it all back together again, in reverse order
  • Use RTV Sealant on the Seal Housing, where it will interface with the Gear Housing
  • Red Loctite on 8 Cap Screw Monel. ABT recommends always using new Cap Screws because the old ones will expand and not function properly. Essentially they are single use Cap Screws
  • The Excluder Ring, if hard to press on, could use PVC Pipe to gently tap it on to shaft
  • Great time to leave props off, sand & Paint Gear Box and Tunnel
  • Final Step is to remember Re-Fill Gear Oil using Header Tank in Forward bathroom
    1. Chevron Delo SAE 80-90 Gear Oil
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