Sidepower Bow Thruster re&re

This is a technically-oriented posting that will not be of interest to most readers. But if any of you own a Sidepower bow thruster you may be interested. It may apply to other brands too. This posting might help a capable DIY'er to re and re their own thruster at home without an expensive repair or replacement by pros.

Last year I had a problem with my SP55S, installed in Invictus from the original build (1997). This is a beautiful piece of well engineered equipment made in Norway.

My thruster began malfunctioning intermittently towards the end of the season. It seemed to lack full power in both directions but particularly when pushing to port. Our moorage at Bella Coola is sited at the head of a long narrow mountainous fjord. It's windy most days and the tides run hard. Having an [operational] thruster in a place like this can save a lot of trouble and money when docking... and save wear and tear on neighboring boats.

Despite this being such a handy piece of equipment I put some effort into learning to dock and un-dock our single screw boat without it. You know, good boat handling, prop walk and all that sorta stuff. Even so, I was still powerfully motivated to get it working properly.

On the bench partially disassembled (contactor unit removed)

So I read the owner's manual and followed their trouble shooting suggestions - no improvement was noted. Importantly though, through this process I eliminated the possibility that the batteries were the problem.

I then Googled the problem and found many more suggestions, which I tried with no improvement noted.

Both the owner's manual and Google leaned heavily towards blaming the batteries. I guess deficient batteries are the most common cause of the problem I had.But I was convinced that the batteries were in good condition and that the problem lay elsewhere.

So I brought the unit home and disassembled it on my bench. Here's what I found:

• two of the four brushes were not sliding easily in their guides
• the armature surface was heavily coated in carbon
• all of the points on the massive contactor showed signs of pitting, some of it severe

Heavy duty brushes and wiring to carry up to 450 amps

Contacts before cleaning

Contacts before cleaning

Over time carbon dust had accumulated around the brushes in their guides restricting free movement. As a result they were not making good contact with the armature. This would cause the voltage to drop and the amperage to rise. The higher amperage may have exceeded the design limits of the contactor and so the points began to erode and pit. This caused the voltage to drop even more..... and so on. A feedback loop as they say.

I removed the brushes from their guides and lightly sanded the sides with 150 grit paper until they slid easily. I used fine emery cloth to clean the armature. I completely disassembled the contactor unit. Then I pushed a fine grit nail file between each pair of points and sanded them to a new flat surface that mated perfectly. Final sanding was done with wet/dry 400 grit wrapped around a piece of flat steel. Reassembly on the bench was simple. Installation back into Invictus was also quite easy - four mounting bolts, a control cable plug and two battery cables.

The cost? Zero $'s - just a bit of effort.

After this treatment my thruster is as new. And I look like a pro again while docking on one of our windy afternoons in Bella Coola.

PS - I was curious to know the total run-time of the thruster during its 17 years of service. There is no hour meter of course, so I estimated as best as I could.

• We average approximately 8 cruises each season with (around 50hours on the main each time);
• I figure that in an average cruise I dock and un-dock 8 times (we anchor out most nights);
• For this calculation, I estimated that for each docking maneuver the thruster run-time is 1 minute; usually it is much less, say 30 seconds, but I'm trying to be conservative here;
• So in an average season I maneuver with the thruster 64 times and run the thruster slightly more than one hour total;
• Extrapolating these numbers over the past 17 years means the thruster has a total run-time of only 18.13 hours. It might be considerably less, say 9 hours.