My Fairline Targa 27 speedometer stopped working at the beginning of 2016 but it wasn't high priority as I had other things to sort and generally use my GPS chartplotter anyway. In 2017 I finally got round to looking at it and initially it looked expensive:-

It was easy to see what had gone wrong; the paddle wheel was missing due to a broken axle support.

I looked around on the web, and whilst it seems possible to get hold of one, the only place with a reasonable price was out of stock.

Nothing to lose by trying to fix it except the paddle wheel cost - which wasn't that expensive from Furneaux Riddall. The repair looked tricky however as the device appears to work by fixed magnet(s) in the paddle wheel generating some analogue voltage or frequency, probably by interaction with a coil in the end of the transducer. The device is a close sealing fit in the boat mounting, so I really can't have any protrusions beyond the original footprint.

Here are x-rays of the end of the transducer (and many thanks to Bluelimit for these) :-

As you can see above, I can't afford to drill into the end or remove too much material. The plastic appears to be polypropylene or something similar as initial adhesive tests did not look promising.

Therefore I decided to construct a new axle support in ABS that would fit around the end - the idea being that this would be a 'springy' interference fit so that the adhesive would not have to work too hard.

To make things easier and allow the support to be thicker, I filed a flat on one side and removed 3 of the four locating shoulders (all but the one on the remaining axle support) :-

These aren't quite finished here but you get the idea.

It took several iterations in the CAD software and a couple of prototypes, but here are some of my designs :-

The near-finished part is on the far right. The one next to that shows the axle model ready to remove material from the prototype.

Here are some of the prototypes :-

To maintain dimensional accuracy, I had to print each one incorporating a 10mm high plinth (left 2 items) and cut this off afterwards. It didn't work so well using the normal 3D printing rafts.

After fettling, the final fit was good enough to be functional without gluing:-

And here is the repaired transducer after gluing and final smooth sanding :-

I'm pleased to say it works great - a small calibration adjustment was necessary. I expect this was necessary due to slight changes of the water flow over the transducer.

The speed adjustment is fairly simple to carry out; on the back of the speedometer, there is a set of 5 dip switches - these were initially set to the neutral adjustment:-

These dip switches are binary-coded at 2% intervals and allow substantial adjustment:-

The numbers are slightly non-intuitive as they represent how far out the speedometer is when set to neutral (0XX00), not how much adjustment you want to make. In my case the gauge was reading about 8% lower than actual and therefore needed to be set to the closest setting to this, ie. -9 = X0000 (or -7 = 0XXXX).

Hope this is helpful if you have similar problems or just need to adjust your SumLog.