How does an impeller work?

We got this question from a reader

Rowing boat impeller designs
Rowing boat impeller – NK large and Coxmate small

Hello, I am currently doing a school assessment about the technology of rowing and I was wondering how the impeller is able to get the reading of splits/watts. What technology is used to measure/detect the speed?

Our answer

The impeller has a magnet inside it and as it spins, the magnet passes over a corresponding magnet mounted inside the boat on the base of the hull (usually in your foot well) and this has a wire connecting it to both the under-seat magnet (for stroke rate) and the box that reads, interprets and displays the data.

The faster the impeller spins, the greater the speed of the boat. BUT you have to calibrate it first.

I’ve not seen an impeller that reads watts – most do boat speed in 500m splits or meters per second. From this the box unit can interpret through to distance travelled.  Watts is a measure of power.

 

Anyone want to add to this?

Buy a rowing boat micro impeller – fits NK and Coxmate products.

3 thoughts on “How does an impeller work?

  1. David Tucker says:

    The impeller is very similar to a trailing log spinner used on yachts. I have a couple of the spinners for electronic trailing logs one made by Stowe and the other by Autonnic. The electronic trailing log replaced the mechanical ones. These were Wasp logs and Walker logs which are now antiques. The impeller is free rotating on bearings so its speed is proportional to the speed through the water. The ratio of impeller speed to water speed is dictated by the pitch of the impeller. Yachts used this technology to give immediate speed through the water indication and more importantly distance travelled.

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