Knotmeter

A device for measuring speed in a kayak or canoe. Small knotmeters are available that operate off of a battery and can display speeds continuously. They use a magnetic coupled sensor so they do not require any holes drilled through the hull.

Note that the speed measured is that relative to the water. If there is a current, that will not be the same as speed relative to a stationary point.

As an alternative to a knotmeter, some paddlers use a GPS. That will measure speed relative to a fixed point, but not relative to the water unless there is no current. If you want to ensure that the speed you measure is the hull's speed through the water, you need to use a knotmeter.