My initial plan was to use carbon fibre ski poles, and I even got a pair of telescopic poles, although only about 1,7 metres long, so some sort of extension had to be made.
Then I changed my mind. I will try to make extensions from 15mm diameter PVC tube with unidirectional carbon outside. The PVC is ductile but soft where as the carbon is stiff but brittle. I hope the combination will make stiff and durable extensions. I make them 3 metres long, and will cut them to the desired length after trying out on the boat.