What type of wood......

Oh, and although ash has most of the virtues, it is not durable. It will get wet and rot if not sealed, even the bit that's in the ferrule of the hook. My method was lots of coats of varnish and then squidge it into the ferrule with lots of sikaflex. (+sikaflex in the screw holes)
 
Nobody mentioned oak, very strong, rotproof easily obtainable unlike hickory and locally available. Make sure the grain is fairly straight, will last forever no need to treat. Best would be a straight branch with sapwood removed with drawknife or any bladed tool.Another choice would be sweet chestnut almost identical properties to oak and available from coppice woodlands as would be oak.
 
My last boat hook was ash and to be honest for reaching things at full stretch it was a tad on the heavy side. The previous one was Norwegian pine and was much lighter. So, for a two metre boat hook I'd still probably use ash, for a three or four metre hook (which is more useful than you'd think) I'd go pine. Probably Douglas fir.
 
Aluminium is lighter still. and more durable.
My last boat hook was ash and to be honest for reaching things at full stretch it was a tad on the heavy side. The previous one was Norwegian pine and was much lighter. So, for a two metre boat hook I'd still probably use ash, for a three or four metre hook (which is more useful than you'd think) I'd go pine. Probably Douglas fir.
 
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