I consider that they are handy tools, particularly on weedy rivers such as the Nene. Often weeds collect just above locks creating problems operating gates and causing propeller fouling. I searched the net to find a replacement, and via a handy WRG document describing canal restoration tools, I found that kebs or weed rakes are also called drag manure rakes. This led me (via Google)to a tool site which had one made by the famous hand tool maker Spear & Jackson for £22.
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Our new keb (or manure/weed rake)
It came complete with 6ft smart profiled handle that looks the part. I made a protective holder to avoid the fork prongs damaging the boat roof or being a trip hazard and we are now "back in business". The web can be remarkable when you know what questions to ask search engines.