Fishing speargun
Spear fishing is a popular sport at coastal regions all over the world. The speargun is essentially the same everywhere in that it comprises a long tubular or solid wood frame, a trigger mechanism and a long, slender spear. Rubber straps are stretched by pulling them with both hands and a steel wishbone is hooked over a notch in the spear. Varying strengths of rubber are available providing varying force and therefore distance travelled of the spear. Multiple straps may be used where the required force is too great for the user to load effectively. Only very practiced spear fisherman are able to load their guns quickly and therefore take advantage of stronger rubbers. The traditional method of loading requires that the butt of the gun is pushed into the stomach or hip while the biceps are required to produce all of the pulling power. This is difficult enough to achieve on land, let alone in the water. It is also essential that the procedure is performed quietly so as not to scare the fish away.
It was therefore decided to develop an alternative method of loading the gun utilising the much stronger, leg muscles. After several early concepts, the present idea was born which utilises a travelling rubber strap mount which slides along the barrel and can be latched into place at its end. A second sliding member with rotating posts is used to push the former mount along the barrel. The rotating posts are positioned 180 degrees apart and pressed on with the heels of the feet. Once the rubber strap mount is latched in, the 'foot slider' can be pulled back towards the trigger end and the posts rotated downwards to be held with the non trigger hand for increased stability. From the outset, the choice of bearing type for the sliding members was of paramount importance. Factors such as minimal friction, corrosion resistance and quietness were all considered. In the end and after testing, the choice was made in favour of iglidur® H370 plastic bearings. These have excellent chemical properties and are actually recommended for underwater use. The barrel is a PTFE coated aluminium tube, which complements the igus® bearing perfectly. The end result is a highly effective speargun which can be effectively loaded. The stronger rubbers can be utilised by less experienced fisherman, giving them the sport enjoyment of their peers. "Predicted lifetime of the gun looks good with very low wear rates. Importantly, the gun is extremely quiet in use. This could not have been possible without the use of advanced plastic bearings such as those produced by igus®. Roll on next summer!"
Jon Prince
Design Engineer
The Design Village