Amphibear

Amphibear is a do-it-yourself flotation kit for an all-terrain vehicle, designed and built in Estonia by Mait Nilson. After about three years of sketches, wooden frame models and test pieces, the first version was finished in December 2003 and fitted to his Yamaha Kodiak, after which the kit was named.

Design

Nilson set himself a list of requirements: the ATV had to float with enough stability for the rider to haul himself out of the water, the kit must not widen or heighten the machine, one person had to be able to rig it in under ten minutes, and everything had to be made from ordinary materials with home tools. He rejected oversized "Bigfoot" tyres because they change the handling, and side-mounted pontoons because they compromised riding safety. Instead, a friend's question - why not put the pontoons at the ends? - led to a layout with one pontoon at the front and one at the rear.

Each pontoon is a heavy truck inner tube inside a sewn textile bag, carried on a bolted frame of 20 mm square steel tubing that hinges between a lowered float position and a raised travel position. Load straps with tensioners set the height of the pontoons, which can be adjusted even while afloat, and a portable 12 V tyre inflator fills the tubes. With the pontoons deflated the ATV keeps its original width, so it can still use narrow forest tracks.

Testing

On the water the machine is driven only by its turning wheels and managed about 2 km/h, curiously going slightly faster in reverse. Side stability proved better than expected: the rider could stand on one footboard without the vehicle tipping. Nilson warned that dense surface weed could easily leave it stuck, and suggested carrying a winch and anchor.

Amphibear II

In April 2004 a second-generation kit followed, prompted by interest from another ATV owner. It was made universal for any ATV with front and rear metal racks, mounts without drilling, has similar front and rear kits, horizontal pontoons, a lower waterline and a stopper with seven height positions. Trials on the Pirita river in Tallinn, in water of around 3 C, showed that a strap around each float was still needed; on the first run the rear pontoon caught on the bank and twisted, but the machine remained stable. Bolt-on mud paddles did not raise the speed above roughly 2 km/h but gave more thrust against the wind.