the yacht weighs 31kg as is- it could have a bit more trimmed in a few places if I got really serious though,

Cameron- the axle extensions are a sliding fit into the rear chassis
axle extension is 25mm x 25mm, chassis is 32mm x 32mm.
my axle shafts are 3/4". you would be better off using 20mm as it matches the cheaper bearings.

The wheels are made by FALSHAW and are about $45.00 each.
they came with the 3/4" bearings and adaptors supplied, but you might need to buy the 20mm bearings elsewhere. use 20mm bearings, 20mm shaft (or long 20mm bolts),and for the steering head get the terrain tamer brand urethane bushes.