bridges (18) campsite (25) cartoons (15) centenary (3) discussion (5) experimental (49) gadgets (23) gateways (11) lashings (21) models (9) raft (81) resources (26) sculpture (15) software (22) techniques (41) towers (42) trebuchets (5) treehouses (17) tutorial (9)

February 4, 2006

Lightweight Racing Raft

This lightweight "outrigger" style raft was an idea I had to reduce the weight so that the raft could travel faster. All of the decisions made in the design were to reduce the weight as much as possible. Compared to the raft design our troop normally uses, which is similar to this pontoon ferry, about 50% of the poles are used, so in theory at least the bouyancy is increased (because the same number of barrels are used). Note also in the central row of barrels how bindings are used between barrels, rather than poles. This saves weight further (if you omit the bindings and try to make do with nothing joining the two parallel poles together, you get barrels that froce them apart and pop through between them)

The paddlewheels, designed by Gregory and Graham Witt, are made by brazing (not welding, unless you want holes in your barrels) brackets onto oil drums and attaching plywood paddles to them. A steel sleeve is placed through the centre of the barrel through which a greased axle passes.

Note the two ropes that extend to the fron of the raft from the two edges of the deck: they are used to tension up the structure and give it some rigidity. One end is anchored with a round turn and two half hitches, while the other end is secured using a Trucker's hitch to allow the rope to be tightened.

As far as speed, I'll leave it to you to figure out whether this raft works out faster: do you think the weight we saved is enough to counteract the fact that we now have 3 barrels providing resistance? I must be honest and say that it wasn't noticeably faster or slower than our normal raft, so this is still an open question.

Of course first prize in terms of drag would be a single line of barrels, but I can't see a way of balancing a raft like that. I am open to suggestions though...
Post a Comment