>> ATLANTIC CROSSING

For the Atlantic crossing we cobbled together a system that comprised a conventional cog and chain arrangement married to a bevel box transmitting power through 90 degrees to a steel propeller shaft and ultimately a 17-inch, 2 x bladed aluminium propeller. An “A” frame in the middle of the boat held a specially designed bearing system impervious to the harsh effects of saltwater. High-tech synthetic grease was used on all moving surfaces to keep the whole thing working. Frame: custom chrome moly “A” frame built by Sonic Cycles in London. Chainring: custom 60 deep tooth stainless steel one-piece cog. Crank: Shimano Dura-ace 175mm. Bottom bracket: Shimano Dura-ace fitted with custom grease flushing system. Rear cog: 12 tooth stainless steel. Grease: Black and Gold synthetic Q40

WEAKNESSES

Although we never had to resort to using the oars, serious flaws in the propulsion design began to appear towards the end of the Atlantic voyage prompting us to consider a revised system for the Pacific. These included:

1. Significant friction losses from the many moving surfaces required to transfer power from the cranks to the propeller blades. These included the bottom bracket, 2 x chain to sprocket interfaces, 1:1 ratio worm gearing inside the bevel box, a deep-sea seal to exit the steel prop-shaft from the hull and a marine seal holding the same shaft inside the skeg.

2. The prop-shaft was hopelessly exposed to potential damage from a length of submerged timber or surfacing whale.

3. Towards the end of the voyage a gasket seal on the side of the bevel box failed causing the lubricant to leak out. This led to over heating and subsequent expansion of the bearings making the pedaling at times impossible. We then found to our dismay that the unit was sealed and the only way of introducing replacement lubricant was to run drips of cooking oil down a cotton thread into a narrow opening where the gasket seal once was!
So the criteria for a new system would be minimum friction loss and ease of servicing, replacement of new parts or the whole system if need be. The main challenge proved to be engineering a way to transfer the drive through 90 degrees and from the pedal cranks above the water line to the propeller below the water line. We had limited success experimenting with twisted quarter inch chains, but finally found a solution in the form of a direct-drive, all-in-one unit.

>> FIND OUT HOW THE PROPULSION SYSTEM WAS IMPROVED FOR THE PACIFIC CROSSING >>

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