Weaverbird's yuloh is now fit for a first trial, and yesterday was calm and sunny, with a high enough tide to float Weaverbird. Well, it works. Kinda. I tied a long line to the mooring, in case it didn't work at all, but I managed a stately half a knot. The faults appeared to be:

• I wasn't developing much power. Maybe the blade could have been bigger.
• There was a tendency for the yuloh to lever itself off the ball, because it was rotating to too great an angle of incidence. I should add a hold-down lanyard.
• Maybe 10 degrees of bend is too much. I didn't touch the lanyard, as just holding the loom angled the blade too much. I may have to add a handle on top, as in the Japanese Ro, so as to have greater control of the angle of incidence.

Some photos of the blade, glued up, shaped and sanded, and ready for glass cloth sheathing, are now in my yuloh album.

David Tyler wrote:

The blade

blade section

The link doesn't work for me, David.  When I clicked on it, I got into an album, but no photo showing.  When I went back to All Album Photos I ended up in my own albums!!

I am but a humble (and lewd and salacious) engineer, and use the word in its engineering sense:

Lubricity is the measure of the reduction in friction and or wear by a lubricant.

- Wikipedia.

The blade

I think the blade should have neutral buoyancy. On the one hand, it should help if it sinks readily at the commencement of yulohing; but on the other hand, the heavier it is, the more energy is wasted in reversing the motion at the end of each stroke. I'm thinking in terms of a central spine of GRP flat bar, 50mm x 12mm, for weight and strength ( I have some left over from making servo pendulum blades), with the edges of hardwood. Making it this way, it will be easy to add a slight concavity to the after face. The width at the tip will be 167mm; the width at the top will be 114mm. The thickness at the tip will be 15mm; the thickness at the top will be 31mm. The radius of the convex curvature of the forward face will therefore be much greater near the tip.

blade section

The pivot

I don't want to compromise the integrity of the thin-walled tube by making holes in it. I propose to use a ring-type rowlock, working over a section of tube that has had a reinforcing sleeve of CFRP added for extra strength and wear resistance (possibly adding graphite to the resin for lubricity).