Making a Yuloh. Experimental Construction of Oriental Curved Oar for Sculling Small Boat

Update 5th Dec 2011:
I have now tested the yuloh with my boat and can report that I made a mistake with the choice of paddle material...a scrap piece of UPVC cladding. I chose it because it is easy to cut and will not rot, but hadn't bargained on it being so buoyant. The trouble is, it floats so well I was struggling to keep it under water!!!!!!!!! My next thought was to cut up a large polyethylene chopping board. This also floats having a relative density 0.93 or so, much greater than the UPVC and greater than Ash wood at 0.54 or Birch at 0.67. Looking at Bamboo itself, that is 0.3 to 0.4, so not a good choice either in terms of keeping it submerged.
Comments welcome.

Introduction (2nd Dec 2011)
I have a 3m long folding boat which you can row, sail, or use with an outboard motor. Rowing is OK but as you are facing backwards it is not that good for exploring...so I turned round and rowed forwards! Not as efficient maybe, but far more interesting and you are less likely to collide with something.
I made a sail out of some inexpensive tarpaulin using instructions from the Internet, and have since found that it would be useful to still have power and maneuverability even when the wind drops. The problem is that of having too few hands for managing the sail and two oars all together. Hence the idea of sculling with one oar like in a Venetian gondola, or a Chinese junk. It is also useful in narrow channels as two oars are unmanageable.
The oar has many names, 'Yuloh' being used in the Orient. It works like a slow propeller blade, reversing direction with each stroke. It has a curved handle, and this is a vital feature to enable easy sculling and good propulsion.

Here's a good idea of what it is and how it works:

http://www.youtube.com/watch?v=UjyE7dyR2X4

There are many photos on the Internet, but very few clear instructions on how to make one. This Instructable hopes to fill the gap for an inexpensive oar that can be made mostly from scrap.

The first problem to solve was what to use for the main 'pole' part, and how to get the curve. After some time the inspiration to use a thick bamboo pole emerged. However, firstly, I did not have one, and secondly it would be difficult to factor in the bend. I expect a green bamboo pole would be fine, but they are not available here. Undaunted, it occurred to me that by strapping six or so small diameter canes together I could achieve what I wanted.

The blade of the oar is made from a scrap piece of white UPVC cladding about 10mm thick.

4 or 6 bamboo canes, 3m long and about 15-20mm diameter at the thick end.
Black PVC waste pipe about 40mm internal diameter
40 or so 15cm cable ties
Metal band type worm screw-adjustable hose clip, 30-50mm diameter to clamp around the poles, but see photos for what I used.
Epoxy glue
Fibreglass tape.
4m polypropylene rope 10mm diameter
UPVC cladding off-cut for blade.

I also used these, but you could improvise to get the same effect. They are just used to get a good grip on the ends of the pole to bend it:-
1 waste-pipe 90 degree bend
1 waste-pipe T-connector

The handle grip is made from a short length of the PVC waste pipe. I chose 20 cm, but you can adjust this according to the width of your hands.

Select your canes to be as closely matched as possible, and turn them all round so the thick ends are together. You may need 4 or 6 or even 8 canes, depending on their diameter, but it must be an even number.

Next you jam the thick ends of your bamboo canes all the way into the pipe. They can protrude if you wish, but mine didn't. I needed to hammer mine into the tube quite hard, but this is better as they need to be gripped tightly together.

Now cut some 30mm lengths of waste pipe to act as bands around the canes; about 4 or 5 will do. These are slipped over the thin ends and pushed up tight to the thick end, spacing them out by 15 cm. You may have to tap the band to move it along. If the band is loose, then take it off and use a cable tie instead. Finish off with cable ties (not too tight at this stage) every 15cm all the way along the pole towards the thin end.

The next thing to do is to bend the pole.

My first attempt at this was to wedge the handle end between two low branches of a tree, and bend the pole sideways about 80 degrees towards a hedge where it was tied with the rope. I left it like this for two days, but when released it bent back too much and the curve was too small.
My second attempt formed the cane pole into a 'bow', as in 'bows and arrows'. In other words I tied up the two ends to each other and pulled tight to make the bend of about 80 degrees . This worked better, and also it was indoors, not out. I placed the waste-pipe 90 degree bend over the thin end of the pole, the waste-pipe T-connector on the handle end, then roped them together making the curve as desired.

Preventing the pole from straightening out.

To stop this happening more cable ties need to be added and all of them tightened up to hold the canes firmly against each other with no gap, using friction to stop them slipping back straight when the rope is removed. This is accomplished by placing the hose clip around the canes near the first cable tie at the thick end. Tighten the clip, being careful not to crush the canes. Tighten it to remove the gaps between the canes as far as possible without damage or deformity. When tight, add the extra cable clip 3cm from the other and tighten both of them up. You can loosen the hose clip now and slide it up to the next cable tie. Repeat this procedure until all cable ties are in pairs and all are tight.

Can you name it?
The pipe clip I used was bought about 30 years ago (!) and it is a brilliant design. It came from a camping shop and has been a real boon. I don't recall the name or the manufacturer; do you know because I'd like another! It comes in three parts as you can see from the photos and the white strip is threaded nylon.

To fix the canes permanently together you need to stop them slipping and becoming straight again when you remove the rope.
When I did this it sprang back a little but was still bent enough. I reckon if you want to experiment with the angle then you could tighten those worm-screw hose clips along the pole length and the angle would still be adjustable.

When you have decided that the angle is right for your situation it's time to do a permanent fix by applying a band of fibreglass tape between each pair of cable ties and each PVC band working along the pole from the handle end. Stop when you are about 50cm from the thin end because later you will have to splay out the canes on each side of the blade.

So, tightly wrap a length of the fibreglass tape twice around the pole, and then apply the Epoxy resin glue to it, working it in with a cocktail stick between the poles and filling the mesh of the tape. Watch out for glue dripping!

Allowing 24 hours for the resin glue to set fully, you can try removing the rope from the ends. Your pole should maintain its curve when you release the tension in the rope.

The blade was 40cm long by 15cm; it is not critical.

The top corners were cut off at about 45 degrees.

Note that the blade is attached to the pole HORIZONTALLY.  Study the photo carefully or your oar will be useless!!

The blade is attached to the thin ends of the canes with an even number splayed out and fixed with cable ties to each side. I used 4 canes, so two each side for me.

Drill holes in the blade to take the cable ties, spread out the canes on each side of th blade forming a sandwich, and attach the cable ties tightly.

You need to fit a row-lock either to the back of your boat, or one side.

Lower the oar into the water and PUSH the handle. You will see that the blade rotates by itself to one side, digs into the water and pushes it back. It is the bend in the oar that makes it turn over.
When you now PULL the handle, the blade rotates the other way, digs in and propels you forwards once more.

You will probably have to use more effort on one stroke than the other to go straight, it just needs practice.

This has been an experiment, and it may be that the pole curve needs to be adjusted, the blade size optimised, or other things.

Your comments and suggestions will be most welcome.

Thanks.
Joe-Zinc