Introduction: One Day Ndrua
This Instructable documents how my girlfriend and I built a sailing ndrua in one day. A ndrua could very arguably be described as a double-hulled sailing canoe which has hulls of unequal length, the leeward hull being marginally more voluminous. The craft shunts rather than tacks and gybes, so some people will call it a proa. I don't bother with these names much and call it a boat instead.
If you haven't already done so, I highly recommend you use the "view all steps on one page" function.
Step 1: Idea Generation Phase
This step is made easier if you have a few half finished long term projects lying around as I do. The smaller hull here is from a now deceased 4.2 metre proa I built in 2003. The other one was intended to be used for my 6.8 metre current proa project but I wasn't happy with its design for this purpose so it too was available.
I saw these two hulls lying beside each other and half jokingly thought that they could be lashed together to create a ridiculous sailing craft of some sort.
Basically if you have some ingredients similar to these (unlikely), sit them a nautical distance apart and lay some sticks between them. Now you have the choice of either convincing anyone who is around that this idea could work, or just ignoring the laughter and getting on with it.
Step 2: Let the Lashing Begin
This step involves what is probably the best combination of building materials yet devised my humanity. Of course I am speaking of seasoned bamboo and discarded bicycle inner tubes.
This fantastic system allowed us to quickly get the crossbeam and deck structure worked out to rough dimensions, while the flexibility and ease of adjustment allowed for fine tuning. The structure we came up with is fairly simple and the photos explain it well enough. Anything with reasonably substantial crossbeams between the hulls and a bit of diagonal bracing would probably work.
Step 3: Add More Sticks
Keep tying on more stuff until things are a bit rigid and there's somewhere to sit. I made some mats out of palm fronds as well, bamboo poles aren't very comfortable.
Step 4: Rigging
I had a nice piece of bamboo for a mast but a windsurfer mast or aluminium tube would have been better. The point where the diagonal braces cross looked about right for a mast step.
Step 5: Painting
I had a half dried up can of acrylic house paint with the following properties:
-Fast drying time
-Water clean up
-Poor adhesion to most surfaces
-Low water resistance
-Delightful nautical grey shade
-In my shed
All in all, perfect for a one day ndrua.
Step 6: Put It Back Together
Everthing was lashed back together and I added a few extra bits and pieces to attach sailing stuff to.
Step 7: Sailmaking
For simplicity we decided to go with a shunting staysail rig, however there are many other optionsoptions for a shunting craft.
Basically I bought a cheap tarp and cut in some slightly rounded edges to give it some camber. I folded these edges over and taped them with low quality duct tape to create a sleeve for the luff/leech wires to run in.
I had some stainless steel wire around which I used to make the mast stays and the luff/leech wires.
Step 8: Float Test
It may seem ridiculous, but the whole time I we spent working on this boat we were not completely sure that the little hulls would have enough bouyancy to float a person. As you can see, the ndrua definately floats, but not by a huge margin. You had to be very careful to keep your weight centred over the hulls evenly so as to not submerge a hull or pair of bows. Due to this fact and all the bamboo everywhere paddling the craft was fairly awkward.
Step 9: Sailing Trial
Up went the mast and the sail was hoisted (yes I even had a halyard). Unfortunately the wind was very light and I couldn't get the sail to fill properly. Nonetheless, I slowly made it across the river on a close reach, fluked a shunt and made it back again, this time on a broad reach. Due to the massive influence of shifting my own weight, I didn't need to use a paddle to steer.
Step 10: Rig Modification
It may have been partly due to the lack of wind, but I never could get the loose footed sail to set properly. A long stickish object was laced onto the foot of the sail which improved things considerably.
This is about as far as experimentation ever went with the One Day Ndrua. The boat was just too small and difficult to sail to be very good for anything much, but it was still heaps of fun. More boatbuilding Instructables are on the way.