Blog
Jan 23, 2006
Sharks, Gators, Greenland skills
Jan 15, 2006
Baidarka double.
Router trials and tribulations.
Jan 08, 2006
Military Architecture.
The future, a highly speculative view.
Jan 01, 2006
Plastics, tule and transforms.
New Year's storms.
Dec 18, 2005
Atka baidarka.
Spruce Odyssey
Dec 11, 2005
Shop and boat ramp.
Coast Guard, Cormorants and the Homeland Boondoggle Boat
Dec 04, 2005
Boat maintenance and black helicopters.
Photos, videos and paddle blanks.
Feb 8, 2006 - Building Boats Again
Work on the two-hole baidarka is progressing. Meanwhile, I've had two new insights. The first regards bow configuration of baidarkas. The second insight regards grain orientation in paddles.Bow Configuration
I was looking at the drawing of an Aleut double in Contributions to Kayak Studies. It's an Unalaska style boat and its bow configuration is different from the Atka approach in that the bow plate has a kind of horn that rises up above the elevation of the front of the keel. This is quite a handy configuration since when you turn the boat over, such as to drain water out of the cockpit, you are likely to rest the boat on its nose. In the Atka bow design, weight is supported by the upswept part of the keelson. Since this part has cross grain, it is likely to snap off, especially when the wood is older and has been weakened by water. The Unalaska design on the other hand puts the weight on the horn of the bow plate, keeping the strain off the tip of the keelson.
Maybe a little hard to see, but there's kind of a rhino horn coming up off the bow plate just behind the upswept part of the keelson behind the bow slit. The horn is higher than the upswept part of the keelson, so it would offer some protection when the boat is inverted.
The nose of the Atka baidarka on the other hand is unprotected and more likely to break off when the boat is inverted and rested on the nose.
The Bending of Boats
When building replicas of boats, I have always wondered if they were drawn accurately. It's hard to tell, really until you build them. One thing I have noticed about Aleut doubles that people have built is that they tend to give the bow paddler a wet ride. Waves seem to come over the deck and slam the bow paddler into his/her chest resulting in much spray and a constantly wet face. This is fun maybe once or twice, but not for a whole afternoon.I am beginning to wonder if people aren't building their doubles too flat. Take another glance at the Aleut double shown above. The paddlers seem to be on pretty flat water and yet, the first two or even three feet of the boat are out of the water. The tail is also riding quite high, seeming to almost clear the surface of the water. There seems to be quite a bit of rocker in the keelson and the section of the boat in front of the front paddler seems to be tilted slightly upward. Who knows, this boat might have been sitting on some logs for the winter and taken on some extra bend, but my guess is that the bow paddler in that boat had a drier ride than I've had whenever I've been in the bow of a double.
Anyway, look at the two pictures following some more evidence for more curvy boats.
The bow is out of the water, not as much as in the photo up the page, but still clearing.
Doubles in winter storage. Considerable curve in the keelsons, even when the boats are sitting keelson down. Also note the quite slender ribs on the baidarkas in the foreground.
Flat vs. Vertical Grain in Paddle Blades
The blades of oars were typically made of flat grained wood. The main reason given was that vertical grain blades would be more susceptible to splitting. Good reason. But I also wondered whether there was a difference in stiffness between vertical and flat grained oars and paddles. I set out on the internet to find the answere, and as usual, found lots of information but no revelation of whether one grain orientation was stiffer than the other.So I went to the Wood Handbook and after much page flipping found that modulus of elasticity, a measure of stiffness is greater for flat grain than for vertical grain. Ok, there we have it. How much difference, I don't know, but I suspect that the more pronounced the difference between winter and summer wood, between the light and dark rays, the greater the difference in stiffness. In general, I prefer more flexible paddles, so vertical grain would be advisable. But if someone wanted stiff blades, flat grain might help. Then again, so would stiffer wood. And I suspect that variation in stiffness between species is greater than variation between vertical and flat grain in the same species.
In between my fruitless search on the internet and the search in the wood handbook, I also called my brother, who works for a lumber manufacturer to see if he knew the answer. He wasn't sure, but he was willing to speculate. Anyway, to put the whole issue on a firm scientific basis, he has sent me some sticks to do experiments on. You will see the results published here, soon as I find enough time to hang weights off sticks and determine the relative stiffness of vertical and flat grain in the same species.