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kayak_building_with_fir

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  1. Hi! Sorry to hear of your troubles. I am struggling also with a twisted frame as well, but I haven't skinned the boat yet. Was the frame straight before you skinned it? If so, I would guess that when tensioning the fabric one side was pulled tighter than the other, did you notice anything like this? What did you use for skinning? Polyester can be tightened with a hot iron. If you think about it where the twist is coming from, maybe you can counteract this force by tightening on the opposite side? There is also this skinning technique, where the skin is tightened with some tightening sews and only then is sewed shut. If you you in with direction to apply the counteracting force, this could be applied? Just thinking out loud, hope it helps Keep us updated.
  2. @labrat: This sums up my thoughts in one sentence, thanks! English is not my first language. If I look carefully at my gunwales, the port side is nice and has straight grain, but the starboard side has a funny pattern in it behinde the cockpit. One week of applying quite some torque did not help at all, did not try with steam though. Today I spent some time trying to figure it out again with a friend. We tried multiple things, e.g. opening the gunwale lashing in certain frames and bending it out (with a shin), but whatever we tried did not match what we predicted. It's kind of tricky, because there is always translation and rotation (=levering) and that in both directions of the change). One more thing worth mentioning maybe, is that most of my scarfs were not good enough. They will hold becaues they have a neat fitting, but the are not as straight as they could be. Also, all these changes did not have a lot of impact on the frame, which is good as it shows the frame design is rather robust. Thanks for the design @Kudzu! In the end I opened the bow gunwale lashes and planed away a bit of the port side gunwale. This helped a little bit, but I did not dare to go any further as it might skew something else. Anyway, as I am out of ideas proclaim my curlew frame as ready for skinning! As I am out of ideas mostly. If it turns out to not track well, I can still add a skeg to make it go straight. What do you guys think?
  3. Today I check all the frame distances between each other and also with respect to a "zero" point, which is a nail in the middle of the keel in the cockpit. Still, all the distances are symetric. Which makes sense, as I double and triplechecked while it was still on the strongback. Also, the gunwales were always level, and also the frames were vertical when checked with a waterscale. When installing the stringers I always tried to match left and right stringer so they needed an equal amount of force to fit to the frame. So my theory is, that one diagonal opposing pair (e.g. top right gunwale and bottom left stringer) is not so well balanced (one is bending inwards too easily, where as the other is resisting this much more). Don't know though how to find it, and also I don't know what I would do with it if it would fit. Anyway, now I put it back on the strongback and level the stern. Then I measured carefully with a waterscale going forward one frame a time and it seemed like most of the twist happens where there is long distance between frames where the cockpit will be. Doublecheck this by leveling the bow and measuring backwards, and voilà, I ended up in the same spot. Now I applied some torque with some improvised levers and bungee cords as shown on the picture, and wait for a few days. @lattenkracher: Doublechecked, was fine. @Kudzu: Thanks Jeff for the hints, this brought me in the right direction. Actually I now think it was the faulty part is one stringer that was not scarf in the straightest way, which is causing the bend. Let's see how it goes, if it does not settle (my garage is about 10°C or 50 degree fahrenheit) I can still try a warmer place, or pour some (hot) water over it. If somebody has a similiar problem, this is what I found: Here it explains how to check and then just use force to straighten it. straightening an old canoe some more discussion This is what I have tried: Are all the distances between frames equal, are the frames vertical (check with a waterscale)? Also check looking from top for symetry of each frame. Did you notice that some stringers took more/less force than others to bend them into shape? Check the scarf joints! Are the extensions straight, or point down/up? Where is most of the torsion happening? More in the front, the back, over the whole boat? Thanks
  4. Hello, the title explains it already pretty well. On the strongback, the frame was level and square. Now I took it out of the strongback and it developed a rotation along the long axis. I took some pictures to show it. I can not really tell what is causing the twist, my guess would be the bow. Stringers are spruce and the weight of the frame is 8.4kg, overall it feels rather flexible. I tried to fixate the bow and rotate the stern clockwise, and it helped a little bit but I think it will go back. Is there a way to fix it? How do I find out what is causing it? Thanks!
  5. Today I cut apart the board(picture from last post) I had into stringers and gunwales. I cut away one side to I have a straight edge, and all the others can i cut with the small tablesaw I have. I had help from a second person. Was quite easy once you figure it out, one has to push and the other has to pull, and then I ended up with these beautiful 4.2m long stringers and gunwales, which I then scarfed together with one extra meter. Really happy how it turned out, as there are no knots, defects, or branches. Also, the grain is quite straight over pretty much the whole length, so it is as good as it gets. The board I bought at a local lumberyard, where I explained what I wanted and they gave me this for 22€. Now it looks like this and the joints are drying: Next I will give it a quick sanding with the beltsander and a 120 sandpaper, and oil it with tungoil as well. Next week will be quite busy at work, so I guess I will only start assembly next weekend. What I still don't know is which lashing/fabric/paint to use, and of course in which colors to paint it ?
  6. Yes indeed! What I had to ask for in the end was "Wertholz Tischlerware" (in German). Yesterday I finished the frames and oiled them with tung oil, turned out quite nicely. But I was lazy and applied a thick layer, I figured it is easier to saturate once and then wait a bit longer for it to dry. BTW, do you have any tips on to find waxed sinew in the German speaking world, and also for the paint used for the skin ? (the skin you have used I saw in your buildlog) Thanks PS: attached are the oiled frames, and a picture of the plank I'll cut into the stringers. Quality is bad, but it's 4m of what can be seen on the picture.
  7. Thank you both, andy00 and lattenkracher for you responses. I was on holiday, so my response is a bit late. Anyway, I have decided that I will built the curlew and went wood shopping. They did not have fir, so I bought a nice thick plank of spruce without knots, which I will break down for stringers and gunwales in the dimensions that lattenkracher suggested (25 x 15mm; 38 x 15 mm) I'll post some picutres in a separate build-log. cheers!
  8. Hello from Europe! I am planning to build the curlew kayak from the book. As can not find Western Red Cedar in my region, so I am planning to use fir instead. Since it is heavier (26 instead of 23 lbs/ft3), but also stronger, I was wondering if I reduce the weight a little bit by making the keel, stringers, and gunwales a little bit smaller in height and width. I did this the following way: comparing the Modulus of Rupture and Crushing Strength tells me that western red cedar has only 80% of the strength of fir. Thus if I scale the cross section area to be 80% of the numbers from the book, it should give me the same strength. Does this sound reasonable, or are there other things that have to be considered? How are stringers dimensioned, or in other words: how did the dimensions in the book were determined? Thanks Some more details are attached: Modulus of Rupture: Modulus of Rupture, frequently abbreviated as MOR, (sometimes referred to as bending strength), is a measure of a specimen’s strength before rupture. It can be used to determine a wood species’ overall strength; unlike the modulus of elasticity, which measures the wood’s deflection, but not its ultimate strength. (That is to say, some species of wood will bow under stress, but not easily break.) Crushing Strength: Sometimes known as compression strength parallel to the grain, this is a measurement of the wood’s maximum crushing strength when weight is applied to the ends of the wood (compression is parallel to the grain). Western Red Cedar: Modulus of Rupture: 7,500 lbf/in2 (51.7 MPa) Crushing Strength: 4,560 lbf/in2 (31.4 MPa) Fir: Modulus of Rupture: 9,590 lbf/in2 (66.1 MPa) Crushing Strength: 5,950 lbf/in2 (41.0 MPa) Ratio for rupture: 78% Ratio for crushing: 77% Numbers taken from here: https://www.wood-database.com/western-red-cedar/ https://www.wood-database.com/european-silver-fir/
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