Lofting errors in the mill creek 13 manual and plans?

I am in the process of building my first MC13 from the kit and and was looking down the sheer panels after scarfing them together and noticed that I had a very slight kink in the top of the panels where the scarf joint is.  I used the scarf offset specified in the manual at 1 3/16".  this got me to thinking and I looked up the table of offsets in the plans and noted the offsets for the lower edge were only 7/8 to 15/16 from the base line in that area.  So being that I am an engineer, I took the table and plotted the offsets in CAD and drew a spline through them.  I did find that at the scarf joint based on the spline it came out to be slightly less than 15/16" and not 1 3/16".  I did also notice in the CAD model that the front half of the lower edge was rather wavy and not all that "fair" based on the offsets on the drawing.  Has anyone else found this to be true or am I just worried about nothing?  I am enjoying the build so far although  I'm only at the stitching phase right now.

Thanks for any input.


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RE: Lofting errors in the mill creek 13 manual and plans?

Input any ten kayak designs into CAD from offsets on blueprints and you'll get waviness.  This is not tomfoolery, but the nature of rounding the dimensions to the nearest one-eighth or one-sixteenth.  It only takes 1/32" to introduce a bump into a CAD drawing.  Unless we give you three decimal points for every offset, it's impossible NOT to have some departures.

The problem is, you're building a stitch-and-glue kayak and not an airplane. Those Mill Creek plans are meant for ordinary people working on the floor of their garage with a wooden batten to fair the offsets.  The tolerances are broad, to allow beginners to make mistakes but still get a beautiful boat.  Pages 53, 54, and 55 in the instruction manual are devoted to the issue of interpreting the offsets and yielding fair curves.  In pencil, on plywood, not on a CAD screen with splines of Euclidean thinness.  

That's for people building from plans.  Folks building from kits should stick with the kit instructions.  The Mill Creek kits have enjoyed 16 years of tweaking for CNC cutting.  The differences between the Mill Creek's CNC-cut panels and those diagrammed in the plans is small; not enough to have the slightest effect on form or function.  But enough to drive the engineers nuts.  

We haven't done a design with "offsets" for panels since about 2005, and no such kayaks since about 2001.  We ship full-sized patterns instead, which removes the need to fret about these things.


RE: Lofting errors in the mill creek 13 manual and plans?

Ok, thank you for the input on the panel waviness. The main thing was the offset on the scarf joint.  I just thought that having the extra .25" at the joint would add an unnessecary hump to the top of the panel and the line would not be fair.  I ended up planing down the hump to make it fair.


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