Monday, March 11, 2019

Defining the shape

While notches for the stringers were pre-cut in the frames and stems, many of those cuts need to be modified.  The notches were "square-cut" as if the stringers simply passed through at right angles, but, except at amidships, the stringers curve inward and upward as they approach the stems.  So the notches need be be beveled to accept the stringers in a fair curve; a total of 120 notches.  It slows down the process, but provides good exercise as it needs to be done carefully by hand.

It has been said that using developable techniques to design boats tends to result in boxy-looking, uninteresting shapes.  But by using multiple chines, and the inherent accuracy and fairness of the resulting curves, I think that the result can be quite harmonious.

Two longitudinals added so far; two more to go.  I will also add a second strip at the sheer, the inwale.  Beginning to look boat-like, but much work lies ahead.

The inwale and a third stringer have been added.  I have an epoxy allergy (rash), so before mixing a batch, I put every clamp near by, set out the spatula, the applicator, pre-mark every matching location, clear out unneeded objects, put on gloves, etc.  With many small joints to bond, I pre-coat matching surfaces and give the epoxy time to soak in before assembly.  After assembly comes cleanup of any excess squeezing out of the joints.  Thin coats of small quantities cause little exothermic reaction, so the resin takes many hours to harden.  If I warmed my shop up beyond 66 degrees F., of course, the setting would be quicker.

The overall length at this point is 179.5".  The curved length of the sheer is 187.04"  The half angle of the bow is 21.8 degrees.  I used an algebraic equation and projections to provide all the offsets for the hull shape.  I integrated that formula (calculus) to find the curved length of the sheer at each frame & stem location.  I differentiated (again calculus) that formula to find the slope at selected points.  Then I used the inverse tangent function (trigonometry) to find the angle in degrees to set my chop saw.

People say, "Math isn't important; I never use it."  Of course, you don't use things that you have little knowledge of.  I have little use for knitting; perhaps it is because I know nothing about it.  The math I just mentioned is not difficult if you are accustomed to doing such things.

Next to-do is fairing the hull.  Not real fun to do; it is careful work in which the progress is not dramatically evident.  But, it is the foundation for what comes next: making patterns for the sheathing.  Will the shape be nice and linear or have a banana or "S" shape?  I still have not made a final decision on sheathing.  Each alternative has its advantages and limitations.

We are readying for a month-long trip overseas; there may not be much progress in the near future.


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