On To Lofting

It may seem a bit ironic that this entry comes very nearly two weeks after my Something Every Week entry.  But, in fact, there has been progress in the meantime.  In the last episode, our ambitious (read: novice) boatbuilder completed the lofting floor and readied himself for beginning to lay down the grid and lines.

First up was laying out the grid for the lofted drawing.  Boat shapes are captured in two dimensions on the drawings in the form of lines and coordinates of the hull’s intersection with three sets of planes in space.  These datum planes are the Stations, which are vertical transverse planes (think a sliced loaf of bread); the Waterlines, which are horizontal planes parallel to the (wait for it…) waterline; and Buttocks, which are vertical planes aligned parallel to the longitudinal centerline.

So to begin the lofting, lines representing these various planes intersected with the lofting floor are laid down.  These will form the grid on which the various intersection lines of the hull shape are projected in profile, plan, and body (i.e. end-on) views.  Here, I’m using an improvised beam compass and some high school geometry to mark the station lines perpendicular the base line.

Next up was to get some battens together to use for drawing and fairing the curved lines representing the boat shape.  These need to principally be straight, uniform, and have appropriate stiffness to be able to be bent into fair curves.  I was able to find a few pieces of lattice at the local lumberyard of suitable dimensions for some of the shorter, tightly-curved lines, but for the longer, gentler curves like the sheer profile and such I needed to make something up.

Making this long batten proved to be more of a hassle than I anticipated.  I found a 14′ length of 3/4″x4″ clear, vertical grain cedar molding which looked promising to rip a couple of strips from to be glued together for a nice, almost 28′ batten.  This is essentially what I did, but the only fence I was able to find for my circular saw really wasn’t up to the job (sloppy fit, etc.) so there was quite a bit of wander on the cut.  This meant a lot of time spent with a plane trying to recover a uniform thickness.  My intention had been to rip to 1/2″.  In the end, as a result of the wander in the cut, it ended up at about 3/8″ thick.  In then end it worked out okay, but what I’d expected to take me 1 to 2 hours ended up taking the better part of the day.  In hindsight, I should have cut (pardon the pun) my losses and ripped two new pieces with a better fence arrangement.  Anyway, here it is during glue-up.  This is close to the longest thing I can glue in my workspace. 🙂 

With the batten made, it is on to lofting proper – the first time something vaguely boaty shaped will appear in the shop!  The first step is to lay down the sheer profile (side-view) based on the height above the design water line (DWL) at each station, taken from the drawings.  With the points plotted on the grid, the batten is used to join them in as fair a curve as possible, tweaking the the locations a tad if necessary.  Even though the batten ended up thinner than I’d envisioned, it seemed to work out well.  It is edge set here, and seemed to be a good stiffness in that arrangement.  This picture is mid-process.   Towards the center  there’s a bit of un-fairness which I was eventually able to get out.

Finally, with the curve fair, it is drawn in.  Since the various views (profile, plan, and body) will all be superimposed, I got some colored pencils to aid in distinguishing which lines correspond to which views.  Profile=Red.

So with that, Ta-Da! The sheer profile! (NB: The only hope you have of seeing it in these pictures is to click and open up the full-size view.)

Sheer Profile From Bow

Sheer Profile From Stern