Construction and Design Journal – 14ft Dory for Rowing and Sailing – Part 2

by Roy Heberger - Boise, Idaho - USA

LOFTING – January 2004

The Lofting Board – It was time for action.  I’d decided to build this boat, so in mid January I purchased the materials (two sheets of plywood and firing) to build a lofting board that was 4′ X 16′. Rather than scarf two 4′ X 8′ sheets of 1/4″ plywood together, I built the lofting board so I could take it apart for storage after the boat saw built.  I backed the plywood with 1′ X 2″ dimensional lumber (firing strips).  It is rather sturdy.  On the upper surface I rolled two coats of white exterior primer paint.  I was ready.

Full-Scale Lines Drawings – In late January, using my offsets from the lines drawings, I started to put points and lines on the lofting board at full scale.  I had never done this before, but given my four-and-one-half years of training in drafting (high school and college), all of the lines drawings I had done the past summer; the readings I had done in Gardner and Manning, in Rossel, and in Steward; and with the two weeks in August 2001 at the Northwest School of Wooden Boatbuilding, I thought I could do it.

I came up with a detailed nomenclature to label all points and lines.  As the reader will see further below, this is a very important step in the process.  Some are full words, while others are abbreviations – all used on the lofting board.  They are as follows:

BL – Baseline; CL – Centerline; BP – Body Plane; HB – Half-Breadth; P – Profile; St – Stem;

S – Sheer; K – Knuckle; B – Bottom; CT – Cabin Top;

T – Transom; GB – Garboard; SB – Sheer board; STBD – Starboard; and PT – Port.

I used my Dad’s, old, steel T-square to establish a combination baseline/centerline and for the station lines perpendicular to that.  Note that the station lines depicted the aft edge of the frames at stations 1-4 and the fore edge of the frames at stations 5 and 6 and at the inside of the transom. Allowing for bevels, these are to be the widest portions of each frame and the transom.  The stem points for sheer, knuckle, and bottom were to the bearding line.

An additional note seems a good idea here.  Because of the “watertight” design of the fore and aft cabins, a bulkhead is to be sandwiched between two frames at each location.  The bulkheads are at stations 2 and 5.  So I decided to use stations 2c and 5a for construction purposes in defining the shape of the hull and cabins.  These are the station frames that will be visible from the finished cockpit.  Lines for the bulkheads (stations 2b and 5b) and for the additional frames inside each cabin (stations 2a and 5c) will be lifted later.  (As it turns out, I did not end up sandwiching the bulkheads between frames as it became evident to me that, that was unnecessary.  Much of this boat may be “overbuilt” as is.)

Frames – Lifting the Lines

Top: Frames laying out for fastening and set for glueing & screwing.

Above: Planing the frames square and sawing the joints.

Using the offsets developed from the 1:12-scale drawings, I located the bottom, knuckle, sheer, and cabin top (all elevations) in profile along each station line.  Except, there is no cabin top at stations 3 and 4.  (Note: I ended up extending the forecabin top to Station 3 as an after thought but at this stage I had not contemplated doing that.)  All such points were clearly made and labeled using a sharp pencil. I drove finishing nails into each station point along the bottom and sprung a baton to obtain a fair curve depicting what the bottom would look like in profile.  I was delighted with what I saw, so I then penciled in the inside of bottom and labeled the resulting line.   I did the same for the inside of the knuckle, the inside of the sheer, and the inside of the cabin tops (a continuous fair curve from stem to stern).  All were fair curves.

Some adjustment was needed at a few of the points along the knuckle and sheer lines.  Corrections were made on the lofting board by erasing the old points and labels and inserting new ones.  They told us about this kind of thing at boat school, so it was not a surprise.  I suppose the original offsets from the 1:12-scale drawings contained multiple kinds of errors – measurement and recording.  Also, the extrapolation from scale to full-sized drawings reveals errors as well.

The fairing baton I used was left over from the Six-Hour Canoe (a solo dory) I’d built in the winter of 2001 before attending boatbuilding school.  It is knot-free medium-density fiber board (mdf – a flexible building material) in a 1″ X 2″ dimension and > 16 ft. in length.  Having a very uniform construction texture it produces very nice fair curves, as long as the radius is not too small.  It works well for all lines in profile and half-breadth views, but would not work well at the stem.  There I used a thinner, knot-free baton left over from siding I used for a home improvement project.  It too worked very well for obtaining a fair curve with the smaller radius at the stem.

Once the lines were established in profile, I went back to the original offsets to locate the half-breadth measurements (widths).  Repeating the procedure above, I obtained fair lines for the bottom, knuckle, sheer, and cabin top in the half-breadth view.  Note again that the lines depicting the fore and aft cabin tops are fair for the entire length of the boat, just as though there was to be one continuous cabin from stem to stern.

Here I will note that while my lines drawings on paper were all separate, but math-related views, here on the lofting board space does not allow for that luxury.  So, the profile and half-breadth views are overlapping.  The lofting board is getting rather busy with lines at this point, but it is only the beginning – hence the need for exact labeling of lines and points in both views.  Friends said to me that my lofting board was beginning to look like a star chart.  They could not see the lines, but they did not study the board either.  By studying the lines, points, and labels I could easily discern what was what.

Now, I was ready to develop the third view or views in this case.  But this time rather than develop the view from the bow and stern as I had done previously on paper, I needed to draw individual body-plane views of each of the frames and the transom.  To be able to actually construct frames on the lofting board, I had to separate the developed body plan lines so that the frames would not overlap. Those points and the resulting set of straight lines depicting the futtocks, ribs, and cabin support beams are the key to building the boat.  Literally, those lines are used to give shape to the frames and the transom.  When the frames, transom, and stem are fastened to the strong back to look like the skeleton of an animal, we have literally lifted the two-dimensional lines on the lofting board to the three dimensional boat.  Cool!  Way cool!

I could have used tic-sticks to obtain each elevation above the baseline or half-breadth from the center line to develop the body-plane views of the frames without actually taking a single measurement.  But I wanted to capture the final offsets to paper, so I measured all elevations in profile and all widths in the half-breadth view and recorded each in a two new tables of offsets.  In Tables 1 (hull) and 2 (cabins) are the new and more precise offsets.  Note that I depart somewhat from convention as I was able to measure to better than 1/8 inch.  So rather than showing just the three numbers depicting feet, inches, and eighths of inches, I showed the last eighth of an inch using a decimal as well.  Because I could be this precise, I was so.  These tables and Table 3 may be used to build another boat.

So, using the new offsets I developed the lines for the frames at stations 1, 2c, 3, 4, 5a, and 6.  I did this by rotating (squaring) the view in profile to a body-plane view so that each frame when drawn on the lofting board was viewed from the bow.  That is, I was viewing the forward aspect of each frame.  This required compensating for the thickness of the frames at stations 1 – 3 to allow for an eventual bevel.  It did not matter at station 4.  It was perpendicular (no bevel required) to the to the planking at that location along the fair curve.

For my records, I recorded the distances between stations (Table 3) in the event I wanted to build this boat again and had not taken good care of the carefully drawn profile and half-breadth lines and developed body plane frame lines on the lofting board.

Part 1 – Part 2 – Part 3 – Part 4 – Part 5 – Part 6 – Part 7 – Part 8 – Part 9 – Part 10

Part 11 – Part 12 – Part 13 – Part 14 – Part 15 – Part 16 – Part 17 – Part 18 – Part 19

APPENDICES

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