Building a Traditional Wooden Boat #2: Lofting

After about 12 hours of work, nearly all lofting is complete and I can finally start some construction! The famous boat builder and author, Howard I. Chapelle wrote in his aptly named book ”Boatbuilding” – ”There was never a boat built in which too much lofting had been done”. By lofting, Mr. Chapelle is referring to the laying out of the lines and drawing of construction details to full scale, a tedious practice he writes ”avoids much trying and fitting”.

Setting up the lofting area

To begin, I cut up a 4×8 sheet of 3/4 plywood to create a lofting “table” that is 12’x32”. This is large enough to draw all 3 plan views (sheer, body and half-breadth) which are drawn over each other. After leveling the table, I rolled out red rosin paper, an option some builders use to draw the plans on instead of drawing right onto the plywood (or traditionally.. the floor of a loft). I then layed out the all important “base line” and tacked a straight edge on that line from which measurements would be made. A large grid is then drawn over the entire area to indicate vertical stations and horizontal waterlines.

Drawing the Profile and Half-Breath view

There are virtually no straight lines on this boat. I was immediately faced with the problem of how to correctly draw long curved lines. An ideal curved line is a fair curve – one which has a smooth continuous flow to it. It turns out to be relatively simple to do, but does require a good eye. The process essentially involves the use of long wooden battens of straight grain and clear of knots. To create the curve, you “loosely” bend the batten around nails which are tacked onto the “grid” according to measurements in the plans. It’s basically “connect the dots”. The boat plans includes a table of offsets which have measurements for where you place your marks. Once the curve looks fair, you draw the curved line against the batten with a pencil, remove the batten and do the same thing for the next line until you have something that looks like a boat. The following photos show the line for the profile sheer (top edge viewed from side) and a waterline (water level at 6 inches viewed from top). Notice how two different views of the boat are drawn in the same space.

Drawing the Body Plan

The body plan is the head on view of the boat and is drawn right over the other 2 plan views that were previously drawn. The measurements are taken from the lofted lines in the previous 2 plan views and the batten is used again to “connect the dots” and draw curved lines for the body plan sections. The body plan shows 7 cross sections of the hull from front to back (stern to transom) with the 5 equally spaced stations in between. The layout of each station are the templates for the actual station molds which will be used later to form the hull. The photos below show the shapes of the hull from head on. The reason for the white paper overlay is to show the construction detail of how the hull planking will join to the keelson and keel on the bottom of the boat. Because there are 7 body sections all overlapping in the same space on the plans, separate pieces of paper are tacked in place as needed for each section so that the details are not a hopeless mess of overlapping lines.

Final Results Example

The following is an example of a different boat showing the 3 plan views. In the actual lofting, these views are drawn right over each other.

Lessons Learned
I’m not crazy about the red rosin paper. It has small wrinkles in it that slightly distort the lines. It’s not enough to throw off any measurements by anything more than 1/64th probably, but it’s not ideal. Next time, I’d whitewash the plywood and draw onto that directly.

Lofting Materials List:

• Red Rosin Paper, Home Depot, $12
• 3/4 Plywood 4×8, Lowes, $23.88
• 1×4x12 clear pine, Home Depot, $12

Project Materials Summary:

• Plans and Book: $60
• Lofting Supplies: $47.88

- Total Project Expenses so far: $107.88

Labor Hours Summary:

• 5/29/09 – 6/8/09: Lofting – 12 Hours

- Total Project Labor Hours so far: 12 Hours

-- Matt - Syracuse, NY