By David Berg, Spring 2009
Written for Rudder, the official magazine of the Antique & Classic Boat Society
See full text below, or click on images to view printed article.
“Dave is known throughout the Pacific Northwest for his impeccable boat building and imaginative use of materials. His one-of-a-kind recreated boats from the minds of some of the great designers of the past have been turning heads for years at local boat shows. Here he shares some of the methods for lofting he’s used on a few of his beauties.”
“My grandfather built a Snipe sailboat around 1938. He was a baker so he built the frames out of oak lard-barrel tops. I spent much of my childhood becalmed in that Snipe on the Lake Coeur d’Alene in Northern Idaho. The Snipe still lives today.
Many people used to build boats for themselves and many publications offered plans. Motor Boating magazine offered what was called the Ideal Series books, with over 450 plans, many by great designers like Crouch, Hacker, and Atkin. [More details on the Ideal Series are found at the end of this article.] Edwin Monk published Small Boat Building in 1934, a book that offered many plans and a concise boat building section. Monk’s book was later published by Wooden Boat Books in paperback. These books can still be found and considering the plans offered, they are usually priced quite reasonably.
Boat plans show three views of a boat. The body plan shows the shapes of the frames with one side looking aft and the other looking forward. These shapes are the sections of the boat as if you ran the boat through a bread slicer. Also shown is the profile view which shows the layout of the stem, waterlines, chine and sheer “lines” and spacing of the frames. The third view is the half-breadth view which shows the lines of the boat as viewed from above. Only half of the boat is shown because it is symmetrical.
Example 1 is the plans and offsets for Sunbeam from Edwin Monk’s book. The three views of Sunbeam are drawn from the data in what is called the table of offsets. Offsets are simply measurements that allow you to draw the plan full size (lofting), up from the base (heights) in the profile view and over from the center (half-breadths) in the view from above. Both heights and half-breadths are used to develop the body plan. The numbers in the left column of the table of offsets refer to the sections of frame locations measured aft of the stem. Number 3, for example, would list the heights up from the base for the keel, chine and sheer at frame 3. The half-breadth data gives the location over from the center line and the two measurements establish each point. Connect these points and you have the shape of the boat at frame 3. Add to this the frame location aft from the stem and you have three dimensions. Loft all the frames and spread them out to create a three dimensional boat. Loft just one frame and you will see how easy it is. The offsets are given in feet and inches or, traditionally, feet, inches and eighths. For example 27 ½ inches is expressed as 2-3-4. Two feet equals 24 inches plus 3 inches and 4 eighths.
Sunbeam is a simple straight section boat, which means the lines from keel to chine and chine to sheer are straight lines. Believe it or not many really sweet boats have straight sections that have the advantage of being easily sheeted with plywood. (This drawing doesn’t show the deck profile, but it is called out: 3 ½ inches in five feet. This is the crown of the deck. The five feet covers the widest beam and as the boat narrows going forward or aft, the center of the crown profile is used as necessary. Thus, as the boat narrows, the crown flattens. The boatbuilding section in Monk’s book describes how to lay this out.) A more complex boat with curved frames would simply have more points between the keel and chine or sheer and chine to establish the curves (see the note referring to frames 7 and 8). Other points would be established on water lines parallel to the load water line (which is usually where the boot stripe is) and buttocks lines, parallel to and outboard of the center line. When these points are established and connected with a batten they form the curve of the bottom or sides of the frames. See the body plan in Example 3 for an example. A batten is used to line points up on a curve just as a straight edge or string is used to line up points on a straight line.
Since boat designs are scaled up from a small drawing there are often small errors in the locations of the points when drawn full size. When connecting points with a batten, the number one lofting rule is “a fair curve supersedes any measurement.” When sighting along a curve, a lump means the curve is “unfair”. Straight-grained, clear wood naturally bends in a fair curve, which is why wooden boats are so pleasing to look at. For this reason straights grain wood is used for lofting battens. Welding rod makes a good batten for tight curves.
Most small boats can be built by lofting the frames and stem only. Monk’s design of Sunbeam includes a stem detail, which includes the location of the rabbet. The rabbet is simply the outboard edge of a notch where the planking meets the stem and the keel. The angle of the rabbet changes as the shape of the boat changes. The bearding line is where the inside of the planking meets the stem or keel. The angle of the rabbet changes as the shape of the boat changes. Boat lines are typically drawn to the outside of the plank and the thickness of the plank is subtracted from the outside of the frames. When lofting, the thickness of the plank is subtracted from the frame profiles and a notch equal to the thickness of the plank is cut into the stem of keel to accept the plank and allow for fastening. The half-breadth plan shows the angles where the plank meets the stem at the sheer and chine but a batten can also be used to lay out these angles after the frames, etc. are set up.
Example 2 from Ideal Series Volume 22 is the Hacker-designed 16’ runabout, Lorraine. These drawings show a way of lofting frames without a table of offsets. The layout of each frame is shown. The same result is obtained but a different method is used.
Another way of lofting a boat involves the use of a photo copier. Example 3 is a sketch and body plan on page 98 of Fostle’s book, Speedboat. This sketch illustrates an early George Crouch hydroplane, one of the first hydroplanes ever designed. Since there is no table of offsets shown to loft from, it was necessary to increase the sketch to full size using a copy machine. There is enough detail in the sketch to determine the full size of the boat. Using this method, I built the boat Commander McBragg (see photo) from that sketch. This shortcut can be used instead of lofting, but lofting is an enjoyable process and provides the builder with a better idea of how to build the boat. The text of a plan gives material sizes, etc, but a builder can improvise by using good judgment and seeing how existing boats were built.
Often a boat plan as designed is not the desired size. If this is the case, you can loft it on paper and then a blue print machine can be used to scale it up or down. The stem profile must be included and the frame spacing adjusted to the same scale when laying out the frames. The frame spacing can also be changed to lengthen the boat if desired. Artistic license is encouraged. The boat Greyhound is a Hacker design that was stretched and modified by the builder Robert Yandt to fit a Sterling Dolphin motor. This boat was on display to the ACBE International Boat Show in Coeur d’Alene, Idaho, Last September.
The boat plan and stem can be lofted on thin sheets of plywood or, if a copier has been used, the paper can be glued to the plywood. Before the frame patterns can be transferred to the frame materials, motor stringer positions should be marked on the body plan and their location transferred onto each frame. When sawing out the frames, also notch for the motor stringers. To make frames, transfer the lines to the framing materials using a small drill bit to drill through the pattern. The pattern will have to be flipped on the center line to drill the second half from the backside for a complete frame. The drilled points are then connected to create the frame profile. With the center lines already located on the frame material the load waterline must be marked on each frame and stem. The frames and stem can then be laid out on leveled motor stringers using the water lines and center lines as references and then the framework of the boat is set up.
Included from Volume 12, of the Ideal Series are the lines of William Atkin’s 1930 plan Rampant. This plan calls for a V-drive, double cockpit with a dodger and flush decks forward. Instead, it was built as a straight-drive, triple-cockpit with crowned decks carried clear forward. (See photo, top of page 18.) Since the boat is quite narrow and double ended, it was built light, with a small 215 cubic inch aluminum V8 with a total boat weight of 1560 pounds.
You may have a motor or even a piece of hardware that you would love to see in a suitable boat, so why not build one? It is truly easier than restoration and is a very rewarding experience.”