Header photo (detail) courtesy Michael Eudenbach

Saturday, March 12, 2011

Lofting 1.0, preliminaries


photo Thomas Armstrong

Sorry about the quality here, but a more defined photo might infringe on Mystic copyright.
Drawn by RC Allyn in 1974, lines taken off a Beetle Mfg. Co. boat that arrived with the CW Morgan.

photo Thomas Armstrong

Batten pinned

photo courtesy Wendy Byar

Lofting floor

photo courtesy Wendy Byar

photo courtesy Wendy Byar

from Wikipedia:

Lofting is a Drafting technique (sometimes using mathematical tables) whereby curved lines are drawn on wood and the wood then cut for advanced woodworking. The technique can be as simple as bending a flexible object (such as a long cane) so that it passes over three non-linear points and scribing the resultant curved line, or plotting the line using computers or mathematical tables.
Lofting is particularly useful in boat building, when it is used to draw and cut pieces for hulls and keels, which are usually curved, often in three dimensions.
Lofting is the transfer of a Lines Plan to a Full Sized Plan. This helps to assure that the boat will be accurate in its layout and pleasing in appearance. There are many methods to loft a set of plans.
Generally, boat building books have a detailed description of the lofting process, beyond the scope of this article. Plans can be lofted on a level wooden floor, marking heavy paper such as Red Rosin for the full sized plans or directly on plywood sheets.
The first step is to lay out the grid, mark the Base Line along the length of the paper or plywood sheet. Then nail Battens every 12 inches (or more in some cases) where the station lines are to be set as a mark for the perpendicular line, which is marked with a T-square. The previous steps are followed in turn by marking the Top Line and the Water Line. Before continuing make sure to check the lines by using the Pythagorean theorem and make sure the grid is square.
The second step is to mark the points from the table of offsets. All measurements off the table of offsets are listed in Millimeters or the Feet, Inches and Eighths. The points are plotted at each station then use a small nail and a batten to Fair (draw with a fair curve) the boat's lines.

from Wendy Byar:

"The beginning of a new boat means drawing the shapes full size from a set of offsets (feet-inches-eighths) that determine points. Battens bent to meet these points are adjusted for fair curves.

The plans for the whaleboats being built at Workshop on the Water and Rocking the Boat are available from Mystic Seaport. These drawings were done by R.C Allyn in 1973. They are the lines from a Beetle Whaleboat. Beetle built about 50 boats a year between 1834 and 1854. A set of lines like this gives all the information a builder needs to produce a boat with the given shape.
The plans for the Whaleboat have a table of offsets in the corner. The offsets are read in feet-inches- and eighths of inches. These coordinates specify points on given lines. They are the given locations where a long flexible batten may be bent along to make a fair line.
The lines on the plans are drawn in three axes, or planes intersecting each other at right angles for the most part. (the diagonals make a fourth set of planes, not at right angles.)

The whaleboat we are building at the Workshop on the Water is about 28 feet long, so we need a drawing surface at least that long.
Four sheets of luan were screwed to the wooden floor and painted white for good contrast with the pencil lines. The paint makes it easier to erase, too.
A baseline was laid down using a very tightly stretched string. Marks were made along one side of the string and a 30' straight line was drawn using a straight edge to connect the marks. This line needed to be true since the rest of the boats geometry is drawn in relation to it.
Station lines were set up every three feet along the base line as indicated on the plans. These lines are 90ยบ to the baseline. They were drawn using the 3, 4, 5 triangle method to assure right angles. Each station line was labeled with its number."

There's more to come on the lofting soon, The photos above are from a trial lofting for educational purposes, the boat will be re-lofted soon, and we plan to follow that. (ed.)

1 comment:

  1. I"m gladsome to mature so more serviceable and informative assemblage on your website. marking tapes and lines