The rules allow several options in the construction of the boat, due to the different weights of plywood available in different parts of the world.
The description which follows is based on the use of relatively lightweight plywood which permits 12mm plywood to be used for the bottom panel. It should not be used unless 12mm plywood of a maximum weight of 6 kilograms per square metre (kg/m2) and 6mm plywood max 3 kg/m2 is available.

The drawings enclosed with this article are intended as a supplement to the official plans and rules which are available from the IODA. The panels of the sides and bottom are expanded views of the panels. Think of an orange peel laid out flat so that when it is folded up it takes the shape of the orange again. Although the method that is described here is meant to minimise the use of frames and moulds, the requirement to check measurements and fairness of the hull is very important to ensure that the hull will measure when complete.

A warning:
the Optimist is tightly controlled by over 60 measurements and the tolerances of the wooden hull are in general plus or minus 5 mm. The tolerances are not meant to allow a builder to exploit the possible shapes available but to allow a competent builder to construct a legal hull. The use of a simple mould made from cheap plywood or particle board/chipboard to form the bottom is recommended. The bottom can be screwed, clamped, or weighed down to hold the bottom curve while fitting the sides.

Materials

As noted above this guide assumes the use of lightweight plywood.
The most widely available type appears to be made using a wood known as Gaboune or Okoume.

The 12mm plywood used for the base is 7 ply and appears to weigh between 16 and 18 kilos per standard sheet of 1220 x 2500mm.
The 6mm plywood used for the sides and transoms is 5 ply (the minimum permitted by the Rules) and appears to weigh between seven and nine kilos per standard sheet of 1220 x 2500mm.

It is important to use only marine grade plywood which lasts longer, is easier to paint and will not delaminate like lesser plywoods. Unfortunately it seems that neither apparent conformity with the British Standard (BS) 1088 nor the U.S. standard PS 1-95 guarantee perfect quality and expert advice is recommended.

For one boat you will require:

1 Sheet 1220 x 2500mm 12mm plywood (7 ply) for the bottom, mast-thwart and midship frame.
1 Sheet 610 x 2500mm 12mm plywood for the daggerboard case. There will be enough left over for a plywood daggerboard and rudder.
1 Sheet 1220 x 2500mm 6mm plywood (5 ply) for the sides, transoms, mast-thwart bulkhead and corner pieces.
1 sheet 610 x 2500mm 3mm plywood (3 ply) for the hog and stringers

If possible get an "offcut" of 18mm min. size 200 x 880 for the mast thwart (saves gluing 12mm and 6mm together). Note: Some saving may be achieved if more than one boat is built together.