Mini-Brig Project: Hull Construction

Choosing Your Plywood:

All of the plans should fit on about two-three sheets of plywood. We used two sheets for the bottom and sides, and extra stuff (like our seat compartments in the brig Libertè), and one sheet for the ribs, stern, and bow.  Remember to use thicker plywood for the frames. You will need other fittings like brass screws, glue, and adhesives which we will get to later.

When buying plywood from your local Home Depot, Rona, Lowes or other wood supplier, you might have noticed that all the plywood is "graded". The most common plywood grading scheme is from A to D, with A being the highest quality with zero blemishes and great sanding, and D being the worst with the greatest number of blemishes (allowed).

Grading also typically comes in pairs where each grade addresses a different side or “face” of the stock piece, ie one letter will address the quality issues of the front face and the second, the side opposite to the face. So for instance, an A-C plywood sheet would be highly finished on the front face with a relatively poorer finish on the back. Similarly, construction grade C-D (referred to as CDX) plywood, is great for structural use but not for projects requiring a high quality finish and durability such as a brig.

Veneer grades

Plywood is also available in different types. The best wood for boat building is considered by most to be Marine Plywood. However, Marine Plywood also carries a high price tag. The brigs are generally dry-stored. That is, they are not moored continually in a wet environment. If you plan on leaving your boat in the water, or do not have a sheltered place in which to store your boat, then marine plywood may increase your boats durability. However, that being said, any boat if not properly maintained, and left to the elements or exposed to lengthy periods of moisture will eventually rot. 

In general, your boat will need regular maintenance, and periodic refinishing regardless of the materials used to build the boat. The better the materials, in theory, the less maintenance it should require and the better it should hold up against weathering.

Marine Plywood:

Most Marine Plywood is usually manufactured from selected Okoume, Poplar and other tropical hardwoods, such as Sapele Mahogany. There are also some domestic varieties of Marine Plywood manufactured from Baltic-Birch, Douglas-Fir and Larch. The best Marine Plywood effectively meets the requirements of the British Standard (BS) which specifies plywood should in its natural state, possess a minimum degree of durability against attachment by wood-destroying fungi. The most common rating is BS 1088, and is generally accepted as the international standard for Marine Plywood. 

Tolko Forest Products® is one of the best manufacturers of Marine Plywood.They are located in Canada, in the heart of the British Columbia. Tolko's AA Marine Grade Plywood features exterior waterproof glue and premium construction of Western Larch or Douglas-fir.

There are also some plywoods available that are not called "marine plywood", but use marine in the description. These plywoods are made from wood that is other than those listed in the marine standard. These woods may be suitable for building this type of boat, but they may not meet the BS 1088 standards. If selecting this wood, be careful of the treatments used on the wood, as this may jeopardize the bonding of paints, glue and resins.

Another type of fairly weather resistant plywood, and commonly referred to as "marine" grade plywood, is pressure treated plywood. Pressure-treated plywood, often called "Wolmanized" or P.T. plywood, is NOT "Marine grade" plywood, and those designations do not make the two products arbitrarily interchangeable.
Pressure treated plywood is common plywood that has been subjected to pressure treatment with chemicals to prevent the wood from decaying, or rotting.
While pressure treated plywood may seem like a good boat building material, is often heavily warped. This is primarily the result of the high temperature and rapid moisture take up during processing. Some plywood delaminates during the process. In addition, some pressure treating methods incorporate water repellent materials. These materials can easily jeopardize bonding so you won't be able to glue or paint the plywood successfully. It is best to avoid pressure treated plywood for this project.

On hulls that do not have to be the lightest weight, I would choose Douglas-fir Marine Plywood over Okoume. It is stronger and more rot resistant than Okoume. However, as younger trees are being used to produced the plywood, there are often more patches and knots and Douglas-fir is becoming increasingly difficult to find in the higher grades. Depending on availability, you may have to settle for an AC or BB graded wood when using Douglas-fir. By contrast, Okume generally has a better overall appearance and is more abundant in higher grades, AA, and AB. 

Examples of BS-1088 Marine Plywood

Marine FirBS 1088 MArine Plywood - Birch CoreBS-1088 Marine PLywood - Sapele Mahogany

                        Douglas Fir                                                Okoume                                   Sapele Mahogany

Where to find Marine Plywood:

Windsor Plywood - the initial concept, which started in North Vancouver in 1969, was to create a specialty plywood warehouse which would bring stock closer to the contractors in the area and serve home owners and do-it-yourselfers. The marketing plan at that time, as it is today, is to specialize in hard to source interior and exterior home finishing products including flooring, doors, and mouldings. Today, Windor Plywood supplies high quality products and supports our local communities.Windsor Plywood has been a part of the growth of communities in Western and Central Canada and the Northwest United States for over 40 years.

Homestead Hardwoods - Established in 1981, Homestead Hardwoods is located 10 miles west of Sandusky, Ohio near the shores of Lake Erie. They  supply yacht, house boat and pleasure craft manufacturers and restorers locally and from around the country with high quality boat lumber and marine grade plywoods. They will ship to any location in the U.S.A. or Canada


Other Plywoods:

There are many other choices of plywoods besides Marine Plywood that can be used for boat building. The main advantage to using such a plywood is cost. However, this may also sacrafice durability - generally nothing beats the best Marine Plywood. However, if carefully selected, certain types and grades of plywood can give reasonable results at a lower cost.

Radiata Pine:  Radiata pine is classed as a medium-density softwood, the biggest problem with pine, is that it can be very soft, which causes it to absorb alot more epoxy, resins, and paint. Radiata pine is known as "clearwood", wood that is free of defects such as knots, holes or other blemishes and is one of the world's best clearwoods. Radiata pine is one of the world's most widely planted plantation species and has the ability to grow to a large diameter faster than almost any other tree species. Some of the best Radiata pine comes from New Zealand, and South America (Chile).

Where to find:

The Home Depot sells Araucos® Radiata Pine, manufactured in Chile from 100% Sustainable Plantation Forests. Araucos Radiata Pine Plywood is produced under the tightest grading specifications. AraucoPly ACX grade panels allow a maximum of 6 wood repairs and 6 synthetic repairs on the face, making them suitable for a wide variety of interior and exterior applications. Meets and Exceeds PS-195 U.S. Product Standards and they use a composed core manufacturing process in which the interior core veneers are composed together prior to pressing, creating a dramatically improved core. This allows for exceptional dimensional stability, and minimizes the ability for warping.

Weyerhaeuser®, a U.S. Company based in Washington State is now distributing through ilevel, Selex® Radiata Pine. It is a plywood that is sanded to a fine, smooth finish. The A-grade faces of the panels have an outstanding appearance free of knots and holes, while the C-grade faces have only minimal natural defects (not greater than 40 millimeters wide). It is generally manufactured from radiata pine grown on managed plantations in Chile, that are third party certified for sustainability to the Programme for the Endorsement of Forest Certification standard. 

Lauan Plywood,  also known as Laun, "meranti" or Phillipine Mahogany is made from trees in the "Shorea" family. Manufacturers create veneer from these trees, which are typically either White Lauan (created from Shorea almon) or Red Lauan (from Shorea negrosensis), and this veneer is glued together in layers to make the plywood.

Because of the softness of the wood, it is difficult to make Luan veneer completely free of voids and flaws. The surface layer is usually completely free of voids, but may have fills and patches. This means you may want to paint your Luan pieces. However, these flaws tend to be miniscule and they do not detract from the chief quality of the plywood.

Home centers and lumber retailers widely stock Lauan/meranti plywood in a variety of thicknesses

AC Fir AC/BC  Grade Fir & Pine Plywood  -

Some AC & BC graded fir and pine plywood may be suitable for boat building, but great care should be excercised in determining both the source of the material and where the plywood is milled. As milling techniques and technology can vary.

The better pine and fir comes from northern climates, such the Pacific Northwest, British Columbia, Yukon and Alaska. It is known as Western White Pine, and is manufactured from a variety of pines including, Lodgepole and Sugar pines. The better Western Pine is milled from second growth forest, which is slowly become scarce.  It has a moderate resistance to rot and decay. There is also an Eastern White Pine, but this is not as well suited to the plywood production, as the trees are smaller and thus produce more imperfections in the wood.

Also available in some home centers is Southern yellow pine, it doesn't refer to any one species of tree, but rather a group of species which are classified as yellow pine (as opposed to white pine), and are native to the Southern United States. The most commonly produced plywood is made from Longleaf yellow pine. Originally, old growth Southern pine was much more rot resistant than fir, but that may not be true with the plantation grown pine now used for plywood.

These plywoods can produce mixed results, depending on how well the boat is maintained, the type of finish and how it is applied, and how the boat is stored. It is a continuing matter of debate amongst boat builders on the long-term savings of using economy plywood. But it seems to be a common consensus, that in some cases, particularly with smaller, dry stored boats, there is some merit and benefit.

A general rule of thumb in determining the quality of the wood is to count the laminations on the edge of the sheet. The more laminations, generally the better the quality of the plywood.

Layout and Cutting:

The first order of operation is to layout all the designs onto several sheets of plywood. 

For our brigs we used BC grade Canadian milled Western White Pine to reduce costs of construction, and to support the local lumber industry. The ideal material is Marine Plywood which is stronger, and very mildew and rot resistant. Another alternative is Lauan, which is lighter than pine, but since weight is not generally a concern, as we trailer our "ship", the added cost versus the weight advantage of Lauan is negated. We also have covered dry storage, and are utilizing excellent paints and adhesives. You can get BC Pine relatively inexpensively from your local home supply center. You will want plywood that is 1/4" - 3/8" thick (we recommend 3/8") , with a little thicker pieces for the ribs, bow, and stern (1/2- 3/4").

We "transposed" the drawings full scale onto the plywood, by using a pencil, tape measure and straight edge. You may want to do a smaller "mock-up" using cardboard/pasteboard to make sure that you get all the measurements accurate. It may help to also print all the sheets from both the Mini-Brig plans. 

Laying Out The Plans On the Plywood. It is handy to have a good straight-edge and a square

All of the plans should fit on about three sheets of plywood. We used two sheets for the bottom and sides, and extra stuff (like our seat compartments in the brig Libertè), and one sheet for the ribs, stern, and bow. Remember to use thicker plywood for the frames. You will need other fittings like brass screws, glue, and adhesives which we will get to later.

A stitch and glue vessel is very forgiving, but it does pay to pre-sand all the edges and true them up as much as possible. The more you sand them and fair up the edges before you assemble it, the less sanding and better product you will have later.

We cut everything using a simple handheld jigsaw by Black & Decker. In all the bulkheads we used a sheet of 5/8" to beef up the stern, bow and midsection etc. You can go thicker here if you want, and the only detriment is weight.

Comparing the cut bow & mid-seat frames to the dimensions on the plans.
NOTE: We did not need to print the plans actual size but worked off the 8 1/2 x 11" sheets

You can cut all the wood in the winter months, but will want to wait for at least room temperature heat for the resins to dry. It is suggested that if you do not have a heated garage, go ahead and sew up the sails during those cold winter months. You might also want to do some ropework ahead of time. You will find that spring will come much faster than you expect.

Double-checking the transom frame to the plans.