Boat Articles, Guides, Commentary and archival articles & helpful information,care of gear and sails
Hardware Installation on wooden boats - Hardware installation methods, problems and principles of Bonding and Fasteners
Buying a boat via eBay - May be interesting If You Plan to Buy a Boat via the internet
Choosing Factors - OutBoards Factors, Advantages and Maintenance
Tips and solutions - Fiberglass, Plywood, Woodworker Building Tips
for use in boats II
Selecting plywood for boats used to be easy, because there were only a few grades to choose from: marine grade and exterior grade, the latter plywood available in two qualitiesA/B and A/C.
Plywood for boats, part II
Lots of boaters appreciate pretty designs and high-quality boat workmanship, and lovely materials but while we admire traditional boat design, many of us find we have to choose the conveniences that plywood provides, without these conveniences there might be no boatbuilding or yachting for many of us: easy launching and trailering , light weight, easy maintenance and low cost! Some boat builders hate plywood material. Many detractors are ultra traditionalists who appreciate only the old fashioned workmanship, and perhaps also derive some odd pleasure from having wet feet and sloppy bilges.
A/B and A/C - plywood for boats
was advertised as having no voids and, at that time, no patches either. A/B 'A" three-ply exterior plywood has two good outside sanded panels with a poorer grade in the center, and lots of patches. They were all made from Douglas fir, and all were glued together with a waterproof glue.
A/C 0.25 three-ply exterior plywood has one good outside panel with patches, an interior panel with knotholes and voids allowed, and an outer unsanded panel, with more patches, voids, and holes allowed.
Since all these uglies could be readily seen on the out- side, they were easily filled with a putty that the boat- builder would make up from Fillite powder and polyester resin.
Fillite consists of tiny, hollow, glass spheres. It's used to thicken polyester and epoxy resins and reduce the weight and amount of resin required.
Don't Use auto-body filler , because it's harder than plywood, and no matter how much you sand it, it will always stand higher than the surrounding wood.
To fill edge voids in plywood, tongue depressors slathered with glue are just the right size. Most of the smaller Boats call for 0.25 plywood. Although many boats from 0.25 A/B and A/C exterior plywood and never lost a boat, regardless of grade. A/C 3/8 exterior plywood, how- ever, is another story.
This is made in both three-ply and five-ply versions. The three-ply sheets have a thick core ply that is very prone to soaking up water, and this will cause the outer veneers to ripple or worse delaminate. So stay away from that material and used five-ply marine- grade wherever 3/8 plywood was called for.
Plywood hulls built before the advent of epoxy marine glues proved sensitive to the wracking forces of movement in a seaway. Additional complications arose when builders substituted cheaper household caulking for marine-grade material or steel hardware store screws for bronze fasteners. Some plywood boats built in backyards during the 1955's had lifespans measured in months rather than years.
Plywood boats are still being built by amateurs, and for a lot of good reasons. They are simple to construct and the materials are readily available. Hard chines, which come naturally to plywood boats, lend themselves to planing hull powerboats. Thanks to modern epoxy glues and coatings, plywood boats can have lifespans competitive with conventional fiberglass hulls. The big drawback of plywood is its inability to bend in two directions at once. Boats built of plywood continue to have a somewhat boxy appearance.
Now comes DuraKore strip composite construction(www.atlcomposites.com.au). What makes this new method so different from its predecessors? The answer is engineering. Neither plywood nor concrete was originally created specifically for building boats. Instead, those materials have been adapted to the purpose. Like most adaptations, the results are not always acceptable. On the other hand, the factory-made wood and the epoxy materials of DuraKore strip composite construction were engineered specifically for building boats. There's no adaptation involved. Arnie Duckworth's "wood" is an evolutionary rather than revolutionary material that combines the best characteristics of wood with lightweight, high-tech cored composite construction. DuraKore is end-grain balsa bonded under heat and pressure between hardwood veneers. It comes either as 12-inch wide planks or as strips ranging
from 3/4 inch to 1 3/4 inch in width and from inch to 1 inch in thickness. Planks and strips are both 8 feet long. Strips are finger jointed at both ends to eliminate tedious scarfing when gluing up battens the full length of the hull.
DuraKore consists of Baltek's presealed AL-600 end-grain balsa wood laminated between two 1/i6-inch hardwood veneers. Sandwich construction gives DuraKore excellent physical properties at very light weight. More than six months of experimentation went into the development of the waterproof glue used in this manmade wood. The ratio of the width of the strips to their thickness was carefully established to assure bending properties that allow the smooth compound curves required in boats.
Hardwoods derive from deciduous trees and are available in various
forms and sizes.
They are used as a building and joinery material, and for surface finishes, furniture
and craft ranges, from bowls and utensils to light fixtures and boats. The great variety
of species, and the level of natural variation within each, provide numerous effects,
and the rich colors and natural beauty of hardwoods create a feeling of luxury.
Properties: Hardwood trees grow more slowly than conifers , so their lumber is stronger, denser and homogeneous , and are perfect for boating & marine industry. Strength varies greatly between species: hickory, the hardest commercially available variety, is five times harder than aspen, a "soft" hardwood.
Domestic hardwoods such as oak, ash, maple, beech, cherry and walnut grow in North America and northern Europe. Common exotic hardwoods, from the tropical forests of Africa, South America, and Asia, include iroko, mahogany, padouk and teak. Such lumber sourced from original forests is often particularly dense; some varieties are nearly impervious to water. Hardwoods can be handor machine-worked. They also expand, contract and change color as they age. Hardwoods resist fire better than softwoods, but charring reduces their strength, so this needs to be allowed for when using structurally.
Hardwoods are available laminated, as veneers (for coverings) or sheets (for shelves). They should be acclimatized on site for two to three weeks before use and sealed with varnish or oil. When cleaning, follow the requirements of the sealant. Repair or refurbish by sanding back and refinishing.