The classes that I teach take place on a Saturday morning. This can lead to some difficulties for those students of mine who work during the week and might not be able to get to the lumberyard - except on a Saturday morning. Note the conundrum? My solution is to do one of two things:
- Give the students a hand-out with instructions for selecting materials for the boat they're building and then give them a "free weekend" to go get their lumber.
- Have a first class with some instruction about the materials and then send them out the next weekend to get their lumber.
Through the infinite kindness of others, I was able to borrow a van to go get the material so that weather wouldn't be an issue. My good buddy Murphy (of Murphy's Law fame...) was riding shotgun on this trip. I seemed to have issues filling the tank, with weather, with traffic, directions. You name it.
To cut a long story short here, what should have taken my 5 hours took me almost 9 hours. The wood is now safely in the barn awaiting the student's touch. Some may ask why we go to such efforts got get a piece of plywood? It's not any plywood - it's marine grade Okoume plywood that's qualified to BS 1088. What's BS 1088, you say?
From Wikipedia :
BS 1088In materials, the BS 1088 specification is a marine plywood specification that applies to plywood produced with untreated tropical hardwood veneers that have a set level of resistance to fungal attack. The plies are bonded with WBP glue. Although the initials BS are for "British Standard", the finished product does not have to be "British made". The standard is associated with Lloyd's of London since it performs testing of products to this standard.Does not follow that it is a structural plywood.
WBP Glue Line -- BS 1088 plywood must use an adhesive, which has been proven to be highly resistant to weather, micro-organisms, cold and boiling water, steam and dry heat. The product's bonding must pass a series of British Standard tests.
Face Veneers -- These must present a solid surface that is free from open defects. Face veneers must be free of knots other than "sound pin" knots, of which there shall be no more than six(6) in any area of one(1) square foot, and there can be no more than an average of two(2) such knots per square foot area over the entire surface of the plywood sheet. The veneers must be reasonably free from irregular grain. The use of edge joints is limited, and end joints are not allowed.
Core Veneers -- Core veneers have the same basic requirements as face veneers, except that small splits are allowed, and there is no limit on the number of pin knots or edge joints. However, end joints are not permitted.
Limits of Manufacturing Defects -- Defective bonds, pleats and overlaps, and gaps in faces are not permitted. Occasional gaps may be repaired using veneer inserts bonded with the proper adhesive.
Moisture Content -- BS 1088 plywood must have a moisture content between 6% and 14% when it leaves the factory.
Finishing -- Boards will be sanded on both sides equally.
Length & Width -- The length or width of a board produced as a standard size shall not be less than the specified size nor more than 6.3 mm (0.25") greater than the specified size.
Squareness -- The lengths of the diagonals of a board shall not differ by more than 0.25% of the length of the diagonal.
Thickness Tolerances -- Tolerances vary as follows.
From the above we can assume that 6 mm material will arrive at thickness' between 6.04 mm and 5.35 mm.
- 4 mm +.02/-0.6 ; 6 mm +.04/-0.65 ; 9 mm +.06/-0.75 ; 12 mm +.09/-0.82
- 15 mm +.1/-0.9 ; 18 mm +.12/-0.98 ; 22 mm +.16/-1.08 ; 25 mm +1.8/-1.16
Face Veneer thickness -- For any three-ply construction, which applies to 3 and 4 mm material, each face veneer shall be not thinner than 1/8 of the total thickness of veneers assembled dry. Since the dry thicknesses of the boards are 3.6 and 4.6 respectively, we can assume that for these thicknesses only the face veneers will be as follows:
Multi-Ply Construction-- This applies to boards thicker than 4.8 mm (3/16")
- 3.6 mm dry x 12.5% (1/8) = 0.45 mm 4.6 mm dry x 12.5% (1/8) = 0.575 mm
- Each face veneer shall be a minimum of 1.3 mm and not thicker than 3.8 mm.
- Each core veneer shall be no thicker than 4.8 mm
And that is the reason we go to the trouble of getting marine grade plywood - guaranteed quality!