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Marine Plywood Help

The information and links below will help you with plywood selection but should never supersede the specifications given by the designer of your boat.

Click on a title to read about it.

BS1088 (British Standard 1088)
is defined by the following 4 basic requirements

  1. Same species of wood throughout
  2. WBP Phenolic or Advanced melamine resin glue line
  3. No core gaps, some small pinhole gaps are accepted
  4. Whole piece face and back, no spliced faces, allowed Grade is normally an A/B

BS6566 (British Standard 6566)

  1. Wood can be mixed in species, normally the core will be different from the face.
  2. WBP Phenolic or Type 1 Ext Melamine glue permitted
  3. Some allowance of core gaps permitted, recommend filling any exposed edges before further encapsulation etc.
  4. Faces can be made up of one or more pieces, spliced together. Grade of face is normally a B/C

The BS6566 is recommended where the wood is being encapsulated, or at least fully sealed.
It is not as structurally sound as BS1088, and does not pretend to be.
This also includes bending strength and modulus of elasticity.
Sometimes, the factory producing the 6566 will manufacture the plywood which will exceed the above conditions, (for example, they may put whole piece faces on just to complete production more quickly for an order that needs to be exported) Customers must be aware that at any time, grade must meet the above to be approved under BS6566 .

Read further for a complete description of grade BS1088.

A summary of the requirements for BS 1088 as interpreted by our company.
The actual specification is several pages long, and we have condensed what we figure are the relevant bits of information.

BS 1088 British Standard Specification for Marine Plywood manufactured from selected untreated Tropical Hardwoods

This British Standard applies to plywood made with untreated tropical hardwood veneers having a suitable prescribed level of resistance to fungal attack with a bond of WBP glue quality between the plies. It does not need to be 'British made material'.

Bonding WBP Glue line
Bonding meeting the test requirements of this British Standard and using an adhesive of the type which by systematic tests and by records in service of the product over many years has been proved highly resistant to weather, micro-organisms, cold and boiling water, steam and dry heat.

Species of Timber
If so specified by the purchaser, Gaboon or Okoume (Aucoumea klaineana), which is classed as non-durable, may be used provided that the name of the timber is included in the mark on the boards produced.

Quality of Veneers
Veneers may be rotary cut or sliced. The method of cutting is at the option of the manufacturer unless it is specified by the purchaser at the time of ordering. Veneers shall be smoothly cut.

Face Veneers
These shall present a solid surface, free from open defects. They shall be free from knots, other than sound pin knots, of which there shall be no more than 6 in any area 30cm square (1ft2), and not more than an average of 2 per 30cm square (1ft2) over the whole area of the board. The veneers shall be reasonably free from irregular grain, due note being taken to the characteristics of the species being used. Isolated pinholes not along the plane of the veneers, and occasional closed splits are permissible. Veneers showing compression failure shall be excluded. Occasional minor discoloration is permissible.
There shall be not more than one edge joint in any 30cm (1ft2) width of the board, and the veneers shall, when jointed, be matched for color. There shall be no end joints.

Core Veneers.
The requirements for core veneers shall be the same as those for face veneers, with the following exceptions. Small splits are permitted, and there is no limitation on the number of pin knots or edge joints. Discoloration is permissible, provided this is free from dote. Veneers need not be matched for color. There shall be no end joints.

Limits of Manufacturing Defects in Plywood
Defective Bonding Not Permitted Pleats and overlaps Not Permitted Gaps In faces. Not permitted. Occasional gaps that occur during manufacture may be repaired by means of well-fitted veneer inserts bonded with a complying adhesive. In Cores. In any edge of a board, not more than one gap, which shall be not wider than 0.5mm. Obviously the presence of defects in cores can only be judged by the appearance of the edges.

Moisture Content.
At the time of leaving the factory, finished boards shall have moisture content from 6 to 14%

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 6.3mm (0.25") greater than the specified size

The lengths of the diagonals of a board shall not differ by more than 0.25% of the length of the diagonal

Tolerances vary as follows.
4mm +.02/-0.6
6mm +.04/-0.65
9mm +.06/-0.75
12mm +.09/-0.82
15mm +.1/-0.9
18mm +.12/-0.98
22mm +.16/-1.08
25mm +1.8/-1.16

From the above we can assume that 6mm material will arrive at thickness' between 6.04mm and 5.35mm.

Face Veneer thickness
For any three-ply construction, which applies to 3 and 4mm 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 3.6mm dry x 12.5% (1/8) = 0.45mm 4.6mm dry x 12.5% (1/8) = 0.575mm

Multi-Ply Construction.
This applies to boards thicker than 4.8mm (3/16") Each face veneer shall be a minimum of 1.3mm and not thicker than 3.8mm. Each core veneer shall be no thicker than 4.8mm.

Wood species used in marine plywood

Fir is used to manufacture XL marine plywood. It is inexpensive and has good mechanical properties. It is slightly more difficult to bend than Okoume.
XL Fir plywood is chemically treated to resist rot but not as heavy as pressure treated wood.

Fir plywood is of the sliced type as opposed to rotary cut plywood.
Unless covered by fiberglass, fir will check. This means that the wood grain will appear through paint and primer. It is an ideal plywood if it's surface is fiberglassed.

Meranti is an Asian wood in the mahogany family. Meranti plywood is rotary cut, has reddish color and an excellent surface aspect.

Our Meranti plywood is manufactured to the highest standard, is graded BS1088 and has the Lloyds approval. It is 20% heavier and slightly more difficult to bend than Okoume but it has better mechanical properties and better resistance to rot. It also cost less than Okoume. Meranti is our plywood of choice.

Okoume , also named Gabon after it's country of origin, is lighter and more flexible.

It is ideal for hulls with pronounced curves. Our rotary cut Okoume is rated BS1088 and has the Lloyd's Register approval.