Marine-grade plywood is available in a domestic PS 1-95 (American Plywood Association) or BS1088 (British Standard Institution) standards. Marine-grade plywood made to the PS 1-95 is generally available in Douglas-fir. The grade of all plies of veneer is B or better, which means it may have knots, but no knotholes. Repairs are allowed and it is typical to see football plugs on the faces and backs of most Douglas Fir Marine Grade plywood. Besides the poor visual appearance of the plug, that area tends to be structurally inferior to other areas that have not been repaired, especially for thinner sheets of plywood. The panels are sanded on both faces. The maximum core-gap size permitted is 1/8 inch, which also reduces structural performance. It is nearly impossible to get A-A grade Marine Fir these days. Most US mills produce AB due to the quality of logs that are available.
Marine-grade plywood made to the BS1088 standard is typically available in Okoume, although, Meranti, Sapele, Agba, Khaya, Makore, Moabi, Movingui, Sipo-Utile and other African and Southeast Asian species have been used. Permissible species must meet the durability requirements within the standard.
BS1088 calls for the same tropical hardwood specie to be used throughout the panel; exterior glue (melamine or phenolic) for the core; no repairs on the faces; no core gaps or overlaps. BS1088 also requires an odd number of plies to be used. Regardless of the type of application, using BS1088 plywood is by far easier to work with and priced competitively to the fir option.