WKTaylor
Active member
- Sep 24, 2001
- 4,028
Help! I am woefully ignorant about marine grade plywood. Here’s my problem…
Marine grade plywood [Douglas-fir] has been used for years as [gaaag] cargo-floor decking in my USAF jet transport. Due to many factors, this plywood has been the accepted ‘norm’ for decades, due to: (a) relatively low floor cargo loading; (b) low cost and simplicity; and (c) good bolt/screw bearing properties [especially when hand-drilled to match existing beam/frame/intercostal floor structure that has NO consistent fastener pattern]. For this reason High quality Douglas Fir plywood [Marine and very high grade construction grades] has remained ‘the standard’ for +55-years of service.
Problem: US manufactured Marine grade and similar high quality construction grade [APA PS1-09] Douglas-Fir plywood is hard to find overseas. We have been asked to ID alternate plywood materials for foreign operators. NOTE: ‘marine grade Plywood’ implies many details not considered an issue with general construction grade plywood, such as: (a) water-proof adhesives; (b) all-veneer-plies are hand-selected for 100% density [no holes, tears or cracks in each veneer ply]; (c) have a high quality surface, both sides; (d) are exceptionally flat and warp resistant; and(e) are highly compatible with adhesives and finishes [coating systems] for tough water-proof construction.
BS 1088 is a world-wide spec for high grade marine plywood. Although there are multiple species of wood materials approved, few are common in the US [except to wood-boat-builders].
Typical accepted wood species per BS 1088 are Teak, Mahogany, European Birches, Sapele, Okoume-Gaboon and Lauan etc [rough descending order of density and strength].
As far as I can see plywood/veneer density ~= plywood strength. Hence teak, mahogany, birch, sapele [etc] plywood is higher higher density than Douglas fir; however they also appear to be stronger in relation to density, [FTu, FTy, FSu] than Douglas-Fir. Like likewise it appears that the Okoume Gaboon plywood is ~15--20% lower density may have correspondingly lower strength than Douglas-Fir.
Problem that I'm having is that our acft can only tolerate a small amount of heavier plywood in forward CG areas [and/or very high foot/cargo-mass traffic areas near the cargo-door]. It is necessary to have equal, or lighter weight/sheet, [relative to Douglas-Fir plywood] installed around and aft of the CG [~1/4-chord of the wing] as cargo flooring. The Okoume-Gaboon appears to have good-enough strength and fracture/puncture/fatigue toughness for its density. This is based loosely on testimony and praise from boat builders who have generally ‘accepted’ it as an acceptable substitute for Douglas fir in US designed/built boats.
Unfortunately 1:1 plywood material data sheets for all [marine plywood] species, side-by-side/column-by-column, simply do not appear to exist. I am at a loss how to compare Plywood materials. One table in a well-known boat-building handbook came close, but omitted several critical values for several species listed above, including Okoume Gaboon [leading candidate due to apparent light-weight and good strength].
OH yeah... I forgot to mention one last detail: our acft has (2) basic plywood panel thicknesses: (a) 1/4-inch and(b) 3/8-inch… which are commonly available in the USA. Marine plywood per BS 1088 is available strictly in millimeters that are listed approximate equivalents thus: 1/4-inch [6.35mm] ~= 6-mm [7-mm does not appear to exist]; and 3/8-inch [9.52-mm] ~= 10-mm.
I cannot say NO Technical Objection to a substitute plywood, when I have no technical basis for accepting or rejecting material based on authoritative properties. Hence our initial response to our foreign customer has been to say “send-funding for us to study other plywood options”… which goes over like a t*rd in a punch bowl with the customer already paying a high price for engineering/technical support.
Needless-to-say, as a current generation aero engineer, metals and fiber composites are far more familiar/friendly to me than wood/plywood.
Anyone have clues as to how to approach this problem???... and/or know of data tables that include strength and stiffness values for the wide range of marine plywood species without exception??
NOTE: I have approached the APA, several US vendors [for BS 1088 plywood] and some BS 1088 manufactures in Europe ... but the picture continues to be missing pieces and is clouded by my lack of familiarity.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]
Marine grade plywood [Douglas-fir] has been used for years as [gaaag] cargo-floor decking in my USAF jet transport. Due to many factors, this plywood has been the accepted ‘norm’ for decades, due to: (a) relatively low floor cargo loading; (b) low cost and simplicity; and (c) good bolt/screw bearing properties [especially when hand-drilled to match existing beam/frame/intercostal floor structure that has NO consistent fastener pattern]. For this reason High quality Douglas Fir plywood [Marine and very high grade construction grades] has remained ‘the standard’ for +55-years of service.
Problem: US manufactured Marine grade and similar high quality construction grade [APA PS1-09] Douglas-Fir plywood is hard to find overseas. We have been asked to ID alternate plywood materials for foreign operators. NOTE: ‘marine grade Plywood’ implies many details not considered an issue with general construction grade plywood, such as: (a) water-proof adhesives; (b) all-veneer-plies are hand-selected for 100% density [no holes, tears or cracks in each veneer ply]; (c) have a high quality surface, both sides; (d) are exceptionally flat and warp resistant; and(e) are highly compatible with adhesives and finishes [coating systems] for tough water-proof construction.
BS 1088 is a world-wide spec for high grade marine plywood. Although there are multiple species of wood materials approved, few are common in the US [except to wood-boat-builders].
Typical accepted wood species per BS 1088 are Teak, Mahogany, European Birches, Sapele, Okoume-Gaboon and Lauan etc [rough descending order of density and strength].
As far as I can see plywood/veneer density ~= plywood strength. Hence teak, mahogany, birch, sapele [etc] plywood is higher higher density than Douglas fir; however they also appear to be stronger in relation to density, [FTu, FTy, FSu] than Douglas-Fir. Like likewise it appears that the Okoume Gaboon plywood is ~15--20% lower density may have correspondingly lower strength than Douglas-Fir.
Problem that I'm having is that our acft can only tolerate a small amount of heavier plywood in forward CG areas [and/or very high foot/cargo-mass traffic areas near the cargo-door]. It is necessary to have equal, or lighter weight/sheet, [relative to Douglas-Fir plywood] installed around and aft of the CG [~1/4-chord of the wing] as cargo flooring. The Okoume-Gaboon appears to have good-enough strength and fracture/puncture/fatigue toughness for its density. This is based loosely on testimony and praise from boat builders who have generally ‘accepted’ it as an acceptable substitute for Douglas fir in US designed/built boats.
Unfortunately 1:1 plywood material data sheets for all [marine plywood] species, side-by-side/column-by-column, simply do not appear to exist. I am at a loss how to compare Plywood materials. One table in a well-known boat-building handbook came close, but omitted several critical values for several species listed above, including Okoume Gaboon [leading candidate due to apparent light-weight and good strength].
OH yeah... I forgot to mention one last detail: our acft has (2) basic plywood panel thicknesses: (a) 1/4-inch and(b) 3/8-inch… which are commonly available in the USA. Marine plywood per BS 1088 is available strictly in millimeters that are listed approximate equivalents thus: 1/4-inch [6.35mm] ~= 6-mm [7-mm does not appear to exist]; and 3/8-inch [9.52-mm] ~= 10-mm.
I cannot say NO Technical Objection to a substitute plywood, when I have no technical basis for accepting or rejecting material based on authoritative properties. Hence our initial response to our foreign customer has been to say “send-funding for us to study other plywood options”… which goes over like a t*rd in a punch bowl with the customer already paying a high price for engineering/technical support.
Needless-to-say, as a current generation aero engineer, metals and fiber composites are far more familiar/friendly to me than wood/plywood.
Anyone have clues as to how to approach this problem???... and/or know of data tables that include strength and stiffness values for the wide range of marine plywood species without exception??
NOTE: I have approached the APA, several US vendors [for BS 1088 plywood] and some BS 1088 manufactures in Europe ... but the picture continues to be missing pieces and is clouded by my lack of familiarity.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]
