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Marine Grade plywood [APA PS1-09 or BS 1088].

Marine Grade plywood [APA PS1-09 or BS 1088].

(OP)
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]

RE: Marine Grade plywood [APA PS1-09 or BS 1088].

If your floors were metal, or fiber composite and the operator asked for approval of a foreign substitute what would your answer be?

You would lay out the relevant material and mechanical properties and next to each indicate either accept or reject.

If they are all accept you reply "It's good stuff, go ahead."

If one or more are reject you reply "No good because of x and y and z. Please see our attached quote for the OEM component."

Right?

So in this case you add an additional evaluation result "Unable to find information".

You've done reasonable due diligence. You know what you need to know, and you can't find it. "Please see our attached quote for genuine Douglas fir marine grade plywood that meets all necessary criteria."

Just because "It's just plywood" doesn't mean that it's not an engineering material.

RE: Marine Grade plywood [APA PS1-09 or BS 1088].

(OP)
MJ... appreciate Your no-nonsense reply.

Pressure to assist a customer with a 'no brainer No Technical Objection' to a situation like this can be significant. However, this situation seems odd, especially due to the international reach of the customer. I suspect there may be a "buy-local/in-country" directive pushing this request.

RE The thickness difference between in# and SI unit standards.

Any thoughts as to "how-to-characterize" plywood strength VS small thickness differences? In metals it is straight forward for similar alloys: Tx/TO

TO = thickness original
Tx = thickness replacement

In-plane [FTu, FTy, FCu, FCy, FSu] strength/stiffness = ~Tx/TO

Bending strength/stiffness = ~Tx/TO^4
NOTE. Due to veneer ply orientations [0, 90, 0, 90, 0, 90, 0 etc] plywood has some-what anisotropic capabilities: Length-wise is generally stronger than width-wise... pressuming both face plies are oriented lengthwise... which are quantified for each plywood thickness as a standard number for the 2-basic orientations.

Here are some of the references I've developed for wood/plywood structure, this situation... any other's I should acquire?...

[my Company's very old Design Manual for wood]
A-A-55057 PANELS, WOOD/WOOD BASED; CONSTRUCTION AND DECORATIVE
ANC-18 Design of Wood Aircraft Structures
ANC-19 Wood Aircraft Inspection and Fabrication
NACA-TN-0296 Bearing strength of Wood Under Steel Aircraft Bolts and Washers
NACA-TR-0084 Data on the Design of Plywood for Aircraft
MIL-HDBK-7 LUMBER AND ALLIED PRODUCTS
MIL-STD-172 FINISHING OF METAL AND WOOD SURFACES
MIL-DTL-6070 PLYWOOD AND VENEER, AIRCRAFT FLAT PANEL
WADC-TN-55-329 Cargo Flooring for Aircraft - Summary of Tests
---
APA VPS PS-1-09 Structural Plywood
APA TT-043 Marine-Grade Plywood
APA Plywood Design Specification
APA Engineered Wood Construction
BS 1088-1:2003 Marine Plywood - P1: Requirements.
BS1088 & 4079: 1966 Specifications for Plywood for Marine Craft
CanPLy Plywood Design Fundamentals
ECOPLY Structural Plywood Properties & Applications Manual 2008
FPL-1300 Summary of Formulas for Flat Plates of Plywood Under Uniform Concentrated Loading
FPL-1316B, C, J Buckling of Flat Plywood Plates in Compression, Shear or Combined Compression and Shear [+ Various supplements to for miscellaneous orientations.
FPL-GTR-190 Wood Handbook - Wood as an Engineering Material
Gougeon Book 061205 The Gougeon Brother on Boat Construction 5th Ed
Handbook of Finnish Plywood
METSÄ WOOD BIRCH PLYWOOD PRODUCTS
TECO TechTip Design Capacities for Structural Plywood Allowable Stress Design (ASD)

Various Okoume-Gaboon Marine Plywood Pamphlets and data sheets [Joubert, Bruynzeel, etc]

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]

RE: Marine Grade plywood [APA PS1-09 or BS 1088].

Here are two that are not on your list:

Japanese Agricultural Standard for Plywood (Unoficial English translation)

https://www.famic.go.jp/english/jas.pdf

JIS W 1101:2000 Plywoods for aircraft

Available only in Japanese as far as I can see. http://kikakurui.com/w/W1101-2000-01.html
Google translate will go a good enough job to show you that what you are looking for doesn't seem to be there.

One exceedingly long shot. You might note that some of the places selling marine okume note "Lloyds certified". There might be some good stuff in their underwriter's files. And your chances of seeing any of it are probably almost zero.

Note also that your nominal 3/8" plywood is likely really 11/32" = 8.7 mm, whereas the 10mm metric stuff is probably actually 9 mm.

Long list of EN standards here: http://apawood-europe.org/official-guidelines/euro...

Possibly some interesting material here: http://www.wisaplywood.com/Pages/default.aspx

RE: Marine Grade plywood [APA PS1-09 or BS 1088].

Specify "enough" but don't overspecify either.

It's flooring, in a high-use area, subject to modest but not continual humidity and water, right? (Not a wing or exterior or fuselage exterior like the ply-built laminates (Mosquito, Spruce Goose, etc.)

If the load-bearing surface deteriorates (due to both continued wear and a modest amount of water/humidity/entry-exit steps) it "can be replaced" and "can be monitored" since the wear surface (the eroded area) is visible from above (from the walking area) and "is visible" (it is right where the wear occurs, right?)
So, unlike a marine hull or inside-the-wing surface or an invisible area where damage will occur continuously but cannot be checked, this area needs to be checked at a safe interval, then replaced with an equivalent thickness local plywood of the same number of laminates and the same "punch resistance" - your replacement MUST be able to resist the local wear-and-tear to avoid the cargo from penetrating the entry way.

Issue a "cover-your-apron" statement requiring monthly inspections, maintenance of those inspection records with the aircraft logs, and replacement in-kind by a locally available plywood when the FIRST delamination occurs, or when the FIRST lamination is worn through.


RE: Marine Grade plywood [APA PS1-09 or BS 1088].

Wk taylor,
BS1088 has been superseded and is replaced by BS 1088-1:2003. It would appear from your research that you have covered most of the bases. As you suspected Okoume is quite soft and may punch through on a floorboard I have used this material on boat floors and have had breakage. Sapele is quite a bit harder , but may also be heavier.
B.E.

You are judged not by what you know, but by what you can do.

RE: Marine Grade plywood [APA PS1-09 or BS 1088].

Have zero knowledge in correct aircraft applications, but I have done business with these guys for other projects. http://www.aircraftspruce.com/categories/building_...

Used to be another company, in Pennsylvania I believe, that I sourced surplus AC parts from and re-purposed. William Strube Co., Don't know if they handle natural materials.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Marine Grade plywood [APA PS1-09 or BS 1088].

The marine plywood has a lot of requirements that you don't seem to need. Identify them, remove them, and look at the remaining list of requirements, select material based on those. Is there not a fiberglass or FRP/GRP option?

RE: Marine Grade plywood [APA PS1-09 or BS 1088].

(OP)
Berkshire...

The loading in our acft is 'considerably more-benign' than previous generation acft. We have a #-load/SF requirement [~pressure load, unsupported between frames and beam-caps]. Payload lateral/fore/aft/vertical-up is restrained by cargo-floor tie-down rings mounted thru the plywood to metal structure. In the case of our acft, the cargo version has the roller system which allow pallets to be slid back/forth without contacting the floor. The tanker version allows cargo such as strap-down bladder tanks or trailers loaded with equipment, spares, engines, etc [tires for independent rolling, load spreading/softening]. In these two cases the load foot-print is soft and generally prevents punch-thru due to concentrated point loads.

Troop/personnel transport configuration allows passengers to sit/move along the sidewall areas in the good/old/painful troop seats configuration. Foot traffic is generally fairly benign to thick plywood that is painted to seal-out moisture.

Old cargo floors [C-46, C-47, C-54, etc... WWII, Korea, Viet Nam era transports] were required to withstand several cycles of 1000# rolling bomb or a 500# barrel rolling on a circular edge ... directly on the floor... what a nightmare for the floor materials!

ornerynorsk...I was aware that Okoume-Gaboon plywood was used on a few homebuilt aircraft, primarily due to availability, very good veneer/adhesive quality and lightest weight.

The critical issue we have to deal with is the AFT CG condition we have with most of our jets. Heavier decking materials aft of CG will be poorly tolerated by the acft/operators. We are about to re-ballast the jet with ~800# of brass in the forward fuselage.

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]

RE: Marine Grade plywood [APA PS1-09 or BS 1088].

WKTaylor,
Okume- Gaboon plywood was also used on Jodel type certified airplanes by the French, and by Slingsby sailplanes in their skylark series of sailplanes in place of the birch plywood used on other aircraft.
The reasoning at the time by Slingsby's was that by using a lighter thicker plywood, they could sand the outer skins to obtain a laminar flow contour over the wing by sanding away the slight distortions caused by gluing.
Anyway this does not help you in your quest to finding an acceptable substitute for Marine grade fir plywood overseas.
Attached is Wikis entry on Gaboon/ Okume ply wood , which you have most likely read by now . Is birch plywood too heavy for your needs? You also have Meranti plywood.
B.E.

You are judged not by what you know, but by what you can do.

RE: Marine Grade plywood [APA PS1-09 or BS 1088].

Will,
Here is a link for a UK company selling aircraft plywood . I do not know where in the world you are trying to source your plywood, you can also get marine grade plywood in the UK .

You are judged not by what you know, but by what you can do.

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