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I did a search for marine tech ply wood . I have the study plans for the bearcat thay say some of the ply i can use are ext does that mean cdx or abx i cannot find abx so far another choice as far as price goes would be marine tech . I am not trying to go cheap but if the plans say it can be used then i will use thanks for any response .Also the ext ply will not be in visible areas.

Love all the plywood questions

ACX isn't a recognized standard. What it kinda/sorta means is that you have an A grade face veneer (sanded) on one side, the rest is C or better (but usually not better - the companies are in the business of making money) and the X indicates exterior type adhesive was used (most commonly phenolic resorcinol glue, which used to be the "gold standard" marine glue before epoxy came along).

This particular grade almost always applies to Douglas Fir but can also be Hemlock or Larch - so you should ask - often times you will see stamps referring to the sheet as Hem-Fir or DF-Larch indicating that the sheet was made with whatever was coming off the rotary cutter when they were making plywood

Since all of these will "check" (sometimes even if you just look at them funny), if they will be exposed to the elements at all, they should be covered with a minimum of 4oz glass cloth in addition to epoxy encapulation.

Because there are C grades involved, you could also have voids resulting from open knots which have not been filled or splits which have not been filled (which are acceptable in a C grade veneer).

I personally have zero reservations about using ACX for frame gussets, partial bulkheads or even certain bulkheads that are not necessarily 100% structural in nature (such as used to separate say a sleeping compartment from the cockpit provided that it was installed over a frame that otherwise was the same spec as other frames in the design etc) or even as a "sandwich layer" between two layers of mahogany if you are building a 3 layer transom (say 3 x 3/4" panels to give you the required clamping width for an outboard when 2 panels would have been sufficient for strength).

But (again personally) would not use ACX for the hull sheeting. It almost always has less ply's than mahogany so any defects in an individual ply will have a much greater affect on the overall strength of the panel.

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

Wes, I am not the expert on ply. Just wanted to share with you. I used Marine Tech for my gussets and found the ply wonderful to work with.

However, the surfaces are B grade at best. If you are planning on using this for your hull you may have to lay up an extra layer of epoxy for a smooth finish.

Also, I understand the product may now be discontinued. I tried to buy some recently and was told it is no longer available. Check your sources.

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Dave

My Riviera build - the Midnight Cry Project

Video of Midnight in Action
Blog

Few things in the world measure up to the thrill and satisfaction of boating in a boat that you built.

Marine Tech, while not recognized as a "marine" plywood by the plywood standard association dudes, is a (superior) domestic panel produced by a single supplier that is supposed to be constructed of sanded outer ply, both outer veneers (B grade sanded with 60 grit) with the inner ply's being "improved" C grades (so pinholes are ok but no open knots or splits or voids).

It is definately superior to ACX and considering some of the AB garbage I have seen that is "marine" it is probably a decent substitute should you wish to use a North American product.

It should not be confused with another product called Hydro Tech which is Phillipean Mahogany (Meranti), which is really a Cedar, that can be any one of almost 1000 sub-species, and not a Mahogany (as if it wasn't confusing enough) but meets Lloyds 1088 standard for marine construction.

So now are you totally confused and not sure what to use at all?

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

Yes to Galamb, I am Totaly confused.
But my little jon will be just fine with the AC.
That huge Bearcat will be going places at hi speed and would need some pretty tightly woven wood.

You might consider this little tale of Woe.
I bought a Plywood boat at auction that was sunk.
The kid was somehow adrift and the water lifted him up and sat him down on a big rock. He got off but didnt notice the water...etc.
It was a Horshoe shaped 'punchout' only about 3 or 4 Mm open across the front of the arc. But it was enough.
So thinking like that, and Galamb's helpful lecture about 5500 or 6800 Lbs per square foot, you might want to pick the tougher stuff for your nice big boat.

I looked at the build photos of the only Bearcat in the customer photos. That guy put a nice big Hardwood keel in his 'boats' that would help greatly to reduce the damage in a grounding.

I hear exactly what you are saying.

If I was building a row boat or maybe a small utility I wouldn't even twitch at the thought of picking up a couple sheets of ACX from one of the big box home stores and painting it (without benefit of glass cloth) with some exterior house paint and then taking her out for a row.

It really does come down to what you are building. And when it's 28' feet long with a 10' beam and plan to use it on BIG WATER, you probably don't want to skimp on the plywood which is forming the skin on your hull.....

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

When you are using it as Wes intends,you don't want to skimp on ANYTHING!!!!

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Thanks for all the replies to my question .I actually emailed Andy that built the bearcat in the Philippines he was helpful. The study plans actually call for ab ext. Would the marine grade fur ply be a good alternative i know it checks but can you just coat with epoxy with out glass in the non vis areas. also i am confused about okume and meranti as far using structurally.

Marine "fir" is excellent structurally and (should) be of superior quality to AB exterior.

Both the Meranti and Okoume (spelled various ways) are graded a little differently than domestic plywood, usually said to meet British Standards (BS) 1088 or 6566 with additional veneer grades compared to domestic.

However, both are superior structural plywoods and not prone to checking. Meranti is heavier (and usually cheaper in price often comparable to Marine Fir) while 1088 Okoume is light in weight and the number one choice for clear finish.

In general 1088 Okoume will have A face veneers and B interior, 6566 Okoume and both standards of the Meranti's will have B faces and BB interiors.

The Meranti can be a little "splintery" (if that's a word) but unlike the fir, can be painted over without the need for fiberglass cloth (although on any exterior components the cloth would provide significant increases in durability).

Any of the above would be more than suitable and all are superior to AB Ext....

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

Incorrect, and missleading.

the X designates the core veneer grades, and has absolutely nothing to do with glue type-period.
Man, I have no clue why this myth seems to thrive. X designation just means the stuff isn't fit for building a doghouse-much less a hull.

The following is shamelessly-poached from APA.


Plywood grades are determined by a veneer quality on the face and back of each panel. The first letter designates quality of face veneer (best side), while the second letter denotes the surface quality of the back of the panel.[6] The letter "X" indicates the panel was manufactured with scrap wood as the center plies, not "exterior" as is commonly thought. The A-D rating is only good for construction (softwood) plywood, not for hardwood plywoods such as oak or maple.

"A": Highest grade quality available. Can be defect free or contain small knots, providing they are replaced with wooden plugs (the fillers having a "boat" or an "American football" shape) or repaired with synthetic patch. This grade may contain occasional surface splits that are repaired with synthetic filler. The surface is always sanded and provides for smooth paintable face quality.

"B": Second highest quality veneer grade. Normally a by-product of downgraded "A" quality veneer. Solid surface, but may contain small diameter knots and narrow surface splits. Normally repaired with wooden plugs or synthetic filler. The surface is normally sanded smooth.

"C": Considered to be a lower end face quality, but a reasonable choice for general construction purposes. May contain tight knots up to 1½ inches diameter, some open knot holes, some face splits, and discoloration. Some manufactures may repair the defects with synthetic filler. Panels are typically not sanded.

"D": Considered to be the lowest quality veneer and often used for the back surface for construction grade panels. Allows for several knots, large and small, as well as open knots up to 2½ inches diameter. Open knots, splits, and discoloration are acceptable. "D" grade veneers are neither repaired nor sanded. This grade is not recommended for permanent exposure to weather elements.

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Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

I beg to differ.

ACX Grade comes from US voluntary plywood Standard PS1-95 for Construction and Industrial Plywood established by APA – The Engineered Wood Association

Your definition came from Wikipedia (and whoever wrote the piece did take some info from the APA but added their own interpretation and made up the rest) particularly the part about "scrap" since the standard (although voluntary) states nothing less than C grade veneer.

The exact meaning of the X is "exposure 1", it is further defined as (quote from PS1-95)

"Interior with exterior glue - This is plywood bonded with exterior (waterproof) glue identified as "Exposure 1" (see 5.8.6.4). Plywood with this glue bond is intended for protected construcion and industrial uses where the added bond durability of a waterproof adhesive is required. Adhesive performance requirements are provided in 5.7.3".



I'm sorry, but PS1-95 (about 40 pages or so) sits in my book case.

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

While I previously would have sided with Caber-Feidh regarding the X - it's something I'd read before - the wiki article doesn't have a citation, and it's hard to argue with someone who has the standard on their bookshelf. Whichever is true, I definitely think plywood manufacturers play very fast and loose with the specifications.

While I can't add much in the way of actual evidence, I will add some anecdotal evidence. I had some scraps of decent fir ACX from a reputable supplier that left outside uncovered. After about a week in standard Seattle rainy weather, the plies were starting to delaminate badly. After a couple months, they were a complete wreck - a useless sodden mass. Not something I'd want anywhere near a boat. On the other hand, I had some 1088 oakume that was under cover, but in the damp air outside for eight years that was still basically perfect - it's on my El Toro now.

Long story short, I wouldn't trust "X" plywood as far as I could throw it.

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Photos of my Squirt build
El Toro I built with my Dad

I totally agree with you. And "X" designated plywood is NOT an exterior panel, it simply uses exterior glue.

It is intended for "protected" use, such as roof sheeting. Since it is covered by shingles, it's considered protected, but if it does happen to get a little wet, it will not delaminate.

It still has to pass the boil test, heat test and a few others (identical to what an exterior or even a marine panel is subjected to) to meet APA standards - where the difference lies is in how successfully it passes the tests.

In fact, if "exterior" panels submitted for standards testing fail to get an 80% grade (or whatever the particular score required is) in one of the tests, they would be classified instead as exposure 1 and stamped accordingly.

Obviously not every panel produced is tested which leads me to dis-trust the quality of most domestic plywood. And if you are ever really really bored and you read through the test proceedures and the requirements you would see that the difference between exposure 1 and exterior is pretty minimal. It is only Marine rated plywood that has to meet exceptional standards and has tons of regulation as to species, veneer quality etc etc.

So I do stand by all my original comments, in that I would not have an issue using ACX for things such as gussets or certain bulkheads supported by frames etc - basically any protected area on a boat, but would definately not use it anywhere on the hull or anywhere that it was exposed.

What is unfortunate is that resources such as Wiki are not policed (for lack of a better word).

"Somebody" probably read part of the material from the APA, but incorporated something that "Bob accross the street" told him and then uploaded his filtered/partially correct information. Nobody verifies it and then potentially millons of people read it and "take it as gospel".

I don't trust anonymous information (and don't expect mine to be trusted either without verification). And in a case such as this, where the APA has an excellent website where you can download all their publication free, if you see someone ref'ing their material, why not go read it for yourself?

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

I jacked the link up, was supposed to be a quote and link to a google-books preview page. I buess that doesn't work. and I got what I had on the clipboard before. Was supposed to be a link to USDA Product Standard 66-1 that calls X or Y as "mill grade" or "bastard grade".

Lee if this one works.
http://books.google.com/books?id=PioDAA ... q=&f=false pages 156-167

ACX is not the same as AC-Ext, although it would seem to be a point of confusion.
Makes one wonder why there would be some ply marketed as CDX-Interior, doesn't it?


edit-
This AM I asked 2 vendors I like. Both said something different. One (An older fellow, been selling sticks so long Noah likely bought from him) said "X" is a slang name, and there is no trademarked gradestamp with an X suffix. (I have never seen one, makes sense) He said it is recognized by the construction crowd as a grade for exterior sheeting. He said there was a time when panels would say "shop cutting panel-all other marks void". There would be an "X" painted across the original gradestamp. It was the cheap stuff.

The other guy is rude, but great prices... he just said if I want that garbage go to home cheapo, he doesn't deal in firewood.

Makes one wonder... if the X in CDX means exterior, what does the "C" in BBC grade mean? Cold? or the B In BBB... blustery? Now I remember why I stick to Russian Birch for my real "job" It wasn't graded by dyslexic box-store stock boys.

Another vague woodworking term with a many different meanings.

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Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

That is exactly why in my initial post I said that ACX (or CDX which used alot for making shipping crates) is not a recognized standard.

How to put this? The APA doesn't really designate what letters or descriptions are used when talking about plywood outside of the "letter grades" for the veneers which are quite complex.

They do "require" that various types are identified - Marine, Exterior, Exposure 1, and Interior and even make some suggestions and provide the mills/mfgs with examples of stamps for the various types - but they really don't mandate that it must be done "exactly this way" (in some of their examples to producers they show "NB - Interior" not even using the recognized short "INT", but instead spelling out everything) - which is probably where the "X" came from in the first place (along with MAR, INT, EXT etc) - somebody just started using it as a short form.

In the end it's probably safe to say that you should use nothing less than "marine" rated plywood unless it will be used in a non-structural component - just to be safe.

_________________
Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it