What is CTBX Plywood Certification? (urgent)

I'm stumped.

I am about to buy the vast majority of the plywood that goes into the boat I'm building. It's 160 sheets of 3mm Okoume. Not a small purchase.

I am down to a few suppliers (at least one of which is probably reading this post). I'll be buying all the material for my entire boat from this supplier if I can figure this out.

I am close to going with a particular supplier, but instead of BS1088, BS6566 or a Lloyd's Certification, they are selling 3mm Okoume plywood with a CTBX rating. The plywood is made by Garnica in Spain.

The rating stamp looks like this:



What is this rating?

Can anyone help me understand this?? I'm fully lost because everything I know surrounds BS1088, BS6566 and Lloyd's Certification. I'm not familiar with CTBX and need to understand this in order to go ahead with the purchase. Thanks!

 

I believe it is a french plywood. Like we make Doug Fir marine plywood not BS certified but true marine ply. CTBX is true marine ply not BS certified.
Not built to all the BS standards. Okoume ply is not the best wood ply for use on boats. No personal experience but have been told that it is weak. BS certified is the GOLD standard. You might google properties of CTBX ply and Okoume ply. Hope others chime in here. I would not make a purchase until you are fully satisfied about what you know about the product.

 

Thanks for that information, Rasorinc.

I'm not making the purchase until I understand CTBX from a few sources of information. My current understanding (which may be wrong) is that BS cert doesn't exist anymore and only Lloyd's Certs exist. I was under the impression that BS standards are not "certified" by anyone at this time. Is that right, or do I have that wrong?

Opening up the discussion to Okoume or not, I'm not aware of any other choice. I had done a hell of a lot of homework and found that Luan isn't made to marine standards anymore. That was what the plans called for, but they are a little dated. I was told Okoume was the next best thing. The wood is for a catamaran, 45' long. This is the major hull component. 3mm ply, scarfed and bonded, in 3 layers then glassed on the outside an epoxied on the inside.

Is there something wrong with using Okoume for this?

How about using it for the bulkheads?

Thanks!

 

Read this and do more research. Okoume I was told is for small light weight boats. It has no rot resitance. These people sell a lot of BS certified ply called Hydro tek. This site describes their plywood which may guide you to further research. http://marine-plywood.us/mahogany_okoume.htm Are you using cold mold method of application for the ply? If so that prosents another problem re: weakness.

 

No, I'm using cylinder mold.

It's 3 sheets of 3mm, scarfed and bonded into one, large vacuum bagged panel:

http://www.multihulldesigns.com/pdf/cm/CYLINDER MOLD MULTIHULL CONSTRUCTION.htm

These cylinder mold boats were originally made with Luan plywood. Many are still in service from the early 1980's and are USCG certified for carrying passengers.

I think the reason to use Okoume is the strength to weight ratio...

What do you think?

Just read the link and it seems to agree. Strength to weight is right on this stuff.

But I'm sure not certain of this CTBX rating. X stands for exterior, but...

 

Here on the forum we just had a discussion on cold mold plywood hulls. I'm still trying to find it for you. Maybe Richard (Apex) will sign it soon--he makes his living building big wood boats and his 2 bits would be very helpful for you. Plywood is always weak in one direction + other problems.

 

Yeah, I was hoping the Europeans would get home from the pubs/discos soon and log in. They're bound to have some inside info on that CTB X rating.

 

what is your rib spacing? 9mm ply seems light to me for a 45' cat. Is it sail or power? I'm building a 30' power cat and using 5/8")3/8 +1/4) up to the deck and
3/4" on the bottom. 2 layers of 3/8" my frames are 30" o. c. and are 2 x4 and 2 x 6. dense yellow pine over 5/8s ply in the shape of the sponsons with cross ties of 2x4 and full ply in between. epoxy and bolted. Keels are 2x4.

 

http://openlibrary.org/books/OL4032174M/contreplaqué_extérieur_CTB-X_dans_la_construction

 

http://www.plysorol.fr/pages/en/men...quality/certifications__labels/ctbx_1239.html

It is rated exterior but I did not see it was rated marine grade. Be careful.

"The NF EXTERIEUR CTB-X quality mark defines plywood panels with Class-3 gluing (NF EN 314-2 standard) suitable for exterior use and exposure to bad weather for prolonged periods.
For example :
Humid, interior environments : Bathroom, cubicle, floor, roller shutter box.
Sheltered exterior environments : Sheathing, roof overhang, wind bracing.
Exposed exterior environments : Wall cladding, barge board, facade, exterior woodwork



The NF Extérieur CTB-X quality mark guarantees :
Gluing quality
The panel’s biological durability
Its mechanical characteristics
The internal control requirements



All (non flame-retardant) okoume and poplar plywoods with exterior gluing in the PLYSOROL range are certified NF-EXTERIEUR CTB-X, a label issued by the CTBA (Wood and Furniture Technical Centre), a certification body appointed by AFNOR.

Plywood panels sold under the NF CONTREPLAQUE EXTERIEUR CTB-X brand are guaranteed ten years, provided that they are used in accordance with DTU regulations and according to the rulebook.

In order to provide you with complete protection against any possible forgeries, the NF CONTREPLAQUE EXTERIEUR CTB-X brand is indicated by an ink mark applied to the backside of our panels which is followed by our identification number such as it appears on the certificate (as required by the regulations)."

 

That is not Marine Plywood. It is like our ABX or BCX or CCX withX being exterior grade. A,B,C, are the grades on the face of the ply. I use this for roof sheeting and have for 40 years. It is not Marine and has voids. I would run away from it as it is not for boats................................................. Check the prices at Homested, the link I sent you. These are all MARINE GRADE. hE SELLS ALL OVER AND HAS A GOOD REP.

 

I know the CBTX plywood as I have used a few thousands sheets on warships and fishing boats in French shipyards. The norm exists since 1978.
The CTB (Centre Technique du Bois = Wood Technical Center) rates the CTBX plywood as exterior and marine. It can be used on boats; it uses glue "type 4" for permanent immersion - generally a phenolic- and uses african "mahogannies" like Okoume, Khaya, Sapelli and even hard wood like Moabi (very heavy, very hard excellent for fishing boat decks)

The glue is easy to recognize: dark red (resorcine-phenol). This glue passes the hardest tests of boiling, swelling, drying, reboiling etc...

hoytedow, the link given is for house building panels under CTBX norm, it won't talk about marine use. The pages in French, of the CTB describe precisely the marine requisites accomplished by the CTBX.
Sorry to contradict rasorinc it's also marine plywood and has been used for that many times. The French quality standards are far higher than the American, and nobody in France would use an APA exterior plywood for a outside wall house...in fact not even for crates. The swedish, finnish, russian, english and french norms have nothing to do with the american APA norms in matter of exterior plywoods.

But there is very big difference between CTBX and "true" structural marine plywood: the number of plies. The CTBX norm only define a minimal number of plies convenient for flat panels. For boats you need the maximal number of plies simply because you are going to bend heavily the plywood.

Happily, CatBuilder is going to use 3 mm plywood to make panels of 9 mm with 9 plies and with only 1/3 of the plies running across at 90 degrees. That means that the panels with be stiff in the length and rather bendable across. That the purpose of cylinder mold...

As I have a long experience of compounded plywood, I can give some precise counsels on this very peculiar use.

CatBuilder has to buy for a sample sheet (When you buy 160 sheets of any plywood, you have always to buy one before to see and test it). For shipping this sample sheet can be cutted in four equal pieces and sent by common ground UPS, that saves on shipping.

When you have the sample sheet, make very simple tests:
A- Visual

1- Thickness of the plies: for compounding the 3 mm plywood must have 3 NEAR EQUAL PLIES. 1 mm each is perfect, outer plies of 0.9 mm and core (central ply) of 1.2 mm is good, 0.8 mm outer plies is limit.
Less is not acceptable because the outer plies will crack while bending, and the final panel will have to much fiber across, thus too stiff.

2- Quality of the outer plies; quality for varnish finishing classe II (European norm EN 635). NO CRACKS, NO DEFECTS, NO REPARATIONS, NO PUTTY, NO KNOTS OF MORE THAN 3 MM DIAMETER MAX and only 3 or 4 small knots accepted on full sheet. Generally with okoume there are no knots.

3- Quality of the core: take one of the small "quarter" panels and cut it in strips of 2.5 cm wide. NO VOIDS ALLOWED. Generally in 3 mm okoume CTBX the core is of same quality as the outer plies.

4- For sure the glue lines must be dark= resorcinol, phenol.

B- Mechanical tests.
Okoume quality is very variable (like any wood).

1- Sand, with coarse and fine paper. The dust must be fine.
2- Sand in oblique like making a scarf. The plies must be perfectly glued together with no discontinuity.
3- Weight it and calculate the density. It must be around 480-520 Kg/m3. Do not accept too light, the mechanical strenght is to low, and it sucks too much resin.
4- Bend the strips: the bend must even and smooth.
5- Torture a small panel and calculate how much longitudinal bending (cm by meter or inches by feet) it accepts until it cracks, re-do with the cross bending. Keep the ciphers that may help.

C- Epoxy compatibilty.
Okoume generally works very well with EP.
1- Coat with resin some strips. Let it cure and measure the depth the penetration of the epoxy. 0.25 mm is largely enough for a sound gluing, you are gluing, and the glue line needs only to be a bit stronger than the wood. Too much resin is useless because it's a waste, and also because resin is stiffer in compression than wood and you final panel may become too stiff for bending.
Make trials, maybe you'll have to thicken a bit the resin with colloidal silica, maybe a light coat of pure resin, followed by thickened resin will do the trick, maybe cotton fiber mix will do the trick.
Keep the saturation for the very outer plies after bending the hull.

2- Divide one quarter panel in 3 pieces of 0.20 by 1.20 m, so a surface of 0.24 m2.
Coat the small panels for gluing a 3 plies and keep the record of the quantity of resin, and fillers needed. That will help to calculate the quantity of EP to buy.
3- Try to keep glue lines of about 0.15-0.25 mm thick. At first sight, the visual glue lime will seem to be 0.65-0.75 mm thick ( 2 wetted woods of 0.25, plus the true glue line) More it's waste, less the epoxy will be unable to fill the small defects and ensure a good gluing of large panel. 0.4 mm it's a max, better to use a bit too much resin than to have unglued parts.
The final thickness must be around 9.70-9.90 mm.
4- After full cure try to bend, torture and delaminate the panel.

General counsel: the 3mm plywood is very bendy. Make a cylinder mold with enough stringers to support a 3 mm plywood without ANY DEFLECTION between the stringers. The plywood must follow perfectly the curve of the mold. Personally I prefer to make the mold covered with plywood: OK more work more money, but it ensures that the 4 panel will be identical, and makes the vacuum bag simpler to put and stop the leaks... And no marks made on the panels by the vacuum hose.

For making the scarfs, the best is a belt sander with 80 or 100 grit and a table guide. Disc sanders are to violent and make uneven scarfs. Planers have tendency to "carbonise" the okoume and to seal the pores thus the glue line may be defective by lack of penetration.
So let's answer directly to CatBuilder:
1- Is CTPX marine? YES for the glue and the wood specie used.
2- Are all the CBTX equal? NO. The number and thickness of the plies may depend.
3- Is the CBTX norm equal to BS1088. YES for the glue, but be careful with the inner plies. The CBTX plywood is normally guaranteed 10 years in weather exposed use. For comparison the best MDF are guaranteed 5 years for highway signals.
4- Is the CTBX quality variable. Unhappily YES like the BS 1056 and 1088. Depends on the maker of the plywood and the final market. I do not know the spanish brand.
3- So buy a sample and test it throughly for your special use. But ay least the okoume is convenient and the glue of marine quality. It's a good start.

 

For rasorsinc.

Hughes, who is a professional NA designing USCG approved charter boats, knows his job and the cylinder mold has been used since more than 20 years with very successful tris and cats. Do not worry about the scantlings; some of the cats have 20 now years of charter and have survived hurricanes.

That needs some engineering precautions (no hard points, no continuity solutions, and good fiberglass-EP outer coat for a high modulus surface). I have made in 1988 a Formula 40 catamaran weighting 1830 kg (4031 pounds) ready to race (with sails and all hardware) in 8 mm (less than 3/8) strip plank, 1 carbon UD of 125 gr/m2 each side and a 165 gr/m2 glass satin outside finition, and just a few bulkheads, most of 6 mm plywood. Last I got news it was in 2007 and the cat was going well and strong. That depends if you want a rigid structure or if you accept some flexing without compromising the final strenght.

My 40 and 44 foot pro fishing boats able of 24 knots , have a bottom in 18 mm plywood, and decks in 12 mm. These boats fish until state 7 sea (60 miles winds 10 feet waves)... But there was a lot of engineering before building...

A lot of boats are overbuilt because the NA and NE are not confident on their design and calculations, and a lot of boat builders have not enough technical knowledge and skills for ultra light building. Also because customers like to feel the rigidity and apparent strength. You know, like the 1 inch monolithic lamination in the bottom some shipyards claim for some floating condos...

 

Thank you very much!! Thanks, Ilan Voyager!

I was hoping someone knew a little something about the certification, but never thought I'd get this much of a guide, which I sorely needed. Thanks!

I suppose I'll travel the 10 hours to go take a look at this stuff. Maybe I can bring some tools, do the testing there and buy it if it's good.

Only other question... this stuff doesn't carry all the marine certs, so wouldn't it be a lot cheaper normally and not in comparison with true BS1088 or Lloyd's Certified ply?

Also, where are the people from Europe?!!? I would think they would have a lot of inside knowledge on this certification or at least have heard of it...

 

Où sont les gens de l'Europe?!?