ACX plywood

It is my understanding, and perhaps faulty, that ACX grade plywood uses a waterproof glue. The chief differences between this grade and marine then, is the number of plys, and the potential for voids in the wood.

Wondering, in a hull, perhaps multi-chined, constructed of plywood, and sheathed in any combination of fibers and epoxy, what would be the affect of these voids? (Haven't gotten to this in class at TLS.)

Sam

 

ACX

Quality of plywood has generally been falling into the abyss for decades. ACX will do the trick for a quick and dirty boat, upon which you will place little value or trust. The use of ACX is very poor economy, in my opinion. My labor is by far, the more expensive portion of the construction of any boat. If I have to burn the boat after a few years, or replace the poor initial materials with the materials which I should have used, my expensive labor is wasted. If you were to sell a boat built with poor materials, your reputation as a builder takes an immediate hit, which is quite expensive indeed.

Voids in plywood are disasterous. They are commonly called "rot pockets", but they can also cause an unfair hull surface, which is hard to disguise, and never totally stable. No amount of surface treatment will decrease the likelihood of a void becoming a rot pocket.

Try googling "BS 1088". This is a marine plywood standard upon which you will never waste money. If all you wish to do is slap together a small boat, upon which you will endeavor to enjoy a few seasons of use, by all means use ACX. I will never buy a boat built with ACX.

DC

 

Thanks for the notes.

FYI, The intended application is a small liveaboard capable of blue water cruising, ala Serpentaire.

I suppose at this point in my life, the notion of "is this possible, and when?" sort of supercedes quality above all else. Of course, safety is a prime issue, and also the usable quality of the boat. Hard to define.


From a cursory reading of Zen and the Art of Motorcycle Maintenance(Pirsig) particularly the piece on shim material for a BMW motorcycle, 'a collapsed beer can at 5c or a shim part from BMW at $50.'

I would welcome descenting opinions on this veritable slaughter of the concept of ACX plywood in a sheathed, chined, hull.

Sam

 

ACX Experience

I made what I thought were going to be templates for a little stitch and glue type of row boat out of ACX plywood. Then after making the actual boat for someone out of 6mm and 9mm Okume marine plywood, I stiched and glued the templates together. The boat is covered in a polyester cloth I get from Defender Industries, MAS epoxy was used for on both boats. The panels were joined with Scarfs on the proper boat and the template boat (Miss ACX) 6" wide butt blocks were epoxied to the interior to join the panels.

Well, both boats float, one is a beauty, but with Miss ACX plywood, the inner voids in the ACX plywood show on the exterior as discoloration and condensation spots. I would imagine they could be a trap for any moisture which may get in. The ACX boat is holding up OK, and is a generally abused marina utility rowboat.

I would suspect that the boat made out of the "proper marine" plywood will be longer lasting. But it also is a recreational skiff on a lake and treated with care and love. Miss ACX is abused and neglected in a saltwater marina, including being occasionally swamped by rainwater.

I don't know if the glues in the marine plywood and the ACX is identical. Exterior plywood glue does seem pretty waterprrof to me. The quality of the wood is much higher in the good quality marine plywood so if you are leaving it bright, you really don't want ACX. The cheap exterior plywood tends to check and splinter a bit.

Anyone tried OSB?

 

Thanks for the reply. Do you think the voids would be visible given a larger boat with a greater thickness of exterior fiberglass sheathing, perhaps some CSM + woven roving?

Sam

 

MAterial Opinion

If I were to build a boat of any size I would use the best quality pywood I could find. Although it seems ungodly expensive, I think it is a false economy to use anything less then the best. I think that the voids may be masked by an extrodinary amount of sheathing, but the epoxy and material would probably be more expensive then using the better plywood.

Additionally you will spend quite alot of time and materials filling the surface of the cheap plywood. You still might have the problems of the "rot pockets" described above.

I must agree with "betelgeuserdude" above, that in the scheme of things there is so much time and labor involved in any boatbuilding project (even 'instant boats') that the cost of the better plywood is marginal.

There are two schools of thought on this. One says that if properly encapulated you can use any plywood, or I guess anything. The other school says use the best plywood possible because you really don't want any hidden voids for both cosmetic and more importantly structural reasons.

 

Wood is mainly air. Worrying about voids in plywood shouldn't be a concern, as long as it is structurally adequate. Any encapsulated wood works fine; just look at balsa wood cores. Plywood with voids and three laminates will bend in less than fair curves. I use it for skiffs that are built quickly. My labor is about twenty hours, and it allows me to experiment with shapes for little money.

 

Gonzo clearly states the philosophy of the "if the encapulation is good enough the plywood can be of any sort" philosophy. I too generally play around with cheap and more usually salvaged plywood for "prototyping".

It is certianlly a greater pleasure to work with high quality plywood. But, Miss ACX indicates that there is certianlly merit to Gonzo's point.

Sadly, Miss ACX is missing, it is unlikely that long term data durability data will be available. I looked near the docks and it did not appear to have sunk, someone stole her I guess, or at least borrowed her indefinately. I am glad I never installed nice bronze oarlocks in her.

 

That should be a form of flattery. She was good looking enough to be stolen. Or maybe somebody thought she was so ugly she needed burning . Oh, well post pics of Miss ACX II.

 

OSB board is a NO-NO. A good alternative in fir plywood, is the MDO board. It has the right glue, and is rigid for strength, in the smaller boats. It will allow for a nicer finish paint job. Fill the voids on the back sides layer. The face has a paper coating to hide some of the wavy grain patterns of the wood. Wet out the face really good, in the initial building, if you will be glassing it, with a couple of coats of resin, for a smoothe coating, before glassing it. This will keep it from delamination, which will occur when you just wet and glass in one step.

 

You should wet the plywood and laminate in one step. Otherwise it will be a secondary bond which isn't as good. Chris Craft built boats with MDO above the waterline that were painted with enamel and forty years later many still survive.

 

Exactly, Gonzo. But some folks on some boards, will advocate wetting down through the glass. This allows for the dry laminates, if one is using the MDO boards, for the first time. I should have added that for clarification. Thanks.

 

Sorry, I misunderstood. By the way, where in the Outer Banks are you? I built boats there for several years in Wanchese and Manns Harbor.

 

SamH ---

You can certainly build high quality boats using ACX plywood.


I suspect for equivalent hulls BS1088 cores would be thicker and have thinner glass/epoxy faces relative to ACX cores.

 

I don't think people are suggesting that ACX can't be used. Many boats that spec it out, or people that maybe using it, are doing so on smaller vessels. This being said, the amount of savings in using ACX versus using a better grade, that has a better surface, and better core layers, will help you minimize a lot of work in filling, finish, and sometimes recutting pieces that will not work quite right, in areas that require bending plywood to fit it, to a jig or certain shape.

Gonzo, I am west of Hatteras Island, towards Morehead City, but have worked service work for Buddy Davis in the 80's, all along the banks and eastern shore of Virginia, on building and fixing Chesepeake Bay deadrises. I use to go to Ricky Scarboro place while I worked in Ocean City Md, when many of the Sportfishermen were starting to get custom boats built down there.