Newbie here with newbie question. Marine plywood or plywood?

[photojunky]

I am going to be building a wooden kayak or wooden rowboat in the near future. If I coat the wood with epoxy/cloth, is it acceptable to use regular ½ plywood, or do I need to use marine plywood? I also plan on painting the boat and will not be keeping her in the water full time.

When I start building, I'll post images of my progress for cheap laughs at my expense.:D

BTW, this is one cool forum.

[USCGRET/E8]

If you're going to glass it, regular Exterior plywood will work fine.

[PAR]

Marine plywood differs from construction grades in significant ways. The veneer count is higher, which makes a more stable product, that is stronger and more reliably bent to conform to boat shapes. The quality of the panel construction is also much better, typically having same thickness veneers, few voids, defects, repairs and rot resistant species used throughout. This can't be said of construction grade plywood. You'll have to seal the plywood which ever grade you elect to use anyway, so it seems to me, like false economy to skimp on the planking, when in the end the marine grades will perform better and last longer. Generally, the planking is some of the finest material used in small boat construction.

[PsiPhi]

Photojunky
I'm a newbie too - and was thinking the exact same question.

What PAR says is correct (of course) and you will get the same good advice everywhere,
however (PAR) my problems is Construction ply is $30 a sheet, Marine is $150.
$120 x 6? sheets (for a average type dinghy) - the difference between $180 or $900 on ply is the difference between a cheap boat and no boat!

Maybe the question Photojunky (and I) need answered is - What are we going to loose by using cheaper ply?
Will our boats "Crash & Burn", figuratively speaking, or just die quicker??

[photojunky]

Holy Sh*%#! :eek: 150 for marine! I think you just answered my question. Besides, this is my first boat so there will probably be some screw-ups so why waste the money on the marine grade when this is just a practice project.

[PsiPhi]

I'm talking Aussie dollars of course (I'm in QLD) - but I would guess their is a similar difference where you are.

[waikikin]

Photojunky & Psi Psi, !/2" is pretty thick ply for a canoe maybe 6mm/ - !/4" is closer to your needs & price difference less, Psi Psi in Aussie some of the misterply franchises have 6mm hoop pine ext type A bond with 5 veneers that would suit dinghy/canoe for about $70A of very good quality, I've cut heaps for fitout etc & found very few voids, also takes epoxy or paint well. Regards from Jeff

[USCGRET/E8]

I assume anyone posting on here has a very small budget as I always do. I therefore base my answers on that. In that you are building a rowboat or kayak I don't see a need for that expensive marine ply, which I had in mind in my previous post. If you were building a fast speed boat, then the marine ply wood be a safer bet.

[USCGRET/E8]

I assume anyone posting on here has a very small budget as I always do. I therefore base my answers on that. In that you are building a rowboat or kayak I don't see a need for that expensive marine ply, which I had in mind in my previous post. If you were building a fast speed boat, then the marine ply wood be a safer bet.

A speed boat I built using 1/4" exterior plywood then glassed. It held up fine.

http://i161.photobucket.com/albums/t239/MACHTECH1990/nnn.jpg

[timgoz]

While respecting others experienced opinions, I myself would go for marine grade ply. When you tally up oars or paddle, vest, skirt (if Kayak), and all the construction materials other than the ply, the ply is not as great a part of the cost.

You hopefully would not skimp on proper technique for a "pratice" boat. Why then should you skimp on the quality of the materials going into it. If done right and with good materials it may last many years. If done right with inferiour materials it may last significantly less years.

To me a boat, any boat, deserves the best you can afford. I am to poor to be cheap.

Tim

[ATCSchaefdog]

Regular plywodd would work great. But the question is...is the boat of your dreams, the boat to end all boats? If it is, then use marine grade, if not, go cheap.
Steve

[catman021]

I've got to echo the popular sentiment here and go with the construction grade plywood myself. On my rebuild(sic), I've looked at both plywoods, fibergalss overlaid foam, composite materials, and being just a working joe, knowing that I'm going to coat/glass it in completely anyway.....for my money saving the money is the way to go. This is also driven by the not so small factor that I can get the cheaper stuff from HD or Lowes and not pay any outrageous shipping fees to boot.

[VKRUE]

IMHO...

I'm with Timgoz.......... "I am too poor to be cheap".

Are you serious about building this boat ? If so, then why not make it a point to build a real craft, with skill. You will develope the necessary skills as you go. Sure, you will make mistakes. But, if your like me... the fact that this piece of plywood cost me $100.00 for a 4' x 4' sheet will be a lot of encouragement to take care in everything you do.

Below is a picture and caption from my blog regarding the making of two gussets and two patch boards for my boats hull... I removed a small section of the hull to replace a damaged section of the keel about 36" long:

http://photos1.blogger.com/x/blogger2/532/1075966638257981/760/z/994637/gse_multipart30497.jpg


Here you see the hull patches. They are made of 3/8" okume plywood with 7 plies. I had purchased the wood thru Boulter Plywood
http://www.boulterplywood.com (http://www.boulterplywood.com/) .

The wood was shipped directly to my house here in central Illinois.

Each patch board was carefully shaped, dry fitted and clamped into place many times untill I was satisfied that the shape was precise. This was a real pain because at the time I hadn't figured out how to flip the boat over yet. The first half (patch) took an entire day. Then I pre-drilled each piece every 2" around the outer edges all the way around. I counter-sunk the outside holes to accomidate brass screws while the inside holes (directly over the keel) would recive silicon bronze ring-shank nails. Don't ask me why I used brass :( I don't know why I used these instead of silicon bronze like I should have. Brass, I have found out is very soft. Everything else on the boat is getting silicon bronze below the waterline and bronze or SS above.

During the intire process of making each of the gussets and patchs I was lucky to have only wasted one small board due to a mistake. After making the first gusset, I got the brilliant idea that the peice on the opposite side would be identical ( a mirror image) to the first. Oooooooooops ! It doesn't work this way.



You will develope the skills as you go if your serious about what your doing.
However, many people might see using cheaper materials as "a way out" of trying as hard as they could. In the end it could be a total waste of time.

Par has given a good explanation of the differences... and he knows what he's talking about too.

Also, if you use the proper plywood to start, there shouldn't be any reason to have to glass over it (if you build the row boat).

Like I said.... In My Humble Opinion

[timgoz]

Another thought. The thinner you go the more important it is to use the best ply available.

If doing a kayak or other very light skinned craft, the voids "found" in inferiour ply are potentially much more problematic.

Is the boat to be used an very small lakes and ponds or to be put to more dramatic tasks. If the later, where you are to far offshore to "swim for it", top quality translates to a proper outlook on safety.

Tim

[charmc]

Yes, marine ply is more costly than construction grade, but the prices mentioned above seem too high. Here is a place in FL that sells full and half sheets, as well as smaller pieces. Prices are 50 -60% of those mentioned earlier.

http://www.buckwoodcraft.com/marine_plywood.htm#Okoume%20Marine%20Plywood%20-%20Quick%20Reference%20Price%20Sheet

Another thought: For a kayak that will be glassed over, I can't see anything thicker than 1/8". Easier to bend into shape, and, with proper technique and internal supports, more than strong enough. The lightness will translate into better performance, and will be appreciated when you're taking it out of the water, as you mentioned.

A bit of philosophy here: If you set out to build something as cheaply as possible, on the assumption that you're not skilled, you're probably going to make something that looks like an amateur built. If you set a higher goal of building something that will be as fine as possible for your budget, you'll look for ways to get the best for less, you'll take the time to learn the best techniques, practice on scrap so you'll do the real thing well, and you'll make something to be proud of.

Here and in many other sites there is a wealth of information about building small boats from plywood, as well as good people ready to give support and specific help. This site describes building a plywood kayak; the planking is 1/8" to 1/4" max, with supports cut from heavier stock.

http://www.glen-l.com/designs/canu-row/kayak.html#avail

Good luck

[VKRUE]

Charlie:
You said everything so eliquently.

A+ for effort and a skilled vocabulary.

[PAR]

The first time you bend a piece of construction grade over a freshly made form and hear a loud pop, followed by a sudden deformation in the nice smooth curve you were trying to bend, you'll wish you'd used a better plywood. Which had more veneers, better quality with no voids to harbor rot or go pop during a critical bend or stress loading underway (after construction) as an over lapping veneer or other internal defect rears it's ugly head and literally explode, inside the plywood panel.

This isn't to say you can't use construction grade, you can, but with certain risks. The risks are: not as strong a product, not as bendable a product, more prone to rot and internal defect failure under load and finishing difficulties.

A canoe size craft will call for 1/8" to 1/4" plywood, a skiff or row boat will call for 1/4" to 1/2" in the sizes I think you desire. A small skiff of my design has 3/8" bottom and 1/4" topside planks, is 14' long and can handle a 15 HP outboard. This would be typical. A larger engine would require thicker planking and a denser framing schedule. This is also typical.

In thin plywood, it's particularly important to get the most effort from all the veneers available in the panel. This means a higher veneer count in a panel, will substantially increase the strength and workability of the plywood. Internal defects are less critical and absorbed across more glue lines and cross veneers. Look at a piece of 1/4" three veneer lauan from Lowes/Depot. The outer veneers, which offer the only longitudinal support for the panel, are very thin, with a relatively thick center veneer, which has it grain running across the panel rather then length wise. These paper thin outer skins offer little more then a pretty surface to apply a stain to, certainly no strength. Take a small piece of this plywood and stick it a bucket of water for a month, without any protection and see what happens. It's likely it will shed its outer veneers along the edges pretty quickly.

Every once and a while, the big box stores will get a shipment of equal veneer 1/4" lauan exterior. This is pretty good stuff and I keep and eye out for it, as I have a Lowes just 2 miles away to keep tabs on. Learn how to check a piece of plywood for defects, construction flaws, voids, etc., because you can find amazing deals, if you know what you're looking for and what a good panel looks like when you find one. The glue has to be WBP if used for planking, regardless of whatever sheathing you'll apply. Internal components of a boat can be construction grade plywood.

[PsiPhi]

Charlie, thanks for the BuckWoodCraft link, unfortunatley deivery to Australia put's the price up a bit ;). I Guess the price differential is greater here than in the U.S..

PAR, and excelent post, thank you, your eloquent narrative of 'popping' ply really has all the woes of painful experience. That, and the techinical stuff makes me rethink my philosphy.

I want to build a sailing skiff for lakes and quiet waters, nothing too demanding, or too far from shore. One of the first things I read about getting a boat said that [I]"...any boat is going to be a compromise..." I think maybe I could use a cheaper ply for the 10mm flat bottom (now that I know how to tell good from bad), and spend a little more on the 6mm that needs bending.

[alan white]

An advantage of marine ply in a dry-sailed boat is that you can build the boat without epoxy (except as an adhesive).
The cost of epoxy and cloth saved probably outweigh the extra cost of good ply.
Properly painted and maintained, the boat will last a very long time. Later, you can skin the boat with cloth and epoxy if desired, but you can never upgrade the plywood.
I would choose marine ply with no fiberglass/epoxy over cheap plywood and glass/epoxy. It is lighter but demands more attention to detail. Wood boats can last 100 years without any epoxy at all.

Alan

[northerncat]

in aus you can get bb hoop pine ply (aa is marine)which if you pick it yourself is equal to the quality of marine ply and at least half the price
sean

[timgoz]

If you build a boat, then later sell it, marine ply construction will demand a higher price than exteriour.

Tim

[photojunky]

Thanks for all the replies. I’ve learned a lot reading all the posts.

Originally the question was ply or marine ply. If I can get the marine ply significantly cheaper than the price of 150 per sheet as mentioned, then I’ll go for it.

I said I was thinking of making a kayak, but I was actually thinking of making more of a cross between a kayak and a long rowboat. I want the slimness of a kayak but I want it to be a bit more stable like a rowboat, although I probably wont be taking it out in rough waters. The bay on a nice day is all I’ll be doing. I was thinking of modeling it after the boat in the image below with a couple of changes. I want to build something a little different that will make people say, “cool.”:cool:
1/8 plywood seems a little thin for a boat 16 ft long. Would I be better off using ¼, or doubling up 1/8 in the area that people will be occupying?

My skill level is pretty good. I’m self-taught and have completed a bunch of wood, auto, and computer building projects by basically looking at books and the internet. My wife say’s I’m like rain-man when it comes to that stuff. :D
http://www.humanpoweredboats.com/Photos/ManufacturedHPBs/Calderdale_front_p.JPG

[northerncat]

short of having receipts i cant see how you would identify that a boat was built with marine ply as it usually painted inside and glassed outside
sean

[VKRUE]

Quote: Would I be better off using ¼, or doubling up 1/8 in the area that people will be occupying?

I read where some people do use multiple layers but, by doubling up the plywood, thereby having two layers, you will create a void between the layers where water can acumulate and start the rot process. I believe that most would advise against doing so.

I was originally considering glassing over my wood (3/8") hull for strength and durability but, everyone specifically advised against it for the reason mentioned above.

[timgoz]

Sean,

I'm speaking of a builder eventually selling "his" boat. It would be a matter of being honest with a prospective buyer about the materials used in the boats construction.

Keeping all important reciepts for a project as big as boat construction would be a good idea.

Take care.

Tim

[photojunky]

short of having receipts i cant see how you would identify that a boat was built with marine ply as it usually painted inside and glassed outside
seanThat would be like lying about a cars mileage. Besides, isn’t omission of the truth like telling a lie? It’s bad karma if you believe in that sort of thing.

[alan white]

Encapsulation is very effective in keeping wood from absorbing water. It works as well for keeping water from getting out of wood. If you completely encapsulate a piece of wood, and then drill a tiny hole in it, and then submerge it, over time it will become saturated. Then it is worse off than a piece of wood that had been left bare. I've seen this happen as a result of a screw hole in a cockpit that filled with water while the owner was away for two years. His tarp had blown off, but he didn't know it.
I bought the boat and had to destroy a custom lazerette and propane locker and rebuild the whole area. It wouldn't have happened if it hadn't been submerged. The teak sole and coamings were unaffected, as if never submerged in water.
The boat had been covered for a year after the cockpit was pumped out. Yet the wood rotted faster than the water could slowly migrate out of one tiny hole.
Well constructed epoxy ply boats have not been around for that long. I can remember a time when nobody I knew of used epoxy to build boats. I see a lot of boats on the used market that are taped or glassed with ployester, and they often are seen to be losing their bonds.
I also see a lot of folks doing repairs and building new using epoxy over inferior woods (I even saw a guy who used waferboard in his cockpit under epoxy, who didn't worry at all since as everyone knows, epoxy is forever!)
Years from now, that ultimate belief in epoxy as a miracle sealant will be seen as what it really is: An excuse to use inferior materials and bad workmanship and get away with it for a while.
Don't get me wrong. In the right hands, epoxy really makes an enormous difference. You can indeed protect wood for a long time. Dry wood is stronger and lighter. But I do see a lot of first boats built with a lop-sided dependance on epoxy to make up for ameteur fits and cheaper materials.
Attention to important aspects of epoxy construction will make the difference.
You CAN use cheaper materials. What you can't do if you are looking for longevity and safety is misunderstand exactly what epoxy does.
Most importantly, epoxy should be used to seperate wood from wood. Water entering a piece of wood should not be allowed to migrate into adjacent pieces. Equally important is maintaing a strict conrtol of the mix ratio. Cured epoxy should be sanded before recoating every time. Care should be taken in drilling holes, especially in places where rain or bilge water could supply a steady flow of water, and absolutely where water could collect (like against a frame that has a clogged limber hole that's right next to a clam screwed on for running a bilge hose---- the clamp's screws weren't both stainless--- one was zinc plated. It corroded away and left a hole. Water got in, and you never realized that that was what rotted the bottom. this wouldn't happen with painted wood. It would dry over time.
Understanding all of the ramifications of epoxy use in sealing wood is at least as important as what woods are used.
Epoxy can work against you later, so any newbie boatbuilder should study the ins and outs of epoxy encapsulating before they start. Using cheaper materials can make sense, but not if they are improperly encapsulated.

Alan

[PAR]

Multiple layers of plywood is a well honored method of construction. I'm just finishing up an Ashcroft method, planked with 1/8" ply. I used resorcinol, but could have used epoxy, if I wanted.

Any layering method requires good contact, so you can eliminate voids between the layers. Cold molding, double diagonal, triple diagonal, veneer over strip, Ashcroft, etc. all require this. This is little more then a modern adaptation of tried and true techniques, generations old.

How did we ever build boats without epoxy. Well, felt, tar, varnish, shellac, paint, lead, copper, pine gum, virginal pee and just about everything has been used between the layers, before real waterproof adhesives appeared during WWII.

Photojunky, on a small boat (most any type) weight is a critical issue. Follow a set of plans and try to refrain from making changes to the structure, such as doubling the bottom planking, in the hope things will be stronger. In the vast majority of cases, just the opposite happens and you've increased panel loading, stress risers, reached fastener strength limitations and a host of other, not easily foreseen or understood engineering issues, which may not have existed before you made changes.

If interested in a better understanding of the structural components in a boat, may I suggest you get a copy of "Elements of Boat Strength" by Geer. Or if interested in just the principles involved, "The Nature of Boats" by the same fellow. Neither book will provide enough information to design a boat, but the individual pieces and concepts can be gathered, absorbed and put to use in your next project. If interested in design then there are several good titles on the subject. You'll be very hard pressed to find success, without a reasonable understanding of the convoluted collection of compromises, necessary to develop a design brief into a craft that meets or exceeds expectations.

Northerncat, I can tell that photo is a plywood boat, just by the looks. I can also tell you it's a taped seam construction too. If you look closely along the edge of the sheer, you can see the tape wasn't faired smooth, a pretty easy give away. It's also a conically developed shape, another dead give away.

[PsiPhi]

Northerncat
Thanks for the tip, I'll look for 'bb hoop pine ply'

Next dumb newbie question: AA, BB, AC/DC, 'hoop pine', luan - I've seen all sorts of references to types of ply. What do they all mean?

[alan white]

Face plies are graded based on the presence of knots and other surface imperfections. "A" means "No defects" (though patching has been done where knots and defects had been, usually shaped like American footballs).
"B" may have some defects, 'C" even more, "D" many defects.
When a board is graded A-B, it means one side is A and one is B. A-A would be used where both sides will be seen when finished. CDX, used for building construction, means C-D grade, exterior application (glue).
Other than that, there are many many other ways of describing plywood--- indicating intended use, species, number of plies, etc..

Alan

[waikikin]

Psi Psi, the hoop pine will paint up to smooth much easier than the luan, it takes epoxy well too. Regards from jeff.:)