Plywood and wood frame choices

I just left Lowe's where I had been doing some very unscientific testing on different ply woods they have, as well as some various pine wood boards, trying to determine some sort of strength to weight ratio. I'm planning a 12 foot Jon boat build, and this boat will NEVER see anything but almost glass calm waters in local creeks, and the occasional sheltered cove in the back waters of some of the lakes. It will run using a trolling motor. Also there are two more lakes here, one is idle speed only where I can run even with larger boats, and the other is trolling motor only. So I'll have plenty of uses for it. This boat will use 2 1/2 - 3 sheets of ply.

On the plywood, I first pulled out a sheet of 1/4 inch pine ply. I don't know the grade but one side is smooth and the other side has some knots and knotholes, but not very many. I wedged the long side against the floor and rack and held the top edge with one hand while pressing fairly hard in the center with my other hand, trying to get a feel for its stiffness as a potential bottom hull of the Jon boat I'm imagining. It was decent, but gave more than I'd like, and was heavier than I'd like, but it seemed to me (then) that it was the lightest choice. Cost is about $23 per sheet.

Next I pulled a sheet of 11/32 (considered 3/8) pine plywood and did the same test. Immediately I hear a bunch of crackling that continued the whole time I pressed on it. That was very worrisome so I'm passing on that. It seemed to resist bending only marginally better than the 1/4 did, has many more knotholes on the reverse side, was noticeably heavier, and made so many cracking noises that I can just imagine a failure on the water. Cost on this is $23.50 per sheet, so nearly the same as the 1/4.

Next I get a sheet of 5mm lauan plywood that is veneered on both sides so there are no knots at all. It's very light weight. It resists bending much more so than either of the first two, made no noises at all, and cost is $14.50 per sheet. This seems to be the best choice for a boat hull.

But I found a fourth choice after this, it's 1/4 inch ply and is used as underlayment for flooring. Very similar to the last one, super light weight, veneered on both sides, no knots, and one side is slick as glass. Same feeling of strength, no crackling noises with bending, and cost is $20 per sheet. Other than being slightly more expensive, this seems the better choice due to the slicker surface on one side and being slightly thicker (1/4 inch is roughly equal to more than 6mm, as compared to 5mm above).

Ok, first question, is there anything at all wrong with choosing to work with either of the last two ply choices for a hull material? My first thought was that they might be brittle, and therefore crack, if I was to hit any objects underwater, rocks or logs, anything like that. Here, the first two plywood choices seem like they might be tougher and more resistive to things like this.

Second question, other than the pine plywoods possibly being more durable to scrapes and bumps, what use would the heavier, more flexing, more costly plywood serve?

Now, also I looked at several choices for wood framing. They had Top Choice soft pine 1x2, 1x3, and 1x4. This wood is common construction lumber and has knots in it in various places. They also had Select pine in the same sizes, and a couple of those size choices in cedar also. Neither of these had any knots, and I've read that cedar is rot resistant so this could be good. I compared the same sizes in the different grades of the woods. The Select felt the strongest, it had the most resistance to bend, but was better than twice the cost of just plain soft pine and also slightly heavier when compared to either of the others in the same sizes. The 1x2 soft pine was noticeably weaker than the same size Select but was close in weight, or so it felt, and it still felt strong enough to stiffen up the ply of a light weight boat. The advantage here is much cheaper cost with soft pine while staying the same weight. The next size up, 1x3 soft pine, seemed fairly equal in strength to the smaller 1x2 in select, and was still significantly cheaper even though it was wider, but ultimately it was also heavier. I could tell a real difference holding three of each board in opposite hands simultaneously. So the advantage there is same approximate strength at half the cost but more weight. The cedar boards were in between each of the others in cost and weight and strength also. Cost being closer to the select than the soft pine, it's still better when you consider how many boards I'd be buying. Strength and weight considered, and also added bonus of rot resistance, this seems the best choice for building my first boat.

Any thought you might have on this, plywood suggestions, wood frame suggestions, I'm open to them all.

 

What assurances do you have that exterior adheasives are used on the ply? I would think the underlayment grade would use waterproof glue. Also, is any of it imported from China?

 

It's probably all imported from China. Does this mean anything specific? Seems I heard something about avoiding Sheetrock made in China but not plywood. I just looked them up on the Lowe's website. The first two ply woods were made using exterior glue. The $15 underlayment was for interior use only, and I could not find the $20 one listed on the site. I'll check the label when I'm in the store next time, but I'm fairly sure it is interior use also.


Where does anyone normally buy plywood for boat building from? Is there not a sealant that would encapsulate the wood completely so that no matter the adhesive, it would still hold together?

 

China has a huge reputation problem with plywood. They (and other Pacific rim countries) flooded the market a few years ago with BS-1088 and BS 6566 marked stock that delaminated at the mere mentioning of moisture.

Underlayment can be WBP, but usually isn't, so is purchasing from a big box store, you have to find the supplier and ask.

Rooster, the reason you had the experiences you had is because of the panel construction used and the wood species employed. Lauan is actually Red Shora or what we call meranti. It's a common and good species in plywood, but the construction and adhesive, within the panel is the key to if it can be used. The underlayment grade is built to a higher standard then the exposure 1 exterior sheathing you heard cracking. It's important to understand the difference among the grades, or you'll by crap and it'll fall apart. If the panel is stamped with exposure 1, it isn't WBP, just moisture resistant and it will fail. If it's marked exterior (no other markings) it's a WBP sheet and suitable, though likely still of very poor quality.

The "select" wood offerings at these stores is nearly as bad as the construction grade stock. The usual choices are,#1 and #2 pine, #1 poplar, #1 red oak, #1 and #2 Douglas fir (usually sold as tongue and groove decking) and some sort of cedar. #1 pine is a select flat sawn stock, with moderate rot resistance, but not very strong, nor does it hold fasteners well. It does glue well and finishes okay too, though usually has to be sealed to even it out. Poplar is better in most regards, compared to the crap they sell as pine, but its color usually means it's painted, not brightly finished, unless stained quite dark. Red oak is also flat sawn and mostly used as trim on a boat, because it rots if you just whisper about moisture. It's strong, hold fasteners well and finishes fine too. It's fine if encapsulated. The Douglas fir is the best bet for structural elements. It does everything fairly well, except it's difficult to finish smoothly. The cedars they use range from not bad to real crap. This stuff is designed to be used for trellises and other landscaping duties. It's weak, splits and cracks easily, doesn't hold a fastener worth a damn and though it smells nice when you cut it, is really only good form floor board slats and trim.

Before you spend any money, you'd be well advised to brush up on the various woods and plywoods available, before you make the same mistake everyone of us has made previously, thinking they'll save some bucks.

Lastly ask yourself one simple question - do you want to low ball the material that will keep your socks dry (the planking). There are plenty of places to make substitutions with lesser grades of stuff, so how important are dry socks. I mention this because most every boat builder I've met is a tightassed, cheapskate that will cut a corner at the drop of a hat, or the sale of their mother (which ever comes first), in a pinch. We've been there, tried it and cursed or now sold mother's name repeatedly. You can do the same or better yet, some research into products and species, as well as marine grade materials.

 

You can build a boat out of anything...plastic bottles, old egg crates...

But you can only build a nice boat out of quality materials. The lower grade meranti ply is cheap and effective...

Use it, build something nice.

The amount of hours, the painting, the sanding, the hardware...all add up to make saving money by using cheap materials a fools game

 

Where do most boat builders buy plywood? All I have available to me are Lowe's and Home Depot and a couple of local hardware stores, all selling the same thing as far as I can see. There are no wood working stores nearby that might sell better grades of plywood.

 

It all depends on where you are, but there are lots of mills in Kentucky.

www.woodfinder.com

Corbin
Forest Products Inc, PO Box 541, 40701, 606/528 3553

La Grange
Northland Corporation, 2600 Highway 146 East, 40031, 800-873-1441, 502-222-1441

Louisville
Northland Trading, Norwood Office Park 1, 7400 New La Grange Rd., Suite 100, 40223, 502/426-0706

www.woodwerks.com (Ohio)
www.marine-plywood.us (Ohio)

Even with shipping, you can get pretty good pricing.