My first build.... questions before I start

Sheet material...available in various weights at Walmart. The thickest stuff is probably 25 or 30 mil, comes in 4 or 5 ft wide rolls in the sewing department. You buy it by the yard like cloth.

 

Thanks, Steve. I may have to check it out.

OBXIce,

An alternative to Steve's method is to dab a bit of thickened epoxy between your ties and let is cure. Once cured they act like "tack" welds and you can pull your ties to run a fillet full length. Make sure you fillet the tacks or you'll have those to contend with later. Removing the ties before you fillet will sometimes let you make your fillet smaller, saving weight and material.

 

I will probably try both techniques and see which works well for me. As stated before, I don't expect this boat to be great. This project is entirely for learning. I am a hands on kind of person. If I do it and make mistakes, I learn better than in a classroom. That is why I am going really cheap first time out.

Thanks for all the help guys. Should be starting this week I hope. I will post some pictures as I work so you guys and gals can give me more tips and tricks.

 

I have to disagree with that statement. Adding glass can more than double the original plywood stiffness and strength. Dynol is better for abrasion resistance but doesn't add much strength or stiffness as it is too stretchy.

 

'Glassing does add strength, but and it's a big but (much like my other half's) in the thin, light weight sheathings typically used on plywood, a hardly measurable difference. Dynel and Xynole add absolutely no strength or stiffness to a plywood panel. For 'glass cloths or other fabrics (uni and multi dia's), you need a signifigant amount of fabric to increase stiffness and strength.

For example, a well bonded 10 ounce (342 GSM) skin is .017" (.43 mm) thick, which isn't much, so you need at least two layers of this, before a noticeable improvement in strength and stiffness if measured. Even at this, it's not much, but doubling this amount will begin to yield a marked improvement in panel stiffness and strength. Strength will come on first, with stiffness lagging considerably behind.

 

Wouldn't consideration of a glass vs. wood percentage add to the argument? A 6 oz. sheathing on 1/2" piece of ply is going to add considerably less, percentage wise, than say, 6 oz. of glass on a 4mm ply panel.

Ounce for ounce, I think your better of with a thicker piece of plywood for strength and rigidity than with thicker laminates on a thinner piece of ply.

 

The following extracts are "pounds to failure" data taken from "The Gougeon Brothers on Boat Construction"

5/32" (4mm) marine ply, without glass 45 lb, with 1 layer of 4 oz glass 211 lb (23% heavier)
3/16" cedar strip with 1 layer 4 oz of glass 162 lb, 2 layers of 4 oz glass 309 lb

 

I believe you are referring to the old data they did on strip plank panels (2rd edition of the book, if memory serves me), which also has some hunks of plywood tossed in for comparative purposes. This is chapter 23 of the current volume (5). Both the strips and plywood were in a sandwich, meaning sheathed both sides, much like what would be used in the method they are talking about, in that portion of the chapter (strip plank laminated veneer and strip composite construction methods). In this application, yep, you gain a substantial amount of strength and a sizable improvement in stiffness, but only because the panel (strip or plywood) is in a sandwich, between two GRP skins. This is not the same as a simple skin on one side. An indicator of this can be seen in the chart on page 275. Look at the deflection rates. The light sheathings on 1/4" (plywood) allowed only 15% or so more deflection, weighed about 30% more (well this is dependent on plywood thickness and type) though added about 50% in yield failure, much of this was because the skins prevented damage from beginning in the outer and inner veneers. Simply put the outer skin prevented "burst out" and anyone that's bent wood knows what this is. The inner skin delayed cellular collapse, until the resin failed under compression.

My point is sandwich construction can save both plywood (thickness) and laminate (weight of sheathing). In the application, above I was letting the inner plywood bonded to the foam, serve as the inner skin (no sheathing to save weight and cost), while sheathing the exterior plywood, but really only for abrasion, not additional strength and stiffness. The plywood/foam sandwich works just like a 'glass/foam or a 'glass/plywood sandwich, but is a bit simpler if you can remove some of the cloth and goo from the equation.

Greg, you're correct in that the thicker plywood panel wouldn't have as much added to it as a thinner panel would, in regard to similar weight sheathing. My point is, a skinned panel is quite different than a sandwiched panel. In other words, if the same 12" squares of plywood and strip planking used in the Gougeon tests, where just skinned on one side, the results would be a fair bit different and on 1/2" plywood nearly meaningless in regard to strength and especially stiffness.

 

I see where you are coming from. I had assumed you were writing of glass on both sides as is necessary for a stripper, since the outside layer of glass does nothing to resist an exterior impact. I have avoided using glass so far - for ply my preference would be the next thickest grade without glass.

- but if abrasion resistance is the main concern then a polyester like Xynole sounds like the best bet; I understand it can't be bright finished. I haven't tried it, although is Dynol called for in one of the plans I have.

 

In light weight projects, Dynel and Xynole are quite heavy products to employ. Something on the order of 3 to 5 times the weight of a conventional cloth of similar weight. With the mass of these types of craft a very light finishing cloth is just about as effective as a heavier cloth, so 2 ounce (68 GSM) to 4 ounce (136 GSM) is just about as effective (though lighter) with abrasion as an 8 ounce. Usually if you bash something hard enough to screw the sheathing locally, it doesn't really mater what weight it was. What does all this mean? In a typical light, stripped canoe, say in the 35 - 40 pound range, the light sheathing might add a pound or two, while the heavy sheathing will add a few more and the acrylic or polyester fabrics will add several maybe a dozen additional pounds to the project.

 

I guess there are ten ways to do it..... so many different opinions. Getting some new tools in the next two weeks or so. I am trying to decide which skill saw to buy. I want to buy some nice tools that will last. I really like the Festools line but man they are expensive. Long story short... three of four weeks from now I will be back with pics and probably a lot of questions. Thanks everybody for your help.

 

Vynil ? Is it transparent ? is it that much cheaper than Peelply ?

Half the benefit of Peelply is that you can see through it to see if the cloth is saturated and bubble free.

 

OBXIce, if you plan on doing a lot of "building stuff", boats, houses, etc. then get the best tools you can. Festools are nice, but frankly I wouldn't buy them, just because I think they think they're worth more then they are.

If you're just looking to hack away at some stuff, as the mood moves you, then homeowner grade tools will do fine and save you a bunch of money.

Most professionals purchase repairable tools, which often are pneumatic powered. These can be rebuilt and repaired as required, so a quality tool can last a lifetime. In fact, I'd owned a few tools for over 30 years. Some are electric, but most air and each has had new brushes, bearings, guides, etc. installed over the years, but because they were high quality, they still work. Then again I work with these tools everyday, so it makes sense, but if you're just looking the beat some wood into a boat shape, every now and then, you don't need tools like this.

Lastly, you can get Harbor Freight tools for cheap. They don't last worth a damn, but you can buy a dozen palm sanders for the price of one good name brand model.

 

It is pretty much glass clear...I have had it stuck on the passenger window opening of an old Ranger for almost 3 years now and it is still clear enough to see through. Remember back in the 60's (laugh-in) when some of the Go-Go outfits had clear see through panels...this is the same stuff...although I suspect it is a bit thicker.

 

I use skilsaw type saws in my boatbuilding, and currently have 3. The one that gets the most use is the cheapest, because it is also the lightest. It is fitted with a piece of ply over the baseplate - I lowered the blade through the ply to get a zero-clearance slot; this gives a much cleaner cut with no splinters.

The heavy-duty one with ball bearings and stronger baseplate is nice but I would have been fine with another plain bearing saw for the one or two boats a year that I average. Having it means the other saw with its ply plate can be left with its blade permanently and accurately set to 90 deg for precision cuts.

Both these saws have construction quality finish cut blades with thin kerfs which provide a finish that can go straight to gluing or sanding, no planing required. When I fitted a blades I spent some time rotating them and watching the edge to ensure they were boths flat and mounted correctly; this pays dividends in the cut speed and finish. These blades cost almost as much as a cheap saw, and are well worth it.

The smallest is a 3-1/2" panel saw which will cut curves in plywood and is great for cutting planks but doesn't have enough power for larger work. It has a short baseplate with an accurate cut-line pointer which lets me cut close to the line, and can be hooked up to my dust extractor system. It is corded which can be a nuisance, but there are some nice battery-powered panel saws around - the lithium batteries are much lighter and longer-lasting than the earlier types and that is what I would look for if I had to buy a new saw; perfect for ply.

Building wooden boats creates a lot of dust; if I had been thinking ahead when I bought my tools I would have checked to ensure they were compatible with a dust extractor system; the sanders have their own dust bags which work quite well but a power planer puts out chips at an incredible rate, ankle deep in minutes! A useful gadget is an air-born dust extractor. Mine is just a ceiling-mounted 20" square fan with a furnace filter taped over the intake: cheap and effective.

If you decide to buy battery tools, try to get all the same brand with interchangeable batteries that can be bought separately - bitter experience talking here . . .