lauan plywood voids

4" to 6" glass tape is overkill. 2" is wide enough. The extra inches are waste of time, money and add extra weight.
The thickness of the tape immediately over the seam is the important part.

 

4" to 6" for abrasion protection isn't over kill by any means, though agreed on very small craft like this, more then strong enough to hold the seams.

 

Simple S&G Seam Reinforcement

Sam, would you be kayaking strictly in ocean and launched from white sandy beach only? then you don't need any additional tape for abrasion and moisture intrusion. Do save your time, money and weight.

If you plan to kayak in rivers and launch from rocky shores then I would get maximum protection you can get. Rocks and flotsams don't always aim for your seams, they seem to miss sharp corners ~40% of the time. It won't cost any significant additional time (10 minutes at most), no additional material other than more tapes (use roller to squeeze epoxy) and maybe additional 1 lb of additional weight.

How?
I would add additional tape under final FG fabric, stretch and tab with Crazy glue (cyanoacrylate). Drape final FG fabric per designer instruction over tabbed seam reinforcement FG tape. Pour measured amount of epoxy over fabric and brush/roll to spread out epoxy evenly. Use roller to minimize use of epoxy without starvation. Rule of thumb is 65% epoxy and 35% glass including fairing. Most time consuming part of ply-epoxy stitch and glue boat build is fairing (sanding). Using this method, you don't incur any additional sanding time, and all external epoxy bonding is primary.

Do your own calculations, go with your comfort level and go have fun

 

It's worth doing a bit of reading here in order to get the true info. As adding a skin to such a boat DOES add a good amount of strength & stiffness to such laminates. Ditto on thickening the skins slightly.

OP, For some empirical test data on what your panel strengths will be like, do a little reading in WEST System's Epoxyworks magazine issue #10. It should put your mind to rest a bit about your construction methods. http://epoxyworks.com/10/Epoxyworks10.pdf Look at the article starting on page 5.

Adding glass skins to thin wood laminates makes them WAY tougher. And if you're Truly concerned about the strength of things, you can use: S-glass, or even go nuts, & do a combo layer of say; S-glass/Carbon, S-glass/Kevlar, or Kevlar/Carbon, with a layer of plain weave S-glass or E-glass over top of it. Such combos may sound a bit wild, but really don't add all that much weight, & will definitely add a good bit of stiffness, as well as strength.

Note: The layer of plain cloth/S-glass overtop of the exotics, in addition to adding strength & stiffness to the kayak's skins, serve to prevent water intrusion into the exotics. As once water has an entry point, it can sometimes wick throughout them.
For such a purposes, even Dyneel or a couple of other types of cloth could be used. As they excel at said purpose(s), particularly as some of them are better at resisting the cracking/micro-cracking that standard E-glass sometimes has problems coping with. Especially in thinner layers.

I'm suggesting the exotic blends like the above, as with said combinations built into the cloths like that, the weaknesses in terms of the properties in one, are made up for by the strengths of the properties of the other material in said blends.

Also, if you're truly worried about the strength & integrity of your plywood, assuming it'll remain flexible enough to work with, vacume bag your skins on with epoxy prior to cutting out your panels. And when I say vacume bag them on, make sure that your ply is fully enclosed in a bag because:
- Thin ply like this wont necessarily hold a vacume if it's only got a bag on one side.
- You want to let the vacume work for you in terms of pulling epoxy ALL of the way through the wood.
In addition, you can go with the belt & suspenders approach in terms of sealing your plywood, by painting the edges of the wood, & holes for (stitching) the panels, prior to wiring them together. This is sometimes done in the construction of larger stitch & glue vessels to provide extra strength to the plywood for drawing the panels together, but hey, if it helps to keep your kayak's panels sealed, then where's the harm?

I can't say that the using vacume pressure to pull epoxy through your materials will turn crap plywood into true WPB, but from where I sit, doing it can't hurt (aside maybe from a pinch in the wallet). Though, like I said, doing the glass & epoxy application prior to assembling things may make the ply too stiff to bend properly in certain areas when wiring the panels together. But push come to shove, you can get creative, & fully bag & glass all of the surfaces of the kayak after it's built (stitched & taped together).

And here's a last minute, wild thought. Have you at all considered scaring up some veneers, & laminating your own plywood, such that it's truly waterproof?
Since all you'd be making is a small quantity of 3mm, it wouldn't require that much effort. Like I said, just a wild, last minute "think". But it'd even let you make one-piece panels, the full length of your kayak. Hence, no scarfing.

NOTE: latestarter was kind enough to catch my goof on which page to find the data on in "Epoxyworks".

 

I assume you meant the item "How tough are they?" on page 5.

A word of caution, their tests were on the weak direction of the test panels.

As I found recently,( http://www.boatdesign.net/forums/materials/3-ply-plywood-50493.html ) while the improvement in bending perpendicular to the face grain can be significant, parallel to face grain was very disappointing, so it will depend on how the ply is supported as to how much benefit you get.

 

I stand corrected, thanks.

 

Having performed these tests a few times, strength and stiffness on a lightly sheathed hull, can be ignored for the most part. Yes, some measurable differences can be noted with thin plywood in testing, but once over 1/4" (6 mm) plywood, these light sheathings are nearly meaningless, in regard to strength and stiffness gains.

The only real advantage is abrasion resistance, which can be dramatically improved, even with very light sheathings like 2 ounce (70 GSM).

On small craft where very thin plywood is used, these light sheathing can be accounted for in the scantlings, but for the most part. These types of boats are way stronger then necessary anyway, with the obvious exception of racers. This is simply the result of limited plywood thickness available, so you have to step up to the appropriate size, which often means the planking thickness is way more, than the calculations say you actually need or you reach a practical limit, such as not asking a canoeist to step into a boat with an 1/8" (3 mm) bottom plank.

If you're clever or designing a racer, you can use these thin sheets, supplemented with a sheathing schedule to offer just the strength and stiffness you need. Once you start trying to sharpen the blade this fine, you usually end up going in another direction such as molding or sandwich core, for the additional weight to strength savings.

 

I completely agree with PAR.
Between 1964-1975 we (CMS) built 29 boats, mostly wood epoxy.
The thickness and stiffness of the wood alone met all the requirements for the necessary design strengths. The epoxy coatings, (Bote-Cote), fulfilled all the requirements to help defeat entropy. End of story.

 

I know when I design a plywood boat, I spec the scantlings without regard to the sheathing schedule. The sheathing is simply a supplemental coating to improve waterproofing and mostly abrasion. Of course on a racer, particularly a small, low power design, this might change, but in these cases weight savings can become an anal obsession and sheathings can become a problem.

 

The boat will be launched from a sandy beach and used in open water....not expecting any rock collisions.

Thank you all for the advice. I decided to go ahead with the build, although I cut out a shorter (4m) and slightly wider kayak in the hope that this will be more durable. Its been stitched together and the internal joins filled with epoxy. I also gave most of the inside a light layer of epoxy. Will post a photo soon. It's become apparent that it may be quite heavy but I will just treat it as a prototype and keep on keeping on.

The only glass that I can find in town is the chopped strand mat, what a nightmare to work with....It must be my technique as the locals seem to be able to build with it. I tried glassing the internal cockpit first and ended up with a huge sticky mess that i will have to mostly cut out and sand back. I tried a brush, roller and plastic applicator to no avail. The mat just pulls apart as I try to spread the resin. Anyone have experience working with this material?

 

Gotta charge the camera to take the latest pics. Here it is half stitched. I know some of you guys may be pulling your hair out at my use of crap materials but it's just impossible to find good stuff where I am. Speaking of crap materials...The locals make little round boats here, instead of epoxy some cover the entire hull with cow manure and then paint a tar like substance over that. Seems to work for them but they are extremely heavy, it takes 4 people to carry a round boat that is 6ft in diameter.

 

Welcome to the real world. That stuff is a nightmare unless you use peel ply or an equivalent. Any cheap polyester ( taffeta is best ) cloth will do. If you lay that over the wetted out mess, you can manually or with tools, smooth it down to a decent shape, and it will just peel off when the goo is cured. Do try some test pieces on any cloth you buy first, to ensure it is the correct type.

Chopped strand matt is a heavy, pig of a product to use on a wooden boat, and really should be avoided.

For a coaming, or similar tricky shape - epoxing block of wood, filling gaps with epoxy/sawdust/woodflour and sanding them to shape then doing a layer or two of cloth is a far superior method.

Filling in the ends of bow or stern sections should be a mixture of some chopped strand, but mostly wood shavings if you cant get glass cloth.

 

Thanks rwatson,
I will go in search of some polyester and try out your suggestion, sounds workable. The only good thing about the CSM is that its $2.50 a kilo. Still looking for real glass cloth but no success yet.

Yeah test pieces from now on otherwise I'm just creating more work. I wonder if plastic wrap/cling wrap would work.....I will give it a go

 

From the pictures, she looks pretty good so far. And hey, a lot of people would pay to get to do what you're doing in 'paradise'. Beats an office!

Just a 'think', but likely by this point you know as much, still, testing out various methodologies of construction & techniques on off cuts & scraps can help heaps. 'Course so can YouTube ;-) [there are links though some of the below listed sites].

Just a thought about your cloth issues. Have you tried using masking tape to cut it into strips, maybe a touch wider than you need. Then lay the strips onto some sheet plastic & wet them out. After which you wet out the wood. And then prior to things really starting to kick, lay your pre-made & wetted out "tapes" onto the wood, & roll/sweege them down good.

I know that working with mat's a pain, thus the suggestion for making your own tapes, & using the plastic + masking tape to hold them together, & make them easier to handle. And even with that, mat's tougher than other fibers.

The "plastic trick" is one which I use, even when I have all of the ideal materials at my fingertips. Down to prepregs & all the fun toys. Ditto on masking tape to make my own tapes. I've even used said technique to make custom width biaxial & triaxial pieces. The heavier cloth means that I use a bit more tape to stabilize the edges of the fabric, & sometimes after things have cured to the green phase, I have to come back with a hair drier/heat gun & an exacto knife, to lift, & trim off the edges where the masking tape is.
Often enough, later re-fairing said edges a bit with some extra resin mixed into some chemical peanut butter texture.

And you likely know, but if you choose to use wire (so that it's smaller diameter gives you smoother seams), once things have cured, you can always heat up the stubborn pieces for a few seconds via wires from a car battery.
Too, some guys will use dowels, or dowels split in half to keep panels in fair alignment when stitching. Plus it gives'em a little more surface area for bonding on such joints.

Also, there's not written rule that you absolutely must use fiberglass, or fiberglass exclusively. If memory serves, James Wharram, & some of the other early pioneers of composites tried all kinds of cloth set into various glues. Even nylon. Although in some of those instances they were looking more to keep out rot & worms, more than to make structural seams.
But it might be worth experimenting with what you have on hand. Mixing fiber X, with Y on a couple of test panels. So you can compare ease & quality of application with strength & beauty to the eye, etc.

I'm not sure if it'll help, but a couple of these were shops in my old home town(s) & were/are great folks to talk to. Plus I'm not sure how shipping works to where you are of late, but if you get stuck, materials wise I'll see if I can scare up some links. Who've you tried, in terms of getting better stuff shipped to you?

http://ptwatercraft.com/ptwatercraft/Welcome.html
http://www.pygmyboats.com/
http://www.bing.com/search?q=pygmy kayaks&go=Submit Query&qs=ds&form=QBLH
http://www.clcboats.com/
http://www.bing.com/search?q=chesapeake bay lightcraft&go=Submit Query&qs=ds&form=QBLH
http://www.redfishkayak.com/
http://www.bing.com/search?q=redfish kayaks&go=Submit Query&qs=ds&form=QBLH

The Port Townsend Center/Northwest Maritime Center might be a helpful resource too. The Wooden Boat Festival http://www.nwmaritime.org/programs/events/wooden-boat-festival is every year, the 1st weekend in September, & has LOTS of great sponsors & participants. And even over just the weekend of the festival itself, lots of boats get built. Take a wander through the event program for some perspective resources.

If you've got a bit of time to sit in front of the computer, there's a lot of knowledge there. Especially as on the surrounding weekends, there are similar festivals on Vancouver Island, in BC, as well as the Wooden Boat Center in Seattle. Thus, there's a few millennium of knowledge floating around that general locale then (all of it transpires within about 150km radius). And is attended by famous folks from all over the world often enough.

EDIT: I was typing while rwatson was posting. A nod to his tips on improvised peel ply. Just that if it's not the real thing, make sure you test it on something else first, as some materials can have chemicals in/on them which will interfere with later bonding, if you have to add more layers of reinforcement.

 

Thanks uncivilized,
I like the tape idea...more experimentation to do, and as you suggest I could try other fabrics. More research to do.

There appear to be suppliers in Hanoi and Saigon (after all, nearly everything is made in China) but I'm roughly in the middle about 900km from each city. I may source materials in the future for the next build but for now its just trying to do it with local stuff.

Its my first attempt so I'm not gonna stress plus there isn't really a time frame. I'd say by the end of the project I could write a small book on what "not to do"

Thanks again, I'll update when more progress is achieved.