Undirectional over strip planking?

I'm not going to debate folks that can't understand the obvious differences between uni-dias, knitted fabrics and traditional cloths. If you're going to debate apples and oranges, then have at it, but be informed, you're taking out your butts if you do as the physical differences under load, particularly in very light structures when stress concentrations on the skin are comparatively high.

It's just this form of ridiculousness that I'm talking about. If you want to mix and match your discussion variables, like this, I can't be bothered as it's gibberish and nonsensical mush. Mixing polyester and acrylic fabrics with 'glass cloth and uni-dis and knitted fabrics in the discussion is just absurd, and out of hand silliness, frankly. So, if you'd like to discuss the physical properties of these materials, that's one thing, but if you arbitrarily intermix them, then don't expect your comments and opinions to be valid or taken seriously.

 

I'm perfectly well aware of the differences between the various types of cloth. That was why I was specifically asking about uni to start with. However that's pretty much been dealt with on the first page and the thread is doing what threads often do and wandering a bit. I'm still not convinced that in the "usual" construction for small boats the "traditional" glass cloth used does not contribute to transverse strength. I might be wrong, but I'd like to see some evidence.

ETA: I should note that I'm talking about panel strength, not the strength of the hull as a whole.

 

I agree totally Sabahcat.
Using WRC for the 0degree strength and the glass Uni for other off axis strength (90 and or +-45 ect... as nesc.) and then providing the stiffness by bulking up or adding thickness with a low density core separating the skins---superb!
Actually working on a project at the moment doing just that.

 

Okay then, maybe we've all veered off course on this thread a little, but the last post shows just the problem. Sandwich construction techniques and light skinned strip construction, two completely different animals and shouldn't be used in the same sentence, so to speak.

We're in agreement that cross grain strength and stiffness can be improved with perpendicular uni-dia or knitted fabrics, naturally with some issues. As I mentioned on the opening page, there are many different strip plank types, so being specific is important. This is simply because there are huge differences between say Load method strip planking, which uses nothing but high elongation fabrics like Vectra and Xynole over a strip core and a Baltek strip method, which requires knitted fabrics and/or uni-dias to be successful. These are just examples and extreme to each other.

If we divide the many possible methods into a few categories then things get simpler. The first category is plane old "wood/epoxy strip plank" this is essentially a carvel hull with narrow edge glued planks, from an engineering point of view. It can be 'glassed, but the 'glass isn't really contributing to the strength of the hull shell as much as it's abrasion and moisture vapor resistance. In this case the high elongation fabrics will be more effective (in both regards) if you can tolerate the weight penalty. Most small boats fall into this category, amazingly enough.

Next would be the "wooden core, light sheathing" methods. These are more composite then traditional structure and typically have no internal framing, just fabrics. This is the biggest column of different methods and should be divided in two. External only and both internal and external sheathings. The externals only are usually closer to traditional, though sheathing thickness can play a role. The both sides method is where things start to get mixed.

For example, there are formulas for reducing the strip planked core thickness for both sheathing weight or, and the usually more preferred method in larger craft, diagonal veneers. This is because it's faster and lighter to use veneers then laminate, but in small craft, not typically employed.

Lastly are the "heavy sheathing strip plank" methods. These are the true cored composite building methods. The core in many cases can be your grand mother's dried up Thanksgiving mashed potatoes, just so long as the peel strength is there and the potatoes stay in place during the cure. Okay maybe a bit extreme, but not as out of line as you might think, given enough laminate thickness.

I have a lot of experience with the Lord strip plank method and it's amazingly light (the lightest of all the strip plank methods), yet uses literally junk core materials. Keels and engine beds are usually plywood and it doesn't have to be especially pretty stuff either, just well coated and particularly well entombed in fabrics. With these types of structures, core compressive strength, peel strength of the resin/fabric matrix and laminate skin density are the keys to success.

When discussing this topic with a rather eclectic, recently past designer. He described it uniquely, which knowing him was his fashion. He said the best way to understand these differences, is to look at the core to laminate percentages by weight. I replied this would be an unfair bias, but he disagreed and his point was if you're using 60% laminate and 40% wood core then you've got a plastic composite of the type seen in most production builds. While on the other hand a traditional glued seam strip plank is 90% wood and 10% plastic. We spent the better part of an hour discussing and categorizing the different common strip planking methods into 30/70's, 60/40's, etc. It was our last conversation and I miss the old, but genial *******.

 

epoxy is heavy, significant gains in strength to weight in glass layups can be made with the use of peelply and it has the added advantage of smoothing out lapped or cut, glass edging.

 

How do you justify a comment like this Uncooked? What is peel ply bringing (or in the case subtracting) to the table that isn't derived with a good hand layup?

 

....leave out the word "significant" and it helps.....

 

John you're killing me . . . shall I squint too . . .

 

Jesus was a carpenter. All of you who insist on layering glass and epoxy over Nature's already perfect composite will go to hell.

Merry Christmas!

 

at least I'll be warm and dry for a change! Happy La Nina and Merry Solstice

 

"shall I squint too".....na mate, sometimes it is simply better to close your eyes.......


...somethings are just too painful....

 

- sorry about that! One of the inmates at The Wooden Boat Forum escaped but he's back in custody again, so you're all safe.

 

well par, peel ply buries and totally flattens the glass in one wet out, whereas a proper weave burial without peelply takes three, 3, to get the weave print out of the picture. greater time and weight savings are to be gained when lapping of the glass or working off non selvedged edges.

Sorry to get everyone so excited over the word ''significant'', my experience comes from years of building competitive boats where skinning five pounds was discussed in tones usually reserved for audiences with the pope.

 

It is nice to use peel ply with hand layup. . Compacts the fibre, drives excess resin out and leaves a much smoother surface Biax fabric print and as a result requires much less fairing and filling. I dont know how much weight you would save, but its Hard to find any reason why not to use peel ply on lightweight, exterior and high visibility surfaces.
I recently watched a French gang of laminators replace the outside skin of a 20 meter cat. Overhead work with peel plied Biax and the results were remarkable, Very little filing and fairing required. Very skilled laminators.

 

an interesting read

Nick Schade of Guillemot Kayaks posted these test results in Jan 09.

The test studies various strip thicknesses and reinforcement types.

http://www.guillemot-kayaks.com/Building/Testing/index.html