Tape seams

I am having difficulties sourcing fg tape for seams where I am located. I can get dynel. I have been trying to find the pros and cons using web searches and would like to hear from the users here

Found the following at http://www.kayakforum.com/cgi-bin/Building/archive.pl/bid/11/md/read/id/18311/

Thats a quote from the page at the above link

Please help me understand taping. Is it the fibre bundles running across the seam that reinforce it? Some suppliers list high tensile strength for dynel, will that make for good seam reinforcement?

 

Tape is usually cut or manufactured on the bias, meaning the fibers run at 45 degrees. There should be no problem getting some shipped. Just look up marine supplies or boatbuilding supplies, or try harder. Tape is going to be easy to find any place where there are boats.
That quote doesn't make sense. Why compare cloth to polyester resin?
99.9% of all tape repairs or construction use fiberglass tape and polyester (or epoxy) resin. Polyester resin isn't as strong, waterproof, or long lasting as epoxy so consider sourcing epoxy as well.

 

Alan you might not have a prob getting it shipped if you were located on an lsland in the middle if the Pacific where shipping cost are extremely high as the regular couriers dont deliver and not having a credit card and living on the otherside away from the urban centres but I cant manage it! I dont think I have to lay down the details for why I cant do that when posting a question to further understanding of how it works

Is a strand of the fibre bundle stronger or as strong as a fibre bundle in the fg tape? If crossing the seam at 45 deg stronger then can I not lay the dynel at 45 deg too? Reading the passage where that quote is taken from, it makes perfect sense. The chap is talking about polyester cloth and destroying the test panel

I can certainly appreciate the sticking with tried and true but what is the harm in stopping and thinking about how it works and why it works and what else can work that way? Tons of boats here mate but they all ply on frames and heavy as hell. I can tell you all about why I want to make a ply boat and background if that is what it takes to learn but I have already done so in another thread which seems to have been mostly passed over which is why I am asking a direct question about what and why

 

Dynal tape or fabric does not have anywhere near the strength of 'glass cloth, while it does add considerable toughness, it's not recommended for tape seam builds, as the only material on a seam.

The polyester cloth they're referring to is Xynol, which is used in a similar fashion as Dynel, except it's even more abrasion resistant, but hasn't the modulus to use as a seam fabric reinforcement either.

Ideally, you'll want a fabric that has similar elongation modulus, as the resin system you're employing. This is why 'glass cloth and knitted 'glass fabrics are used. There are other fabrics you can use, though these tend to be costly and wouldn't be easy for you to get.

You'd be best advised to look up the boat builders in Suva and Tautoka. Safeway Marine would seem a logical choice, though they deal with polyester, you could order through them. Hammerhead is another option. Call around and see what you can find locally and tack your needs on the end of their next order.

 

Thanks for some clear information PAR. I think I am having trouble understanding modulus and tensile strength. I thought modulus related to stiffness as in two fishing rods of equal dimensions but one made of higher modulus material, that one will be stiffer. While tensile strength meant the amount of stress that can withstand while being pulled apart? i.e the force presented on the fishing line unless the line is tied directly to the rod tip and the tip pointed at the fish which is when the rods tensile properties come into play

So do seams rely on stiff and strong taping rather then just strong? I have checked with many boat builders in the urban centres and pretty much the only response has been that the guys import privately and don't resell or keen to help out. I haven't tried the names you have mentioned but will try to call or drop in for a chat, thanks.

 

Neither do I have clear the meaning of "elongation modulus".

 

There's more to strength than the knowing the stress to break something, particularly with plastics, mostly because it doesn't tell us anything about what's happening while you're trying to break it. This is where elongation comes in and we can measure this a number of ways. Elongation is the word we use if we're talking specifically about tensile strain on a stress/strain curve.

In this conversation, the choice of a modi-acrylic or polyester fabric (Dynel and Xynole respectively) have quite low elongation properties (modulus), but are coupled with resins systems with dramatically higher properties. Simply put, these fabrics will fail long before the resin, which is a poor combination and engineering choice.

 

Thats makes sense. You have given me another idea though

 

PAR, frankly I do not understand too well your explanations even though I believed to be an expert in strength of materials.
Curves stress / strain, as you call them, are drawn in a coordinate system with two axes, one of which, generally horizontal, is the elongation (varying the distance between two points previously marked. Nothing to do with any module). And not only for plastics but with any material.
I do not understand the term "elongation properties (modulus)."
But as all this has nothing to do with the original thread, we'd better forget it.
Thanks, PAR, for your attempts to explain

 

I'm sorry you're having difficulty understanding, but the topic of this thread is precisely about just this aspect. The OP is suggesting the use of a material with less than desirable physical properties, combined with a resin system.

If, as in this case, the reinforcing fabric reaches it's ultimate elongation point, long before the resin does, you've selected a poorly suited reinforcement material or an overly strong resin system for the application. Since the resin system choices are fairly standardized (poly, epoxy, etc.) the variable is the reinforcement material, which for best performance will have a similar elongation and elasticity modulus.

 

PAR, since you insist, this is what Saqa is asking for :

Analyzing now your explanations, this statement "...... the reinforcing fabric elongation Reaches it's ultimate point" is not correct at all. The calculations must be made so that stress (not elongation ) in any of the layers is not greater than a certain percentage (much less than 100% of course) of the yield point of its material.
The resin, in my opinion, is not considered durable material and, therefore, neither elongation nor its yield point, are taken into account. (Not saying it is not resistant but not considered in scantling calculations).
"...... the Variable is the reinforcement materials , which for best performance will have a similarly elongation and elasticity modulus . " : I do not know if this is true or not, but in any case, is not useful for calculations. Designer has to consider many variables but what he has to get is that the stress in any of the layers does not exceed the allowable stress which, depending among other things on the application method, will have one value or another, perfectly defined by the regulations .
All the above is my interpretation of the problem. If I am wrong, I will have no difficulty in recognizing.

 

I can only envision two hull panels either flapping, pulling apart opposing directions or one pushing up and the other down against the seam. I could be missing something though

Strands in tape that cross over is the tie and anchored on each panel with resin and the short length across the seam over the fillet encapsulated in resin?

Which fractures first? The now short length of the strand over the fillet or the remaining major legs adhered to the panel?

I take it that the bit over the fillet is the weaker point?

In my hands a few strands of rigid fg with resin is brittle when bent over a tiny distance like a fillet. And way flexible if bent over a longer length. I take it that strength here over the fillet comes with significant bulking up?

Trying to learn how dynel will react in that environment. Will the anchor in the resin embedding over the panel or the strands over the fillet be the weak point. Will it just rip out of the resin really easily and be a danger or will it break really easily and again be a danger?

Does it make an acceptable strap to attach two hull panels when embedded in resin? I know it doesn't fracture easily when bent over a short distance like a fillet

 

I get confused with technical stuff, but I believe a low modulus material is elastic while a high m is not so elastic. So it seems that in a stretching or flexing mode, with a low m fiber and a high m resin, it's the resin that will fail first.

In a fiber/resin laminate, it is basically the fiber that takes the load and the resin distributes it to the other fibers. Epoxy is a better glue than polyester and works better in resisting the shear forces between the resin and the individual fibers in a laminate, and so it works better in distributing the load throughout the laminate.

As for using Dynel for the seams on a stitch and glue boat...

http://www.raka.com/xynole.html

 

Cool, if dynel is same as xynole then that clears it up straight from the source

 

What does joining by resistive elements mean? Wood or similar behind the seams? Glued and or screwed?