Different types of fiberglass cloth explanation question

[Jasper Windvane]

I have very little experience so ?? The only fiberglass I've used is shiny, smooth material.. but there is biaxial cloth, etc..
what is the difference between these glass cloths?

[bcooke]

Stealing from the Jamestown Distributors website...

Biaxial fabric is non-woven. It consists of two layers that are stitched together, and instead of the fiber strands lying along the roll and across at 90 degree as in conventional woven fabrics, they lie at +/- 45 degrees to the edges.

The stuff I get from JD has some mat stitched to one side which makes for a thicker laminate. Sort of like the modern equivilent of roving and mat... (inside joke :-P) When you look it up in the catalogues you will notice it often comes in much heavier weights than woven cloth. I use it for structural tabbing and for building up a thick piece quickly (i.e. building solid fiberglass core under my mast step). I am out of my element here but the strands at 45 degrees to the edge (and presumably the anticipated loads) transfer the stress better.

It is quite strong but doesn't finish up too well so if you need a nice finished surface you could put a lightweight layer of ordinary woven cloth on top.

As for the myriad of other fiberglass clothes, I don't have a clue. I have never used them.

-Britton

[bcooke]

From an earlier post today I was inspired to go back to my $2.99 WEST SYSTEM boat repair manual.

On page one is a better answer to your question.

3 basic types of cloth

mat,
woven cloth and roving,
uni-directional, bi-axial and tri-axial.

...

Stitched fabrics (i.e biax) allows for a higher ratio of fiber to resin which results in a stronger and stiffer laminate.

Hope that helps.

[CharlieJ]

Also in building tack and tape boats like I do, Bi-ax is used to tape the chines on larger ones. Gives great strength. Ordinary fiberglass tape winds up with half the strands running longitudinally, which contributes little or nothing to the strength of the joint. Bi-ax with the strands oriented at 45 degrees has ALL the strands crossing the joint- much stronger.

But on smaller boat, it's really not a necessity- ordinary cloth tape/matt (or roving) does the job quite well. Matter of building for the forces involved. No sense over building- all excess UN-NEEDED strength does is add weight.

[bcooke]

Ordinary fiberglass tape winds up with half the strands running longitudinally, which contributes little or nothing to the strength of the joint.

Where was this good advice when I was building my nutshell?!

Oh well, next time. :-)

[Rachel]

Also, I've seen a "biax" mat combo wherein the strands DO run "the normal way," like regular cloth. Not sure if one would still call it "biax." I believe I read in Dave Gerr's "The Elements of Boat Strength" that there were certain applications wherein that orientation is preferable. I'll look it up later and add that information.

[CharlieJ]

On your Nutshell, the regular tape more than likely contributed adequate strength FOR THAT BOAT.

I've built quite few boats designed by Graham Burns of B and B Yacht design. He specifies when Bi-ax should be used and when it isn't needed, he specs 3 or 4 inch tape. In fact, the only boat I've built of his that DID require Bi-Ax was a 22 footer, with a cabin. A big sharpie cruiser. And then he spec'd 2 layers of 15 oz.


When I build one, I go by the designers specs- hey- that's what you pay him for.

Of course on the boats most of us sail, we have to figure it out for ourselves when doing repairs or mods.....

[bcooke]

I suppose since the joints are screwed and glued with thickened epoxy the choice of fiberglass tape isn't too important :-) Tape isn't even part of the design of a nutshell.