Knitted fabrics. 45/45 vs 0/90 vs 45/45/0

As I understand it, the strength in the glass in in the direction of the continuous strands.

I have seen somments that 0/90 on stringers for example, 1/2 of the glass is "just going along for the ride".

This is probably an all encompassing question, but in what situations should each type of fabric be used?

45/45 for tabbing?

Uni-directional for stringers and capping stringers?

triax for hull bottom and sides?

Confused...

Ian.

 

Hmm... the fiber direction corresponds to the load applied to the structure.

0 90 is balanced. A flat panel perhaps



Triaxial makes sense for hull sheathing when longitudinal strenght is needed.

double bias makes sense when the fabric must close a joint.

Uni directional when fiber orintation must be customized.

The orientation of fibers is the science of composite engineering.

If you have the opportunity to watch a custom build composite boat being laminated it would be an enlightening experience. If you have the chance to get the laminate schedule for the boat being built , grab it. The schedule will show the expected loads and the engineers fiber orientation solution

The problem with composites is that once the structure is completed its hard to see the laminate schedule.

On a wood or metal boat your eyes will instantly detect reinforcements to meet expected loads. Every structure and its engineering is logical

 

Ian,

First realize that the fibers need to be as straight as possible to give the best strength.
Knitted fabric does not have any direction straight if you really mean knitted.
If you mean woven, like a typical cloth the fibers are not exactly straight, but a lot better than knitted.

If you have a typical cloth (0/90) fibers the 0 direction supply the bending strength for your stiffener. The 90 fibers supply resistance to splitting along the length, so they are not completely useless. If you could actually calculate how much fiber you need it would probably be less than the 50% a typical cloth provides, so you probably have more than you need. If you want, to be more precise you could put on a very light cloth for splitting resistance, then put unidirectional "cloth" to improve the bending strength. This should be lighter overall, assuming you can get the excess resin out - most of us home builders have way too much.
Basically all of that would be a waste of time for most of us.

Personally I would use 45/45 cloth (if it doesn't cost too much) only for tabbing or to go around a highly contoured seam, just to make it easier to lay down. The typical way is to just cut your 0/90 cloth on a 45 degree angle, you get the same thing.

All the rest of it probably requires you to be a composites designer to get any value. An Engineering degree would be just a start.

 

Thanks for responses. By knitted, I am referring to DB1708, etc. Stitched is perhaps the correct term.

Are layup schedules that secretive that we can't get access to them?

Nothing fancy or high tech, just some solid built boats.

A Hunt Yachts 25 Surfhunter as an example? What type of layup and what type of fabrics are used where.

Just curious.

Cheers!

 

hI
i see by your post you are a trifle confused by the differant types of glass !! ok lets take it a step at a time ! Take a sheet of paper and draw just a rough shape of a hull displaying the top sides only at this stage . now think about the shape of the topsides . theres two ways to run the tree layers of glass within the triaxle 0/45/45 ,0 runs length ways always or the other one 90/45/45 where the 90 runs vertical always !!
Just remember that short strands are strong strands !! which could be better for the top sides ?? now they are both triaxle !! same weight just one layer is differant .

Now apply those same thoughts to the hull bottom !! by the way this hull has 3 rows of strakes almost fill length of the hull bottom . From a construction point of veiw this can be significant in the eventuall ridgidity of the bottom so there is something you have to do very early on in the actual construction process if you want to make this hull strong
There's a little thinking involved here so i will wait for you answer !!

Knitted fabrics are woven,woven is knitted !!
Stitched materials are just layers of unidirectional glass and just flat one on top of the other then stitched together !!
Dont get confused between the two

 

Check this page for some explanation. Page 8 shows a machine used to make multiaxials, and page 9 shows some variations, and include a schedule of what is possible.

http://www.brandscomposiet.nl/products/documentation/n/B20 Glasvezels.pdf

Unidirectional: Used where loads are predominantly are in 1 direction. Tops and bottoms of stringers, masts, light poles, keel struts, etc.

Biaxial +/- 45: When used over a seam, both directions of the fiber help to keep things in place. So great for tabbing. Also great for experienced shear loads, like the sides of stringers. It also increases torsional stiffness. When boats are built so light that torsional stiffness becomes a problem (popping out the liner for example) then replacing a layer of 0/90 with a layer of +/-45 usually solves the problem.
It also usually is a drapable fabric. (although this can be influenced by the stitching used, or even stabilisation theads in 0 and 90 direction added)

Bidirectional 0/90 is basicly a replacement for wovens. Same fiber orientation.

Triaxial 0/+/-45: used in boat hulls, when built in woodcore. The wood provides plenty of fiber in 0 direction. The triax is applied athwartships, so the 0 fiber of the triax runs in 90 direction on the boat.

Triax 90/+/-45: great construction for small production runs on a multiaxial machine. The 0 direction is a pig to set up, the other directions are much faster.

Quadrax: basicly a style that produces a quasi-isotropic laminate. Like CSM, but stronger. when loads are evenly distributed, this is great fiber.

You can add a veil, csm, unifilo to the multiaxial.
You can vary the fibers (carbon, glass, aramide, flax)
You can do coloured stitching (black on carbon, or colour coded for different styles, or a black thread a couple of cm / inch from the sides, to help overlapping in a straight line)
You can leave out the 0 direction in the sides, to help minimise thickness buildup on overlaps
You can have them cut in strips (great for tabbing)
You can vary the stitching style. Denser, tricot, 0 direction encapsulated (leaves small runner channels in 0 direction)
You can add stabilisation fibers in other directions than the multiaxial is built off (to minimise drapability)

One other thing: When using an impregnator, I try to avoid 0 direction threads, which can run off, and annoyingly wrap themself around the roller. (or leave the last 2 cm out)

 

Tunnels - I hope you are expecting me to say to fill the strakes. I agree... kinda like baby stringers down there.

I have read some fill with high density foam. I assume one beds the foam in some putty, allow to set up, then sand / grind flush and glass over. I have also read that you fill with some type of putty. Which is considered preferable?

Cheers!

 

Herman - What page? I do not see any links.

Ian.

 

Yah...I love to learn the trick for putting strakes onto a hull. For me, elegant, tapered Strakes are time consuming

 

Yip you got it !! They need to be filled !!but point to remember is it need sto be done so in the case of a severe grounding and rippin off that its the strake that goes and you can get home again without sinking ,so yes put some decent material in there and like everything make a good job of it not just rubbishy stuff and a she'll be right attatude !!.
This is my recipy after the gel coat and after the first skin of csm glass .
1 X CSM 450 + 800 GRAM DOUBLE BIAS !!
1 x CSM 450 + double bias + 450 csm and H 80 foam cut to shape and a radiused corner pressed into the wet glass ! and left to go hard the leveled off flat with the glass you have put on .
1 X 450 CSM +Double bias + 300 csm
From that point you do the laminate for the rest of the hull .
Ues they are like mini stringer the always get hit first the get banged knocked and ripped but the water should not be able to get into the hull laminate if possible . small boats the rollers in trailers take loads of weight all directed at the strakes .
Dosent mater if the hull is 14 feet long or 44 feet long same thing applies !!

one strake a side or 6 a side fill them all !!. they has 3 corners that bend when the bottm goes up and down and one or all three will eventually start leaking over time . strange as it seems the heavy matt or fabric is the thing the pulls out separates and delaminates in bad cases the totall length of the strake and at speed the water pressure works on the cracks and finds the weak places and you have a leak !!!

Strakes are one of the few places i recomend using Foam core not any kind of wood are even Balsa . wood exspands and with great force in the case of solid timber . USE FOAM !!

 

So you are suggesting:
1 X CSM 450 + 800 GRAM DOUBLE BIAS ! on entire hull.
1 x CSM 450 + double bias + 450 csm and H 80 foam cut to shape and a radiused corner pressed into the wet glass ! and left to go hard the leveled off flat with the glass you have put on .
1 X 450 CSM +Double bias + 300 csm just for strakes

then continue to layup hull.

What about the strake filler putties? http://multimedia.3m.com/mws/mediaw...TSeSSSSSS--&fn=Bonding Putty Product_Sele.pdf

3M For All Lightweight Bonding/Filling Strakes
Features: 1"- 2" Bond Line Capability
Highly Thixotropic with good vertical hang
Extra Lightweight - 5.8 lbs/gallon
Strake Filling

 

Am not into fillers of any discription and I never use putties at all any where if possible !! its get hot in bulk !,it shrinks !,it cracks ! etc etc . use what you would normally use when making the hull core is core its there for a purpose to be strong and yet flexable .

 

Got it on your opinion of the putty.

Was my understanding of the glass layup in the strake correct?

Ian.

 

Non of those filler i would recomend to fill strakes with ,most will be loaded with q cells or simular and it has not guts what soever . .

 

sORRY I DIDNT READ THE FIRST PART AS I WAS BUSY WITH ANOTHER EMAIL AT THE TIME . HAVE CORRECTED IT SINCE !! tHAT WAS JUST BUILDING THE STRAKE THATS ALL . THHEN THE HULL LAMINATE STACK GOES OVER THAT !!