6" 6 oz biaxial tape

[marvinwus]

Boat Builder Central is selling 6" 6oz biaxial tape. Would this be an appropriate substitute for the 9 oz fiberglass tape on the CS17?

[JeffM]

I'd like to know, also. The biaxial should be nearly twice as strong as straight tape of the same weight, since every fiber crosses the joint.

[Peter HK]

The biaxial should be nearly twice as strong as straight tape of the same weight, since every fiber crosses the joint.

As I understand it though, as every fibre is at 45 degrees, the strength is about 70% of a fibre at 90 degree orientation.

Peter HK

[PJPiercey]

A woven fiber has less strength than non woven fibers. Biax is non woven. So the result would be better than 70%.

[Tom Lathrop]

Depends on what is meant by "strength": rigidity, ultimate breaking strength, elongation, repeated cycle failure, etc.?

Biaxial cloth is non woven so the fibers run straight in layers instead of woven over and under their opposites as in woven cloth. This means that in order to bend, the fibers of biaxial immediately come under tension which makes this material far more rigid than woven cloth. The woven cloth must stretch as a unit before the individual fibers straighten enough to come under tension so it remains much more flexible.

Ordinary woven tape has been proven good for seams and sheathing in small boats for many years but does little to stiffen any structure for the above reasons. When stiffness is desired or one heavy layer is easier to place than many thinner ones, biaxial can be useful.

Using glass fibers at 45 degrees across a chine will certainly make a difference to laying at 90 degrees where only half the fibers cross the seam. Just how much and what kind of difference is somewnat controversial. I know of no source of objective tests that have been made. I think the 45 degree layup is better but don't have any proof.

[JEM]

keep in mind it's not good for a bright finish. It will look cloudy.

[Howard]

This almost sounds like the basis of a research project for some engineer type who has experimented with epoxy and fabrics and written technical articles about them for boat building publications. Do we know anyone like that??? Hmmmm.

This is beginning to sound like one of those cult myth things (strength of woven tape vs. biaxial) where even experienced builders will differ on opinion. Perhaps not.....perhaps there is distinct difference and a place for each?

All I know is that I did some tests with tapes and epoxy prior to committing to building a stitch and glue boat and in every case, the wood or plywood or tape to plywood bond failed first. Never had a piece of tape fail in the middle over the fillet, where presumably the difference between the two tape styles lie. Based on my observations and gut instinct.....and nothing else.......if I was concerned about a joint failing, I'd use wider tape to increase the bonding area.

Does anyone know of an instance where a stitch and glue boat came apart because the tape itself failed?????

[PJPiercey]

I was told by the sellers of the biax to expect about a 30% increase in strength when going to biax from the same weight woven. I chose to go with 12 oz biax vs. 9 oz woven. Based on the following:

"Directional fabrics ( biaxials, triaxials) are much stronger while lighter than the common woven fabrics. They cost more by the area but almost the same by weight. As they use less resin (less weight), the resulting composite does not cost more than the low tech one." I also found the biax much easier to work with. It conforms to shapes and corners much, much, easier. The end result was a stiffer, stronger boat at about the same price.

Paul

[Joe Nelson CS#35]

The 12 oz biax is great stuff, when you need that kind of strength. It is hard to wet out...almost requires a glassing box or wet it out on plastic sheeting. I roll out epoxy on my glassing box, wet out the biax with a plastic scraper, roll it up and then roll it out where needed. To save on epoxy, try to do most of your taping at one session. You will waste some epoxy in the wetting out process...but the subequent piece will pick up what was left from the last piece. Its is really hard to wet out on a vertical surface, or around a fillet or chine. Pre-wetting is the best bet. It is also more difficult to fair...as it is thick and the weave is large. Its not a bad idea to cover the biax with some light cloth, slightly larger than the biax...ie 8" tape over 6" biax. This covers the weave and also helps to transition the edges more fair. On my current project, a Tolman Skiff, I am using the 12 oz biax covered with 6 oz tape. The biax carries so much resin that the 6 oz tape almost wets out on its own. My personal opinnion is that the 6 oz biax would be a sufficient substitute for one layer of 10 oz. woven. Especially if you are going to sheath the boat with glass and wrap the chines, etc..

[marvinwus]

I purchased the 6 oz biaxial tape from BoatBuilder Central and will be using it on my CS17.

[PJPiercey]

When I use the 12 oz biax I just fair it out with Quick Fair from Systems Three. I have never felt the need for glass over the top. 12 oz biax, Quick Fair, and then System Three's high build primer. I found this to be quick and easy. Also, I didn't find it hard to wet out. I used a mix of medium and slow hardener to give more working time and the glass would continue to wet out as I worked ahead on the next pieces. I just layed the cloth down on the precoated joint and then wet it out.

Paul

[Joe Nelson CS#35]

Seems to be a lot of Pacific Northwest builders! I am glad that Graham's designs are being widely accepted here!