Kevlar Cloth?

[Gerwin Brommer]

Brian :

Spot on !
Do you share the opinion that UD tape is better than woven cloth ? ( in case of carbonfibre )

[befu]

Can be

Brian :

Spot on !
Do you share the opinion that UD tape is better than woven cloth ? ( in case of carbonfibre )

Well, I got some but I have never used it. Do not even know if I still have it?!?!

It definately can be better, but I am wondering about where to apply it. The UD is fantastic in one direction only. Because there is not any fiber going 90 degrees, it is only the matrix strength in that direction from what I understand. I think the main benefit of UD tape is the fibers are all straight, they are not forced to bend up and down as the weave crosses each other.

Now, the part that throws me off is where are you using it?
For joining hulls, I would say no. You want the strength top to bottom accross the joint, so the tap would have to be cut into short sections.

If you are laminating it across the bottom of a Vee hull angled 45 degrees to the centerline, that would help the torsional strength of the the hull immensely. But you need two layers, one at 45, and one at -45.

That is where a cloth comes in nice. It is a compromise of fiber strength, but for those of us who are not professionals at this, makes it easier!

What are your thoughts on it?

brian

If you want to stiffen a hull

[Gerwin Brommer]

I should have been more clear, when I say UD tape.
I meant, UD 45degr. multiple layers.
Indeed, I'm using it for reinforcing the joint on my 50" mono.
http://forums.offshoreelectrics.com/...highlight=xray
The tape I use is 5" wide.
And i also covered the bottom of the hull.
I truely believe I know can jump on my hull.

[DISAR]

Befu you are very well informed! Correct amount of resin is very imporant. Regarding the comparison between polyester and epoxy is that epoxy is way more expensive, and the disadvantage of polyester is that it smells a lot and is workable only for 15-20 mins max. which is a disadvantage if you want to lay large and complex surfaces.

Brushless55, I wish these were by boats! The photos are taken from the H&M site. As already mentioned by Gerwin and Brian the correct amount of resin is important and use 24hr curing epoxy. I would suggest before putting in your boat to do a test in a similar curved surface to see the result and make any corrections.

Gerwin sorry for the interruption we were typing at the same time.

[Gerwin Brommer]

I've been told that polyester "ages" much quicker.
Gets brittle and looses it's strenght ?

[befu]

few items

Gerwin, didn't even know they made tape like that, cool. 5" is pretty wide, do you cut it down? The other thing I used for joining hulls was kevlar pulp. Mix it up with polyester resin and cover the seam, worked great.

I do not know about it getting brittle. I have hulls over 10 years old and they still seem good. Of course, haven't really beat on them either! They make a whole lot of full size offshore boats out of the stuff. Might have to look that up.

Layup time. You are correct, but polyester allows you to cheat.

Epoxy is a two part system, a resin and hardener. They react by joining together and making the new solid molecules. It is very important to have the proper ratio of resin to hardener because you need the proper amount of each to react together.

Now polyester is different. Many call the MEKP a hardener, but it is a catalyst. If you add one drop to a glass of resin and mix it up, it will harden. From what I know, the MEKP starts a chain reaction and the molecules grow upon that reaction. The more catalyst, more reaction starts so it cures quicker. In warm weather you use less catalyst, colder more. That is one trick. here is another, put the resin in the refridgerator and get it cold. Then mix it up and gives you more of a pot life. When it is spread out onto the reinforcement, it warms up quicker. You can do this with Bondo also as it is polyester based. The real trick to doing this as DISAR points out is getting the wife to go along with it due to the smell!

Brian

[Gerwin Brommer]

No serious European rc-boater uses polyester.
Don't ask why, we just seem not to like it.
I personally use Ampreg 21 by SP-Systems.
Nope, I didn't cut the tape down. In the link I gave in my previous posting you can see the boat with the tape.
One thing I do to use as less epoxy as possible in my hand lay ups : I heat up the epoxy after mixing.
It makes the mix thinner so the fibres are soaked much quicker. You can even remove epoxy with tissues to make sure you use
as little as possible.

[DISAR]

Polyester is not used very often because epoxy adheres to the surface better, I think.
I only use polyester when making molds where large quantities are required.

[Gerwin Brommer]

By European I mean European rc boat manufacterers.