Greetings

Hopefully you'll get this, I'll check later after a "knocking the froth off a few" with some new friends.

: The main reason for using CF or Kevlar is strength and only strength. High
: strength fabrics allow builders to build lighter. The layup can sustain

Well, yes and no. Fiberglass is much cheaper then CF, but CF performs much better then the the primary FG functionality. CF in my opinion suffers two shortfalls: it's opaque and black with all the related problems and issues; it's expensive. Kevlar on the other hand is one of the aramide family and it too has shortfalls, one of which to me is the impossibility to sand.

: heavy impacts even tho' there are fewer or thinner supporting layers of
: 'glass. But there is a trade-off. Thinner layups are more flexible and
: mean ribbing and other stiffeners need to be added.

That goes back to the choice of number of lay-ups and not the material itself however in destructive testing I found that 4 layers of 5 oz CF performs better then 5 layers of 6 oz E-type FG in bending. I haven't the data on the laptop but I'll post it when I get home. The ribbing I chose to use was based on an analysis by a friend of a approimate hull shape of the kayak to forces expected. Instead of using for the second or third layer (depending on the area) I laid "ribs." Diane and Rikki's yaks are muck more rigid and lighter then mine, and I built them to be strong, hence, the CF.

Still, I find CF easy to work with, works well though I have this fear of non-wet-out areas in multiple-ply lay-ups. The same is true of kevlar. BTW: the inside roofliner (an internal, hidden liner for rollover protection replacing the existing metal stiffener) of the 4Runner is a kevlar layup, only because I got a deal on a length of remnant that had snags in it.

: I've only seen one CF hulled kayak and I think there was Kevlar in the fabric
: because there were gold flecks in the weave. The boat was very long, very
: skinney, very light but not anything that the average paddler could
: handle.

CF and kevlar mixes are out there but jeeeeeez, are expensive as hell. I think it's overkill, but it looks pretty. Good thing about those weaves, if done right, you can avoid the gelcoat or paint to save weight and it looks pretty good, too.

Down side to all composites is exemplified in aircraft that have composite structures, like the F-14 Tomcat and F-15 Eagle. Aircraftmen bang on areas of the composite structure with a mallet lsitening for the sound. Delamination sounds like a dull, sort of dead thump versus a solid lamination which sounds "bright."

: In paddle boats hull shape and finish are probably more important than
: lightness. If the hull isn't slippery a layer of CF or Kevlar won't help
: it.

True, and weight has an effect in several different areas. There's some discussion going on in this group about surface finish I'm still thinking about, too. I don't think anyone thinks that CF or kevlar added to a hull will make it slippery. FG, CF, kevlar, Dynel, polypro, or whatever cloth are cloth for construction not for surface finishes. I think you're thinking about the idea of using carbon for abrasion but I'm not so sure about the effectiveness of that.

: When you want stiffness and light weight think PLYWOOD. Good ol' plywood
: produces hulls that don't seem to have any "give" in them.

Yes and no. Plywood actually is great stuff. It's strong yet resilient, after all, it's layers of wood, the remarkable material that wood is. Believe me, you're talking to the number one guy around who believes in plywood (Spruce Goose, a zillion wood hulls of all sizes and shapes). Still, in yaks, a friend really destroyed a Coho on a reef. I think for strength of a yak, ya can't beat a stripper (how's that for the match to light the flame!). A hardwood stripper with multiple layers of glass inside and out can be dropped sideways of a 12-14 foot wave crest and ponded around, then endo-ed off another wave to spear into the bottom without breaking the seam or breaking (as happened to me 31 May 2002, beginning at 15:23:22 PST when the first wave was measured at the nearby Scripps Institute). I think a SG would have busted because of the hull shape in seams.

: My kayak is a notorious "Yare". It weighs 29 lbs. is 16 ft.long and
: is only 3mm (one-eigth inch) thick. It's as stiff as an i-beam. It won't
: survive a ballpean hammer attack but it's as light or lighter than most
: miracle-fiber hulls and it only cost $300 to build. If I could figure out
: how to build one with more room for my big feet I'd do it again.

Too true. Ernie's first yak was a Coho and it was around 33-35 pounds. That was a good yak, too. I just broke out the 1/8 inch ply front bulkhead for a new idea and I used a hammer to bust it out. A quarter inch plywood would have took a helluva lot more then a hammer though. Still, we built the yaks to go through water, not fields of ball-peen hammers, and your Yare has been doing just fine, right?

BTW: how do you like the Yare? How does she perform, pros versus negatives, what would you do different, etc. I'm always adding to my knowledge.

hope this posts, chat in a bit. sure wish I had a yak with me.

Mike