: Hello all,
: I'm part of a team of sixth-form students partnered with an engineering
: company trying to find applications for a new carbon-fibre composite. I'm
: investigating kayak paddle shafts. I already know they can be made from
: aluminium and
: carbon/glass fibre/kevlar composites, not to mention wood.

: I would like to do a mechanical properties comparison between the new
: composite and the existing materials, however I ran up against a problem:
: the paddle manufacturer sites I have visited do not specify *exactly* what
: kind of composite they are using (e.g. 30% glass fibre, 10% Kevlar in
: polyester resin [no, I just made that one up :-)]).

Hi Stephanie,

I would recommend contacting the paddle manufacturers directly. Agree to strict confidentiality. Explain this reasoning to your design review committee, so they don't think you're making things up when you present your findings. Hide the identifying numbers in statistics. Offer the manufacturer a copy of your report upon completion.

: Does anybody know of the website of a manufacturer of this kind of tubing
: that will have that kind of information there?

I think by this point in the paddle design cycle, most paddle mfr's are using a proprietary tubing, and finding a simple tubing spec on a general tubing supplier's website won't be quite what you want to use.

: I know composites are synonymous with 'horrendously complicated', and
: different manufacturers will be using different kinds, but even some idea
: would help enormously.

Again, try the manufacturers. As far as I know, the CF shafts are 100% CF, probably in a polyester or vinylester resin matrix. Similarly, glass shafts are 100% glass in poly- or vinylester.

The carbon-kevlar shafts you can pretty much guess by looking at them. If it looks like 50%-50% CF and Kevlar, it probably is. Most of them are made of a composite weave, rather than separate layers of CF and Kevlar. The CF is much stiffer than the Kevlar (you knew that, of course), and the Kevlar will flex beyond the CF's yield point, causing breakage in the CF layers. If they're interwoven, the Kevlar raises the point at which CF experiences catastrophic failure.

: Also, what kind of Aluminium is commonly used to make shafts? (e.g. something
: like Aluminium 7075 T730)

I'm sure it's 7075, but couldn't tell you which alloy. Aluminum shafts aren't all that great...mostly limited to beginner and rental paddles. They are a valid data point, but don't spend too much time on them, either.

ZuZu has some amazing CF/Wood composite shafts. Wood is an amazing material with a lot of elasticity and toughness...it's worthy of some serious consideration.

: And some general questions: Are carbon fibre shafts not recommended for white
: water paddling because they are brittle?

There are CF whitewater shafts, but they're generally heavier. You add more layers of CF so they're unlikely to experience catastrophic failure. But then, you're close to the weight of a glass WW paddle shaft. This makes them REALLY stiff. In whitewater, though, you don't spend as much time stroking forward (like you do when touring), so it's not like that's placing an undue burden on your joints.

:How dangerous is it to have a shaft break in use?

If the shaft breaks and the jagged end is impaled in your femoral artery, and you're 15 miles from the nearest road, is it dangerous?

: When choosing the flex in the paddle shaft you're trading efficiency in
: paddling against comfort (am I right?)

Yes. There's a happy medium. Too flexible, and it's not any more comfortable, but very inefficient. Too stiff, and it's pretty uncomfortable (to some), but very efficient.

: So what does it actually feel like
: to use a paddle with a very high (flex?)

Like a soggy noodle. If it's springy, you feel like you get an extra kick at the end of your stroke. If it's not so elastic, it's a soggy noodle.

:or low flex?

Very, very responsive. I haven't paddled long distances with a very stiff paddle so can't comment on shoulder or wrist soreness at the end of the day. I mostly paddle with relatively stiff wooden paddles, but they're not so stiff as to be unforgiving. My WW paddle is CF, but as I mentioned before, you're not cranking out the repetitive strokes, so it's not as much an issue.

: Any help would be much appreciated

Best of luck on your project!
I did a Materials Science project (materials selection) on whitewater kayaks as an undergrad. It was a lot of fun...but most of the conclusions we came to had already been met by manufacturers....

Shawn Baker
MS Construction Engineering
Montana State 1999