SOF kayaks...use of kevlar cord

[David Geiss]

Has anyone had any experience (good or bad) using Kevlar cord as part of skin over frame kayak building? I bought some from Platt Monfort this past spring and am both amazed at how strong the stuff is and perplexed as to how I will use it w/o adhesives.

About to start experimenting but thought a post might yield some ideas. I tend to use split bamboo fro ribs and like the thought of incorporating this kevlar cord as well.

Platt's BIO is pretty impresive...now there was a fellow who liked to experiment. He had a background in aviation. RIP Platt.

[ 10-29-2005, 03:35 PM: Message edited by: David Geiss ]

[Cuyahoga Chuck]

The Kevlar (roving I think)strung on the boat frame was an adaptation from lightweight aircraft. I've read Monforts description but don't remember any of the specifics other than it makes the lightweight wooden framework more rigid.
Most SOF's owe their design to ancient Inuits who seemed to have figured out how to build such a sturdy framework that the only adaptations we do revolve around using the materials that are available to us today.
If you'd like to put your query to the mavens of SOF try this web site:
http://rtpnet.org/robroy/baidarka/
The old description of Kevlar was "it's 10 times stronger than an equal amount of steel".
Don't know if that's technically true.

Charlie

[ 10-30-2005, 06:35 PM: Message edited by: Cuyahoga Chuck ]

[Todd Bradshaw]

As I remember, the Kevlar roving was used diagonally to help reinforce and stiffen the framework (ribs and stringers) on some of his ultra-light constructions, which were then covered with heat-shrink aircraft Dacron. These boats were sometimes nearly as light as one pound per foot of length, so the frame would have to be made from pretty small, lightweight stock and the Kevlar supposedly was a key ingredient in getting adequate hull stiffness. I imagine that they may have glued it to the wooden structure when it happened to cross it, but in most places it didn't touch the wood and it certainly wasn't laminated to the wood or skin the way most composite reinforcement is done. You could probably do the same thing to a more conventional SOF boat's frame, but unless you are reducing the size of the framing stock they seem to do pretty well without it.

[Chris Stewart]

Originally posted by David Geiss:
perplexed as to how I will use it w/o adhesives.

If you don't use adhesives, you won't need the kevlar.

Notice that on the Aleut kayak below, the ribs and stringers are as light as in Monfort's designs (about 5/16"), but once the kayak is skinned it becomes rigid enough that no diagonal roving has been needed for the last 2000 years of trial and error design. The kayaks do flex, but since the joints are lashed, nothing breaks. I believe Monfort needed to use the kevlar roving because his boats are open rather than decked, and thus do not get the stiffening "box" effect the deck provides, and his glued rather than lashed rib/stringer joints would break unless he used the kevlar roving to make the boats extremely stiff.

But, since you've already bought the kevlar, if you really, really want to use it, try this:

Native builders lashed the ribs and stringers together using continuous lengths of baleen, with the baleen either going from gunwale to gunwale

http://www.arctickayaks.com/LinesAleutMAE-AC.pdf

or stem to stern

http://www.arctickayaks.com/LinesCopperEskimoCMCIV-D- 1057.pdf (http://www.arctickayaks.com/LinesCopperEskimoCMCIV-D-1057.pdf)

If you used a similar lashing method, but went diagonally between rib/stringer intersections rather than straight along a rib or a stringer, you might achieve your goal. I think you would have to alternate your lashings, starting the first on the starbord side and ending on port, and the next starting on port ending on starbord because if you did the whole kayak starting from one side before going back to start over from the other side, you would have pulled the kayak out of alignment.

[ 10-30-2005, 07:48 AM: Message edited by: Chris Stewart ]

[George Roberts]

David Geiss:

The basic design model includes:

1) wood is strong and stiff in compression.

2) kevlar is strong and stiff in tension.

This model results in one type of structure.

One can use other design models. They will result in different structures.

[ 10-30-2005, 02:16 PM: Message edited by: George Roberts ]

[David Geiss]

It was not a huge investment or anything but was just curious about the material. I have been more than happy with spruce or fir gunwales, traditonal ribs and chine stringers, and solid and composite deckbeams.

Then again, I like to tinker. I think I fall somewhere in between perhaps two schools of thought on SOF design/fabrication. I have a deep respect for the indigenous ways and the cultures of native paddlers and hunters but am always open to innovation so long as it does not pervert the essence of the craft.

E.g, I used split bamboo, milled with a crooked knife, for ribs. I never saw it done before, so I gave it a try. Used individual rib/keel and chine/keel lashings. Had the bamboo laying around from a grove I found by chance in South Fla. So far so good.......very light and no splits after much hard paddling. I also played around with rataan....that stuff was tougher to mill into rib shaped lengths and it seemed heavier than ash or oak ribs......so I gave up on that (still think I may have a use for that for deck beams on another boat).

Also used plyboo flooring for aft deck stringers....seems like very light and resilient stuff...no "delams" to report.

In either the Arima or Zimmerly text, I believe I have seen transverse lashings from gunwale to gunwale keeping deckbeams in place.....just a thought that simple nothches in the gunwales to keep the deck beams from moving fore/aft and up/down might be stabilized very nicely with a light and strong transverse kevlar lashing. Only benefit I see there is keeping the gunwale intact ( as oppose to mortising or drilling for a dowel) and maybe some weight savings.

As far as wrapping the hull diagonally across the keel with the kevlar, I agree that it is probably unecessary unless, of course, it lends some measurable additional strength thus permitting a smaller rib/chine stock. I like the amount of flex I have but increased hull rigidity (w/o using mechanical fasteners or adhesives) might paddle nicely too. :D

I think Chris' idea of a diagonal alternating lashings is interesting. Food for thought. I'm noodling around with sketches for a double.............

[ 10-30-2005, 08:00 PM: Message edited by: David Geiss ]

[Doug Canada]

Question?
- Is a "kevlar" skin prefered over the "Dacron" skin?
(as per Platt Monfort recommendations http://www.gaboats.com/ )
- Would a carbon / kevlar hybrid cloth be even better?

Doug

.

[frenchiebuilder]

and kayaks get dragged a fair bit.