Boat Building Forum

Find advice on all aspects of building your own kayak, canoe or any lightweight boats

By:Pete Rudie
Date: 7/26/2001, 2:40 pm
In Response To: Re: Sam, what is your opinion? (Tony)

I recall a thread on this topic that was interesting until degenerating into a flame war. If stiffness is resistance to deformation and strength is ability to absorb loads without breaking, it seems logical that increased stiffness does not necessarily equal increased strength, for the reason stated below. We come back to the problem that wood has tremendous strength along the grain, but very low strength across the grain. That is, the force necessary to separate adjacent wood fibers is much less than that required to lengthen or shorten them, and that in a nutshell is the paddle shaft problem.

Perhaps one solution is not to use glass as reinforcement, which has good strength but is brittle, but rather dynel or one of the other polyesters or aramids, which allow some elongation before breaking? I seem to recall that dynel has about 5% elongation at break, vs. less than 1% for glass. Can't remember the source, so am happy to stand corrected if wrong. But the JR Sweet catalog carries dynel tube for this application, see below (scroll down to Dynel Sleeve & Cord).

: As I remember, Sam Mcfadden's experiment has proved that encasting wood in
: fiberglass does not increase the utimate breaking strength, but rather
: lower it.
: The theory is once a minor break starts, the localized stress is unable to
: redistribute to other area, thereby, concentrated in one single spot.
: Result in the utimate failure of the entire unit. If component (either
: wood or fiberglass) is designed to be able to handle the stess single
: handly by overbuilding, then, why do we need the other?
: Sam, what is your opinion?

Messages In This Thread

Paddle Rehab *Pic*
Chip Sandresky -- 7/25/2001, 7:22 pm
Sand aggressively
Paul G. Jacobson -- 7/26/2001, 2:43 am
Re: Sam, what is your opinion?
Tony -- 7/26/2001, 1:36 pm
Re: Sam, what is your opinion?
JimC -- 7/26/2001, 5:15 pm
Re: I'll just have to make another :)
Chip Sandresky -- 7/26/2001, 7:34 pm
Re: Sam, what is your opinion?
Sam McFadden -- 7/26/2001, 3:07 pm
why d'ya think that is, Sam?
Les Nightingill -- 7/26/2001, 4:41 pm
Sam McFadden -- 7/26/2001, 7:06 pm
That helps a lot, thanks Sam *NM*
Les Nightingill -- 7/26/2001, 9:45 pm
Pete Rudie -- 7/26/2001, 2:40 pm
Re: Dynel?
Sam McFadden -- 7/26/2001, 3:25 pm
Penetrating epoxy *Pic*
Pete Rudie -- 7/26/2001, 1:03 pm
Re: The Celtic knot....
Shawn Baker -- 7/26/2001, 5:43 pm
Re: The Celtic knot....
Pete Rudie -- 7/26/2001, 6:36 pm
Nick Schade - Guillemot Kayaks -- 7/27/2001, 9:10 am
posting proceedure?
Elliott -- 7/26/2001, 1:43 pm
Re: posting proceedure?
Pete Rudie -- 7/26/2001, 2:19 pm
Re: posting proceedure? *Pic*
Elliott -- 7/27/2001, 8:12 am
John Monfoe -- 7/28/2001, 4:58 am