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Re: Plywood vs. wood & stiffness & hollow vs. stri
By:Bill Hamm
Date: 4/22/2010, 2:58 pm

: Thanks for the replies so far. I too noticed that the scraps of
: plywood that I have seem to flex more and are heavier than
: similar pieces of pine I got lying around in the garage. But my
: scraps were not exactly the same so I sort of extrapolated the
: feel I got from holding each of them and trying to bend them by
: hand. The plywood being only 1/2 of itself or so in the stiffest
: direction explains it - I had not thought of that.

: As for the stiffness, I agree I do not want a very stiff paddle.
: But, in taking in consideration that I want a lightweight layup,
: I expect that there will be plenty of flex anyway. I like some
: flex but I tend to err on the side of stiffer rather than too
: soft for when more power is needed or in rough/moving water.

: Lastly, the reason for me to look for the stringer variation is
: that someone who has experience with doing both kinds of paddles
: has had better luck with the ones that had a stringer. The ones
: that did not have a stringer tended to brake under heavy use due
: to compression fractures (both had foam inside for shaping
: them). He used fiberglass with carbon strip reinforcement under
: it and laid that all over the foam core.

: What I'm thinking of doing is creating a plank that has the outline
: of the GP as seen from the wide side, then glue to it two pieces
: that when seen from the side (as if holding the paddle with the
: edge towards me) will create the other dimension of the paddle.
: So it forms a + shape that should provide rigidity as well as
: the outline for the general shape. I think of placing 4 strips
: of carbon in each of the sides, wetting them with epoxy, then
: placing stiff square section foam blocks in each of the
: quadrants of the plus and clamping that down lightly. That would
: have the effect of compressing the excess epoxy out of the
: carbon cloth while simoultaneously achieving a 3-dimensional
: sandwitch on all sides of the stringer.

: Once the epoxy cures, I will need to sand it down to shape the GP.
: Once this is done, all that's left is to put the outside sleeve
: (I'm thinking either carbon or carbon/keclar as I did with my
: last paddle repair), wet that, vaccum bag it to cure, light
: sanding + fill coat + more sanding + clear coat and I'm done.

: I was not sure if this single outside layer of "medium
: weight" sleeve that comes to about 1/2 mm thickness per the
: specs combined with the "+" shaped wood stringer
: reinforced with carbon would be comparably stiff to a full WRC
: paddle or not. Any guesses? I suppose I need to make one and see
: if it needs more or less...

All my greenland paddles so far have been solid WRC and have held up just fine and I'm not a lazy paddler. Adding a spline of a different species would stiffen them up considerably and probably make them prettier too. I don't like the feel of composite paddles anymore, much prefer oiled softwood so I've never played with adding a composite layer.

Bill H.

Messages In This Thread

Material: Composite Sandwich Stiffness
Kocho -- 4/22/2010, 11:41 am
Re: Material: Composite Sandwich Stiffness
Bill Hamm -- 4/22/2010, 1:22 pm
Plywood vs. wood & stiffness & hollow vs. stringer
Kocho -- 4/22/2010, 2:22 pm
Re: Plywood vs. wood & stiffness & hollow vs. stri
Bill Hamm -- 4/22/2010, 2:58 pm
Re: Plywood vs. wood & stiffness & hollow vs. stri
Kocho -- 4/22/2010, 7:58 pm
Re: Plywood vs. wood & stiffness & hollow vs. stri
Bill Hamm -- 4/25/2010, 12:31 am
Re: Material: Composite Sandwich Stiffness
frankp -- 4/22/2010, 12:41 pm
Re: Material: Composite Sandwich Stiffness
Bill Hamm -- 4/22/2010, 1:45 pm
Re: Material: Composite Sandwich Stiffness *NM*
Bill Hamm -- 4/22/2010, 1:43 pm