: Here is a material question for you boat and paddle builders. Which
: material will be stiffer and lighter on its own and when
: reinforced with glass or carbon on both sides you say? Marine
: plywood ¼” thick by 4” wide by 8 feet long or a plank of
: pine wood of comparable dimensions?

: I'm posting this question on some of the boat building forums too,
: so if you see it there too feel free to reply wherever.

: How about balsa wood or other lightweight “core”? I know
: material like that will be lighter and more fragile when on its
: own compared to wood or plywood. But when reinforced to the same
: strength as the plywood or wood will it be lighter and stiffer?

: In a summary, what will be the stiffest, lightest, and strongest
: DIY layup that will not break the bank? I already have some
: carbon cloth and fiberglass tape that I could use to reinforce
: the plank with. I am also considering adding some Kevlar so that
: I can avoid catastrophic failure if the thing breaks. I can
: vacuum bag that whole thing too.

: As a background, I will use this as a stringer for internal
: reinforcement of a lightweight Greenland style paddle. I plan to
: have reinforcements placed at 90 degree angle to it so that
: stringer will not be the only thing inside but that does not
: matter for the question above. More FYI - in addition to this
: “skeleton” the paddle will have external composite shell
: (made from carbon or fiberglass or carbon/Kevlar sleeve) and
: foam to fill the void and provide shape for the shell while
: curing. I know others who have done similar paddles and were
: happy with the results, just curious if I could improve on the
: plywood for the stringer they used without going into much more
: expense.

: What would be a good thickness for the board? Would ¼”
: sandwiched b/w 2 layers of carbon on each side be weaker and
: more flexible than a sandwich of two 1/8” planks with three
: layers of carbon?

: I am pretty sure a core b/w layers of fabric will be stiffer than
: three layers of fabric without a core but if someone has a
: different opinion, please share -;)

Any plywood is going to be stiffer on it's own than pine or other similarly light weight wood of the same dimensions. The weight issue complicates things, though. Plywood will typically weigh a little more than pine or balsa or basswood, or cedar or any other similar wood of the same dimensions. The glass isn't going to add a significant amount of stiffness. Carbon fibre or kevlar would add more stiffness than glass will, but by itself fiberglass isn't very stiff at all. It's the wood that supplies the stiffness and the glass provides the resiliency/strength in the sandwiches that we use for boat building.

The 2 layers of wood with 3 layers of glass/carbon would be heavier than one layer of wood with 1 layer of glass on each surface. If this is just for core stiffness, the single wood layer ply will be plenty strong enough to add the stiffness you need, assuming I understand correctly how you're planning to use it.

As for a paddle, why not just make it hollow and fill with foam? I made a paddle of 2 layers of carbon fiber (12 oz I think) that is completely hollow and plenty stiff enough. I just layed the carbon around a pvc pipe that was waxed then pulled the pvc out of the tube once the epoxy cured on the carbon fiber. Strong, light and only cost me about $20 in materials (I used epoxy I already had on hand.)

FrankP