Hello all,,, blade repair help

[rockhoppernc]

Hello all, hoping I have come to the best place.

I was given a waterstick white water paddle with a cracked carbon fiber blade. I am going to repaire it and use it for a flat water solo canoe paddle. I plan to make a couple braces and lay some kevlar down on top to hold everything together on the back side and lay a few wide strips across the front. also plan to do the same thing on the side for balance.
my question is can you lay kevlar over top carbon fiber?

 

[Todd Bradshaw]

Yes you can. You want to sand the bonding area with fairly coarse sandpaper first and unless you know what resin they used, epoxy resin would be the best bet as it will stick best to just about everything. You would also want to keep in mind that once applied, it is extremely difficult to sand or feather-out a Kevlar patch. Instead of sanding away cleanly, Kevlar fuzzes and it's nearly impossible to sand away the fuzz. You can fill over the Kevlar with coats of resin and sand the resin smooth, or top it with a thin layer of fiberglass and sand that smooth, but just don't hit the Kevlar itself. Kevlar will yield high tear strength, but unless you use a lot of it (like maybe two to three layers per side) you're not likely to gain back much stiffness where the break is.

Since the break is cross-wise, across the blade, the ideal patches would run lengthwise to the blade, spanning a fairly long distance and bridging the break. The ideal, stiffest and lightest material to do this with would be non-woven, carbon fiber tows. These are narrow flat bands of carbon fiber strands about 1" wide that come on a roll. You put down a light coat of resin, lay the tows down (lengthwise on the blade) and carefully saturate them with resin. Being non-woven and just strands, all of the material added tends to be aimed in the proper direction to re-stiffen the blade, something that would take a lot more woven cloth, since half of its fibers would be pointing the wrong direction to help.

 

[rockhoppernc]

thanks for getting back to me,
I do have some fiberglass sheet as well, but think the kevlar will be stronger in the longrun. Was thinking that two long braces almost at long the blade( longways) on the front of the blade would work best and covering them with kevlar sounds good. and on the inside where you get your push in the water, about 5 or 6 inches wide and a few layers thick would work...what do you think?
or should I make my bracing and cover the entire paddle and leave an inch or two gaps around the patch, that way I could add a few layers and over lap each one. you think I should cover the front and back the same way?

 

[Todd Bradshaw]

What do you mean by braces?

You would want to put the bulk of your reinforcement on the back side of the blade for a couple of reasons. (1) This type of paddle is made with what most of the manufacturers call a "dihedral" blade. This means that it isn't a flat surface. The power face (side toward the paddler) has kind of a ridge running down its center. This helps prevent the paddle from fluttering as you apply pressure when taking a stroke. You don't want to mess this up. You might apply a layer of cloth or some directional fibers to the power face to renew its tensile strength, but you want to keep it smooth and not make any drastic changes in the shape of the power face. And (2) the bulk of the paddle's stiffness is generated on the back side by building it up enough to resist the compressive forces that take place during a stroke. The big round rib down the back and the convolutions on either side of it are major players in this aspect. These are the areas of the blade where it will be most critical to rebuild the original strength. The back side will also tolerate a little excess bulk being added better than the front side will, in terms of how the blade feels and moves through the water. If you plan to add some sort of built-up bracing, the back side would be the place to do it.