We’re having some internet issues today so if our post is weirdedr than usual, you’ll understand why! It’s funny the internet folks say it’s AT&T and AT&T says it’s us!
We talked briefly about working with high density rails. All of the surf style Flyboy Wakesurf Boards have some manner of high density rails. We’ve built a wakesurfer or two with perimeter frames, parabolic rails and all manner of wood, foam and composite structure rail build ups. One of our favorite and best performing wakesurf boards had basswood parabolic stringers that intersected the rail boxes. One issue with that intersection of stringer wood and fin box is that there was a huge hole in the stringer at that point! We never experienced any breakage, but when the area is half wood and half plastic it’s definately got some potential to break or focus forces on that joint. The other issue that we had when dealing with wood as the material for stringers is the differences between any two pieces of wood. Being organic, no two pieces will be the same. Possibly the differences were minute, but we’d just rather have both of the parabolic stringers identical. That can only be achieved when using material that is uniform.
So possibly machine from some substance or constructed using composites. One of the big advantages of a composite structure os that we can make it to the final shape we want during the layup.
Ok, so that talks about the parabolic stringers, they are different than perimeter stringers in that they are inset more from the rail, whereas perimeter stringers ARE the rails. Placing the stringer material further inboard isn’t so much a problem, it’s what to do with the rails that becomes the issue. If we glue on some low density eps on the outside of the stringers and then still further out glue on some high density rail material, we sort of end up with the second glue line acting like it’s own separate stringer. Not really a good effect. What we want to do instead is have the rail material be one chunk of uniform solid material. It would be possible to get a big piece of last A foam and machine it, but we don’t have access to a CNC machine for this build. We also don’t want to glue up individual pieces, as we mentioned, that gluing sort of impacts the functionality of the stringers. Instead what we want to do is use a medium density pour foam to make the rail material.
We like 5 pound density foam for the rails and we’ve ordered some polyurethane pour form from the good folks at smooth-on products.
One issue with using pour foam to build up rail material is exotherm. The two part pour foam generats a ton of heat during it’s short cure cycle, in fact it gets so hot that it can melt our low density one pound EPS core material. Not a good thing to have your core all shaped and ready to attach the rails and then have all that hard work MELT from the heat!!!! So our plan is to insulate the core some what by cooling the substrate with ice prior to pouring the pour foam and also to build up a composite stringer using 5 layers of carbon fiber tape. In effect we’ll have a carbon fiber composite parabolic stringer and then we’ll pour high density polyurethane foam in a mold that holds the core centered in the middle.
Ok, that was a lot of information we tried to convey and we apologize, it’s just theorethical at this stage, but as we progress, hopefully that will make more sense.
One of the first steps in the process will be to make a mold that will allow us to pour the polyurethane foam into that will help shape the foam and also minimize the effect of exotherm on the core material. Obviously if we get sloppy and have some of the pour foam hit the core, it will melt it.
Our plans for building the mold are to shape a slightly oversized blank that is generally in the shape of the finished outline. We want some extra material so that we can shape out any irregularities left from our molding process. However, we want to minimize this excess material first of all for cost savings, but secondly to reduce the heat build up from the exotherm of the curing polyurethane foam. The larger the volume of foam that is curing the greater will be the heat buildup. So we’ll try to keep that excess at a minimum. Also, we don’t want huge, thick, heavy rails and a perimeter frame, so we’ll try and keep the actual material we add to the perimeter of the wakesurf board to the least amount possible, while still giving us the desired effect of a parabolic stringer system
Lastly, you may remember back when we vacuum bagged some carbon fiber into the hole we cut into the foam to install our rail boxes. We want to implement that concept to help tie the fin boxes into the parabolic stringer system, that won’t wind up impacting the stringers as happens when we routed THROUGH the stringers.
Molding and composites and all of that wrapped up in a tidy composite sandwich! It’s definately looking like a complicated process, we’ll see how the final product turns out!
Thanks so much for following along and we hope that you’re gearing up to answer the big grand prize drawing for an Inland Surfer Flyboy Division James Walker signature wakesurf board.
If you don’t win that give away, be sure to attend the NorCal INT League Wakesurf contest On June 24th where one of the entrants will win that AND a Calibrated wakesurfer, plus other great prizes. You don’t have to podium to win, just enter and you might win one of the cool prizes!