Sunday, July 30, 2017

Borderline Breaks

The things we can learn from board repairs ... for example where you should not put your feet. Let's start with the end:
This is my blue Skate 110 which I bought to replace the white Skate 110 that I wrote about in my previous post. The picture shows the end result of my latest repair attempt. If you click on the image to see the larger picture, you'll notice a slightly different blue in the repaired area, which extents from the back of the pad to the edge of the board at the "F", and extends forward to the "N".

I discovered a soft spot towards the rear of this area last fall. Upon exploring, I discovered that the glass and the PVC foam underneath had a break. I dug out the core foam all the way to the sandwich at the bottom of the board, filled the void with polyurethane (PU) foam, and glassed it over. The PU foam is harder than the original EPS core, forming a hard "plug" that connects the bottom and the top - good enough, I though.

When putting the fiber glass on top, I noticed bubbles forming: the new structure had several little "pinholes". The inside of the board was still under a bit of pressure, and the air coming out pretty much kept the little holes open. I tried to fix this with an extra coat of epoxy while the board was cooling off, hoping this would pull the epoxy in and close the pin hole in the process. However, this did not work as expected, and I saw bubbles forming after a few sessions.

The next repair attempt including removing the glass around the pin holes, and glassing the entire area over again. This repair held for a couple of month, but then I noted a new soft spot right next to the initial repair. I used some Solarez since it was freestyle time, but that barely held for one session. So .. time to try again.

When I opened the board up, I saw that the initial repair was still intact; however, the top glass fiber layers were broken right at the edge of the repair. When I made the initial repair, I did not rebuild the PVC sandwich layer because I had neither divinicell nor the vacuum setup. I figured that having the PU plug extend to the bottom would make it stable enough; but what I had not considered was that I would have a hard plug right next to the somewhat softer, slightly elastic sandwich construction. This create a "Sollbruchstelle", which then indeed created a break.

This time, I tried to do things right. The first step was to open up a relative large area that included the previous repair area, and digging out all the soft EPS foam. I then hooked up the area to a vacuum pump to see if I could draw any moisture. This removed some slight dampness from the top of the EPS foam, but the vacuum trap remained empty after several hours. Fortunately, very little water had gotten into the board.

The next step was rebuilding the foam core with PU foam:
That was followed by sanding the excess foam off, and removing additional foam to allow re-building of the PVC sandwich. After some filling, glassing, and sanding, here's what the repair area looked like:
When you look closely, you'll notice a slightly different color along the top and right side. This is the edge of wood veneer reinforcement. It extends about two thirds of the way to the edge  near the front of the repair area, but not nearly as far at the back. The original soft spot that had developed had definitely not been covered by wood.

Using wood veneer as reinforcement under the rear footstraps makes a lot of sense, since wood has excellent mechanical properties to absorb and distribute the impact after jumps. Extending the wood past the padding makes sense, too: the padding under the foot pads is not very wide, and my size 12 feet need to be quite deep in the foot straps for my heel to be on the padding. Most of the time, however, I sail with just my toes in the foot straps, so my heel rests on the board next to the foot straps. I must say that I find it somewhat peculiar that the wood reinforcement did not extend further back. There are several possible reasons for this, like to much deck curvature, or "interference" by the fin box. Whatever the reasons were, it seems my heels were often positioned right next to the reinforcements, which eventually led to damage. It's no surprise that the damage was on the right side of the board, either: my home spot Kalmus had starboard jumps most of the time. Even when not jumping, just going over the chop there would put a lot of stress on the back heel, which does not even have any padding underneath.

I am quite sure that the reinforcements in my older Skate 110 were quite different. I use the old Skate a lot more often than the new one, and often with bigger fins, which lead to more outboard foot placements and more back foot pressure, but the old Skate never got soft in the back. The old Skate seemed to have a lot of carbon reinforcement, while the new Skate seems to have wood veneer instead (although the areas I repaired on the two Skates are different). But mainly, the old Skate 110 actually had two sets of footstrap positions, including a more outside one that's missing on the new Skate; and the padding on the old Skate extends further to the rails. So placing the back foot more outside on the old Skates was not a problem, but it appears to be a problem on the new Skate, at least when sailing in heavy chop or jumping a lot. Maybe I just need to go to tiny little freestyle fins to enforce a more centered foot placement and less back foot pressure...

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