Internal Thermal plastic modifications
More discussion on cross drilling or shotgunning.
By drilling holes in your internal parts with a hole cutting bit on a drill you can remove a small amount of weight from your seat and other outfitting components like thigh hooks. If you decide to undertake this procedure you should do so with some clear understandings. First of all, the weight reduction will be minimal. We're talking ounces not pounds.
Most importantly, you must understand that these modifications will reduce the structural integrity of your boat. This may very well increase the likelihood of your boat folding in a pin. If you decide to use the information below, you are doing so of your own accord and we accept no responsibility for your actions. We are just providing information, not making recommendations.
The internal components of your kayak are likely made of thermal formed plastic. This material comes in a sheet that is vacuum formed over a male mold. The thickness is often determined by parameters such as the depth of the vacuum pull rather than the thickness needed. This means that your parts can sometimes be stronger than necessary. One easy way to determine this is to simply flex the hell out of your boat. If you grab your thigh hook and crank on it and if you see the surrounding boat flex before you see the hook flex then it stands to reason that you can reduce the strength of the hook slightly without consequence.
When you shotgun or cross drill the piece you are reducing the overall weight by the amount of material that you have drilled out (i.e. not a whole lot). For a part like a thigh hook I have seen people that have drilled both sides, but I would recommend only drilling the top as drilling the bottom may lead to flexing. When choosing your pattern there is one thing that you should keep in mind. Make your best effort NOT to make a straight line with your drill holes. If you stress your part to the breaking point it is certainly along this line that it will fail. Make a tight random hole pattern trying to achieve a balance between the material being taken away with the remaining (structural) material. There is no scientific data here, just wing it. Close your eyes if that helps, or call me I love tearing up other peoples boats.
Center pillar holders, or "bat wings" serve the function of keeping the front wall from falling flat. When doing any mods on this piece keep in mind that the piece does almost nothing until you are in a pin situation. At that point you are counting on the bat wing to keep your wall from popping out and allowing your bow to crush. So if attempting a mod on this piece give some thought to where it will stress first. The wall will push against the wing and try to flex it out. So, there are some surface areas that are not necessary and some that are very necessary. I personally did not drill any of the inside surfaces but you must make your own decision on what is right for you.