AG is right on the simple resin flange tip. And yes Greg, doing the cloth as you do makes it an an integral part of each other thereby distributing the load better from side pressure to the fins.
I’ve always found it interesting that FCS states that the X2 round FCS plugs are the strongest connection they offer? The reason I state that, is becuz they are basing it on the skin to skin connection that we pioneered in installing fin boxes in sailboards.
Side wall fin box blow out was common while we were learning to land big airs. The commonly used Fins Unltd. fin channels were a 2 part mold with the side wall welded to a bottom plate. It was not sufficient for the load they would experience which resulted in failure of the side wall structure. Our road led to “woodies” both lateral and perpendicular, flanges, double stringers, drilling & attaching nuts & bolts at front/rear corners of the box, capping the boxes with fiberglass plates to the bottom of the board… among other things. It wasn’t until I started installing footstrap plugs into the deck deep enough that the fin boxes routed into those delrin plugs we made, that actually eliminated box blow outs on all the sailboards I was sending to the Gorge, Maui, and the Bay area…
The final solution happened with the advent of a one part mold fin box with a post manufactured by Chinook.
But I strayed from my original digression about FCS claiming the X2 plugs are the strongest connection they offer. The answer is Yes & NO! In theory, they are correct, but what they leave out is the shortcomings of that approach. First, the “skin to skin” connection they developed with their tooling creating an “H Pattern” to the deck is minimal using a ring of reinforced resin connecting to the deck laminates. To add to that, you have poor design in the X2 plug from the get go. In this, I mean that the rectangular slots that receive the fin tabs have so little material between the receptacle to the outside wall of the plug itself. Load bearing of the receptacle - the rectangular receiving end of the two tab fins, is experienced greatest at… the corners of receptacle, which makes them prone to cracking. Apparently FCS felt the skin to skin H Pattern and the reinforced ring of resin to install the plugs was sufficient enough to reinforce the weakest point of the X2 plugs.
For the same reason a round waterbed doesn’t need a frame but a rectangular one does, what you end up with is a plug that cracks at the corner of the receiving part of the plug and an H Pattern that will punch into the deck laminates when sufficient load bearing occurs. Yes, it may take a lot for these failures to happen, but you then have a repair that may have been better avoided by using the easier to install, more sound approach as found with FCS Fusion.
The reason I feel Fusion was a better approach is because the material surrounding the rectangular receptacles is far greater than found in the circular X2 plug. The “footprint” is structurally capable of handling greater load distribution due to its greater base and outline. It is lightweight and very easy to install one. There is no punching into the deck or cracking at vulnerable corners. Both FCS Fusion and Futures boxes are type of flanges offering increased lateral resistance generated from load bearing on the face of fins.
Finally, when the Fusion system first came out, it was stated they were originally designed for use with EPS cores. I installed a lot of regular 10" fin and deck boxes into EPS sailboards as well as PUPE’s, and it was immediately apparent to me, that if they worked well in EPS cores, they would work even better in PUPE’s. That prompted me to drop use of X2’s 7 or 8 years ago, and since then my boards have been available with either Futures or FCS Fusion as a standard offering.
