…just run with what you have. Since we don’t know how precise a cut/opening you made around your inserts, short of carefully drilling a hole from the deck to meet your side fin plugs to create some type of a skin to skin bond it’s a moot point.
Lo3… you are very lucky that you haven’t had any problems. Probably the heat the epoxy generated when you dropped yours in penetrated and melted the material around the plugs that would look kind of like that coconut strand candy. I’ve seen this with windsurfer deck mast track and fin boxes later on when we did do a repair… we could not believe they held up for so long!
I know there are many people that still use the round FCS plugs (X2). They base the strength on what we learned about how to reinforce sailboard boxes that we were consistently blowing out during the great windsurfing boom of the 80’s. The problem was 2 part molded fin boxes like what Bahne designed for Fins Unlimited. They had a bottom plate that was fused to a side wall that included the track that holds the metal slider that accepts the fin screw and binds the fin into position.
The problem was that the amount of lateral stress a surfboard fin experienced was minute compared to a sailboard using a mast and sail that would transfer all that leverage down to the fin for resistance and subsequent direction. We were also learning how to get 50 feet of air off waves and didn’t know how to land yet.
POP! Would go the box!
Once I developed the production process of dropping the foot strap inserts into the hot coated deck of our sailboards, we would then rout the fin box, which just happened to butt directly up against the inserts. Not everyone making sailboards in those days had this advantage because they were buying shallower, pre-molded foot strap inserts. Our riders were leading edge guys attacking Jalama, The Gorge, Hookipa, and Chrissy Field… we made our own inserts from delrin rod and they were deeper than other inserts. I remember the shop that sold my boards in San Rafael saying “your boards are the only ones I get that the fin boxes don’t blow out”. Eventually this problem was eliminated by the advent of one piece Chinook boxes, but not until we had conducted one helluva lot of R&D incepting, woodies, lateral supports, custom flanges, bolting the corners of each end of the box together, and capping over the fin boxes with glass.
So my story is to illustrate how vastly important a skin to skin connection is when dealing with the lateral stress/torque/leverage/load a fin gets under normal use.
FCS based their “H Pattern” on exactly what my WS was about.
Here’s the problem. The density of surfboard foam, and the size of the reinforcing ring around the round plug is (often times) insufficient to handle the normal wear and tear of today’s style of acrobatic surfing. More importantly, if you look at the tiny amount of material the plugs have where the square slot receives the fin and it’s proximity to the outside wall of the plug, you instantly realize that this is an incredibly vulnerable spot for cracking.
To illustrate my point, look up the thread where a guy posting as Duuuude (my own fin box) made his own inserts and is now making his own leashcups. The inserts are red and accept FCS fins. Then note HOW much material he has left from the slot to the outside wall.
The FCS Fusion was originally designed for use in EPS blanks. They are those peanut shaped inserts with high density foam underneath the flange, and have raised ports that sand flush after being glassed under the laminates. When Fusion came out I dumped the round plugs and used Fusion ever since. They are very strong, lite, and extremely easy and quick to install in EPS or PU. How strong are they? I secretly conducted my own test by shaping a blank, dropping the Fusion inserts into the (PU) blank with milled fiber and PE resin, sealed the blank with a slurry of PE resin/milled fibers, and had a rider GO RIDE THE BOARD W/O GLASSING IT. The Fusion held. Why? because a precise tight routing, coupled with a wide base area that has a peanut outline specifically designed** to resist side torque** (that peanut shape) was** more important than fiberglass over the top of the insert.**
An engineer could argue that the skin to skin is stronger than the flange aproach, to which Iwould only say “in theory you are correct, but X2 is a substandard and labor intense application that promotes failure”.
And the evidence is a daily event:
Fin slots crack
The resin milled fiber O ring around the inserts can be off center when placed in & crack
The plugs get punched down below the glass surface and/or punch thru the deck.
In the meantime, the flange has inherently superior resistance to cracking at the fin port, is a no brainer to get a precise rout for installation, and has MORE SUPPORT AREA to distribute the load coming (predominantly) from the sides of fins.
At the end of the day, would you rather have your round plug crack or push down… or have your two tab fin base snap off in an undamaged box allowing you to quickly and inexpensively replace the fin and go back out?
I rest my case.
P.S. …yeah that test board got a bunch of dents onthe deck, but doing R&D nearly always involves expense for a possible gain.