The fin base and screw tabs see incredible loads. Any non fiber reinforcement is doomed for failure sooner or later.
The Load must be spread over a wide area, both lateral stresses, and stress on the fin tab(s)/roll pin from any frontal or rearward hit.
Also the roll pin, is best eliminated in favor of two tabs in my opinion. The roll pin needs to be located precisely so that the bottom of the fin is jammed flat against the bottom of the box at the same time the pin is touching the top of the groove within the box. Much easier styped, than accomplished.
Also it seems there are some differences in the location of the groove in boxes. The ball spring plungers from the early days of MrMiks fins would be pushing on the edge of thge bottom of the groove in my box, trying to push the fin upwards out of the box. as such the BSP’s were a hindrance to a tight fit and would seek to help eject the fin from box in my board, and the BSP holes also induced weakness in lateral strentgh and fin tab strength as well.
Without the ability to print/drill holes or square up from base of fin into fin body to add carbon bars/rods, then fiberglass needs to be run from the sides of the fin into the base, and a good amount of it which would require thinning of the wood below in order to not sand it all off to get it to fiit
Super hard and strong woods will of course last longer with teh grain going from tab up into fin base, but will fatigue and break This wood grain orientation also makes the screw tabs on single fins weaker. Plywood is generally so soft that even encased in epoxy it will compress and allow rocking of the fin on teh box which then accellerates the wobble and stresses involved on the weakening tab while allowing it to suck water and get even softer.
Having fins break at the base or the tabs just shearing off barely touching sand, is a session ruiner. Even with another fin on hand one needs the tools and light and perhaps reading glasses to remove the broken bits and reinstall another.
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I’ve had two more sessions on my 6’11 with a new toe side rail fin and either the half size GW fin or the half size AW tubercle fin in the center box. My new toe side rail fin has more surface area than previous, with more surface area in the tip, and every frontside wave I got, when going slow, it seemed the board pivoted around that larger rail fin and simply pushed the tubercle center fin sideways for a lack of drive and tail drifting shoreward. If I was going faster then laid into the bottom turn it felt great, but going slow was frustrating, and generating speed on mushier gutless waves was a lesson in futility as it seemed there was little fin to push off of.
The first session I got so frustrated with the lack of ability to generate speed, as the swell had not really filled in as hoped at that time, I went back and got my longboard with one of the most recent GWhale fins, and laid into a few backside bottom turn top turn combos that felt simply awesome and reminded me just how awesome this fin feels.
I’m currently thinking the Gwhale fins cut to half size used in shortboards as center fins is not a valid strategy for gutless conditions where one needs to generate speed. I’ve moved them back overhanging the back of the box, but I’ve found on my 6’8" that I liked the smaller center fin moved unnaturally forward. So moving the tubercle fins further back to account for the high aspect ratio is widening the fin cluster and at slow speeds it is not feeling good. Once I am going at a good clip it feels good, but on my toeside rail on the drop, avoiding a bottom turn there is a lack of drive, and that slippery feeling prevents accumulating more speed which could then eliminate the slippery feel.
I generally only ride this board in chest high +, but eagerness to try the board and new fins has me trying it in lesser wave size, and I am struggling. Also quite rusty due to Covid closures, which are happening again as cases surge.
I am not quite ready to write off the Drela AG10 ‘batfin’ without more sessions, but I think its flat sided sharkier predecessor, was faster and crisper. I glued a zippered fin size pocket to the thigh of my Shortjohn, and will carry at least one spare center fin and perhaps the sharkier toe side rail fin in future sessions.
Iam also thinking I should modify a Gwhale fin to sit further forward and be deeper. Something about the fin being too far back on a round pin is bothering me.
Also while the super high aspect ratio Gwhale fin works insanely well in my traditional longboard, perhaps a more maneuverable multifin shortboard needs fin rake and tip area to force larger turning radius and more drag, and modifying the Gwhale from full sized fin to half sized shortboard center fin, is a formula which cant really translate.
The tubercles and one’s leash are also an issue. My leash much too easily sinks and gets caught on a tubercle, and even when I notice it when sitting on my board, and try to extract it while sitting, I cant unless I get off the board and undo it by hand. I’ve tried neoprene sleeves to make the leash float with little success and with more drag . I’ve an old ‘back up’ leash from the early 90’s( XM) which is much better in this regard.
My fear with tubercled rail fins is the leash getting caught even easier, and trying to ride a wave with leash wrapped around a fin is frustrating to say the least. I’ve not used a leash on my Longboard so it has not been a factor on that.
