Does anyone know what the deepest twin fin depth has been, not counting twingles or NP Duo’s.
What about max cant angles? Disregarding bonzer runners.
I recently broke 1 and lost the other of 5 7/8" deep 7/16" thick high aspect ratio ~12.2 chord ratio very stiff twins with 8 degree cant, and they were feeling magical till some SOB dropped in on me and I ran his board over.
I got another pair in the works, but they were cut out at 5 5/8" deep and they are not really doing the warm and fuzzy thing for me, appearance wise…
Just wondering if others have pushed the depth boundaries on twins, and what they might have been.
You saw my post in the fin thread about the 6.1/8" twins, right? That set hasn’t been ridden yet but the other set I did of that size has been working pretty well for that surfer. But he’s a big guy riding a fat board and that’s a massive fin (~26") when compared to a 5.7/8 MR template (~22") and again compared to the largest retail thruster fins that are in the 16"-17" range.
Just flattening the trailing edge of an MR template with a Brewer style shape that has no recurve will increase the 5.7/8 fin area from ~22" to ~23.5", which itself is a big difference. Then if you add more base to the fin (I added 1/4" to the 6.1/8" fins beyond what the MR template scaled to at that size you’re easily up over 24".
Once you get over 20" in a high-aspect fin template you’re generating considerable torque on your fin system install. I went to psycho lengths on my install because I didn’t want the box to roll or crack due to the foam moving more than the box. Normally I’d have favored a rout-in or glass-on install for a fin that large but that board was travelling so I didn’t have that option.
I am running 5 probox in a 6’11" cedar HWS, and they are recessed into layered glassed cedar, heavily reinforced from within the board and what might be considered heavily overbuilt, but I am into the finbone to footbone connection, weigh 215LBs, and built it intending it to be my last shortboard for the rest of my surfing life.
I am not worried about sideways torque on the probox or the surrounding board , although a frontal impact did rip the grub screw out from one probox recently. I lost one twin fin and the other is Broken. Routed out broken pro box after a failed attmpt to bridge the break, new one is installed and capped ready to go, I just do not like the more traditional shaped rail fins I now have available and fear the ones I am making can’t live up to the memory of those I lost/broke in the impact.
The high aspect twin fins I made, had almost no raked tip, and they, in 8 degree inserts in the proboxes, along with one of Mr Mik’s turbucled 3d printed GW fins cut down to half size of ~ 4 7/8 depth as a thruster fin, well it was an outstandingly quick crisp and solid combination of fin and board that was too short lived, and I want it back.
When originally designing their outline, i had watched a few you tube videos showing Silky sharks or blacktip reef sharks, when they are all agitated and nearing attack mode with their pectoral fins pushed downwards almost under their bodies, and decided to try and mimick their pectoral fins.
I have some suitable wood fin blanks for a significantly deeper high aspect twin fin that might be my next fin making project once the current ones are finished.
I think I posted before about admiring your fin. I’ve always been a sucker for the Brewer type templates.
I’ve used Probox before and they do work but the inclusion of the inserts makes me nervous because of how little material is left on the box itself to keep the screw in. I can just imagine a frontal impact tearing the screw right out of the top. I do like the full tab, though.
I’m thinking about adding a third and perhaps 4th grub screw to probox to spread any frontal impact load across more of the box and fin tab. I am also thinking about using the probox without insert, as a mold and set a fin into some epoxy once I get the fin shape position and cant that I like the best, dialed in.
I guess there is a serious nod to Brewer in the fin above, but it is much higher aspect ratio.
Below are the ones i should be prepping for glass right now, rather than being on this laptop.
I am not so happy with their outline, but I’ll see how they go before writing them off. Originally I was wanting more the surface area of a thruster fin for them, or as rears for a quad set up. as I was not expceting to lose or break the twins. But I really liked the twins with near full size turbucled trailer.
Some guy I see out ocassionally on better days said he was going to give/lend me a pair of curved carbon fins for FCS1, that I would like to try but I’ve not seen him in months.
I’ve not done the twinny with no trailer fin, yet, with this board, and been a long time since I rode a pure twin fin.
The fins I’ve made to fit probox are a friction fit, the grub screws are for retainment only . When I use factory fcs fins in them they wobble until the grub screws are torqued against the tabs, and this has to add a lot of pressure to the grub screw portion of the probox on every turn.
I love the probox’s function with the adjustability, but this weakness around the grub screw is unsettling and I am not seeing an easy way to beef them up. And with the rather severe high aspect ratio fins I have been favoring, that front grub screw will continue to be in peril in any frontal impact, more so than a lower aspect ratio fin would.
