Still experimenting with untraditional fin designs in this board.
Since the smaller sharky cedar rail fins and Mr Mik’s cut down 0.45GW center fin was way too loose, allowing hyper twitchy overrotation when pushing hard, I tried those same rail fins with a 0.5GW fin, whose Probox tab is about 1/2 inch farther forward on the fin, allowing the fin to move 1/2" farther back in the board. It is also raked back slightly more than the 0.45GW fin and slightly deeper. This made a huge difference in reducing the hyper twitchy overrotating feel when pushing harder, and I was having a lot of fun learning to enjoy this combo, in some pretty good groundswell.
Unfortunately, I lost one of these 0.5 GW fins. I had originally made these to accept the grub screws for being rail fins, with flats for grub screws on one side of the tab, and did not make a recess flat on it for being a center fin with opposing grub screws. I just torqued the opposing grub screw into the Fin and said good enough to try. It was not. That fin is now gone.
1/4 the way through a hard backside bottom turn, I fell flat on my butt like all three fins sheared off, but on retreival, only the center fin was gone, to my relief. I have the other ‘rail’ 0.5 GW fin as a backup, and that fin now has grub screw flats on opposing sides which should not allow the fin to eject so easily from the center probox. I do suspect my leash had partially ripped the fin out on a previous ride… the turbucles not only catch grass and kelp, but leashes too. I caught one wave with the board as a twin fin with these smaller sharky cedar rail fins. It was a 18+ second period swell, well overhead set wave, courtesy of the Southern hemisphere, that closed out, but only after I made It a good distance, being reminded how twin fins are just so incredibly speedy on open face. As a twin with these sharky fins with no raked tip, there was zero stability which made for a scary late drop, but which earned a bunch of hoots.
The next day I put a Wavegrinder fin in the center probox, the larger stiff version in cleaner similar conditions. A long period strong swell largely walled with some select corners available. The WG fins had previously imprinted on me a tracking feeling whether the full size WG2 in my longboard or the smaller WG fin as quad or thruster center fins in this board. I thought it might work well with the super pivotal and loose sharky rail twin fins. I was wrong. These Wavegrinder fins are also super high aspect ratio, and have the winglet on the top. This wavegrinder fin with the smaller sharky cedar twins felt atrocious, Slow and unresponsive and dull, as if the leash was wrapped around the fin, but it was not. Obviously the winglet and my board’s tail rocker did not agree. One wave when I was up higher in the face, it felt good and responsive, briefly, but anywhere outside this part of every wave, and it felt like a sea anchor and I blew a few good waves because of it. I had the other 0.5GW fin in my pocket, with a fin key, but the pocket’s Zipper head came clean off in my fingers after removing just the key, and would then balloon up afterwards, had I ripped the fin from the pocket, swapped fins and kept riding. I considered kicking out the WG fin, breaking off its tabs, riding the board as a pure twin, as it felt so horrible. I did not and this WG fin ruined my session, then the wind came up before I could get the 0.5GW fin in the board and paddle back out.
Anybody want to buy some larger WG fins, the 5.7 inch deep ones? I have lent out the 4.8’s a while back and not seen the guy since. I would have used the 4.8 had i had it. It was Ok with more traditional shaped thruster style rail fins.
These High aspect ratio sharky or turbucled fins are a trip. These are an extreme experiment, in high aspect ratio in multifin boards, but for being large deep fins that look so untraditional and just wrong, they have noticeably and undeniably less drag than smaller more traditional dol-fins shapes. They also allow for a much tighter turning radius, to an almost ridiculous knee collapsing degree. They are super quick, super loose, with a lack of self centering and stability, compared to a more traditionally shaped fin. I wonder what a more youthful rubberkneed surfer could do with more speed and a tighter turning radius should they get over their untraditional look, and try them.
Why do all multifins need to perform the same tasks of adding stability and self centering? …and thus be the same general shape and size.
They obviously work and work well, but How much self centering and stability do all the fins need to have? Seems to me other than being traditionally visually acceptable, this is the only benefit from the raked tip, at the expense of added drag and resistance to turning.
Well, shedding grass kelp and leashes is certainly a benefit of more traditional fin shapes, Can’t deny that large factor, but from a tight turning radius, and low drag perspective, high aspect ratio is a different level, a much different feel, and I am digging it. I can still draw out the turns, but I can push harder and reduce that turning radius too with higher aspect, I don’t necessarily need the fins raked tips limiting the turning radius or adding stability and drag, not all three of them anyway.
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The purple turbucled fin in the pic below is a cut down version of Mr Mik’s 3d printed Albatross Whale fin, which was a more extreme version of his Gullwhale fin, now just called the G-Whale fin. I made a mistake in the location of the probox tab, I want the fin farther back, but will try it like this first before modifying the tab to allow for a more rearward position in the board.
The larger sharky twin fin, that I retained after the collision, and which was broken,( the other lost) has been resurrected. It is on my port rail, for going left. Its trailing edge grew with the extra thickness from the extra glass used to rebuild it. It is ridiculously stiff. Hard to imagine water pressure alone deflecting the tip more than a few mm.
I also modified one of Mr Mik’s large single red Deaweeder fins to fit Probox center tab with no fore aft adjustment. This fin’s filament had issues with interlayer adhesion, and was quite flexible in my singlefin longboard box, before I added 2 layers of 1.43 oz cloth up the sides of it. That fin is not quite ready to go yet, and none of these modified fins of Mr Mik’s designs, have been made to fit probox perfectly, yet.
Getting the grub screw bottoms to rest perfectly on flats on the fin tab, is yielding fin tab receptacles much different than any factory FCS1 fin I have. The receptacles are higher, deeper, at a different angle based on trial and error fitting and seeing where the grub screw threads dig in. While simple fin retention is easy enough to achieve via finkey torque alone, I want the whole fin to fit tightly in the receptacle, with no wobble, and the grub screws flattened bottoms resting on a perfectly angled receptacle on the fin tab. Should be easy to achieve this, yet it isnt. I’ve been achieving an ‘just OK’ fit so far, before going further towards ideal if the fin rides well, the going further part has not been followed through on yet, despite the 0.5GW being a good performer.
I have a whole other fin panel ready to cut into, to make new rail fins. The latest cardboard fin template I made is based on the larger sharky twin, but is slightly lower aspect ratio with a slightly more raked tip, but nowhere near traditional fin designs. I need to see how the larger rebuilt sharky twin goes left , before backing off these weird looking high aspect ratio sharky fins and working my way towards the middle ground compromise. I am thinking my happy middle ground will be much sharkier looking, than dol-fin looking, but time will tell, and I’ll enjoy the experimentation.
Edit/Add… as i don’t want to bump up the thread, just to add the following:
The Purple 0.5 AW fin was not feeling right in the center box in two different sessions with the larger rebuilt sharky cedar fin on my backhand rail. The overrotation when pushed hard was as bad as the 0.45GW, which makes sense as their trailing edges line up when pushed all the way back in the center Probox. The extra depth of the purple fin does not make up for the loss of width. I intend to try it again once I move the tab 1/2+ inch plus farther forward on the fin allowing it to be that much further back in the board. In point and shoot speed on mode, not turning hard, it was certainly quick and responsive, but on light turns with the board flatter in the water the whole board would arc around on the inside rail fin as if there was no center fin and there is more toe-in than there actually is. It was a bizarre feeling and reminded me of how the full size turbucled Albatross whale fin felt in my traditional 9’7" log.
I have modified the yellow 0.45GW fin to overhang the box over a half an inch farther, but not yet tried it. I have also gotten the red 0.5 Deaweeder fin base to fit nicely, and be strong enough, and rode it today for the first time today with both smaller sharky cedar fins, and it felt really good, really responsive. 3 of my rides felt rather incredible from a speed and maneuverability/turning radius factor and the top turns and carves i pulled off, but as I gained more confidence in this fin cluster, I was able to overpower the fins on 2 frontside bottom turns which felt awkward. I would not say overrotation like the board was turning too tightly, buckling my knees, but more like the tail was drifting when pushed that hard and shortened the turning radius by ‘pulling the parking brake’ instead.
The modified red DW fin also got some carbon rods and SS screws up into fin through fin base and the grub screws press either onto a carbon rod or SS screw. No fore aft adjustment, the tab is the full width of probox receptacle right now. I did not sand the epoxy ‘fill’ coats near to the best of my ability pre surf today, a bit rushed, figuring I would do that if I decided I liked the fin. I do like the fin, and yet it was nearly continuously humming on each and every wave, and hummed loudest on those bottom turns just before the tail started drifting towards shore. Gonna go fine tune this fin now and hope the swell holds as this is a good combo despite being able to overpower them on some frontside bottom turns. Never before have I had a fin humm for so much of the ride.
The next rail fin template is still being contemplated. Same general surface area and depth, but tabs farther forward on fins and with a smidge more rake. Kind of wishing I installed the proboxes further back in the board, but i was not familiar with high aspect ratio fins when I laid those plans.
The rebuilt and slightly larger/thicker sharky cedar fin on my backhand rail with purple center fin, felt like too much fin in parts of the left, like it was locked in a track despite the happy go lucky nature of turbucle center fins in a partial stall. I liked this fin template best with the 0.45 GW fin whose first turbucle overhung the front of the probox, but that 0.45 gw fin is now modified to sit further back on the board.
This rebuilt sharky cedar fin is slightly larger and thicker, and while quite stiff before it partially broke, is much stiffer now, and seems to have lost that feel it once had. I think while the smaller sharky cedar fins template is just too upright, that their depth and size/surface area is in the ballpark for a rail fin in this board.
Might have to try replacing the 8 degree insert with the 6 degree on my frontside rail, see if the smaller sharky twin then holds a bit better on those hard frontside bottom turns with a properly located back foot. All these sharky cedar fins have some extra cant built into the fin tab, although I have not measured it precisely. Its likely around 11 degrees total with 8 degree Probox inserts.
