Show us your home-made fins ....

General Discussion
581

Nice, i dig the colors…

As MrMik said they are at risk to break at the screw extension. It’s almost certain because of the direction of the grain. I would reinforce them there even before using them. Especially the cherry wood one which otherwise will last a long time. I don’t think the cherry will snap at the base, it’s a strong wood and the grain is well oriented. Even if it hits the bottom sideways, I think the board would get damaged before the fin. The plywood ones I can’t tell but the quality looks shabby, they could break anywhere.

Phillip, in the file I sent you the base is separated to machine it separately with the wood grain running along the length, so it can’t break at the extension. I epoxy the base to the fin, being very careful with alignment, then I drill holes that go through the base and at least an inch into the fin. Then add the screws after dipping them in epoxy. This is just a safe prototyping method but I haven’t had any breakage that way.

582

I’m probably going to have to sand the flanges off regardless. I didn’t think all the tool paths through and the bottom of the flange has a really nice fillet from the ball nose bit I was using and doesn’t fit in a box properly. Depending on how the fins fit I may have to adopt a version of your fin base. Again these were all meant as test fins so if they don’t fit or work it isn’t a big deal.

583

Ok, I took the bait. I have to try this fin design.

Are all of the fins center fins? Any sides with flat foils being used.

I’ll make a pair and test em out

 

584

The only tubercled rail fins,  without a 50/50 foil, that I am aware of, are those WAO made of Padauk as shown in post #4 of this thread:

https://www.swaylocks.com/forum/109011/hello-first-board-wooden.

 

I was considering flattening one side of the top half of the Gwhale but…never did.

585

I screwed up with this Koa fin.

 I should have initially put the tab at the rear of the fin.  I dropped it when foiling and broke the screw tab, then glued in an oak wedge to replace it, which compromised too much lateral strength.

It broke during a pretty hard top turn, there might have been kelp involved.

The second photo just barely shows the head of the SS screw from Koa through white oak, and back into Koa.

 

It was a very lively fin, before it broke.  It likely aided in stretching the fin box, as sometimes i would not remove it post surf and re oil it,  and the Koa likely swelled.

 

I rebuilt it, glassing it, but it lost its former lively spark in that process.

 

You can see where I cut grooves into teh fin and inlaid fin rope/roving. It was a good lesson  employed years later  on MrMik’s early printed fins, when I needed to strengthen the screw tab.

 

 

 

 

 

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586

Regarding Stainless steel screws and Epoxy:

https://www.jamestowndistributors.com/userportal/document.do?docId=221

 

I’ve had this occur, and it caused water to wick up the screw into the wood fin.  I was able to pull it out with my fingernails and a bunch of rotten wood dust and paste came out with it.

If you use Stainless inside the wood, make sure the screw’s  head is submerged as well, not just the threads.

 

I’ve got some stainless in The purple  0.5 AW fin.  Tapped and threaded for SS machine screws with submerged heads.  Will report back if it proves troublesome in the future.

 

Anyway be warned Stainless steel, is not perfect for this application.  Perhaps titanium  :slight_smile:

 

 

587

Man you guys are awesome. I feel like everyone here is way more invested in the survival of these fins than I am. I made these all as tests to see if the cnc process can be used to make fins relatively easily and to play around with some weird fins. I’ve read Mr Mik’s journey designing the whale fin several times and despite not yet riding one, I am stoked to just try it out. Even if it breaks. The plywood ones I expect to break, the plys held too many secrets until they were machined. I also switched to hard wood because I ran out of conveniently sized plywood. I don’t think the cherry one will break because it feels pretty sturdy, we don’t have kelp to deal with, and I am not a hard turning machine. I’ve only ever broken one fin, my second home made attempt and it was more due to poor design and poor craftsmanship (my glassing sucks). 

Ideally I think I am going to try to mimic Mr. Mik’s dual screw fin base, with a few material differences. I keep thinking a solid fin with a wood core base, surrounded by thickened resin, machined out, and then the whole thing glassed with a layer or two of whatever cloth I have laying around.

I also want to work in Hans halo method.

I also really dig the engraved logos, pictures, sayings, and names on the sides. I’ll probably try Hans thing with cutting out an inlay and filling with matching resin. My wife also wants me to do a live edge river fin, like the tables that are so fahionable these days.

I am ready for the weekend, the cherry fin should be surfable, there is a swell coming, and most importantly I don’t have to work!

588

Yeah that’s why it’s worth to use the high grade plywoods. I also had issue with the cheap plywoods warping due to internal stresses getting released during machining. A good machine strategy can help to keep it flat while machining, but you’ll end up with twisted fins.

The high grade plywood is much more predictable! Sometimes a knot surfaces, but that gives it some character.

You’ll love vacuum bagging! Just throw some resing on the weaves, put a fin in between, just like making a drippy sandwich, throw it in the bag and magic happens!

And the great thing is, the method has structural benefits, it’s not just cosmetic!

Enjoy!

589

That surprises me, can you explain a bit more, please?

590

Well, with this I refer to the halo around the fin.

But because the cutouts do not add an extra production step, I consider them as one. (there is obviously extra machine time and there might be custom work hours).

The halo increases the bonding strength between the two fiberglass sides considerably (at least using epoxy, don’t know about polyester). The laminates are vacuum bagged onto the halo, resulting in a very solid connection.

The halo also adds extra room for abrasion when hitting sand, rocks, … , increasing the durability of your fin.

591

The only thing better than high grade plywood is free plywood, haha. But seriously I think I’m going to be using fancy woods because local hawaii hardwoods are usually considered exotic.

592

Well there’s plenty more in the quick and dirty prototyping stage.

1- Thrusters, Sharp tubercles, 3% camber rail fins foil, just out of the machine, need sanding and finish.

2- Plain spitfire planshape thrusters, 2% camber. Two choices of central, the big one can be used as single with the side-bites.

3- Another curved side fin, 3% camber, less tubercles.

 

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593

Really like the look of those thruster fins.  .

The ‘quick and dirty’ part still baffles me, as I imagine the amount of effort required to get anything resembling that without a CNC.

Do you machine the tabs to the same thickness of fcs fins, or make them a friction fit inside the plugs @ ~ 0.5mm thicker?

 

The spitfire fins, I believe would need to be moved back on the board a good amount, since all accepted trailing edge shapers dots are considering the raked tips and the center of pressure is moved backwards on such a fin.  Obviously this puts all the load on the rear tab and is a no go.  I think that first tubercle can be extended a good 3/4 inches and the rest of the spitfire fin located back further to accomodate, but the rear tab is still going to take a majority of lateral loading. 

The finbox location ideally would be moved to accomodate super high aspect ratio fins to spread the load more equally along the box/board, rather than adjusting the fin tab position.

 

With my limited experiments so far, the size and sweetness and position of the back foot sweet spot changes drastically with rail fin position with different fins or just using the ~1/2 inch that the probox can allow fins to move fore or aft…  On my board, since I always have a tendency to initially put my back foot way forward in front of rail fins, I positioned fin boxes up the board further then lined up the wings with trailing edge.  A rounded pintail throws a wrench into the equation too and I’ve been moving all my sharky fins back on the board, but still well forward of the usual 11 1/4".  Before I began on my high aspect ratio fin kick I found I liked my backhand fin farther back and my toeside fin more in the middle to the probox range. 

 

My newer sharkier rail fin templates have less base  length than standard, are  significantly deeper, and the trailing edge is about 1/4 inch behind the wing now buyt thats sure to wander with more waves ridden. 

I’ve no idea what turbucles will do in regards to fore/aft rail fin positioning.  Their ‘soft stall’ tendency is still too fresh and unexplored with regards to multifinned boards, and there is no base of experience to work from.  I just think the best starting point regarding the higher aspect ratio,  is the center of mass being the same as accepted positioning of regular raked dol fins.

With the higher angle of attack possible before stalling with tubercles. and that gradual progressive stall with a drag free feeling during the stall, is SO different, I can only guess what other ranges of cant/toe in, and foreaft positioning can become acceptable. 

It strikes me that the turbucle fin in a stall is kind of like a ‘powerslide’ on a BMX bike, where the back wheel  slides out but the wheel keeps spinning, compared to the person who locks up the back brake and slides sideways, and loses a majority  of momentum by locking that rear brake.

 

I’d really like to see what a top 1%,  rubber kneed surfer, could do with such fins.  I imagine that one could ‘grind the coping’ for a lot longer, at higher speeds, and reenage the fins smoothly at will.

So many variables… not enough surf sessions

594

They look awesome!

What sort of machine do they come out of and how do you design the shapes?

595

Looking forward to trying this soon. Straight edges, high efficiency tips, and forward sweep on the centre one.

 

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596

Very interesting.  

 

Interesting on the middle photo, how at first glance, the center fin appears to be canted at 35 degrees.

 

Let us know how it goes.

 

 

 

 

597

I’ve thought about forward swept fins. I think they will work better on airplanes than surfboards. The fluid will have a tendency to flow from tip to base instead of base to tip. I think that this could cause the board to kinda dig the tail in and slow down. Again just my thoughts we won’t know until you try. Fins do look sharp though, literally and figuartively. Whats the green and grey tabs made from on the side bites?

Also what board is that? I assume its made by you. It looks like a not so mini simmons. My next board is planned to be a midi simmons around 7’ maybe shorter. I might need some advice.

Definitely give a ride report.

598

In theory the forward sweep should provide higher angles of attack before stalling, and better stall characteristics - stalls at the root before the tip, and water flow will move upward toward the bottom of the board, where it’s “fenced”, rather than downward, as it stalls.

Due to the inherently less stable nature of such a design I have pushed the thickest part of the foil a little more rearward than usual to help try and minimise this tendency toward instability and to dampen the sharper response down.

The green tabs are just scrap fin panel cut offs, and the grey ones are G10 strips that were sold as knife handle building materials, which happened to be 20mm wide and 3mm thick, so I just had to glue the two strips together to get the required 6mm thickness, and then cut as required.

I did make the board. It’s 6’5", with low rocker, and a slighty rolled bottom the whole way through. It gets used as single, or an in line three fin, in small to medium waves, and it’s a lot of fun. It doesn’t work well as a thruster, until it’s edging towards double overhead. This is something I didn’t think it would be capable of, nor did I envisage ever testing it in. But a mistake made in rushing to get into a small boat to surf a wave “around the corner”, that “could be a little bigger”, in Indo led to this discovery.

599

Special Edition G-Whale 7 FRR for my son.

A pain making so many layer changes.

Sanded to 80 grit for better ‘Tripping’ (of the boundary layer).

The protective covers and their content are a little further improved, including more functional Allen key tools, a groove to hold the small tool lanyard, and space for storage of extra-long grub screws (for use in extremely deep fin boxes).

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600

Really intriguing. Will the tuburcles only work on vertical high aspect fins? Or is it too soon to say?

all the best