Can someone lend Keef a Fangy fin to lure him out of retirement

Absolutely fangman, I'm a horder everything is still there ,there's a matter of putting it all together
I'm into modifying cars , but mite put the gear together for a warm windy westerly at primbee this winter, I have a new new shallow water fin to try,
Inspired years ago by the fangman but never got around to make it,
Keep up the good work your killing it

Tested the Green Machine FF22 3d print with flex trailing edge on pretty choppy Albany day yesterday with encouraging results. Unfortunately I hit a submerged object like a rock/razor clam early on. The 3d print was fine but turns out DiChloroMethane does not weld to mono film like it does with PETG so the trailing edge was pulled out of its slot about 2cm and flapping around. Had to get back and travelling 30-32kts in the weed meant the trailing edge was pulled further out. Used some scissors to cut the bottom 6cm or so off and continued sailing. Fin didn't feel quite as solid as before but at least the remaining trailing edge stayed in place for the rest of the day.

Spent the day swapping boards and between this fin and the regular Al Fangy. By a long way the 3d printed fin felt completed locked in and solid in chop both upwind and downwind. I spent a lot of time in the big chop areas trying to either make it break or spin out which it did neither. The regular Fangy spun out a lot more and felt quite dangerous in comparison. (Again, this fin is worn so it's not a true comparison).

Polars below tell more of the story. On big board (97litre) pointed 3 deg better upwind than regular Al Fangy before I hit the rock and lost the bottom 1/3 of flex edge. After that incident it it pointed the same as FF but Fangy was way sketchier/dangerous. Switching to the smaller 86 litre board, the damaged flex fin pointed better by 1 deg than the undamaged flex fin on larger board and a wopping 9 deg better than the regular FF. Even in the big chop in the middle on 2nd time out still did 3 deg better than the normal Al Fangy dealing with less chop. (this is on both tacks) Zero weed issues with no gasket, felt the safest on this fin and zero structural issues.... Top speed was also on the printed fin (33.79kt).

Already replaced the flexy edge using epoxy like previous fin to secure and need to test further/maybe borrow a fresh FF22 to compare before trying the idea on different fins etc.

Time for an update. I have been continuing to play with the FangyFin code that generates a 3D CAD model given and outline and some geometric parameters. It works reasonably well now, but is not particularly robust, so the code tends to fall over more often than it should. I added a Bambu 3D printer to the toys in the shed and have now progressed to churning out a fin or two. The fin below is to investigate higher chord thickness, (12%) coupled with an increased concavity in the trailing third of the profile.



I used Flex's technique of PETG filament shell filled with epoxy. The infill is 10% so it was a cinch to pour the resin. The carbon rod stiffeners are whatever diameter I could fit. I some cases I used old carbon sail battens filled with epoxy and then stuffed bundles of smaller diameter rods inside. I was aiming for slightly increased flexibility along the trailing edge, but super stiff in the main body. The stainless rods are epoxied in situ with no nut. The experiment here being to investigate whether the long section of thread will provide enough anchorage on its own. I have done away with preloading the printed PETG model under compression. I want to see if the high amount of carbon rod and epoxy can do all the heavy lifting in this layout.

I also attempted to print a Tuttlebox mould and create this section just by pouring resin. I failed spectacularly when I forgot to put separator on the inside of my mould. After cutting away the 3D print like a drunk blind man swatting mosquitos, the resulting tuttlebox is rather rough and ready. Next job is to get it wet. And if its worthy, finish and polish it up to a decent level and see how long it lasts.

Some thought bubble fins at varying stages of completion.,The FF22 is in the photos as a size reference.
The little fin is an experiment with an extremely thick profile, sandwiched into 18cm depth. Trying to generate lots of lift for light winds and shallow/weedy water. Was in the post above.


The biggest fin is 248mm depth. A massive 15% chord thickness, lots of trailing edge concavity. Trying to see if I can get FF28 levels of ability and control. The top 4 cms is sacrificial and to be replaced with an ellipsoid bulb once I get an idea of abilities/polar plots so I can compare.



The middle fin is unusual in that it has a almost constant thickness for two thirds of its span, that is, the % chord thickness increases slightly as you progress toward the tip until the final 1/3. There is less tip surface area. I want to see if the lift benefits compensate the expected drag.
The coupler on the front bolt is a result of a rookie mistake. I measured the length of bolt I needed to get to deck height on the thickest board. I cut at this length. I was left with a bolt that was beautifully flush with the deck... with no thread exposed for me to put the put the nut.

decrepit said..
Looking good Ross, you may have made just what I need, a very low aspect fin that works in wider boards.

See my light wind board thread

Oh snap! I was just posting on your thread. I will try these out and if they are not atrocious and worthy of investigation, fling them your way. Of course it relies on them not cracking/snapping/failing in the meantime.

I think there are 3 choices, hands, feet or teeth.

I have been boffinising over the past few months and churned out a number of fins to play with and evaluate. I will post them over the next month or so in no particular order.

The first few fins are experiments with biomimetics.
This first one is an FF25, 8% chord, 400cm^2 with a flexible trailing edge.

The body of the fin is translucent PETG filled with Bully Boy Basil's araldite brew. The leading edge is stiffened with carbon rod. With previous fins showing no sign of mischief with decreasing amounts of carbon rod, and they have in turn been replaced with eucalyptus dowel, I decided to try a full dowel construction. So in this model, the fin base and body are joined and strengthened with wood dowel and threaded rod only.

The trailing edge is an ellipsoid of TPU95 that is glued into the PETG base. The trailing edge is now able to twist off a little under heavy and shock loading. There is a more pronounced trailing edge concavity toward the base of the fin foil.

very cool Mr Fang

Nice Ross, what glue did you use to join PETG to TPU? Or TPU to anything? Nothing I've tried works properly. Tetrahedrofuran supposed to be the best but worse the Dichloromethane. That only lasted 30 secs though in windsurf application. Best seems to be heat welding. Went through 10 variations of TPU only fins trying to get balance between stiffness and flex, then other projects took over and currently on back burner. Should upload a video of lessons learnt...not sure if I will get around to it though...but if you have found a glue that works........?

Flex2 said..
Nice Ross, what glue did you use to join PETG to TPU? Or TPU to anything? Nothing I've tried works properly. Tetrahedrofuran supposed to be the best but worse the Dichloromethane. That only lasted 30 secs though in windsurf application. Best seems to be heat welding. Went through 10 variations of TPU only fins trying to get balance between stiffness and flex, then other projects took over and currently on back burner. Should upload a video of lessons learnt...not sure if I will get around to it though...but if you have found a glue that works........?

A slight bit of undercut and compression so that the TPU is physically locked into the guts of the fin. I then used Fat Bully Boy Basil's Brew of araldite and an occasional hapless small insect to bond it all together. Originally, I had the threaded rod piercing the front section of the TPU to act as a rudder post, so if this version falls apart in short order I will revert to physically anchoring. ( assuming it's worth doing at all!)
I have a full TPU fin variant almost done so I will post that one soon.

The next fin is FF30 with a shorter base chord and rake of 36 degrees. I printed this one in PLA.
PLA is the cheapest print material. It is reasonably strong and easy to print. It is not particularly flexible and tends to snap. It is not happy with UV or prolonged water exposure.
To counter this I have encased the PLA in a couple of thin coats of epoxy. The photo shows the fin prior to final sanding and finishing.
I had some small issues with warping at the join. Over the next few fins, I have modified my printing techniques to minimise the issue. The cut line was placed at perpendicular to the leading edge. The effect is to place the print layers diagonal to the flow
The purpose of this fin is to see if the stiffness and strength of the rods and epoxy technique is adequate with increase wing root loading. To a lesser extent, I want to evaluate how well or badly the PLA performs with time.

The dog looks sceptical.

Knowing the dog, I'd say it's pissed off, it's walk along the estuary catching crabs, has been significantly delayed because of extensive work on fins.

Poor dogs, they only think they rule!