Holy Grail of fin modification

[BraceMaker]

@gator1 you're gonna have to for a bit - I've flopped call, also this was practice on an old Goode fin, gonna try again on my D3.

 

Learned a few things though, before I do it again I'd Probably set up to move the fin between cuts and cut the depth pass on all areas, instead or re-indicating the depth on each pass.

 

I'd also probably debate doing this on my horizontal mill - but I've gotta make a half nut for it before that will work.

[gator1]

What's "flopped call". Typo or work duty change?

 

Ya I wasn't gonna comment but glad that was a practice Fin. I figured it was a 4.5 beer cut on the top edge of that last groove.

 

I scribed the deep edge cut, touched the scribe with the cutter, backed off the fin, raised the table .025, cut the deep edge then just feathered off till it quit cutting.

 

 

[Than_Bogan]

Jeez does everyone on the internet have a machine shop!?

[gator1]

Nope, only the studs.

[BraceMaker]

Flopped - bad luck, people out sick and having babies.

 

At that 4th beer and screwing around with an old fin I just scribed lines, but I should have touched off, set a stop on my table, then backed off and advanced the depth, then go up to the stop, Lock the table and run my cut.

 

And I probably shouldn't have done a climb cut w/o really locking the part down either!

 

There's a reason you aren't supposed to screw around with power tools.

 

 

Honestly, if I were not to have a mill, and from the time finding an angle plate to clamp to, computing the angle that would feather out in .725" with a .025 depth etc. I could have done this job with a file in less time.

 

If you want to make one at home, use a metal ruler and a scribe, take a good file along the scribed line on edge to get the depth, then lay it flat across behind and feather it off. Its aluminum and you're removing .025" of material... its not rocket science.

 

 

 

 

[BraceMaker]

Oh a DRO would have REALLY shortened the set up time on this as well.

[BG1]

@gator1 I scaled the width of the step at about .500 from your picture and you listed it as .025X.725. Could you confirm the width please?

[gator1]

.500. My bad! Brain fart.

[BG1]

Thanks @gator1

[BraceMaker]

@BG1 - that makes a lot of sense - mine didn't look near as deep as his did.

 

I took my step from .025 to .05 - using a technique closer to what @gator1 described.

 

Bit of a fun machining project for someone of my limited abilities - one thing I noted, I'd used an angle iron section to clamp the fin to for machining, and it had a bit of warp so I remachined that flat prior to redoing my slots. Much nicer outcome.

 

Gator - what would you say the importance of the taper is? Just convenient due to the end mill you were doing? Could single passes .05 deep with whatever taper it takes for the single pass of the end mill to clear be similar? Or is the .05X.725 mathematically accurate for the hydrodynamics you were expecting?

[gator1]

I think the deeper longer trench will increase the speed at which you'll notice the tail washing out more easily. But I don't know if that's good or bad. I liked mine the first try, don't know which way is better. My flow package says you increased from mid teens up to mid 20s mph washout speed. Sorry I brain farted the dimension.

[Horton]

are you actually using CFD?

[gator1]

I'm using a plastic injection mold flow package that is probably not accurate. But theoretically should be.

[DW]

@JTH: I was talking to our CFD manager and we concluded that a decent simulation model will be incredibly complex based on all the various interfaces and elements that have to be done accurately to get a reasonably correct answer. It appears one of the more challenging parts of the model will be the water spray off the side of the ski and how to model that wall of water as it will affect the calculations back to the fin to water interface. We have discussed not only modeling the ski but also doing a tourney boat model...If it was easy (actually read inexpensive), it would already be done.

[Horton]

@DW that roughly matches my understanding.

[gator1]

Agreed. All I'm doing is looking at a flat plate with a step. Nowhere near the whole enchilada.

[gator1]

So. Guys. This is getting really fun. I'm cutting a .020x.020 slot into the surface of the fin from the deep edge of the seaplane step up to the top of the fin. So the edge of the .020x.020 slot will appear as a channel when looking down at the fin box from the top of the ski.

 

Any predictions on what will happen?

[A_B]

You shoot 3 streams of water up in an awesome display of spray and you are featured on the next BOS t-shirt...

[BG1]

@gator1 Your original design worked just like you said for me. The entire ski would sink down the last quarter of the turn with no/very little overturn, if I was slow enough at that stage. If my speed was up through the turn it had no effect. Maybe the slots could be a little deeper so the effect would start at a higher speed. It may be like everything else with a fin. .010”in step depth could make a big difference. Not 100% sure I follow your .020X.020 channel location. Can you post a picture when you’re finished cutting it? Are you going to use a hacksaw blade to cut this channel?

[gator1]

@BG1‌ That is mega cool! I do believe the deeper the step the higher the speed where the affect starts to kick in. Mine does kick in at nice speeds, so maybe a little variation in depth, maybe a little different reaction to technique or ski its mounted on. Thanks for the update.

 

As I shorten the rope it appears to have more of an effect, maybe because I have to turn sharper at the shorter lengths. Really seems to help at 35 and deeper.

 

It'll be interesting to see what @BraceMaker‌ finds with his double deep steps.

 

Well, @AB‌ , that's probably what will happen, but not the intent. I am already the poster boy for the BOS tshirt awfulness (I'm the shirt model in the thread looking for a new design). Please note I am in much better shape than that photo suggests. The current design is not very slimming.

 

I am going to cut the slot in with a hacksaw, will post pics.

[gator1]

I cut a channel as shown to let air be sucked into the speed step. Only on the front step. The channel goes all the way up to the top edge of the fin.

 

The affect was pretty cool. The steps make my weak side turn better, before the air bleed the affect was rather "digital". Turn felt normal, but if I pushed on the tail it would seem to suddenly wash out easier.

 

This air bleed seems to make the affect I'm looking for more "analog". The easier washout is there, but starts earlier in the turn and is more easily controlled

 

[ThePantsManCan]

I just did this mod. Its hilarious, I cant wait to ski it again!!!!