I reckon the pizzas will be awesome

Time for another experiment - the FF18bulb. I was looking at different methods to interrupt the tip vortex and reduce drag. After a bit of mucking about I settled on a bulb. This is the mock up - thanks to Flex for the sceenshot.

I got it cast up and modified the bulb by making it a blunt beaver tail with a relatively flat lower surface similar to the keel bulb on Wild Oats XI. The reason for the mods was to make it safe and to provide a large flat surface to skid across soft mud rather than dig in. The lower surface also acts like a ski and provides a little vertical lift. The bulb has no keel weight righting moment purpose whatsoever. (It doesn't have vertical stabilisers like the Wild Oats version below.)



The bulb was placed on a FF18 V4 so I could directly compare the performance with and without the bulb. After some fine-tuning and even more mistakes, the results are getting clearer.
The FF18V4 is a fine foil with low drag, low lift and susceptible to spin out compared to its older siblings. The FF18bulb version has much greater resistance to spin out and some improvement in lateral lift. Possibly it's a little draggier in the weed, but I am not sure about this as both go through heavy weed without a fuss. Neither is good in chop, but the bulb is the better of the two.
The big difference is the performance once into the 30 knots range. The bulb starts contributing noticeable vertical lift. The tail on my heavy Xantos 310 gets 'hard' under foot and the board trims flatter and rides a little higher. The board drag is reduced to such an extent that 30 year old plastic wrapped board has passed the 35 knot mark!
The next step is to use the fin on a smaller board and see if I can find the point where the vertical lift becomes too much and makes the board unstable, or the induced drag from the bulb is greater than the board drag.

I sighted it today, and it does look rather special

powersloshin said..
Definitely worth exploring the possibilities, I would think a bulbed fin could be a size smaller than a classic one ?
It would be great if you could send one to Lake George for volunteers to test it

Not in time for this season p'sloshin. . I am still very much in the infancy phase with this thought bubble. My next version will be to marry the bulb with a cut-down FF22 or something with a more powerful lateral lift component than the skinny FF18's family. Atm the FF18bulb is good through heavy weed and an interesting experience at higher speed at low AoA downhill. The bulb seems to make an underwhelming feeling fin better, but as an all-round experience, it is not nearly as accomplished as any of the classic FF family.

Not really a true Fangy fin but certainly inspired and loosely based on one. This is a 3D printed version that doesn't have a flange (no need for a gasket) and is stretched to lower the draft to 16cm. Came up with the build technique playing around with Annular fin designs and seems a cheap and quick way to make and test concept fins before committing to more expensive build techniques (cast, CNC, fibre glass, carbon etc). Works on the principle of keeping the 3D print in compression and is just a laminate of 3D print over a 1.5mm sheet stainless core covered by one layer of glass (mainly to stop bits falling off and polluting the place). This particular fin worked way better than expected on big board with big sail on low wind day. Downside was it flexed too much so had to point board correspondingly further upwind but still could head upwind just fine. Could not make it spin out until took into reasonable chop. Felt fast for such a low wind day so will be interesting to test in higher winds. Maybe its flexibility was why it didn't spin out? Seems good enough fin to add a few more layers of glass to stiffen or machine one up... Video of how it was built and first test here for those interested

Just a little excursion on cut outs. The donor was a post-anodising munted FF24. In my hands, the fin below is almost spin out proof and a confidence inspiring bit of kit when pushing onto choppier water. Fab on reaches and bear-aways in less than perfect conditions on shallow/weedy runs.
Before you get excited with an angle grinder, the downsides I have noticed so far are:
- A distinct loss of max lift. The ventilation pathway is gone, but at the expense of leakage from the high to low pressure sides of the fin.
- A distinct loss of low end lift, for the same reason above, which manifests as bugger all drive out from a gybe if the speed drops too low.

I haven't figured out if there is a overall drag penalty yet. I think there is a reduction in the lift versus drag ratio because the lift is noticeably less. At higher speeds where the viscous effects of the water are less important, I am guessing things might not be so clear cut. For now, much more experimenting to do...

Reasons for doing this to a fin would be limited and I reckon there would be better fin options to explore first.

Imax1 said..
Makes me wonder if a normal upright fin would benefit from a cutout ?

Never seen one of that type of fin. I thought they were something to do with unicorns, mermaids, or Walt Disney
Yes the initial spin out motion is interesting, you think it's about to let go, slides a smidge and then comes back into line. I thought it was just my awesome cat like reflexes, but if it's happened to you too, I guess it must be the fin cutout then.
The pressure leakage over the total area of a long fin I would guess would be proportionally less and therefore the fin could benefit. The fact that it isn't done a lot commercially makes me think there is not enough benefit and/or, as you say, structurally too hard. (Apart from Wolfgang Lessacher's stuff of course)

Fangman, that fin looks suspiciously the same as the fin you donated to the weird science cooking experiment quite a few moons ago. The good news is I ground all that goo you had on it and looks like can salvage the fin. The bad news is 6 months after melting the previous fin I am still struggling to get two thermocouples to read roughly the same to be relatively sure of the temperature before cooking this bad boy. Two dodgy ebayers, three thermo couples and two controllers later one would think some combo would read roughly the same but at temp I still get 80degC+ or so separation. Initially I thought the issue was temp distribution in the furnace (i.e. much hotter at top) and seems adding a ventilation system is usual way of equalising this out so made one up using a junk vacuum cleaner motor. Helped a little (enough to give the illusion I was on the right track) so took Imax's advice and turned it on the side to make a pizza oven and thus reduce the potential temperature gradient.

Oven definitely now awesome for Pizza but didn't do bugger all for the temp difference issue so back to thermocouples or controllers. Saw your post, so bit the bullet today and ordered another controller and thermocouple. The hope is two out of 4 will read similar. Once arrive, will cook this fin regardless based on the highest temp reading I get. The point of this heat treatment exercise is to get rid of that porosity you can see on the thick bit of all Fangy fins. 90% sure that is caused by slow cooling of the thick bits in casting process. Will do absolutely nothing for performance of fin but may make aesthetically better so can polish up the middle and make anodising the fin much more uniform.

Seems I can keep my actual pizza oven at 540degC much easier than all this effort by fiddling with logs, air etc but figured this approach was better long term solution...definitely on the way to being wrong here...will see

Oh bloody Nora! That's where that fin went! I turned the shed upside down looking for it - on the plus side I found all sorts of excellent stuff I had forgotten I had

Imax1 said..

fangman said..

Imax1 said..
Makes me wonder if a normal upright fin would benefit from a cutout ?

Never seen one of that type of fin. I thought they were something to do with unicorns, mermaids, or Walt Disney
Yes the initial spin out motion is interesting, you think it's about to let go, slides a smidge and then comes back into line. I thought it was just my awesome cat like reflexes, but if it's happened to you too, I guess it must be the fin cutout then.
The pressure leakage over the total area of a long fin I would guess would be proportionally less and therefore the fin could benefit. The fact that it isn't done a lot commercially makes me think there is not enough benefit and/or, as you say, structurally too hard. (Apart from Wolfgang Lessacher's stuff of course)

Are you saying I don't have cat like reflexes ? Cos I do , more like ninja cat reflexes . If you were to lube up my belly with a block of butter I could slide for 10 , maybe 15 , metres on slick tiles . And make no noise .

Video or it didnt happen !

fangman said..
Top view with flattened/ beaver tail.


The underside of the 'skid' showing a bit of wear and tear from testing on the real estate.

That looks very nice Ross!!!

A sneak peek at what the next gen FF might look like. Once again all thanks to Flex, who cannot stand an idle 3D printer, the virtual prototype was married to Flex's transfer plates and tuttle box. The trailing edge ellipsoid is a result of a porridge of ideas and thought bubbles around spin out mitigation and drag reduction. The momentum of surface layer of water is kept higher in the region of most likely ventilation and there is a nod to Whitcomb's Area rule to reduce drag, along with a blend of NASA foil profiles at various stations along the wingspan.
It could all be complete bollocks, but I am closing in on a 3D higher resolution mesh CFD analysis that hopefully will tell the tale. In the meantime, Nefario Flex will weave his usual inspirational outside the box stuff and probably have this print on the water. No doubt there will be a fab little video detailing its fate...

yeah Flexafario! Fab to see it wasn't an uncontrolled 'fission' reaction on its first outing. How cool is the freeze frame of the spinout flow!?. Is the back end of the ellipsoid tucked up too far under the board for the camera to get a glimpse? (I am not suggesting you drill more holes in your camera board for viewports)

What's with the little squared to the board radius at the front instead of a blended front ?

That spin out shot , showing lots of air . I've always imagined a huge amount of air to spin out . It would be interesting to actually know where the air comes from . That way we could counteract it. Do we know if the huge amount of air sucks from the front , side or rear of the fin / board ?
Im sure flex could build a glass bottom , rear third of a board with a camera pointing down above the fin.
That would give information on where the air comes from.
Its strange that we can get complete air under the board with no problems, and then it does it's funky spin out thing on solid water.