Forums > Stand Up Paddle Foiling

Takuma Kujira

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Created by Filow > 9 months ago, 16 Sep 2020
Filow
225 posts
16 Sep 2020 12:29AM
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Hi,

anyone tried this new beast ? Is it a real revolution or just a marketing gimmick ? Curious to get real life user feedbacks

Piros
QLD, 6879 posts
16 Sep 2020 7:12AM
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The hype is real , feedback from team riders has been next level . I should have got my hands on one this week , looks like next week now . Check out the video on the insta or Facebook link below. Just let the vision tell the story they look insane . They'll come out in 4 sizes 760 , 980 , 1210 and a 1400 pure downwind wing.
www.instagram.com/p/CFHu30Jh8xw/?igshid=11xd0d0kpa1ee

www.facebook.com/TakumaConcept/videos/765128657554061/


Stingersup
WA, 93 posts
16 Sep 2020 10:20AM
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Will be interested to hear how they go

colas
4986 posts
16 Sep 2020 12:36PM
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From the theory, they help at high angle of attacks, pre- and post- stalling.

Basically, they kind of delay flow separation along the bumps, but triggering it early between them. And for some conditions it is better to have 50% of the foil keeping a well-locked laminar flow by "sacrificing" the other 50% rather than have the whole wing stall. But they add drag in normal conditions (everything is a compromise).

I would guess that their usefulness depends on your style of riding. e.g. if you are pushing your wings near stalling conditions a lot of time by hard turns, tricks, etc... and the way the rest of the foil is designed. I will be very interesting to see the feedback of riders on when they seem the most useful. And I can see it being useful on the other side of the spectrum for beginners, that are often at too slow speed, especially when learning how to pump.

Interesting!

The Wikipedia page is quite complete: en.wikipedia.org/wiki/Tubercle_effect

kobo
NSW, 1064 posts
16 Sep 2020 5:25PM
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Interesting foils, getting hard to evaluate new foils just by watching talented fit riders on them , I recon they could make any number of foils out there in the market look good.
Must admit I bought an Armstrong after watching Sky Rama , thinking if he can do it on an Armstrong then maybe it's possible for me ,and I can't blame the gear.
Having said that , It would be good to have some type of science based assessment for foils , maybe a Hydro water test setup with sensors that could be attached to the foil to measure lift, drag, efficiency, resistance to turn etc,
so you could compare apples with apples.

frenchfoiler
498 posts
16 Sep 2020 4:46PM
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This new wing look sick, the lol foil was already good from all the feedback so I'm gessing this one should be really good.

I should be able to try soon.

hilly
TAS, 7195 posts
16 Sep 2020 8:42PM
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Blame Laird

lairdstandup.com/products/surrator-1

kobo
NSW, 1064 posts
16 Sep 2020 8:47PM
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Haha, could always use as a bread knife if it doesn't surf any good.

colas
4986 posts
16 Sep 2020 9:12PM
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kobo said..
Having said that , It would be good to have some type of science based assessment for foils


The thing is that how to judge the measurements (the "evaluation function") is tricky.

For instance, if something adds 5% drag, but prevents stalling or breaching by 5%, the real life benefit for a foiler may be night and day, because stalling will abruptly end your ride in a potentially dangerous crash, while you may not even notice the 5% added drag. One 5% will ruin your session, and the other won't.

exiled
362 posts
17 Sep 2020 3:17AM
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colas said..

kobo said..
Having said that , It would be good to have some type of science based assessment for foils



The thing is that how to judge the measurements (the "evaluation function") is tricky.

For instance, if something adds 5% drag, but prevents stalling or breaching by 5%, the real life benefit for a foiler may be night and day, because stalling will abruptly end your ride in a potentially dangerous crash, while you may not even notice the 5% added drag. One 5% will ruin your session, and the other won't.


Colas makes an important point here. Go Foil's real initial innovation was rolling out a foil that was user friendly enough for people to learn on. The kite world had plenty of higher performance foils out at that point, but no one could ever hope to paddle into a wave with one. the Takuma LOL gets good reviews basically because its a really easy foil to use with very good (but not the best) performance characteristics. What I really want to see are 'non-expert' reviews for this Kujira, but that means waiting, and I'm getting antsy.

Personally, I think the level of design convergence between these and the Gofoil NLs is a good sign for both of them. But that's just me trying to read tea leaves.

kobo
NSW, 1064 posts
17 Sep 2020 7:29AM
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Yeh that makes sense,, there is probably too many variables and needs to assess foils in a scientific approach.
I think the best chance of getting any idea atm ,is when a private independent person buys and rides 2 or 3 different foils over a reasonable time frame , and then writes a comparison of their experience.
The guy who did the review on the MFC,Armstrong,Axis foils a while back was a good example, he bought all 3 and rode them the same amount on the same days etc and tried to eliminate as many variables as he could, and gave an honest review after a decent period of riding them.

exiled
362 posts
17 Sep 2020 12:31PM
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For sure, All three companies should have sent him a tip, because I bet he sold some foils for all of them.

kobo
NSW, 1064 posts
18 Sep 2020 8:37PM
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colas said..

kobo said..
Having said that , It would be good to have some type of science based assessment for foils



The thing is that how to judge the measurements (the "evaluation function") is tricky.

For instance, if something adds 5% drag, but prevents stalling or breaching by 5%, the real life benefit for a foiler may be night and day, because stalling will abruptly end your ride in a potentially dangerous crash, while you may not even notice the 5% added drag. One 5% will ruin your session, and the other won't.


Hey Colas,
A little off topic but, do you know about the difference between a sanded finish vs a gloss finish in regard to foil performance ?

colas
4986 posts
19 Sep 2020 12:39PM
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kobo said..

A little off topic but, do you know about the difference between a sanded finish vs a gloss finish in regard to foil performance ?


A sanded finish will be faster and keep the laminar flow longer, that's true for all submerged surfaces. But I have not seen specific data other than the classic experiments in basins with boat hulls & torpedoes.

I have stumbled upon this blog that details an empirical sanding method for foils however:
www.riftboards.com/sanding-your-hydrofoil/
- sand the foil with 500 grit
- sand parallel to the leading/trailing edges (to promote small vortices that will act as "ball bearings" between the foil and water)
- except the leading edge, smooth it to 2000

The blog is wrong however on the trailing edge, you should do a Donaldson trailing edge, not the unreliable method he presents, as it is too dependent on the ratio of the actual height of the square edge to the water speed to work.
www.seabreeze.com.au/forums/Stand-Up-Paddle/SUP/The-definitive-solution-to-fins-and-foils-whistling-humming--The--Donaldson-trailing-edge-

kobo
NSW, 1064 posts
19 Sep 2020 4:36PM
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Thanks Colas, I knew you would have the info , Interesting most foils are sanded finish but not all, gofoils are all gloss now.

colas
4986 posts
20 Sep 2020 1:45PM
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kobo said..
Thanks Colas, I knew you would have the info , Interesting most foils are sanded finish but not all, gofoils are all gloss now.


Yes, even Gong new clear finish on foil wings is glossy. I should sand mine, but I am a wary of lowering the resale value...
I guess glossy just looks nicer and sells more, even if it is slower...

martyman
WA, 314 posts
20 Sep 2020 2:05PM
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I dont think we reach fast enough speeds for it to matter to be honest

jondrums
154 posts
21 Sep 2020 11:26AM
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Because of the inspiration in this thread, I filled about 50 scratches and gouges in my GL210 and sanded the wing back to perfect with 600grit. Took it out this morning, and no obvious difference to be honest.

colas
4986 posts
21 Sep 2020 4:14PM
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It is very difficult to feel a speed difference in a "continuum", i.e. having only the speed increased by some percents.

In my experience, drag reducing enhancements (sanding hulls, quobba fins, ...) are felt most noticeably with a "butterfly effect", when a small drag reduction triggers a big change: it can be getting on a plane for a windsurfer, trying to get on the highest line possible on a wave with Quobbas, etc... Plus we cannot feel speeds, only accelerations.

For a foil I would guess you could feel things better in situations where a bit less drag can mean the difference between success and failure. Dockstarts? Pumping?

juandesooka
615 posts
22 Sep 2020 12:21AM
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colas said..


For a foil I would guess you could feel things better in situations where a bit less drag can mean the difference between success and failure. Dockstarts? Pumping?


I am with Martyman, I don't think these differences would be noticable short of elite racing. So many other variables in surfing, it just blends in the mix.

Colas: one of the very subtle testing areas could be light wind wing foiling. It is such a thin line between madly pumping vs getting unstuck and flying. I've found one strand of seagrass can be enough drag to make it impossible. So maybe the 2.56549% improvement would be felt there?

jondrums
154 posts
22 Sep 2020 8:46AM
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Interestingly enough, just today I had the opportunity to speak with a highly respected engineer who previously worked on America's Cup boats. He says that the common belief about sanding to 600grit being fastest is complete rubbish and that a mirror finish will absolutely definitely be faster on a hydrofoil. Mind you, only the first half or so of the mast/tail/wing matters - by the back half the flow has separated. He says that the fuse won't matter at all. So, now I'm going to go up to 2000 grit to see what that does. Sorry this is burried in totally the wrong thread. But we all read all the threads anyway, right?

Hdip
384 posts
22 Sep 2020 9:01AM
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Can you refinish my 900? The right wingtip has a wicked hum right now. I can feel it vibrating at one specific speed. Thankfully that usually only happens on the drop.

frenchfoiler
498 posts
22 Sep 2020 2:07PM
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So back to the original subject, does anyone tried the Kujira yet ?

colas
4986 posts
22 Sep 2020 8:37PM
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juandesooka said..
Colas: one of the very subtle testing areas could be light wind wing foiling. It is such a thin line between madly pumping vs getting unstuck and flying. I've found one strand of seagrass can be enough drag to make it impossible. So maybe the 2.56549% improvement would be felt there?


I guess so!

To jondrums: www.researchgate.net/publication/272030783_Drag_reduction_using_superhydrophobic_sanded_Teflon_surfaces

And "Gogte et al. (2005) investigated drag reduction on a hydrofoil coated with a hydrophobic sandpaper. Their results showed up to
20 % drag reduction."

And also this interesting post on the kitefoiling seabreeze itself, that also puts ventilation prevention into the picture, as superhydrophobic surfaces seem to promote ventilation but pushing away water and "sucking" air in. But I don't know if ventilation is as much as a problem with SUP foil wings.
www.seabreeze.com.au/forums/Kitesurfing/Foiling/Polish-makes-you-go-Faster--?page=1

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In my sailing days, I used to use a hydrophobic compound on my dinghy hull (think Rain-X). It made a difference when trying to get the hull to break free from the grip of the water and on to the plane. I could get planing a couple of knots boat speed lower than my competitors and therefore exploit the advantage. It does work.

For foiling, I think it would work in the opposite way. Generally, due to the high and low pressure surfaces of the mast and wings, you have a different set of problems if using a hydrophobic copound. We sand the mast and wings to create a rough texture to make the water "stick to the surface". This prevents ventilation.

The race guys will have a cow if you even touch their wings or mast due to the fear of sunscreen on the fingers which will create a hydrophobic barrier on the surface which leads to ventilation. The wings come glossy but usually get sanded. Front third of the wing/mast with 1200 wet and dry and 400 for the back 2/3rds. The rougher texture creates a better bond with the water. Water on water friction is less than water of solid polished surface.

Many off shore race yachts have a textured finish on the hull to create that boundary layer of water to promote the water on water friction.

Don't put hydrophobic coatings on your foils!!


In summary: sanding definitely have effects, but with some maybe detrimental.

Shlogger
397 posts
22 Sep 2020 10:38PM
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I do know that after a lot of use in the summer, I can see all my sunscreen touches when I rinse w fresh water after a sesh. I grab the Dawn and 1000 grit to get it wetting again. I did notice a less secure feeling when about 33% of my Foil was wearing sunscreen. ;)
As stated in an older post, when you start to really scratch up your foil, easy fix is a can of spray filler paint for the deep gouges, sand, and then hit with a good spray can paint that says it bonds to plastics. My Naish Wing tips look like new. Basically keeps your wing from eroding to the point of structural damage.

nesterg
6 posts
24 Sep 2020 12:44PM
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Research on models of the humpback whale flippers which the Kujira is modeled after shows that it not only stalls at a much higher angle of attack but when it does stall it is more gentle with less loss of lift. It also has Significantly more lift and less drag. So you can Ride a smaller foil which will have the same lift as a larger foil but have less drag and less weight.
Now to some actual (second hand) observation. I was downwind foiling in the Gorge on a Takuma 1300 foil and was riding with a mate who got to demo the new Kujira 980. It was not a big day, and I felt like I should have had my 1600 foil but was amazed that my mate got up on that small foil in small downwind conditions (he is 175 lbs. what's that maybe 78kg) The second run he really started to smile as he got comfortable with it. He said it was fast and turny. I personally am interested in the 1220 size.

Hdip
384 posts
6 Oct 2020 2:07PM
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What's the wingspan on the Kujira 980? Similar in width to your 1300? Or is it much wider?

frenchfoiler
498 posts
6 Oct 2020 10:10PM
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Hdip said..
What's the wingspan on the Kujira 980? Similar in width to your 1300? Or is it much wider?


From the designer : "wingspan 800 mm ratio 5.1"

Piros
QLD, 6879 posts
7 Oct 2020 10:13AM
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My mate has one and we both ride the 1300 , the difference is insane , his pump speed is just so high and it's just so fast . He pumps around effortlessly doing circles around the pack , pretty amazing to watch. Couple of guys have been using the 980 on the wing ding , no one can get close to them for speed. My mate can also dock start it he's 85kg and just ordered the 780 . These things work amazingly well the only con compared to the 1300 is the 1300 does have a slightly lower stall speed but given it's got so much more wing area you'd expect that. The new tail wing that comes with the 980 bis insane one of the best tails I've seen .

exiled
362 posts
7 Oct 2020 8:48AM
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Is 98 kg gonna be too heavy for the 980? I'm on the 1600 LOL right now, but unless i use the biggest shim it feels like too much lift most of the time.

Hdip
384 posts
7 Oct 2020 9:20AM
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All I've heard is the 980 is similar to the 1300. So all 3 sizes will be comparable to the 3 LoL sizes I assume.



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Forums > Stand Up Paddle Foiling


"Takuma Kujira" started by Filow