Forums > Stand Up Paddle Foiling

Takuma Kujira

Reply
Created by Filow Wednesday, 16 Sep 2020
Filow
202 posts
Wednesday , 16 Sep 2020 12:29AM
Thumbs Up

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, 5983 posts
Wednesday , 16 Sep 2020 7:12AM
Thumbs Up

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, 41 posts
Wednesday , 16 Sep 2020 10:20AM
Thumbs Up

Will be interested to hear how they go

colas
3959 posts
Wednesday , 16 Sep 2020 12:36PM
Thumbs Up

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, 366 posts
Wednesday , 16 Sep 2020 5:25PM
Thumbs Up

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
168 posts
Wednesday , 16 Sep 2020 4:46PM
Thumbs Up

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
WA, 5579 posts
Wednesday , 16 Sep 2020 6:42PM
Thumbs Up

Blame Laird

lairdstandup.com/products/surrator-1

kobo
NSW, 366 posts
Wednesday , 16 Sep 2020 8:47PM
Thumbs Up

Select to expand quote


Haha, could always use as a bread knife if it doesn't surf any good.

colas
3959 posts
Wednesday , 16 Sep 2020 9:12PM
Thumbs Up

Select to expand quote
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
308 posts
Thursday , 17 Sep 2020 3:17AM
Thumbs Up

Select to expand quote
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, 366 posts
Thursday , 17 Sep 2020 7:29AM
Thumbs Up

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
308 posts
Thursday , 17 Sep 2020 12:31PM
Thumbs Up

For sure, All three companies should have sent him a tip, because I bet he sold some foils for all of them.

kobo
NSW, 366 posts
Friday , 18 Sep 2020 8:37PM
Thumbs Up

Select to expand quote
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
3959 posts
Saturday , 19 Sep 2020 12:39PM
Thumbs Up

Select to expand quote
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, 366 posts
Saturday , 19 Sep 2020 4:36PM
Thumbs Up

Thanks Colas, I knew you would have the info , Interesting most foils are sanded finish but not all, gofoils are all gloss now.

colas
3959 posts
Sunday , 20 Sep 2020 1:45PM
Thumbs Up

Select to expand quote
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, 7 posts
Sunday , 20 Sep 2020 2:05PM
Thumbs Up

I dont think we reach fast enough speeds for it to matter to be honest

jondrums
28 posts
Monday , 21 Sep 2020 11:26AM
Thumbs Up

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
3959 posts
Monday , 21 Sep 2020 4:14PM
Thumbs Up

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
374 posts
Tuesday , 22 Sep 2020 12:21AM
Thumbs Up

Select to expand quote
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
28 posts
Yesterday , 22 Sep 2020 8:46AM
Thumbs Up

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
90 posts
Yesterday , 22 Sep 2020 9:01AM
Thumbs Up

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
168 posts
Yesterday , 22 Sep 2020 2:07PM
Thumbs Up

So back to the original subject, does anyone tried the Kujira yet ?

colas
3959 posts
Yesterday , 22 Sep 2020 8:37PM
Thumbs Up

Select to expand quote
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

Select to expand quote
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
109 posts
6 hours ago , 22 Sep 2020 10:38PM
Thumbs Up

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.



Subscribe
Reply

Forums > Stand Up Paddle Foiling


"Takuma Kujira" started by Filow