Looks interesting:

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www.mauiultrafins.com/MUF7_english/News/Entries/2011/4/21_DELTA_the_shape_to_comeMaui_Ultra_Fins_next_generation_fin_under_test_on_Maui.html

Had the same idea and made this one at the end of last year. I haven't had the chance to use it yet though. It should be good on flat water but would be a bit too small on chop. They are also probably the ugliest looking fins yet

Built a couple about 8-10 years ago. Mine had spans about 15cm with leading edge rasor sharp and varying between 50-65 degrees. They had some advantages. They were great in weed and I could sail literally right up to the shore. I think I went down to 5% thick. I used a biconvex profile a la Starfighter.They were quite good going deep where the short span was not a problem but coming back was not so much fun. Even on a 50cm wide board it was impossible to stop the windward rail digging in when you put your front foot in the strap. Not enough leverage on the shallow fin to keep the board flat.
The leading edge vortices did allow for an interesting experience starting. You could start off with the board crabbing controllably at a 35 degree angle and as you picked up speed the angle would decrease until you were sailing normally. Spinning out at speed was less fun. While the LE vortices allowed the fin to maintained lift the leeward rail was still going sideways and the short fin would pop out (without the board in front of the fin base to flatten the chop).
Overall, they didn't seem any faster than a good "normal" speed fin and were a pain getting back upwind.

Maybe "mauiultrafins" needs to invest in CFD's, will save them lots of $$$ in research!

C3 Slingshot is the measure for wide chord fins.

Nah, the C3 X fins were better. Have both and much prefer the X2 over the Slingshot , pity Boogies not making them still.

I'm doing some research on rudder for boats at the moment.

having a wider fin does have the same affect as making it longer.

but it does reduce the leverage wide boards need and also it reduces the lift in comparison to a higher aspect ratio of the same area.

So if you want a freestyle fin get a short wide one and if you want a slalom fin get a long narrow one.

Which is pretty much what they do anyway. So i don't really see them being able to market this at anyone aside from freestylers.

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wespyyl said...

I'm doing some research on rudder for boats at the moment.

having a wider fin does have the same affect as making it longer.

but it does reduce the leverage wide boards need and also it reduces the lift in comparison to a higher aspect ratio of the same area.

So if you want a freestyle fin get a short wide one and if you want a slalom fin get a long narrow one.

Which is pretty much what they do anyway. So i don't really see them being able to market this at anyone aside from freestylers.

When sailing deep off the wind, you dont need much lift from your fin as the sail isn't generating as lift (due to the lower true-wind). So arguably, a shorter find could reduce your planform drag; likewise a thinner profile will reduce the planform drag.

Will it be enough of a reduction though? And what are you trading it for? ... So it might be suitable to target speedsailing.

Maybe this wide base design is because of the strength limitations of the material? First the wide base will give you also a physical thicker base. With a cord of 140 mm (that is wide base) and a 5% profile you will end up with 7 mm thickness. With a more conventional fin the base would be around 95 mm. Taking the same 5% profile will now result in a physical thickness of only 4.75 mm.
And second the center of effort is closer to the base, so the bending moment is reduced when the lift remains unaffected. So the wide base fin will have much lower internal stresses, making it able to use thinner profiles where conventional fins will break.

I have to be honest. I have never touched a slingshot, or other wide base fin. So i don't know if the profiles are really thinner compared to conventional fins. Maybe someone can measure the thickness at the base of a wide base fin? What i wrote above is just theoretical physics...

I have been working on some CFD in a 3D environment to do some more research into the effect of the outline and profiles on the fin performance and taking into account the true bending and twisting of the fin under load. Unfortunately I also have to work and study, so there is at the moment no progress on this project.

Hi Michiel,
that MUFin won't have any trouble with stiffness.
The base is 260mm wide !!! (Scale it off the box slot which is 155mm and length 16cm)
So, even if it is a 5% chord, it will be still be 13mm thick and if it's 6% it will be 15.6mm and just about fill the box.

I'm not afraid that the wide base fins are not stiff enough. I was thinking just the other way around; the wide base gives us the ability to use very thin profiles without overloading the material at the fin base.

Boogie,

You are refering to the DELTA WAVE FIN, and this topic is about the DELTA WING SERIES. According to the website of MUFins this is a new concept for wave, freestyle, slalom and speed.

Ran the fins thru some computer foil software. For the same lift at 41kn and normal AoA for speed I got about 50% more drag for the MUF Delta due to the low aspect ratio and increased surface area needed to generate the same lift as a "normal" speed fin.

And I bet a wide based fin would work incredibly well on a wave board as turnability is not as much a result of shape but of length. The way I see it wave fins are swept back to get as much surface in a short length. It's not the shape with lots of sweep that makes the fin turn well, it's the actual length of the fin. You would be able to go very short with a wide base fin and have better upwind performance and speed from it as it would have less twist.

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yoyo said...

Ran the fins thru some computer foil software. For the same lift at 41kn and normal AoA for speed I got about 50% more drag for the MUF Delta due to the low aspect ratio and increased surface area needed to generate the same lift as a "normal" speed fin.

and it has got some area.....26 x 16cm delta is around 210cm 2.
Venom 24cm and Vector EX 26 are about this area.