Can you help me with some prints or rought dimensions:

Friend will try to make me weed speed fin. So, I need it for my lake, to bi around
25-27cm to cover range like slalom fin around 33
need to dive in the water as small as possible
Some prints or suggestions are welcome
thanx
Thinking about some vector delta weed prototype or similar fin

as i know he can do g10, and carbon, don't know for method, but i think that he have some hand skills.
I am interest to have similar fin like vector delta weed speed 27
I don't know for angle degree and what you sugests
Lake is very tricky, grass, maybe few tree parts under water, never know what you can pickup :)

He made lots of fins, and he have excellent finish
He use autocad for measure design
On pictures my custom delta looks mean
wood inside, and orange glass/carbon outside...
Only need to find good angle and size
to cover like my slalom cca 33cm, even 31

No
I can't find that post and pictures of fin

Looking at weed fins in general the leading edge angle is about 45 degree. So i suggest you stick to that.

If your friend can handle 3D files with his autocad version I can make a 3d model for you. A simple outline and constant profile over the fins span would not take a long time for me to make the 3D model.

About the profile. I don't think you should use the eppler foil, a simple naca 0009 looks better and the SD 8020 looks even better than the naca. See: http://www.worldofkrauss.com/foils/show_compare?sform_contains=&items_per_page=-1&commit=Compare&id[]=616&id[]=1132&id[]=1744

But for a wide base speed fin maybe you should go for a relative thickness of 6%-8%. With a base width of 145 mm (approximately equal to the vector weed speed) this would results in a physical thickness of 8.7 - 11.6 mm. For comparison: the physical thickness of a SL7 31 cm at the base is approximately 9 mm. But the sl7 has a base width of only 95 mm.

testing the new one tomorrow 25kn hopefully crack 40..

wkc read the post have a think, do what seems right to you, and do it thats what i did and its worked out real good... gone from hating weedy's to quite honestly its the best fin i have in my quiver are the one I have Made...

and i cant stop !! itching week in week out !!

decrepit said...

Depends what you want the fin for, they look OK for an all round fin, but the entry looks a bit too full for a speed fin.

It doesn't seems like there is a big difference at the leading edge region. The naca and eppler are almost the same. The SD 8020 is a 10% foil, and there for clearly different. But when you scale this foil down to 9% i guess the difference becomes very small. The front part of the SD 8020 would roughly be the same as the other two, but the thickness near the trailing edge will be somewhere between the naca and the eppler.

And just to be curious, why do you think it is better to have a sharper entrance for speed fins?

so
thickness 6-8%
rake 45 degrees

and what size you recomend me for 6,8 sail and 100 litres board ???

21 or 23 ???

ok, thanx again
so thick 8,5
45 deg
23 cm

decrepit said...

23 as long as it's also wide, (full length of box), if you have a more conventional profile, keep the same area by going longer.

full ?
not like this one www.vectorfins.com/fins/

if I get it right on english
width of the fin must be like width of the box
there is no problem that fin is mooved from box saddle, right ?

so, you suggest that fin is positioned like tuttle box, not set to front
here is a rough print what is the plan

Personally I like the bottom 1, but I think Lelos would like the upper 1.
It would be interesting if you made both, and see which you end up using the most.

The only thing I don't like is the sharp point at the tip, that looks deadly.

like this


????

ok, thanx, if I get right my english
all like on picture only upper right point little rounded, not like knife
right?

Yes, you are probably right. The difference in RE between the data available and the real life situation is too big to make an honest comparison. I should have thought about this earlier... Do you know if there is any data available for high RE?

I'm also doing some CFD on fins. But I look at a 3D case so my results cannot be compared to the available data of 2D analysis. I'm still in the preparation phase, so I did not yet compared different foil sections in my simulation set up.