Gday Boys and Girls.
Ive got a 101 and a 76 isonic. I after some advice on what fins work best on these boards?
Id use a 7.6 and 6.6 on the 101 and 6.6 and 5.5 on the 86. Im a 100 plus kg and love to push on the fin. So something stiff and fast.
What do u guys reckon?
Cheers
first of all is it a 76 or 86
if 76 then i have one although i'm light i used to use it with mainly a 30 or 32 pointer
it can handle a 34 and my favourite combo was 5.0m and a 24cm weedy in the 76
as for the 101 i'm not really sure
hey big boy !! 
by the way loooved the images from the lake 
fins are a funny thing u have to keep trying to get that combo right, not just for the board and sail but for the conditions. you may get some info from here but were all individuals and have totally different styles in riding n rigging size ect
look at the fins you have and evaluate what are they doing and what they aren't. the crap ones that dont do nothing for you, chop em rake them stiffen them up or fatten them up to give u an idea of what you want from them
fins make a MASSIVE difference to ride quality confidence can turn a pig of a board to an absolute legend!
for my money i would go C3, Delta are doing some good fins too, always by them bigger then u can chop them down :-)
Sam hase some nice C3 in at the mo cheep too
oh and sailing them at the lake in crap conditions will make everything feel **** you need to go test fins at a good spot with consistent wind and conditions that suit what your going for .. this is the most frustrating part of it as we live in the windless state of NSW. 
have fun come round I'm playing with fins at the mo ;-) if I can help I will
G'day Maui,
I've got an Isonic 86slim and a 101 as well (i'm 80kgs). I have C3 venoms in 30cm & 34cm for my 86 which i use with my 5.9 & 6.6 and love them, i've just aquired a 26cm which i use with my 5.0 on my 86 in real high winds (I know its not a perfect match but i dont have $$$ for a speed board yet). In my 101 i use a MFC RC40 (40cm), its ok but i'd prefer another C3, its good enough though as i use this in light winds (up to 15kts) with with my 7.4 and in the conditions i use this combo its about hr's and distance rather than speed.
Like Leo says though, try as many as you can as its a pretty personal choice.
Have a look at the C3's. If you go this way, look at getting the StingII. I have found them alot better for slalom/speed (compared to the Venom). The Venoms are great also. They are quite flexy and work very very well in chop where top speed is'nt a issue (i have pushed a 38knot run with a venom 32) And a 41knot run with the StingII 32cm. The StingII is quite stiff and i perfer them over the venom.
I run 30-34stingII in my 81L JP slalom with a 7m and works great. My dad has the 92L JP slalom and runs stingII 32-36cm.
For the 101 maybe go a 36-38cm.
For the 86 maybe go a 34cmhttp://www.c3-fins.com/C3_windsurfer_fins/C3_windsurfing_fin_home.html
cant believe Isak gets the thumbs down sure he's sponsored by them give the kid some credit . fins I've chopped into a few and there the best built fins Ive cut through ;-) "sorry bugy" bar none... solid all the way trough and some of the best fins I've sailed
sure there Xy but if youve ever tried making fins you realise very quickly its not a cheep game.
C3 there the go for sure 
most isonics here run on either C3 or Gasoil (seems to be the fastest but also the dearest)
Thanks leo. Im not sure why either. Considering C3 is linked with starboard as well. Thought my comment was valid to his question
I only have mentioned C3 as thats all i use. Other people are quite welcome to mention other fins.
I use Select on my boards but only cause I can't (or won't) spend so much cash on a fin....
I only have mentioned C3 as thats all i use. Other people are quite welcome to mention other fins.
In all honestly i thought i could get away with smaller fins. Im now glad i asked.
Leo, how about a sponsership? You give me a quiver of your free awesome fins and ill just get some rippin good speeds! maybe. Works for me bro I'll have to come around soon and get you to route my weedys out so i can wack some carbon in there. Need to stiffin those puppies up.
Thanks for all your advise boys. I might have to hit up sam at wsns for some demos of the C3s.
Okay my 2 cents.
With the 101 I've used between a 40cm down to a 33cm fin. 40cm Talon works really well with my 7.8 Blade although I can get by with a 37 KA Slalom which I used most of the time with the 7.0 & 6.3 Blade. Lately I purchased a 35cm Select S07 and have found this to also be an excellent choice with the 7.0 and under. It never lets go and I'm always surprised when I read that the selects are sh1t fins as I've never had any problems performance wise with them (they have been known just to fall out of their housing though).
The 33 Select S09 did work but being on the heavier side* it was prone to letting go when pushing hard so I'd stick with something around 34 - 38 cm in length (you could get away with significantly shorter such as a lower aspect fin if sailing flatter water though)
My iS76 I've used a 31 Tectonic Goldwing, 30 KA Slalom, 31 Select Caspar, and a few other experimental fins. My go to was the KA Slalom but lately I've found the Caspar very solid too. Horses for courses though.
*I'm around 93kgs and sail open ocean.
Just remembered but I used to use a 40 C3 Venom with the iS101 successfully but hated my 46Venom in the iS122. Ended up getting rid of the Venoms although I would like to test run a Sting as I think these would suit my sailing style and conditions better than the Venoms. C3's are well made too.
Hi Mauiboy,
I was using Select 33cm sl7 with 7.0 and 6.3 and 29cm Select s07 with 6.3 on my isonic 86- worked very well until one day as someone else mentioned the 33cm fin fell out the tuttle base
. I weigh 86 kgs. Since i have purchase a Black Project R325 and it is a great replacement for Select and made of one piece G10 so shouldn't fall out this time
. Seems to be very fast across the wind and downwind a great power out of gybes. Like the other guys mentioned try as many fins as you can as it seems everyone seems to like different fins. With 6.0m around 30cm is the go and 7.0m around 33cm.
Hope this helps - Good luck.
Cheers.
Thanks sausage.
I normally use a 40cm Venom in my futura111 but like it most when well powered. Feels really nice in powered conditions. I just upgraded to an Isonic and am undecided if I should go a larger Venom or maybe a Sting. I probably would have gone for a 42cm Venom so it's interesting that you say 44cm. Will be using it with a 7.8m. Cheers for the links, will read when I have a bit more time.
My (80Kg, open sea windsurfer) two (unsponsered) cents:
I used the 101 with Sonntag fins SL-P 38cm and was pretty happy in the low/mid (mostly 7.5) wind. The fin produces lift and is easy to control. In higher winds I changed to a Talon 38/36 with the 6.5/6.0 sails (GTX Race/Vapor mix).
Considering your weight, I would consider using a powerful carbon fin to get the board flying.
I've never used the 76 but the 86 with Talon's in 30, 32 & 34 cm. Dail range is 4 wave sales up to the 6.5. Sorry I can't comment on the 76.
Our pros are now testing the new Vector Volt vs the Talon and it seems like the Volt provides more grip and lift while staying controlable. BvS used the Volt as well, which is also available in Carbon, that said, I would like to compare that fin against my Hurricane which I use now. The reason why I not recommend Hurricane fins to you is that the delivery take rather long, but I'm now using a set SS, SS2, SR5 from 37 to 47cm and couldn't find any better fin in the market. However, I'll try to get a ride on the Volt carbon next time I have a chance.
Here is is pic from the Volt carbon
