Testing new iSonics and new Sonntag Fins

The new Sonntag Fins will be tested soon in Tarifa! And I look forward to do it, this will be to understand how the fins work with the (new) iSonics.

The following will be tested: the all new Sonntag SL-R series, the revised SL-P and the revised 2 SL-S, sizes from +-30 ~ 50cm. These will be compared with the older Sonntag Fins models to make it possible to translate experience of the past into an advantage for the future. Can't wait for some windsurfing :)


Erik Loots

Erik is windsurfer for 10+ years. In his daily life he is professional in construction dewatering, advisor, troubleshooter. Erik likes adventures, explore and to challenge himself. During his life he is trying to get the best out of it and have respect for the earth, nature and future generations. The modern world is about sharing, in this blog Erik shares his experiences, selfreflection and lessons learned.


  1. Hi, I am about to buy some Sontag fins to use with my Isonic - any feedback would be really useful

    1. Sonntag fins always best choice!

  2. I notice that you are testing the SL-P and SL-S. In emails with Joerg, he is recommending the new SL-R

    Also what would you consider to be the best sizes for an Is110 for use with 8.6, 7.8 and 7.0 (I am using North WARP's)

    I sail speed and slalom - focusing more on Slalom in 2014

  3. Hi Matthew,

    I tested the new 2014 iSonics with SL-R and SL-S, mainly the iSOnic 107. It was interesting too see the new iSonics need a bit longer fins compared to the older ones.

  4. How did you get on with the SL-R in the Is107? I am about to order a 40cm and a 43cm, however, can't make up my mind between the SL-R and SL-P

  5. Matthew,

    Depends on the conditions you are sailing and personal sailing style. SL-R is somewhat more downwind focussed and SL-P is more overall design. Both designs are pretty balanced, so you can't actually go really wrong (unless your fin is to big/small). Just ask Joerg, I think he has even more usefull feedback from Australia, I know Sonntag Fins+ Isonics are tested there right now.


  6. Erik
    After lots of email with Joerg, I decided to go with a 43cm and 40cm SL-P, I know that the SL-R is probably a little faster (although Peter Volwater did just manage over 44kts on an SL-P 34cm, so can't be too slow). Ultimately, I think that the all round performance of the SL-P is probably better, even if I sacrifice a little right at the top end.

  7. Shane O'NeillMay 10, 2014

    I've been using both SL-R and SL-P fins in my Isonics. For the 2014 Isonic I'm very happy with 38cm SL-R with a 7.0 and 7.8 although often 40cm with the 7.8 is good. Once you're powered with good trim the SL-Rs fly upwind. I think it depends on the water state too. If the water was flatter where I sail I would use predominantly SL-Ps. Both designs are exceptional so as Erik said you really can't go wrong with either.

  8. Shane O'NeillMay 10, 2014

    Sorry- that's referring to the 2014 Isonic 107 for the 38-40cm fins above. Forgot to put the "107" in..!

  9. AnonymousJune 20, 2014

    Hi Eric,
    my name is Valentino, I am an Italian windsurfer and I would like to ask you advice about the Sonntag fins.
    I already own a few (large) SL-P and I reserved a production "slot" for a few new ones in 34 to 42 cm (3 sizes to be decided) to be built at the beginning of July. But I am undecided if SL-P or SL-R.
    Now I am riding the new Mistral boards (Lockwood) 112 and 137. I hope you had a chance to test them or know something about. Those boards seem to require a flat trim. I mostly ride in places with heavy chop caused by lots of kiteboard wakes and it's hard to get really good speed. Outside of the bay I can find smoother water with wind swell. Even a speed pro like Andrea Baldini has an hard time to do better than 35 knots there; I am able to top at 32 - 33.
    Can you please advice about the differences between the SL-P and SL-R in your personal experience? I suspect that the newer design can be faster, but I don't know if that is true for all sizes and all conditions, or just in some cases (from what Joerg suggests it seems that SL-R's are definitely better in larger sizes)? What about power/lift, does one have to pick an SL-R in the same size as an SL-P? Is the top speed difference (if any) balanced by a better average speed?
    Thank you very much for your help and best regards,