Speed fins - How small to go and when are Asymmetrical faster?

Lots of variables in going fast and faster. With that in mind a 21 speed will be the smallest that I would fit to a 49 wide board and it would be quicker than the Venom. Have a look at the Atomic fins as well, same designer as the Ka sails. Getting some good results with those too. I hope this helps

To go faster, assuming flatish water and best deep downwind angle (around 130 Deg off the wind):

- More wind optimum is mid to high 30's, but at Lake George it's probably 5 knots lower for the same speeds as it is super flat and you can chose your angle very easily.
- A narrower board for your weight (CA40, Mistral 41cm, Starboard 44cm etc). I switch to CA40 and 5.2m at high 20's.
- Assy fin does help as you can confortably sail a smaller fin which = less drag. The Tribal assy 18cm is at least equal lift to a symmetrical 20-21cm. and still gets upwind pretty well. I use the 16.5cm Tribal assy quite a lot.
- Go a smaller sail when powered up. I am close to your weight (72-74KG) and have my fastest speeds on 4.4/4.7m, 5.0/5.2m. A smaller sail set deeper is lighter on the board allowing to to 'fly' higher and still has the same power as a larger, heavier sail set flat for control. Larger sail also has more drag. There is only a certain amount of power you can balance with your weight. Sure, you can downhaul and flatten your sail out to maintain control, but then you have too much drag and weight on your board. The one type of conditions where smaller board, sail and fin is not so cut and dried is when the wind is up and down a lot and you need to be able to sail through the lulls, but in my experience, not many good speed spots really require that.
- The newer KA Speed sails are deeper and more powerful for their size than the Koncepts of a few years ago. For your size, use them on an RDM mast.

I owned the W49, a very good & easy speed board, I used a c3 slingshot 21 with it.
As per above advice, you may get a smaller sail (4.6 eg), rdm mast are "compulsory".
Assy fins are very safe on the run (anyway more than syms!), you can (almost) forget the spin out.
I now have a Mistral ab+ 47 and a speed 41, I use mxr UFO HA assy on std tack 20 / 22 / 24 for loft speed blade 4.6 (20) / 5.1 (20) / 5.6 (22) / 6.3 on the 47 only with 24.
On port tack I have 2 select hot rod assy 21 & 23 (I'm 1.78 m / 80 kg, during strong sessions i wear a Side on weight jacket with 3 or 4 kg lead)

The C3 Venom's are designed for control in difficult conditions. In flat water they are far from fast. I sailed with Venoms in the past. Used a 26 under my JP 49 but switched to a 21 and 23 Slingshot. Speeds went up with 3 to 4 km's. The biggest disadvantage Venom's have is that they have trouble getting the board up to speed in flat half wind conditions. They aren't made to let the board stay flat and ride on the fin. When entering a gust and bearing away into your run you can feel the Venom's slowly lifting the board and accelerating. They normally took a 2 step bear away to get the board properly up to speed.

The slingshot keeps the board flatter and easier riding on the fin. The moment the gust hit you can feel the board speed up instead of lifting first. This way the speed is significantly higher when you enter your run. Biggest disadvantage of a Slingshot is that it can't hold a lot of pressure while making the turn entering your run. You need to be sensible with your back foot pressure.

Also sailed the mXr's Ufo wide's both normal and asy's. Didn't like those in low to mid conditions they had a nasty habbit of spinning out completly un-expected. Fully powered up they worked pretty decent but like the Slingshots you very foot pressure sensitive. Like Sailquik said the mXr asy's don't like sailing the wrong side. Same with the C3 Strike, asy Venom, those also didn't like the wrong side. Both mXr and C3 couldn't handle pressure. You could hear the fins gurgling and feel the board crabbing through the water.

Sailed the Slingshots for 3 or 4 seasons under my JP 45 and 49. Had a 20, 21, 23 and a proto 23 with a thicker profile. Made the switch to Z-fins and never looked back. Have got Z asy, asy wide and regular wide. All very easy to sail. Give plenty of lift without losing control. Plus they can handle the back foot pressure unlike the C3's and mXr's. The asy speed is perfect for sailing behind a bank or fixed course. It's amazing to feel the board accelerate when a gust hits. The asy wide and regular wide are my go to fins for flat open water spots where you can make runs where you want. Very controlable fins also when it get's a bit choppy. Size wise check the chart on the Z website it's spot on. The Z asy's are much easier sailing back and do pretty well sailing upwind. Hardly no tendency to spinout and when they do spinout you can feel it happening and can easily pull the board out.

Haven't sailed the Tribal sym or asy speed yet. But do know a lot of guys who do and all seem to enjoy those fins a lot. I don't know how they hold up against Z's. But I do know from guys who used Select Hotrod's/Caspers and Tecto Nomad/ Hornets the Tribals are a big step up. I think it would be the same compared to the Venom's you're using. Allthough a good and very easy to sail fin the Venom has it's flaws for speedsurfing specialy in flat conditions. Size wise I see a lot of guys using the 22 Tribal Sym and 20 asy speed under 48-50 wide boards.

Definitely 19.5cm

If you ever get the CA40, get the 18cm

Great topic and comments so thought I'd add a few as I've been sailing my Starboard 2009 W49 on and off for the last 10 years with C3 and more recently Tribal fins.

My top five 2-second speeds have all been on the W49. Top speed was 45.75 knots with a C3 22cm Asymmetric Strike, next best was 45.34 knots with a C3 slingshot 23cm fin. Also managed a 44.21 knot run with a 28cm Venom. So, a variety of fins used that all worked well with that board. The Slingshots have been my go-to fins for that board though.

For larger slalom boards, I've mainly just used C3 Venoms, with a 34cm Venom in my 86L iSonic being my most used combination, often getting over 40 knots (top speed 41.85) and always feeling fully locked in and in control.

Over the last few years, I've been using Tribal MK1's (28-38cm) and they feel great and fast but do spin out unexpectedly at times. So, I probably agree with some of the comments above that the Venoms aren't necessarily super-fast, but are super controllable, allowing you to go fast!

I've just started using a 25cm Tribal Sym Speed in my iSonic 55 (76L) and that feels good. Haven't really had much of a chance to test it out but think that combination will work well. I've still got two of the C3 Asymmetric Strikes, so will need to start using them again (20 and 22cm) when the conditions are right (in the Luderitz 44)!

As far as sails go, all the above has been using either a 5.6 or 6.2m.

I think the key to going fast most of the time is just looking for gusts and then bearing off more and that's when being in control gives a lot of confidence.

That 19.5 Tribal Asy should also help!!

Yes Sam gave me the other one, said it was too assy to use here, thought I may be able to use it somehow, but so far it's just been sitting in my shed. Could be good at the spit when it's a bit square. To me looks like if it's an ideal wind direction, you'd almost have a negative angle of attack