tried to ressurect an old thread.....but too old..wouldn't allow 
anyway... 19cm speed demon on a 57cm wide board, with 6.2m . good ? or not big enough...or too big ? also will sail with (once I get it) a 5.4m.
and if I throw my 7.0m. would a 21cm be good ?
thanx
Hey I was using a 19cm Speed Demon on my Patrik 87 at LG with sails of 5m and 5.6 it was pretty perfect and it was dam windy at times, I tried a 17 and seemed a bit small. The Patrik is 57 wide and 35 at one foot off the tail. I used the same board with a 6.2 with a 21 Speed Demon and it smoked upwind so I'm pretty sure the 19 would have also been fine. Guessing the 21 would be OK for a 7m. BTW I loved these fins they performed very well for me.
so today I got to test/try the 19cm fin on my 57cm wide slalom board with 6.2. it was fine..It just wasn't a good test day....or WS day. wind was gusty something like 8mph to 30mph. but when the gusts hit....fin seemed really nice. these could be my goto fins.
I didn't have any foam pad b/w the offset and board. I was able to get the gap pretty tight...but did have a slight gap. I noticed cavitation which was from the slight gap. (which is the equivalent of having blade of grass wrapped around your fin)....even still it performed well.. I already fixed the problem. so now just need another 'good' windy day. and forecast looks crappy 
.
I think 19cm would be too small on 7.0. I could get it to work...but I would need quite a bit of speed to be able to push off of it..
21cm I think would work now that I sailed the 19cm...but I have a nice weed demon for that.
a question for the peanut gallery. how much do you move the mast base in the mast track from a regular fin to weed fin generally (if at all) ?
I've been using the 19 on 55w and 63w boards with 6.2m sail, the 17 on 55w with 5.5m and smaller gear. The 21 on 63w with 7.0m. A strip of foam pad on the offset helps get the gap to board closed, prevents weed catching. And setting mast base back 1cm than usual when using those fins.
Great fins and yes, I reckon the 19 would go well with a 57 wide board and a 6.2, and would still probably be fine with a 7.0m if that sail felt OK on that size board.
I got to use nearly all of my Tectonic Speed Demon fins at Lake George this year (all except the 14cm) and tried quite a few combinations of board and sail sizes. I ended up with the following guide (I'm 95kg), which includes (for comparison) when I'd be using Tribal MK1's or Tribal Weedspeeds on that same kit. Ends up being pretty much the same as what Dezza has suggested above!
with these types of fins...I guess you have to be fully powered up to really get the performance compared to a more traditional fin ? The other day I went out on my 19cm 55W board (I think it is somewhere around 80L) and 6.2m. I was powered up but not fully powered. And my board was going sideways a bit on a beam reach. bearing off the wind wasn't much better. I am thinking you have to be fully lit to get these fins to work? or is it too small? I see some using the same setup with success.
Or is something out of whack with my setup do you think ? ie mast track position ?
one more question...anyone know the surface area of these fins ? sent an email to tectronics to get some info.
I suspect those fins are too small for the boards and sails you mention.
I used the 21cm with IS80 (60cm wide) and 5.7m sail and it was fine, very solid.
I used the 17cm with Mistral 47cm wide speed board and same sail and it worked quite well.
I would suggest you need at least the 23cm for a 7m sail and board that carries it.
All boards and rig combos are different, but this is just what worked for me. Hope this helps. 
Select to expand quoteskyking1231 said..
with these types of fins...I guess you have to be fully powered up to really get the performance compared to a more traditional fin ? The other day I went out on my 19cm 55W board (I think it is somewhere around 80L) and 6.2m. I was powered up but not fully powered. And my board was going sideways a bit on a beam reach. bearing off the wind wasn't much better. I am thinking you have to be fully lit to get these fins to work? or is it too small? I see some using the same setup with success.
Or is something out of whack with my setup do you think ? ie mast track position ?
one more question...anyone know the surface area of these fins ? sent an email to tectronics to get some info.
What's your weight? How big is the chop?
The 19 cm is the go-to fin for my wife on a 54 cm wide Isonic with a 6.3 or 5.6 m sail. I've used the same combo a few times, and it works for me at speed and on flat water (0 to 10 cm chop) when fully powered. More chop, and I'd pick the 21.
I also have the 23 for larger boards (89 and 99), but had more spinout problems than expected with it. The 23 does not have the "nose extension" that the smaller sizes have. I ended up adding a Fangyfin-style fillet to it, and with that, it works well on reasonably flat water. I'm around 200 lb/90 kg.
on a good day I am 80kg. it was not ideal water conditions. chop maybe 1 1/2 foot to 2 foot..sailing diagonal to the chop. usual we sail a bit through the chop to get to the shallow/flat section. but I turned around before getting to the shallow section. wasn't expecting high speeds in chop...just wanted board to track straight. I am thinking of the 23cm. to use with my 6.2 and 7.0. and if I end up getting a 5.4 then the 19 I think should work.
I mainly use the weed demons (which are awesome fins), just trying the speed demons out b/c there is one spot that we sail where the depth is 1 - 1 1/2ft .
You'll notice quite a difference between Weed and Speed Demons in 2 foot chop. The extra length of the Weed Demons really helps in chop. I'd rather use a 31 cm Weed Demon than a 23 cm Speed Demon if the chop is a foot or higher (and the water deeper than 1 ft).
I'm 91 kilos.
I use Speed Demons in shallow water and Weed Demons in deeper water.
I have my mast base in the same position on the mast track on every board.
With the speed demons.is flat water vs a choppier water really make that much a difference in regards to fin performance. If so why is that ? Curious . Should I move my mast back a bit than with a weed demon.
Select to expand quoteskyking1231 said..
With the speed demons.is flat water vs a choppier water really make that much a difference in regards to fin performance. If so why is that ? Curious . Should I move my mast back a bit than with a weed demon.
Chop makes a huge difference in the performance of the fin, due to the relatively shallow depth of the fin. The fin is most efficient in shallow, dense weed and flat water. It can perform in small chop, i.e 100 to 200mm, but is much less efficient.
With most weed fins I find I have to move the mast base back to compensate for the more rearward centre of effort/lift of the raked back fins. This allows the sail to stand up at the right angle and not drag in the water or on the deck at speed.
That said, the Speed demons have a lot of forward offset/overhang and that does partly compensate for that by keeping the centre of effort/lift closer to a normal fin.
These short 'Delta' type fins are as a general rule, not that good at resisting spinout in chop or rough water. They are better suited to sub 30cm deep water with weed that keeps the water flat or ripples quite small. If there is shallow water with little or no weed, you will usually experience less security - more spinouts. In deeper water there are far better options.
That said, the Techtonics Speed Demon is one of the best of these 'Delta Type' fins (one of my personal top 3 ) at resisting chop spinout if used in the appropriate size.
Size is critical in my experience. I have experimented with fins 2cm less in depth and that is enough to make the difference between spinning out often and rock solid. The width of the board and especially the tail seems to be the deciding factor. Smaller fins work better on narrower tail boards, even in very flat water, wider tail boards need a deeper/larger fin. I don't experience any noticeable difference in top speed going slightly larger, but do find it can make a huge difference to security over chop, upwind ability and reaching speed.
Lake George water is often denser/saltier than other places e.g- Budgy.
I've found I'm better off with a slightly larger fin locally than I can get by with down there.
I bought an 18.5 atomic because it held like a rock at Lake George. Back home I found it was spinning out occasionally and I went better with the 20cm.
Talking the 80ltre isonic ( 59wide??) with a 6.2m sail.
Select to expand quoteAUS4 said..
I'm 91 kilos.
I use Tectonics Speed Demons in shallow water and Tectonics Weed Demons in deeper water.
I have my mast base in the same position on the mast track on every board.
