Maui Delta XT vs BP Free delta RT

Warning: yet another soapbox nerdy rant ahead!
Bottom growing weed has the effect of increasing the 'dynamic viscosity' of the water. This in turn will decrease the Reynolds number and increases the Ncrit. Laminar flows last longer. Laminar flows produce higher lift for less drag. Laminar flows are *generally a happy place for fins to be. All high rake fins will benefit from this water state and perform far better than in turbulent water. The drag becomes the dominant factor and the rake and effective length of the leading edge being the biggest contributor. So if your local strip allows you to sail in smooth water the whole time, go for the shortest fin that provides the lift you require and that you are confident using.
( * I am not aware of any supercavitating design for shallow weedy water)

BUT, if your speed strip requires sailing in choppy water, especially upwind work, the above situation reverses. You will now be faced with low Ncrit and high Reynolds numbers. This is the time when your fin's ability to deal with these conditions becomes very important, as all these two factors are pertubating. Your fin must now deal with turbulent flows AND produce enough lift to resist sail load and to point upwind.

As you have probably guessed, this is when the comprises in fin design to decrease drag in shallow weedy water come home to roost. Whether those compromises are acceptable depends on the sailor. For the 'no compromises' sailor, a low drag short fin will be diabolical for upwind work in chop, but once you finally make it to the top of your speed run, and the holes in the cheese align, you will reap the rewards of the lowest drag and a high speed run.

For the average sailor, some degree of compromise between lift and drag will put more grins on the dial as we don't all have the same skills/strengths sailing. So for me, it's defo a 'horses for courses' scenario, with not only, no two speed courses being the same, but not everyone's expectations of a great day on the water being the same either. Finally, before I climb down from my soapbox and finish this little rant, it has been calculated that once the board is planing the fin is approximately 15% of total drag. Most of the drag is you and the sail, and then your board. Pick on those before blaming your fin for low speeds :-)

I can sort of follow Fangy's theory explanation as Im not real bright. Its obvious that we all sail in different weed/depth conditions but the number of different fin shapes and profiles is quite large. Horses for courses, if it works for you it probably wont for someone else. I sail at Budgey a lot for a non local and have tried several different rakes, depth, and plan shapes. Some work, some don't. Some work on days when the weed isn't scary and bus size and its easy to go through. Then lately its been super thick and for the first time Ive tried a Delta just for the rake so I don't kill myself. I have a hand shaped fin of the same rake but its for bigger gear. I was pleasantly surprised. I then borrowed a smaller Delta from Millsy on a strong day and it was fine. I havent tried the 2 fins that are up for discussion so cant comment. But all the boys say they love them so who knows?? Try and ye shall discover what works for you.

If any one wants to try a kestral all they have to do is ask and i am sure we can organise something , as stated before all the fins work you just gotta have a go and see what suits you and than stick with it and the rewards will come

I have a 20cms BP50 weedspeed that I love and use in slightly deeper choppy water at Budgy ( NE direction). I don't usually aim it at the thickest weed as I feel a little bit of a tug hitting those..I haven't really tried it in the thick stuff.
It hangs in great and I can push on it ( unlike a delta).
I just tried the 16 kestrel for the first time yesterday ( they don't make the BP50's in less than 20cm deep). Very impressed. I did find out you should check for weedbergs before you gybe.. ( it's been 4 months since I sailed the really thick stuff). No fin would cope with a large dry weedberg. . The kestrels hung on great in the small chop and ripped through the thick weed upwind and on the bearaways.
I was so impressed I got overconfident coming back across the channel well powered in 1- 11/2 ft chop and didn't allow for the fact that it was a 16cm fin with a 6.2m sail so I spunout and fell in and then once I got going again I went sideways all the way back in.. I was very tired so I didn't even try and straighten out of it.
The 16cms was great and I did bearaways right through the shallows on a few runs ( brown pants stuff waiting on hitting bottom and going over the front but I didn't).
Tibor took a great pic of a a delta , Kestrel and delta Xt laid over each other to show the comparative angles..I'll see if I can upload a pic via my phone..

Very interesting comparison photo. Well done and thanks for posting.

Fangy I don't have a Kestrel but 19cm Delta v 18cm XT from the reverse side

I thought of that later.. It was a combination of my fin and Tibor's two fins so I'll have to wait till next time to get a photo from the other side.

Thanks Legless.

Just heard that MUF is going to be making the Delta-XT from 10cm!!!! in 2 cm steps (10 cm, 12, 14, 16 .......26 cm)

It will be interesting to see what a 10cm Delta XT will do!