Maui Ultra Fins Delta Fins

Aerodynamics and hydrodynamics are very similar. So what's so special about a delta wing?

I used one for the first time the other day and was very impressed, I picked it up on eBay for $160 brand new. I have heaps of weed fins but wanted something for going fast and that would work with bigger sails. I got the 20cm PB version and it is super sweet in my 120 freeride board with a 7.2, actually I'd say it's perfect for it. I was out at lake Illawarra in about 18 knots, I could run right into the shallow areas at full speed without a problem, These are zero weed fins...Nothing sticks. I could bog the board into the weed then just sail away, gybes or tacks you just sail away clean and just pop back on the plain. I never had the clear weed once during a 4 hour long session, I have weed fins for my twin that are 16cm and I need to stop an clear weed from those on occasions. It has great upwind performance when fully powered, you can load the fin up as much as you want...I couldn't break it loose a speed. When marginal but still planning it was a bit harder to work up wind, I broke it loose once in some real heavy chop but the spin out is in slow motion and easy to recover. The only thing I notice was that you had to point it off the wind a bit more to get it going, Similar to the technique to get a quad plaining early...and pumping it up onto the plain in marginal condition was a bit harder then with a stock fin(42cm is what I'd normally use with this combo). The only other thing I found is that I had to move the mast base forward a few centimeters, it was actually very sensitive to mast foot position. It didn't like the normal position that I'd run with that sail, it just bogged the board down and would not release unless really powered up. I moved the base forward about 2-3cms and it made all the difference to how quick the board poped onto the plain. As a weed fin I'd rate them 12 out of ten, Can't wait for the next session with in.

Jase.

Hey Guys,

I tested my MUF delta slalom fin for the first time on Sunday. I had a real shocker unfortunately. I found myself constantly spinning out. The fin is 19cm, I was on my Futura 101 and I was running my 6.5m Naish Redline. Wind was approx. 18 - 25kts from the SW (give or take) I was off Primbee point on the yacht club side of the jetty. Water was pretty flat with a slight chop at times. I found it ok off the breeze but really struggled to get any height. Managed to get better results when I got really powered up before trying to point but sooner or later spun out. Also tried different track positions with similar results.

Any thoughts on my problem? Technique? Tuning? Equipment? Is the board to wide? All the above?

Myself used my 19 inch freeride MUF delt fin on Sunday at Canton Beach and I really liked it. It did not spin out once. Once going I could head to windward pretty easily and off the wind it felt great. If there was more wind it would have been better off the wind but overall it was very enjoyable. The fin cut through big clumps of weed with ease. The only time I fell off due to weed was mid gybe when the board slowed down due to it hitting a lump of the stuff.

The key was the water was very flat due to the weed. In choppy water the fin is no good.

So in my estimation these delta fins are great for flat water, they cut through the thickest weed with ease but once it starts getting choppy, its not so good.

Hi Guys,
I've been running the Deltas for over a year now (a Slalom 17.6cm and a Speed 16cm) and have had quite a few people quiz me on them. He is a bit of a summary from my point of view:

(1) Common sense tells you that the low draft, high rake design will produce a different feeling fin to a high aspect upright fin so don't think that it will magically reproduce the latter's performance for shallow, weedy water. If you like to push really hard on a fin with back foot pressure (and back hand pressure) and produce that flying-off-the fin feeling then this is not the fin for you. The delta fin is designed for shallow, weedy water, where an upright fin doesn't work and in my opinion is the best attempt yet to give good performance in these conditions.

The key selection criteria for a weed fin, in my opinion, depends upon the conditions you sail in - what I mean here is the depth of the water, the "choppiness" and most importantly the type of weed. Choose a weed fin that has the lowest rake (i.e. most upright) that successfully sheds the weed. (Note that I'm not making any comment here about 30 degree fins vs 10 degree fin - I don't consider a 30 degree fin a weed fin!)

I reckon there are 3 types of weed shedding required of a weed fin - first : shedding weed from stationary up to planing ( e.g. when starting off in shallow water and the fin drags along the weed picking it up - if it doesn't release it is very hard to get the board planing). High rake required here. Second : being able to sail over floating weed clumps and not "jerk" the board (to a stop or substantially slow down). Inability to do this mean a trip over the handle bars! High rake required here. Finally : being able to handle "normal" floating weed when planing. This probably the easiest for a fin, so only moderate rake required here. So depending on your conditions you may get away with a 40 degree fin. At my local speed strip (Lake Illawarra) experience has shown that this is usually > 45 degrees. I haven't sailed at Canton so I'm not sure what rake will work there.

As we all know the fastest section of water at your local (weedy) speed strip is the shallowest (unless you have a canal!) which means that to go the fastest you need a short draft raked fin. This is where the Delta shines at LI - short draft, high rake.

Most fin manufacturers have up to about now settled on a maximum rake of 45 degrees, generally saying that performance is too compromised for higher rakes. MU Deltas were the first fins, to my knowledge, to produce something different - a highly raked fin that works! This has been a revelation, particularly for my local speed strip. The Deltas are, however not perfect, and local luminary, Keef, has spent considerable time improving upon the design (see above). This brings me to my second point.

(2) To get the best out of the Deltas you will probably have to change your sailing style - I had to! Generally the deltas do not like a variable load, or said in another way they do not like shock loading as they will spin out. Variable loading can occur when you get hit with a gust and you muscle through it by pulling in on your back hand and "locking: your back leg. It can also occur when bouncing over chop - which can cause your body to swing "in and out", changing the load on the fin. It can also occur when bearing away in a gust to get the big slingshot. I found that you have to sail with a "sensitive" feel to what the sail is doing and what you body is doing with that power, and actively NOT changing the load on the fin ( at least quickly) - sounds impossible but it is not - just a matter of training. I suspect that windsurfers that have found an immediate liking to the deltas natural sail with a "soft back leg". And visa versa. NOTE; I am not saying one type of sailor is better than another - just different styles. As an example, I found that to get the best out of the slingshot was to to take a much wider arc to bear away when the gust hits so that the board could accelerate more slowly (or probably better said; so the board speed could build up in a more constant way).

(3) The upwind ability of the slalom fin is impressive (given point 2) but almost non-existent for the speed fin.

(4) I was surprised that the slalom fin felt better in my 49cm speed board than in my 55cm slalom board. I suppose the lack of immediate lift is not as suited to the slalom type board, however a bigger delta may have be more suited to this type of board.

(5) I have "scrapped" the small speed delta - the thin foil was just not suited to any chop or gust when going deep - far too insecure at speed for my liking and with no upwind ability just not versatile enough. Fast though......

(6) The slalom delta fin is fast - I have set my fastest 2 sec speed (> 41knots) using the 17.6 on my 49cm speed board, when the lake was littered with floating weed clumps. I don't think any other fin could have coped with the weed condition on that day! (No "handlebars" that day either!)

I guess it is horses for courses. Be prepared to learn a bit if you want to get the best out of the deltas.
Having said all that, the weed at Lake Illawarra is at an all time low at the moment so I've moved to using 45 degree MXR UFO weed fins and am loving them. When the weed returns (which it invariably will) the MXR's will not be my fin of choice - it will be the Deltas or some variation on them.

I have one of the deltas and I went up a size than you would tyipically use for a sail / board combo. This was on the reccmendation of the manufacturer. I also figured as little more fin would be more forgiving and I can allways take a bit off the size if need be.

Now just to get some wind and time so I can try it out .

A while back I borrowed a weed fin from a fellow sailor up at Canton (thank you, but can't remember his name) This fin was around 28cm but had really small surface area / depth. It was all carbon from the looks of it.

I expected it to be to small and useless with my 62 cm / 90L Slalom board and a 6.6m, and the wind was marginal anyway. I was totally surprised, once I got a bit power the board really stood up planed along nicely using a decent amount of backfoot pressure. Obviosuly the stifness of the carbon really made a difference. I wish I new what the fin was??