26

Re: Mast list for Super freaks

OK Geoff, I will bite one more time, then I am off to the airport. I am flabergasted that someone joined the forum more technical than me. Welcome!

Your first point. Yes you are correct and the "roundness" of the leading edge is typically proportional to the depth of the cord. My point was that drag seems to be related to both of those factors but I don't know the exact relationship.

Your second point, Sure they are different. I can't remember my fluid flow courses from 40 years ago, but I think that the effect of diameter on drag would be much more significant with turbulent than laminar flow , but still related to both, so it seems that you are reinforcing my point.

Your last point I don't understand. A powered up good no cam sail takes on the shape of a cambered sail, so I don't see the difference.

But with all due respect I am starting to argue for the sake of arguing as I think that the core issue is really a relatively minor one. I am going to save my energy to debate with you on the other posts where I have a lot more energy as I can more realistically maintain the illusion that I am making a contribution.

Aloha!

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27

Re: Mast list for Super freaks

Hot Rod 490 has such a thick wall of pure carbon it acheives similar stiffness to an SDM at this length. But it gains HUGE strength in the process. We do only RDM because we do not like swimming. Way easier to make a nice SDM bend well, and may be lighter but it will not be very strong in comparison.

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28 (edited by Geoff 2007-03-04 17:37:45)

Re: Mast list for Super freaks

Well, I don't know how to post images, so I'll try to describe.

Very turbulent flow behind a round shape. The bigger the diameter, the worse it is, and this is the dominant aspect of drag.

When a foil is attached to one side of the round shape (i.e., as in a non-cammed sail), there remains turbulent flow on the round side (windward side), but the sail side has laminar flow over it. So there is a little bit of drag behind the mast, which is why airplane wings have some thickness (to eliminate this drag). My point is that it must not be large relative to the drag of the sail as a whole, because if so non-cammed sails would be a lot slower than cammed sails. They're slower, but not a lot slower. The roundness of the windward side of the mast does have an affect, as it both contributes to frontal area and (in the case of a non-cammed sail) there is an area of turbulent flow immediately behind the mast that fills in to the windward side of the fabric (which when powered up is fully deflected to the leeward edge of the mast).

One can therefore conclude that mast diameter, in and of itself, must not be a dominant factor in the drag of the sail. So being, if the "feel" of an RDM is better / more slippery than an SDM, then the cause of this difference in feel cannot be the effect of the diameter on drag, but must be due to the difference between and RDM and SDM on sail shape. More likely than not, this has less to do with static shape than dynamic shape (i.e., changes in sail shape as the mast bends under load).

Ultimately, the point of my threads is that it would seem that the bigger the sail, the less the ability of an RDM to control this dynamic change in shape. The implication is that, above ~460 cm, an SDM outperforms an RDM. The posted mast rankings in this thread are consistent with that theory (but do not prove it by any means).

Jeff H is seems to be of the opinion that, at least in some sizes (presumably big ones) that an SDM is easier to make light and high performance, but that they break like toothpicks in a garbage disposal (that's been my experience!!!!). The reason to go with an RDM in the 460 & up range is durability in surf. This is relevant to lake sailors like me, since I don't face a lot of surf. For us SuperFreak lake sailors, at 460 and up we might well be better off with an SDM.

GEM

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29

Re: Mast list for Super freaks

I would absolutely agree that the only reason for a RDM on the big Freaks is a breakage issue in the surf. I would stick to SDM's in no surf conditions.

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30 (edited by Surfingsen 2007-03-05 03:51:00)

Re: Mast list for Super freaks

I love this discussion smile   (being a engineer too!!) So I will put my 2 cents in too....

IMHO if you want the most efficient foil you shouldn't be looking at a SF but on a race/speed sail with cambers etc. since the biggest cause of drag is the big shady caracter standing next to the sail big_smile

Of course you should have the optimum foil on what ever sail you are using !!

The entire package has so many variables - sail, mast, boom (flex), boardtype (rocker, scoop etc.), finshape and profile, sailor, stability of the wind, waterstate - that the influence of the mast diameter on the efficiency isn't what you are feeling but more the flex of the mast and the entire package working together (or the opposite)!! But when you have all the other things in place - of course you should look at the diameter.....

With regards to efficient foil I saw in the british Windsurf mag from the Weymouth Speed Week that a british guy has made a sail with a variable luffpocket (for speed)

So this post has gone of the tangent, but the discusion is interesting about which mast works with the SF

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31

Re: Mast list for Super freaks

Geoff, posting images is as easy as writing "img" withing closed brackets. There's a link to the left of where you write your posting. Check the link here: http://www.hotsailsmaui.net/forum/help.php#img

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Re: Mast list for Super freaks

Hi Surfingsen,
How many engineers are there on this forum!?

i think that you are absolutely right that the drag of the rig is nothing compared to the large unaerodynamic thing holding the sail, but the discussion started with trying to explain why a SF rig feels lighter with a RDM. And I do believe this to be a fact. My wife and I who are on the opposite ends of the  engineering spectrum came to the same conclusion. While I agree with all your other factors I think that you can keep them consistent in a mast comparison and the RDM just feels that much lighter and easier. And since all those variables stay the same the only explanation that i can hang my hat on is less parallel drag from the reduced diameter which translates to less "push" required to keep the rig forward so it feels lighter and more balanced.

But, I also agree with Geoff that over 7.0 a RDM does not have a noticable benefit unless you are a real fanatic like me and need a RDM to go in the surf.

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Re: Mast list for Super freaks

Thanks, Niclas, I figured it was one of those, but wasn't sure and was in a real rush.

Dolf, I really don't think mast frontal surface area has much of a difference in rig feel. I think it far, far more likely that the RDM provides more luff cloth and alters the shape of the sail in a non-uniform manner, and effectively moving the Center of Effort (CoE) lower and more forward. This gives the sailor 1) more mechanical advantage over the sail, and 2) a feeling that the sail is pulling more forward than sideways. Both of these would make the sail "feel" lighter. If the RDM alters the shape when the mast is flexing, it is also likely that these dynamic conformational changes affect the CoE as well. I think these effects are dominant, but much harder to quantify than mast dimensions.

Surfingsen, I have no disagreement about race sails being more efficient foils - until you need to haul it out of the water before you get hit by the wave setting up to bounce you into the tumble-dry section. Given that, plus the fact that much of the time a wave sail is either luffed or backwinded, and a camber-induced sail makes less sense for a variety of applications. But if you want to go fast mega-overpowered, cams are the ticket.

GEM

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34

Re: Mast list for Super freaks

Ok ...add 1 more to the list. Geoff, I will Agree that the RDM must have an effect on the sail shape both static & powered, & that this is probably the biggest reason for the sails different "feel". However I think your analysis, of the changes produced is flawed. The extra tension caused by larger diameter in the lower part of the sail, will actually induce more static draft as well as move the draft & consequently the COE lower in the sail compared to the RDM. As to front to back draft position I would also guess that it might push the draft further forward in the area of increased tension.
   Also I think your assumption about cambers being best for top end may not prove true either. Look at the SuperSpeed ........ not a camber in sight......


Caleb

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35 (edited by Geoff 2007-03-12 15:48:15)

Re: Mast list for Super freaks

Welcome, Caleb!

Hopefully TA will comment on the nuances of mast / fabric interaction. You might be right about the effects of RDM on the sail - I was mainly theorizing as follows:

As one increases the diameter of the mast from a theoretical 0 (infinitely thin shaft), to a diameter with an upper limit = the diameter of the luff sleeve (i.e., so there is no excess fabric not touching the mast), I THINK (but don't know) that the effect will be to make the seam where the sail joins the luff sleeve to be retracted towards the mast. I don't know if that's increased tension, or a change in conformation at the same tension. Whatever it is, it seems to me that pulling this seam forward can only flatten the sail.

I've always assumed that RDMs are more "rangey" because at any given downhaul tension, there will be more shape, and thus better bottom-end for an RDM. If this also adds to the ability of the sail to be floppy / flat at the top end, then an RDM would help at both ends of it's range. Hard to beat that!

As to what happens to the CoE with an RDM, I would welcome comments from TA or Jeff. In particular, one question in my mind is if the CoE moves up and down, not just fore and aft on the sail.

And...as to the effect of cams...I think there are a lot, a LOT of camless sails that are wicked fast. But the sails on the race podium almost always have cams in them.

I don't know how designers think about cams, but I think of them in three modes: 1) underpowered, mechanically deflected, 2) fully- to over -powered, fully deflected by the wind, and 3) way over-powered, mechanically restrained by the cam mechanism.

In contrast, RAF sails in the analogous modes are: 1) underpowered, under-deflected, less drag but little lift either, 2) fully- to over-powered, fully deflected by the wind, and 3) way overpowered and distorted without no mechanism to control batten position (aside from the fabric).

RAF sails are thus superior in waves because phase #1 is useful when surfing and maneuvering. RAF sails are inferior in underpowered slalom / B&F / course conditions, because energy is lost during pumping as the fabric rotates and stretches and doesn't have a stable foil shape. So the main factor in determining RAF vs cambers, at least for me, is what I want the sail to do in phase #1 (luff or be stable for pumping and gliding through lulls).

In the fully-powered condition, #2, there is very little, precious little difference between otherwise similar sails. I think you could probably determine a winner on the speed course, but it would be a damned good race and I would bet more on the specific sail and how well it rigs than on the cams.

In the over-powered condition, cams are advantageous because they help control the foil shape, which is exceeding design parameters and beginning to distort. In this situation, shape control can substantially prevent degradation in performance because any shape diverging from the designed foil shape is bad (more drag and harder to handle the shifting CoE).

That's not to say that sailmakers haven't learned a lot about controlling foil conformation with just the fabric, spar, and battens. And for sure, the smaller the sail, the more the fabric material and battens are likely to do just fine. Long ago, I had a 4.7 NP Mark IV with a bunch of battens and cams. It was very flat, and I never thought the cams added much to the sail, but to really test the theory I probably should have sailed it in 40 kts (but back then I wasn't good enough to do that). Today, I would probably think about cams in a speed sail in that size, but not for anything else. My sense is that the smallest sail that clearly and demonstrably benefits from cams is about 6.0. I could see, for instance, use for a single or twin-cam 6.0, but would probably want 4 or maybe more cams in a 10.0.

Again, the choice of cams or no-cams is mainly dictated by the intended use - I can't see having cams in waves (been there, tried that, never again!). Conversely, I prefer the feel of cams when I have to pump hard to a plane and when I'm trying to keep planing in a lull.

That's just my anecdotal opinion on it; don't know of any data (I suspect HSM and others have some, but it is proprietary). Would gladly hear other thoughts on the matter!

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36

Re: Mast list for Super freaks

Geoff I could be wrong here too, but I picture it being like this:
   Draw two arcs indicating the mast sleeve. Now draw an arc from the centerline of the sleeve at the top tangent to the inside of the luff sleeve arc down to the centerline of the luff sleeve at the foot end. Next offset that curve to represent the mast diameters(both RDM & SDM), the area where the mast curves intersect the inside curve of the luff sleeve represent the region where draft is mechanically induced into the sail via luff curve.
   If you did this exercise you would see the difference between how I imagine the SDM interacts with the luff curve vs the RDM. I could be completely off base here & I know that I have dramatically oversimplified things & left out so many other factors such as seam shaping etc etc.. That said, my understanding is that an RDM will induce less draft in the sail(especially down low) than SDM given the same luff curve.
   As for cambers & stability I think that TA & Jeff have quite allot of experience designing extremely stable cambered sails. I have sailed the Hot race sails from about 1991 & stability was always one of their strong points. So when they release a non cambered Speed sail, I have to believe they have found a way to achieve that without cams.
  As for pumping I think cambered sails do not necessarily pump better but do tend to have more Static draft & so more "initial" punch. Pumpability seems to be much more complex & for me seems to have much more to do with the leach shape then the hardness of the leading edge such as would be the case for cambered sails.


My .02

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37

Re: Mast list for Super freaks

I'm looking at a 8.0 SF as my next purchase.  I'm 150 lbs and would sail it mostly on inland lakes, but also Lake Michigan (which can get gnarly).  Being light, I usually masts that are slightly on the flexable side.  I'm planning on getting a HR 490.  My next sail down is a 6.3 SF.

Anybody think I should consider an SDM instead?

thanks, Drew

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38

Re: Mast list for Super freaks

At 150 lbs, the RDM will work better than a stiffer based SDM mast.
Plus it will not break on a hot day!

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39

Re: Mast list for Super freaks

Drew,
I'll second Jeff's advice. The 490 Hot Rod works great for the 8.0SF for my 83kg and Joanna's 63kg.

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40

Re: Mast list for Super freaks

Caleb

You might be right about the effect on shape - Jeff or TA please clarify for us?

As to stability of non-cammed sails, obviously HSM has success without them. But with all due respect, they don't yet hold the records (at least not that I'm aware of), so the jury is out on that. There's so many factors, I would not judge simply on being the record-holder....but this is one area where I'm more aligned with Barry Spanier's thinking. Obviously, I'm not totally aligned because my SuperFreak is on order and I couldn't disagree more with him on the recent thread where he was dissing dacron. I thought he was way off the mark.

FYI - I've abandoned reading Maui Sail's forum because 95% of it is about nothing but race sails and I'm just not interested in that stuff anymore. HSM's forum is much more diverse (kudo's JH).

As to pumping, I agree and think a lot of preferences on pumping have to do with style. I don't like pumping non-cams, but can see that others might like that feel. I agree that the leech has a lot to do with it, as does the fin, frankly. There's soooo much technique in pumping (both the sail and the board) that this is to me totally a personal preference. I used to be pretty good at monster pumps, but now that I'm not trying to out-dragrace everyone, I've given it up...

GEM

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41

Re: Mast list for Super freaks

Geoff you miss one very big point...
Records are made by sailors not bij sails.
For records and champions (is there a big difference?) you see every time the same bunch of super talented and routined guys: Dunki, Kevin Pritchardt, Antoine Albeau, Finian Maynard en sometimes guys like Buzianis.
As long as they sail with the big more traditional brands (Mauisails is a young one but with  a very experienced/trad crew) those brands will hold the record.
Give Albeau a Hot and he will rull too.
That said: if you read asbout speedsurfing the biggest holdback in speed is the drag of the board and fin, not the sail.

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42

Re: Mast list for Super freaks

OK I am not sure where to begin there are so many points raised. First off lets deal with some aerodynamics:
1. Air is completely incompressable in the enviroment we sail in.
2. The air behind the mast is static - the wind sees a virtual airfoil. This is why you do not see dramatic differences between wide sleeve and "RAF" sails. The difference in fact only really becomes significant at high angles of attack like racing upwind.
3. NACA foils are somewhat primative (well they are 50 years old), but try a NACA 64a010 for a good fin foil.

4. An asymetric airfoil will have a different center of effort depending on the angle of attack. Therefore as the apparent wind changes with a gust, heading change or speed change the center of effort of the sail changes. This is not desirable as it makes the sail hard to handle and would be considered unstable.We get around this by using twist and dynamics within the sail to keep the centre of effort in more or less the same place.

Interestingly nobody has mentioned that Finian set the world record using a skinny mast. I think that sail only had 3 or 4 cams.

Cams can have very negative effects if used in the top of the sail. We found that out a long time ago!

We design the sail and mast as a system and if you use a different mast you will not get the exact performance we intended. Could be better, or it could be worse - but not what I had in mind! We design for the Hot Rod RDM.

If I had my way there would be an intermediate diameter between SDM and RDM that would be better for big masts. In pure theoretical terms every mast should have an ideal diameter for it's specific length and stiffness. Obviously that is not practical or desirable.

Dolf I have not forgotton about your 520 - Don't blame Jeff! I am still finishing up work on our freeride mast. Once that is complete I wll work on a 5something mast, possibly 3 piece.

We will continue to explore camless sails. It is my belief that eventually the cam will become extinct as it is akin to a strut on a wing. Sure it helps, but there are better ways of doing it that are more efficient!
Right now windsurfers are so brainwashed into believing that you must have a cam to go fast that you cannot sell a camless race sail. I don't think I can single handedly change that point of view. I need to get some other designers on board with it. It is kind of like Jeff's Superfreak, people will refuse to believe it works until they try it!

I'd love to keep rambling on but I have work to do.

Cheers,

Tom

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43

Re: Mast list for Super freaks

Tom,
I believe you. Is that a start?

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44

Re: Mast list for Super freaks

I'm speechless!

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45

Re: Mast list for Super freaks

Thanks Tom....covered pretty much everything.

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46

Re: Mast list for Super freaks

Tom,
I don't believe that. Low key and quiet ok, but speechless?

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47

Re: Mast list for Super freaks

A big THANK-YOU to Tom. Very much appreciate your input.

Jeroen - I totally agree with you on the sailor point, and about the fin/board as well. And I don't think I missed the fin point, but my agreement on the fins was disguised as needing to pump the fin / match it to the sail.

You ask if there is a difference between records and champions, and I think so. In sports where champions are crowned in open racing, it's rare to see a record in the championship race. That's because strategy, tactics, guile, and pure desire come into play, whereas in records the conditions have a lot to do with it, and the best strategist, tactician, cunningest fox, and the one who wants it the most may not be there.

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48

Re: Mast list for Super freaks

As opposed to speed sailing where the biggest, dumbest (sorry Finian) guy wins? Obviously you have to be stupid to try to do 50 knots on a windsurfer - that's dangerous! Actually Finian is pretty darn fast on a race course too - I think he (any top pro) is more important than the gear he is on. I think the gear is more important to the average sailor than a pro. The average guy does not get to sail that much so he can't deal with equipment that is difficult or requires a lot of skill.

Ideally in the perfect world none of us live in every piece of equipment would be perfectly matched - yes that would be better. But even then it would have to be matched with the rider, the same perfect set up may not be perfect for everyone. In fact there are as many "perfect" set-ups as there are sailors. At the end of the day you have to use what you've got and learn how to make it work. That's what the pros do!

So in short, stop debating and go sailing!

By the way I like to use Finian as an example as he is an old mate and more importantly he does not spend much time on Maui! This helps avoid unpleasant confrontations in the Kanaha parking lot! (kevin is not that big, I might consider insulting him in the future).;)

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49

Re: Mast list for Super freaks

Well, I WOULD get out and sail but it chose to start snowing again today.  Right when it had gotten warm and the lake ice had melted...

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50

Re: Mast list for Super freaks

Do you ice sail? Brad does:
http://www.youtube.com/watch?v=1_lRk2FS-aw

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