"T" foils on F14

We have now sailed two Alpha F14's (one with "T" foils and one without, and we have even swapped the "T" foils from one boat to the other), over several races and just out together "testing", for some time. We have "swapped" boats as well, all with the object of a "yardstick" test against each other. So far the results that we have obtained is that the "T" foils, throughout the full range of conditions, make a consistent and definite improvement over an identical boat sailing without “T” foils of between 9% and 11%. This is better than any results that we had anticipated and has completely justified all the R & D, design and mould work that it has taken to finish this project. Now we will just have to see what results are obtained from racing against all the other classes in “open” competition.

Are they providing lifting force or just making the rudder more slippery through the water?

They'll have two benefits Jake. One will be the reduction of tip drag as the rudder is turned (they will act as end fences). The other is grip on the water to prevent the bows from diving.

The only drawback I can see from these is storing them. You can not just throw them into your sailbox.

Other than that, these look like a sweet sweet upgrade. I wonder if this will be eventually used on more boats? I know Stealth F16s have T foils, now the Alpha F14s. This is great news!

Have you experimented with the rake of the (horizontal) foil for optimum performance <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Now, now Robi. Surely you're not telling us that you simply 'throw' your (non-foil) rudders into your sailbox? <img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" />

<img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

I am a little concerned with drag, when the boat is not at optimal trim. Also drag when you turn the rudders whilst flying a hull.

Would also pick up a lot of weed and be hard to clear.

Yes, if you get a weed or a trash bag, lobster bouy line or anything else wrapped on there you will have to stop, lift it and clear it. That won't be too fast! Unless that sweep is enough to let it slide off.

Oh, and I could see where it would help keep from a picth pole but as for the speed improvment, 9-11% of what? <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />

Adding a spinnaker to a boat gives roughly 5% improvement to a boat's yardstick, give or take less than a 1%...... So your figures may be out.

How about adding T foils to the daggerboards too? Admittedly, it would make installing and removing the daggerboards a hassle, but it would also reduce tip vortices.

D. Ho
TheMightyHobie18 1067

There is no "detectable" extra drag from the foils, in fact the opposite seems to be more the “consensus”, the actual “T” foils don't hold any weed (their rake lets any weed “slide” off) but the rudders (or any other rudder system for that matter), will catch weed, in exactly the same way they would normally with or without T foils. The helm is balanced at all times with or without both hulls in the water. The foils primary function is that they reduce "pitch", both nose down and nose up, (from 2 knots to 20 plus knots) and keeps the hull platform sailing virtual horizontal to the ambient water surface at all times, and thereby stopping the mast and sail from "darting" forward and back as the hulls pass over surface undulations, this keeps the sail working more consistently (and efficiently). It greatly surprised us when looking at sailing attitude comparisons between the two cats on video, of just how much the mast of a cat without foils oscillates in relatively “flat” water and light winds when compared to a cat with foils that showed next to no pitch. Then, of course, there is the bonus of being able to make radical “bear away” (or up) manoeuvres with or without kite, and the bows never dipping more than a couple of inches.
The performance figures ARE slightly subjective as some were taken from race “finish time” differences between the two cats and calculated against the elapsed time of the races, while many more were taken “free” sailing over a variety of distances and comparing the two different times between the cats to their overall times for those distances, and as such I am not “claiming” them as being “written in stone”, but, the greatest difference we had was 12.5% and the least difference was 4%. More importantly, there never was any time that we tested, in any condition, where the cat with T foils was equalled by the non-foiled one, which would seem to indicate definitively that, what ever the exact difference is, there is a distinct advantage using T foiled rudders.
As an aside Stephen when we added the spinnaker to the F14 our yardstick dropped 11%. (And the F14 is one of, if not the only cat with spinnaker where the area of the spinnaker is quite a bit less than the area of the working sail(s))
And ROBI you are absolutely right, it’s a “pain in the butt” not being able to put them in the standard sail box, that’s why we are altering our moulds for our sail boxes so that we can do just that (quote) “just throw them into your sail box”.

I think they look SEXY. Good work Darryl.

True, however when a standard rudder catches weed, you can kick the rudder up quickly to clear, or fly a hull enough to get the rudder out of the water. With the T foil, you can not kick the rudder up and flying a hull will not see the weed fall off the bottom. The only way to clear it would be to lift the foil partly up, hang over the back and use your hands... = SLOW


They may reduce pitching, however when the boat is not trimmed with the foils perfectly horizontal..... ie too much nose down or nose up..... What about the resulting drag as the foils are fighting the trim of the boat???? It may not be pitching but it would be like running with the hand break on if not trimmed correctly. These foils are non adjustable also. I believe the I14s will trim their foils neutral for down wind raking the rudder further back (nose up) as the breeze increases. Then they rake the rudder forward (nose down) for the upwind legs.

I here a lot of 'Talk' about how good they are, but am yet to see it backed up by hard data after controlled professional testing. Hence why I am the skeptic.



This is effectively using the foils to fight against the boats tendency to drive the nose down. The foils fighting against this = drag..... Better to use crew weight more effectively to control the boat trim and better seamanship on the maneuvers ie smoother maneuvers instead of using the foil as a hand break to keep the bow out.

Also, sometimes you need to round up quickly, lifting the bow up…… Such as when you are surfing down a wave in pressure and want to flick the nose up over a wave before plowing into the back off it.



To use the Tornado as an example which saw a yardstick adjustment after not only a kite was added, but a larger main sail and addition of extra trapeze........ The big T's yardstick dropped initially 4.35% from a VYC off 69 to 66. Later adjusted down to 65 which is a 5.8% drop from the original yardstick.

So if you were seeing differences anywhere near this let alone in the double figures.... You have other factors adding such a large influence on the results, that it renders your results inconclusive.

I doubt very much that the addition of foils will see anywhere near the performance increase that adding a spinnaker to a boat would.

We know first hand through strenuous testing just how they do perform and I did not start this thread to get into an "answer and question, bun fight" session concerning the pro's and con's of some "sceptical theorising" of how or how not foils do or do not work. I have simply posted our FIRST hand experiences of our testing of them "out in the real world", under an enormous variety of sailing conditions. Now any one can draw on all sorts of theoretical situations where they can extrapolate as to "will they do this" or "I feel they will do that" or any thing else that they can imagine, but before "digging too deep at hole" perhaps it would be prudent to actually see how they perform first hand, then these opinions may carry the weight of proof and not just supposition theories.
It’s not just some theory but documented fact that we took the YV yardstick of the 4.3 Alpha Omega from 88 down to 77 in twelve months. Now that was also something that the majority of sailers said was "impossible" as well.

I do remember one particular sailor, having done more then a little scientific modelling of beach cats, who was derided as delusional when the quotes his estimate of final performance. I'll bet he is grinning from ear to ear with this validation.

Wouter

Not a 'bun fight' mate.... I am genuinely interested and throwing my thoughts out there. Am very interested in peoples reply and would love nothing more to see it proven. I am not big on the ‘It works because I say so’ but am after at least some well thought out answers. I have an open mind but will not be lead blindly into believing. I was hoping what I was giving was constructive criticism.

If anything…… Some of what I have said could be thought about and if it is valid, used to improve systems or sailing techniques. We all learn through each other.

We currently see the F16 and now F14 class using foil rudders. No offense but these 2 classes are far from professional classes. Why have we not seen other more professional classes trial these. May be most of these other classes have something in their class rules forbidding this ????????

Also, this is not directed personaly at you but the entire foil / no foil debate.

Personally I see no fundamental scientific reason why the F14 can not acquire bigger performance increases from the upgrades then the Tornado.

As a shorter platform it is more held back by depressing the bow during gusts and short wavelets. It is a widely accepted phenomenon that shorter boats do tend to behave more nervously. Mathematics with respect to bouyancy distribution clearify this. The f14 is at the other end of the spectrum when compared to the Tornado and as such is will receive proportionally the greatest benefit from T-foils.

Also the boat was relatively slow at VYC = 88 is is always easier to make a slow boat more fast in absolute sense then making an already fast boat equally faster. This is also an effect of proportionality.

10 % of 88 = 9 points
10 % of 64 = 6 points

But also the aerodynamics involved will stimulate such a discrepency. The Tornado is more held back now by limits in efficiency while the F14 was more held back by limits in power and the ability to sustain that power in a low drag attitude.

I've noticed mayself plenty of times on a 14 ft boat that each time a gust came in I needed to sheet out alot to prevent the bows from diving. Noticeably more then on a say an 18 footer or 20 footer. With the T-foils this could well be negated allowing the driver to drive the F14 ALOT harder then before.

Reasons like this can easily acount for bigger gains to the F14 when using an upgrade then when using the same setup on a 16, 18 or 20 footer.

Personally I feel the 16's can still do well with a T-foil upgrade but 18 foot and higher it could be insufficient to make application attractive. I know for certain that it was proven ineffective on a A-cats. But then these boats are alot longer for their width then the F14's are.

Wouter

As far as yardstick goes..... I guess Forster will be a test.

F14 - 77
H17 - 82.5
H16 - 81.5
Mozzie (sp) - 80
TheMightyHobie18 - 78.5
Taipan cat - 76.5

F14s without foils - Berny's 430
F14s with foils - AO

I am not doubting the yardstick of the F14 and Forster will be interesting.

I am questioning the effectiveness of the foils and to this date am not convinced. But hey, if you want to believe, then go right ahead, and I will continue to doubt until convinced otherwise.

Also I am not doubting that the foils reduce pitching or alows you to load up the boat more...... I am questioning at what cost (drag)

Good job

I did not think the reduction in drag would be worth the effort. I did not think about the increase in stability.


Did you reduce the area of the rudder, when you added the T-Foil?


A few thoughts:

The thought 10 years ago was to reduce the area by tapering the foil. I don't know what they found when they tested actual aircraft. The test data is controlled.

I have noticed that the newest aircraft have smaller winglets and there is no abrupt transition between the wing and winglet. It looks like a decreasing radi curve.

I also wonder if you need a end foil on both sides of the rudder. i.e. instead of a T could it be a L or an almost J.

I would not argue about this. It is beginning to look like the waxing or not waxing the hull debates



Carl

Hi Darryl
Can you post some of the video of the two F-14's saling together...one with and one without? Sounds like you put some serious effort into the evaluation of the T-foils.

Whether or not a "professional" class came up with the concept... uses the concept in its class... or approves of the concept... has nothing to do with whether the concept is valid. Keep up the research and thank you for sharing with us your findings.

Regards,
Bob

All in good fun, boys.




The answer to that is partially yes. Alot of classes do have rules like the overall width rule that prevent T-foils from being used. Other reasons are that builders don't want the additional hassle, so don't expect Hobie or Nacra to develop and introduce stuff like this into the cat scene. Other reasons may well be pure scientific in nature. As I wrote in an earlier post; it can be quite possible that longer boats do not get the same boost from fitting T-foils then the shorter boats like the 16's and 14's. It was tried in the A-cat class and discarted. However the length to width ratio of the A's is far higher then the other classes. The A's are just alot longer and also alot smaller then the other boats. And of course they have less weight in that carbon mast. All factors that limit the possitive effect that T-foils can have.

I have personally sailed with T-foils a couple of times and I must say they truly make the platform very stable. I own a boat without T-foils and I do feel a significant difference despite both being F16's. I dare not quote an performance increase % but I'm convinced that the T-foils can't be just waved away. I wouldn't be surprised if well designed T-foils turned out to be an advantage that just a score of sailors overlooked for such a long time.

Afterall how long did it take before the bulk of (professional) sailors and classes started using wingmasts ?

In this line of thinking I have no special regard for professional classes. More often then not they are more conservative then non-professional classes. Most development is done in small and tinker oriented environments.

Wouter

“More often then not they are more conservative then non-professional classes. Most development is done in small and tinker oriented environments.”

Wouter I think you have stated that very tactfully…

I would go so far as to say the “Professional” classes…as well as established 1 design in general… take an adversarial position on innovation…“It’s all about the sailor”… the boat is just a means to an end…To others it’s all about the advancing of boat design regardless of the repercussions to established classes.

There is plenty of room for both points of view…and lots of room in the middle…but please Stephen do not use “professional classes” as any indication whether a new innovation has merit or not. Even if proven positive beyond a shadow of a doubt…those with the mind set of “it’s all about the sailor” will vigorously resist any change to boat design which redefines the level of the playing field.

Regards,
Bob

I have only one sail to support this in a Stealth F16.

All IMO of course.....

The T foils make the ride down wind very much smoother and you can drive the boat much harder. There were times while I was getting used to it that I was thinking that "I'll need to bear off in this gust to stop the bows going too deep, when in fact I did not; the foils gripped and the boat just went faster.

I agree 100% with T_A that they are adding drag as they are holding the back of the boat down and you could go faster with crew weight further back.


but you run out of crew weight ! At some point you have to shed power to keep the bows out (and so not going at full speed). Yes, by adding weight to the back of the boat by moving back you fix this, but you can only get so far back.

From sailing the boat only once, I can see that it will by critical to sail the boat all the time with the foils not dragging until you need them. The foils could make people lazy as the bows just don't dip anywhere near as much.

Consider this

2 boats are exactly the same except one boat has T foils on the bottom of the hulls.

Boat A and boat T (has the foils)

In light wind with NO waves

Boat A should be slightly faster than boat T as the T foils have more drag.

In light wind with waves

Boat A might be faster as it has less drag, but, boat T will slop around less on the waves as the T's prevent some of the wave action moving the boat around (so the rig shakes around less), but boat T has more drag and this will be compounded by the wave action.

In moderate wind and small waves

Boat A should be slightly faster as it has less drag, but boat T may have some small benefit from the more stable platform

In moderate wind and waves

Boat a might be faster as it has less drag, but, boat T will slop around less on the waves as the T's prevent some of the wave action moving the boat around (so the rig shakes around less), but boat T has more drag

In strong wind with smallish waves

Boat A might be slightly faster as it has less drag, but boat T will have benefit from the more stable platform and will also be able to drive the boat much harder downwind as there is less probability of pitchpole.

In strong wind with big waves

Boat A might be slightly faster as it has less drag, but boat T will have benefit from the more stable platform and will also be able to drive the boat much harder downwind as there is less probability of pitchpole.





Now my views are thus :

1, T foils add a little (and it is very little) drag as you have more area in the water.
2, T foils make a massive difference sailing downwind in the windier stuff as the boat is much less tippy for/aft and so can be driven MUCH harder. Once you are standing at the back of the boat, you cannot go any further back.
3, When the wind is lighter, crew positioning is vital to ensure the foils are not dragging.
4, I've not sailed the boat in waves yet so cannot comment.



Another thing, over the last 8 years, I have gone from sailing a 20 foot boat (Hurricane 5.9) that was a dream to sail down wind in the big stuff, loads of volume up front and so we did not really factor in pictpoling into many sailing days

Then I moved onto a 17 foot 6 boat were you do have to be a little more carefull (still loads of volume up front). I've now gone to the Stealth (waiting delivery) and we'll see how that goes, but on my first sail,it was behaving more like and 18+ foot boat than the 16 foot boat that it is.

IMO T foils are the dogs danglies....

Scooby,

I agree with ost of your points except that a more stable rig will have more power because the reduction in "hobby horsing" will leave the rig powered up more of the time. Add that factor to all of your wind and wave ranges and it seems that the T-foils would be a better solution around the bouys.

I don't know much about the rules in the Tornado Class, but F18 Rules don't specifically rule T-foils out, except Rule A.2 which includes "Formula 18 class rules are closed class rules, what is not expressly permitted is prohibited."

T foils are forbidden on the Tornado as they are not expressively permitted in the class rules. Chief measurer himself confirmed this some time ago.

I probably have missed it somewhere, but is there a reason why T-foils cannot be used on kick-up rudders?

The reason they won't work on "conventional" rudders is that you wouldn't be able to use the rudder in anything other than the fully down position - there would be too much drag otherwise when you have the rudders down just enough to sail out of shallow water.

I am (trying) to say that the rig stability helps.

I currently believe T foils are the way to go !

SPEED BRAKES! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

But why would there be water drag if they are in the fully "up" position? Maybe a little air drag.

And being able to flip them up briefly would help to get grass off the rudder blades. Grass is a major problem in many areas of the United States.

I thought maybe the reason for needing a casing so the rudder can go straight up and down was because the foils cause increased stresses on the transom?? Or maybe too much stress or "drag" for existing rudder systems to keep from kicking up??

OK foil fans…… I am not having a shot at you and commend what Darryl and the Stealth boys are doing……. However I have some questions and am asking for answers.

You do not have to address my questions and can side step as much as you like, but if you do, you will not convince me of the benefits.

Wouter’s comment about foils possibly having a greater effect on a smaller boat was very interesting and was constructive feedback.

Below are my queries and it would be appreciated if someone knowledgeable could comment on them.

1) I believe these rudders will catch weed and other debris and be difficult / slow to remove compared to non foil, kick up rudders. Do you agree or disagree. If you agree, then have you thought about how to rectify this. If you don’t agree….. Then why.

2) I am not doubting that the foils reduce pitching or allows you to load up the boat more...... I am questioning at what cost (drag). Whilst there would be minimal (still some) drag when perfectly trimmed, what about the drag when the foil loads up at the top or bottom. The reduced pitching and ability to load up the boat more may feel like you are going quicker…… But are you.

3) How much drag is produced from them in large chop when pitching is inevitable?

4) What testing has been done. Tank testing???? Have you done extensive side by side 2 boat testing with boats identical in set up and crew weight. Taking results from racing is far from an accurate way to gather data.

5) How experienced are those doing the research in controlled environments and gathering data.

I will try Steve,
1. We have sailed through weed with two identical F14’s, and both caught weed on their rudders and were forced to extract that weed. One cat had T foils the other didn’t. The T foil cat slid the rudder up in the case and extracted the weed, slid the rudder back down and continued sailing. The other one had “kick” up rudders and swung the rudder up cleared the weed and swung the rudder back down. Conclusions were that the swung rudder was quicker BUT the difference was very little. Definitely not enough to be a deciding factor in “rejecting” the T foils.
2. When you look at the so called “drag” from T foils, you have to approach the question not from a “static” two dimensional perspective as if the boat was standing still and the bows went up and the transoms went down, (or visa versa) if this was the case there would be enormous loads (not drag) transferred from the foils directly to the transoms, but instead the hulls are moving forward THROUGH the water when the bow “dips” (or rises) and therefore we have a three dimensional “global” situation. Think of the foils not so much as resisting the vertical movement of the hulls, but more so as directing the direction of the hulls through the water in the vertical plane, exactly the same as the rudders do on the horizontal plane. Because of this the change to the angle of incidence of the T foils to the actual direction of the movement of the hulls is very small (only a few degrees) and as such the resulting drag is approximately the same as that caused by the rudders when steering in a straight line (which never in actuality really happens as even in a straight line we are always steering a little up to counter leeward drift) This is why when you calculate (quite simply) the potential “load” that the area of the foils can generate (IE for the Stealth numbers have been bandied about of 100 or more kg’s) it would appear that the transoms need to be substantially reinforced to take that extra load, BUT in reality due to that “force” not being by any means a static vertical load the transoms can handle the T foils without any additional reinforcing.
Our testing so far, between two identical F14’s, one with foils and one without showed that over the full range of our extensive testing the cat without foils could never match the cat with foils under any sailing condition.
3. The so-called drag does not seem to be a “variable” with the different sea states. The drag is a constant relatable to the actual speed of the foils through the water. The greater the hull speed the better they work I.E their efficiency goes up with speed greater proportionally than the increased induced drag.
4. Read my original posts you will see that we yardsticked TWO identical F14, one with and one without T foils
5. I think that my academic qualifications together with my lifetime spent designing, testing, building, and selling catamarans may just qualify me to perhaps have my “testing” practises accepted as valid.

Thanks Darryl, that has swayed my opinion some....

I do still not like the idea of the rudders catching weed though. Most places we sail, weed is really a problem. Forster is a problem and will see how they go there. As you said, the problem may not be enough to justify dismissing them. There is obviously a potential problem there, that those developing the systems will or may have already have looked into. A solution may be found, or it may be just a case of bearing with this disadvantage whilst gaining advantages else where.

Look forward to watching the continued development and see if bigger classes start experimenting with them too. Wouters comment about boat size does have me intrigued.

Steve, I think not only boat size would be a deciding factor, but also hull shape. The Tornado dont have much volume along the keel line compared to current designs, so even our "big love" might benefit from T-foils. A design like the F-18 Blade with lots of volume low down will probably benefit less, except for keeping the boat under control downwind in wild conditions.

I sail a Stealth without 'T' Foils and would love to try the T's just too feel the difference. I only have two conerns about T's the first is the nodding dog syndrome. I cann't see how they could reduce this due to how waves are formed (sea swell not lake waves) in the first place. Infact, T's could be slower in some instances. The other concern is that I quite often find myself sailing downhill with my windward rudder tip just flicking in and out of the water. When a gust hits using T's and before I can react the windward rudder might still lift out and when I bear away would the T prevent the rudder/hull to come back down as quickly as I would like whilst trying to bear away. If so this would counteract sailing 'harder' downwind. In saying this I have spoken to John Pierce, Jalini and Wayne and I don't think they would ever go back to normal rudders so their advantages must out weigh their disadvantages.

Has anyone addressed how these rudders are used in water of unknown depth? I've kicked up a rudder or two in areas I thought were deep enough (the Keys mostly), and while it's a pain to run back and reset, at least it didn't break the rudder.

The same is true for hidden lobster trap lines that aren't marked or are somehow sitting below the surface. If the T-foil rudder caught one at full tilt, would it kick up (or out, or something), or just bring the boat to a screetching halt?

If there is no provision to kick up, would it be prudent of the sailor to keep the minimum daggarboard depth greater than that of the rudders?

The problem is that you have to be at a complete standstill to kick them up - or the foil will want to drive the rudder down as the boat moves forward. The solid rudder trunk does also allow very precise control over the angle of the t-foil while under way - and that's got to be really important. This kind of trunk is used on skiffs like the 49'er (throwing stones <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />). Even our I20 style kickup rudder systems will allow the rudder to angle back just from loading (especially when the springs wear a little).

I also sail a Stealth without T-foils although I have on a few occasions borrowed a pair.

I don't believe they cure the "nodding dog syndrome" - that's based on racing alongside a T equipped boat and noticing that it was pitching up and down in the same way that my boat was. Mind you, we do get a pretty nasty short chop quite often which doesn't help.

I've always thought that the problem would be with the increased drag in light winds. That doesn't appear to be borne out in practice however with boatspeed for "T" and "non-T" boats being very similar.

I've not noticed any additional problems with weed. Where I sail (the Firth of Forth) the problem tends to be with floating seaweed around spring tides. Whilst the damn stuff does get caught on the rudder and usually requires a guddle over the back to clear it, I've not noticed any getting caught on the foils.

If you hit something with a cartridge rudder (with or without foils) something may break. But as you'll have already hit it with the daggerboard you probably won't be going too fast!

I've only briefly sailed with T-foils in strong breeze - about an F5 as a squall line came through as I was on my way out to the race course. In those conditions you cannot understand how amazing the foils are until you've tried them. There is no tendancy for the bows to dig in at all (even with no spinnaker up), you just make the boat go faster!

My conclusion is that in big breeze the T-foils are faster because they let you push much harder. In light breeze I don't think they're faster - but I'm not convinced they're slower either!

From what I am reading from guys who have/are sailing with the Stealth system, it appears to me that they perform much better with stronger wind (greater speed) and have a far less noticeable effect in the light?? To me that would indicate that the working surface of those foils could be a "little on the small side". We had a similar effect with smaller foils early, and it was only after I did some recalculations and we enlarged the foils that an appreciable performance improvement was documented throughout the full range of speed, BUT most dramatically in the light (and particularly choppy)

They seem to be trying "foils" on everything! try this link for a video of an 18' skiff (in a very old and battered condition) completely hydrofoiling, does 14.7 knots in a windspeed maximun of 6 knots on Lake Geneva Switzerland. First sail on the water with foils.
http://www.jeanpierreziegert.ch/video/FirstFlight.mov

There is also another way of looking at it :

-1- The T-foils are at the very back and so could acquire large effective stabilizing with only small forces.

additional comments. Roughly the centre of volume on a cat is below the main beam or just in front of it. This means that its leverage arm can easily be about 2.5 mtr = 6 ft. That is quite alot. The leverage of the sails is about 4 mtr = 10 ft. Say a gust that requires a 150 kg crew to move back 1 meter (large gust) can also be resisted by only some 60 kg downforce on the T-foils. At the typically effeciency of a hydrofoil (Daggerboards/rudders) the increase in drag (momentarily) is only about 6 kg's which is only a portion of the increase in saildrive due to the gust (about 50 kg's). So you invest

So yes there is more drag (momentarily) but the setup can still harness a net increase in drive that a more conventional crew probably could not harness in the same way. Because How quickly can you move backwards and smoothen out the gust with the mainsheet ? The T-foils can do that immediately. It sure felt that way when sailing the Stealth personally.


-2- The T-foils are only "ON" when they are tilted sufficiently relative to the water surface. So when the crew learns to place their weight such that in stable winds the T-foils are not working then the basic drag linked to them can be quite small indeed. The T-foils when then only see large drag when they are being used due to a gust or something, but here their positive effects may well outweight the increase in drag.

Additional comments : So it could well be a case of wehn you don't need them then the added drag is just too small to notice. Afterall how many of you could notice the speed difference if they sailed with rudder boards that are 4 inches longer ? The increase in area will be about the same in both cases. And ofcourse when you do need them then their effect is immediately noticed. Also note that the switching between "on" and "off" is always alot faster then any crew can react manually.


-3- The T-foils counter forces are proportional to the angle of attack the hulls make relative to the water surface (travelled direction). Meaning that the drag is proportional to the exitation of the boat as well. Small exitation = little effect to be won but also drag = small and the other way around. It could well be a case of only paying the penalty when the positive effects are large as well.


-4- A 4th benefit I always envisioned is that T-foils can act as a 3rd weightless crew member. Meaning it has the effect of putting more weight on the back of the boat allowing significantly more drive in a blow while not despressing the hulls in deeper when its effect is not needed. Also because it is at the far back of the boat it will achieve more resistance to pitching for a given depressing of the hulls the any additional crew weight. As such it is very effective in a big blow.

Also not that a T-foil with a 10:1 ratio in acquired lift (downforce) will always allow nett more saildrive when in use.

Say 50 kg more saildrive by a 4 mtr leverage arm will require the T-foils, 2.5 mtr from bouyancy pivot point, to work at a laoding off 4/2.5 * 50 = 80 kg's leading to a drag increase off 80/10 = 8 kg + plus something for depressing the hulls in deeper say about 5 kg. Therefor the nett increase in saildrive is 50 - (8+5) kg is 37 kg's.

Now you try to harness that increase without T-foils by moving your crew weight around and trimming your sails. From personal experience I can tell that that requires alot of skill and concentration and even then you may well not achieve it. All the while the T-foils do it automatically.

I would love to try the T-foils on my Taipan as my boat does require alot of attention on fast reaching in considerable wind. And I don't have weeds to worry about.

Wouter


Wouter

and they'll make that pitchpole all that more exciting once the t-foils clear the water and loose all their downforce...wheeeee! Better opportunity to be thrown clear. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Amen to that! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

I will add my experiences to this debate.

We first tried the T-foil rudders 5 years ago, it was immediately obvious that they completely altered the sailing characteristics of the boat.

This is not one of those changes that you make and you are not sure whether anything actually changes, I say again the boat is totally different with T-foil rudders.

Next we had to check whether or not the difference was fast. Like Darryl we carried out 2 boat tuning with identical boats except for the rudders. In no circumstances was the non T- foil rudder equipped boat any faster.

In any kind of wave pattern whatever the wind strength the T-foils were quicker both upwind and downwind and in winds > 12 knots the T-foils where again quicker.

We also tried them on our formula 18 HT boat and the effect was just as marked.

And more recently the current Sptfire European Champion purchased a set and tested them he also confirms my/Darryls comments

I have no idea how much drag the T-foils create, and quite frankly I don't care, catmarans go quicker with them on so whatever the figure it is less than the drag of a normally equipped hull travelling through the water.

We did no tank testing (I think you will find that not much tank testing time is bought by any beach catamaran manufacturer since it is cheaper to build 2 boats and do the job properly on the sea).

As to the weed question, obviously a dagger rudder is harder to clear than a kick up rudder, just as a dagger board is harder than a centreboard. Perhaps if your water is very weedy these are not for you.

My credentials for carrying out these tests are that I was a full time member of the British sailing Team racing Tornado, my ISAF World ranking got to 9th, I was paid to sail by the Royal Yachting Association and my job from 1997 to 2000 consisted of 9-5 most weeks 2 boat tuning, with 8 -10 regattas a year thrown in, I have done thousands of hours of this work.

I would entirely echo Darryls findings and since we are the only people I know of who have done this and we both completely agree the chances are that we are not mistaken.

There is one further effect that is also noticable although I didn't pick up on it for ages, and that is that not only is the boat smoother through the waves but it is also smoother through gusts. Put simply the T-foil equipped boat lifts a hull more slowly when the gust hits, we think that this is because as the gust hits and the rig drives harder, it tries to push the bows down, of course the T-foils resist this, and the windward t-foil obviously adds load to the windward hull slowing down the hull rise and so squirting the boat forwards.

I have already made the decision to go with foils. I see them as the future. In regards to the last part of your post. The windward hull lifts slower with the foil in a gust but the foil will break the surface at some point. Does this come with a rush of lift?

John,

How much are a set of T-foils?

[edit] I guess that question should also be directed to Darryl.

Gareth

Very good John, thanks for yours and others comments..... Would be interesting to try them on an F18.

Any idea of a price for these blades and rudder heads to hold them? I've heard about $1,000 US. Also, if the T foils make the rudders more effective, maybe the rudders could be shortened? That would give you a little more reaction time to see the bottom before you impact it and bust your $1,000 rudders!

Also, have there been any problems with the T foils coming off after long periods of hard use, or cracking where they join the rudder?

You all have noticed the America's Cup designers have been putting end plate type wings on their keels for years now, (but never on their rudders) of course for different reasons, but there must be some improvement in drag or they would have dumped them and they do computer testing, tank testing as well as side by side. It must work... <img src="http://www.catsailor.com/forums/images/graemlins/blush.gif" alt="" />

Mate, Know of any of the pointy end of the Interntional Moth class that doesnt have at rudder foils? Even those who havent made the move to "flying" International Moths.. Ok they may not be "professional" sailors but I suspect they are possibly some of the most skilled sailors professional or Am around..

As for I 14s..
I believe your misunderstanding why International 14s have rudder foils.. Its not to reduce nose diving although that may be a beneficial side benefit.. The reason Bieker started the I14 rudder foil tren is to reduce the aft wave and hence make the water "believe" the hull was 16 not 14 foot.. So trimming of the foil is required for the incline of the hull to the water.. As Im sure your aware I14s sail flat upwind and a slightly nose up position downhill.. As for benefits Bieker suggests med to light air will show the BI14 rudder theory.. Not when the I 14 is airborne..
This is evident in the positioning of the I 14 rudder foil.. Bs foils are above half way up the rudder not at the base like the Moths or cats..

Just a few thoughts..

S

Not quite true, the Foils are also used to remove the pitchpoling issues that 14's have as a result of going to more skill like shapes with fine(r) bows.

THe trim the nose of the boat down for upwind sailing and the trim the bow up for downwind sailing.

Hmm.. Well Bieker put the first foils on his B3 to increase water line "length".. If you look at his foil they
1:are assymetric...
2: Above half way up the rudder..
3: yes they are movable to maintain water flow aft of the stern.
BUT the pitchpoling issue wasnt the driving force behind Biekers motivation.. The B4 has a fuller bow and hull shape to the B2 & B3.. The bows of the I 14 is regulated by a mid length mininium measuring point. Since skiffs have a wedge shaped hull profile they cant really go any finer than the B3 under the current rules.. In fact the B3 is fuller than the earlier "Zero" hull which was legal under the old Australian Skiff rules..

I dont know if Bieker's thoughts are still on the I 14 website or his home website..

After Bieker was Luggy.. Who built the "flying" I14.. His foils were designed to fly so his original foils were at the base of the rudder and again assymetric to generate lift..
The lifting foil was replaced by symetric foil..Again at the base of the rudder becaues the rudder was already set up for foil at that position..

Must admit I havent kept up with the current state of play.. BUT Biekers foils are NOT designed for anti-pitchpoling.. Pitchpoling is secondary..

The 14's we had at Grafham (ages ago) were loving the foils because they could trim them to allow more drive downwind; if this is not how Bieker was expecting them to be used then hohu,- it is how they were being used, but I know from talking to the guys (and I am sure there was an article in the yachts and yachting mag over here stating that they use the foils to allow them to drive harder downhill) that they made the bear off at the top marj easier and that they could drive much harder down wind.

I have not read or heard too much into the I14 rudders, but from everything I have heard from the AUS fleet, Stuart is correct.

I believe the biggest gains were made upwinf where the foils tricked the boat into behaving like it had more waterline length by reducing stern wake.

On the downwing the foils are left pretty neutral or maybe a slight hint of raking them back. Up wind the raked the rudder forward. This also helped lift the transom out of the water.

Reduced pitching and nosedives was just a perk to the theory.

Downhill an Int 14 has its bow lifted by the kites. As do other skiffs.. Have a look at the 12s where they bounce down hill almost on their sterns with no wings..
At the top mark one doesn't have time (well I didnt) to tip the rudder, vang raise the plate and get set.. One has enough time to vang off while the crew pulls the plate.. get back and bear away.. Even then one bears off really when the kite goes up..
When the kits is up I would guess the lift by the kite is a 70 kgs or so..
The issue comes when one is jumping waves.. If the third or so wave is bigger you snuff the bow. Or the waves and the bounces are out of sequence and one lands in the trough and not the top of the wave.. If the kits remains full the lift pulls the bow out and up.. If not you swim..

I do know however the fleets here are probably more experienced than the UK fleets.. So maybe that is a factor?

Just relaying what I was told, don't shoot the messenger, if they were wrong then so bit it.

Now Darryl that is not the entire story, is it?

I love what you have done with the boat, but lets face it, adding the kite alone did not drop its vyc from 88 to 77. Making the boat a good 50% lighter and increasing its stiffness, improving sail plan, taking away the fore beam and fore tramp, moving the position of the dagger boards and changing thier design. have all contributed to the performance gains.

I would suspect the new boat would have been low eighties/ high seventies without the kite.

Please keep experimenting Darryl, when you crack 75 vyc I'll buy one!

p.s. I have watched a lot of video of the boat, and none of it shows the boat tacking, is tacking still an issue for the AO design?

One thing that has been stated over and over is that these rudders "must" have more drag than a non-T foil rudder and this seems to be one of the main arguments against them. One preson alluded to the fact the A Cup boats use end plates on their keels and it was noted almost all new airliners use winglet foils on the ends of their wings. The SOLE purpose of these is to reduce the drag of the attached keel/wing. It has also been mentioned that the rudders are almost never in a perfectly neutral position in regard to the boat- they are almost constantly at an angle (ie loaded). Going upwind they are certainly loaded. The "endplate" effect of the foils in these conditions serves to decrease the tip vortices and drag and could even potentially result in a rudder with less drag than one without the foils. This would completely negate all the "They have more drag" arguments against them and may explain why even in light air T foil equipped boats seem to be at least comparable to non-T foil equipped boats.

Kirt

Now that is a very good point !

Parasitic drag will surely be larger for the T-foil rudders, but the end-vortex of a single foil will be reduced by the T-foil. Winglets on airplanes give a small drag reduction, so small that some modern designs dont even bother with them. In addition the angle and shape of the winglets are critical to make them perform, and this is on airplanes which operate in far more stable conditions than I think a rudder do.
I dont have the math to calculate the differences in drag, but dont believe the drag is the key to this. I believe it is the increased effectiveness of the rig.

Here is a very good article on the development of winglets.
http://oea.larc.nasa.gov/PAIS/Concept2Reality/winglets.html

Is it really so important as to why "T" foils improve the performance of a boat? Isn’t it quite sufficient that they DO? (And by no small degree) As I see it, there is a LOT of improvement from the fact that the sails are always at a more constant attitude to the wind and therefore they are always working more efficiently in all wind strengths than for a boat without foils. The rest is the foils also maintaining the hull in an attitude where it is able to accept that extra "power" and still "put it down" through the water retaining controllability/stability.
Is it necessary to fully understand the workings of a computer/calculator before accepting that by using it you can do more complicated computations with it than you can in your head?
THEY WORK guys, surely that’s enough?
In some ways I hope that sailers DON’T put T foils on their cats. The less that are out there, the bigger the advantage we have. If everyone “puts them on”, we’re all “back to square one” and we have to look elsewhere for efficiency improvements.
Someone asked about the cost of the T foil rudders? Our cost for a T foil rudder is only about 5% to10% more than for our “normal” ones, and this is only due to the fact that they are slightly larger in surface area and take a little longer to lay up. We don’t intend to charge any extra for an F14 with or without T foils.
DAZZ, I think you are confusing the yardstick for the 4.4 Alpha, which was a heavier “older” design than the 4.3.
The 4.3 was the cat that we built primarily the same as the F14 (as a “prototype test” boat). Although it was constructed in “polyester”, “normal CSM” and had an aluminium mast, it was “comparable” to the F14 and approximately only 15 Kgs heavier. We sailed it competitively for three seasons, established the 88 yardstick, then sold it on to a “non racing” sailer, it is a “unique” cat, a “one off”
I will go out on a limb here and suggest (only suggest) that the yardstick for the F14 WILL settle somewhere around the 73, 74, mark (maybe, just maybe, lower?). There certainly is much more potential for them to perform better than they are at present. As with any class, their “final” yardstick is dependent entirely on just how many of them eventually get out on the water regularly competing.
P.S. The Alpha F14 tacks "on a pin" (I am not sure which video you have been watching DAZZ, but in the DVD that I have been sending out on request, it is shown tacking and jibing). As to the "strength" of the T foils, we have given them the "crash" test many times as well as "loading" them repeatedly against up and down "flex" and so far they have proved strong to the point of being, "over engineered"
STEVE, I think someone wrote earlier that because it wasn't expressly mentioned/allowed in the F18 rules, then "T" foils are disallowed on F18's (Tornadoes as well) -they will never know just what joy they are missing.

Darryl,

questioning the "why" of things is just human nature so please bear over with us. When Descartes said "I think, therefore I am", the folloup was an immediate "Why?" :-)

OR "say what?"

Well, it is much better than "who cares"..

Wasn't Descartes "beheaded"????

What thuh?

Do the foils affect leeway at all? I'm trying to visualize how they work when the hulls are angled with respect to the water surface (when you're flying a hull, for instance).

How do they work uphill/downhill in medium/large ocean swell (1-3 meter, 5 second period type swell) with wind chop?

I don't have an engineering degree and I didn't stay at a Holiday Inn last night, so a lot of this discussion is over my head right now...

Thank you Darryl for sharing your ideas and results!
Your posts here are most interesting and stimulating and contribute to making this forum worthwhile.

But I think most of us agree that trying to understand why something works is a prerequisite for developing technology further.

The most significant mechanisms of operation have been presented already by Darryl and others:
- Reducing pitching, thereby preventing airflow over the sails from becoming detached.
- Keeping the bows from going down downwind, allowing driving the boat harder.
- Reducing tip-vortex drag - if one gets the wings right.

However, I would like to add one factor that may contribute positively in some conditions:
The horizontal wing may act as a paddle as the boat pitches in small waves, hence the wings MAY contribute forward motion. This effect will be stronger if the wings are allowed to move some degress up and down (as I14-wings do?)

Darrryl: What kind of rudder fittings do you use?
Can you show us more pictures?

Stein

Look at the top

That's what happens for being too cleaver.. Beheaded, boiled in oil, have to drink hemlock.. It goes fast.. I feel he is a necromancer of the dark arts and he must be an evil doer!

The rudder fittings are "the most simply that are practical" I.E the top and bottom fittings on the transom are stainless pins set in an aluminium casting (standard, off the shelf fittings) and the rest is a top and a bottom hole drilled through the carbon fibre/ Kevlar (50/50) that the stocks are made from with a moulded shape allowing for those holes. We like to simplify EVERYTHING as much as practical so that the greatest percentage of our boats can be built "in house". Saves a lot of time and expense. It's also nice not having to rely on multitudes of "outside" suppliers.
The T foils seem to have no noticeable effect other than those already described, the windward and leeward performance as regards pointing/leeward drift, appear to be the same sailing with T foiled rudders or without, the foils work the same with the cat heeled or not, and lifting one rudder completely out of the water has no different “feel” or movements than the same without foils, over “long swells” the foils tend to keep the decks parallel to the “average” water surface therefore traversing slow, long changes to the surface (as in long swells) the hulls will follow parallel to those change, but through “chop” the decks stay level and instead of the bow going up and down, the whole hull rises and falls -level- (but with much less movement overal than with the "pitching" motion of a cat without foils) also without the (nodding dog) rocking.

Scooby,

Thanks for the picture.

Do the foils make the overall beam wider, i.e., extend past the widest part of the hull?

Not in the Stealth F16, but they look like they might on the F14.

Many thanks for sharing first hand information about foils.

Some comments:

- Rudder foils may ride in the back wave. The effect is simmilar to having a longer waterline.

- Your foils seem to be symetric in section and horizontally placed (zero angle of incidence). Still, they generate upwards lift most of the time. Explanation: in order to form the back wave, flow in the stern is upwards. From the foil's point of view, this means a positive angle of attack. As a result, whenever the boat is horizontal or with a bow up attitude, your foils lift the boat from the water, reducing wetted surface.

- The concept of curved corner L shaped foils is to increase effective span. I don't know why and how. Learned that from articles about Cogito and Hobie's foiler. This shape deserves a try in the F14. Please!

I hope to be able to add information to this thread when my boat is launched. My rudder's foils are different, though. See the picture attached.

Cheers,

Now THAT I find really interesting (even exciting), LUIZ (the foils in the photo). There are several things that you have done with those foils that I would like to know the effects of under actual sailing conditions, I would like to know from you just how well they work with the position of the foils so far from the tip, whether there is interaction/interference between the “wake” of the transom and the foils, whether or not their proximity to the surface effects their performance, and by using a “delta” shape for the actual foils, are they more effective at reducing “tip vortex” from the foils. There are several other lesser questions but as the foils that you have decided on are similar to ones that we considered but decided finally not to go with (mainly for manufacturing reasons), and as a consequence we did not conduct any testing on, I am more than curious as to the outcome. THEY SHOULD WORK (and work well). There are several things about your set up that I find very attractive and which I like very much, and I look forward with not a little anticipation to hearing of your “test” out come.
GOOD LUCK from down under mate, great to see an individual willing to put their ideas to the “ACID” test
P.S. They are symetrical foils?

Luiz,

can you send me the articles on Cogito and trifoiler that you have. I'll really appreciate that.

wouterhijink(at)hotmail.com

Thanks

Wouter

Let me agree with Luiz. You need to review the theory on this.

Wouter,

I read both articles in old editions of Multihulls Magazine. They are not available online or in digital format. I'll try to locate them to scan and send to you. Allow me some time - I think they aren't at home, but in the weekend house.

Note: I do not subscribe or recommend multihulls magazine anymore.

Darryl,

After five years of construction, ACID is a rather appropriate word… for my stomach! I knew nothing about foils before purchasing the boat's project and learned what I could during construction. It is still going on, so there’s time to learn more. Hopefully not much (I hope).

All remarks are based on what the designer said, not on research or first hand experience. In other words, I am just forwarding information and elaborating on it.

My boat is designed to reach maximum speed with the central hull just skimming the surface. It is not intended to fly two hulls - which is good for cruising.

The rudder foils are asymmetrical. They are placed close to the surface so that lift is maximized by the back wave flow and goes to zero suddenly, when the central hull leaves the water. Note that there is a “step” in the lift function: from very high lift to zero lift. In comparison, your rudder tip foil generates positive lift most of the time and becomes slower - eventually negative - as the bow points down. But the lift function is continuous, without steps, meaning that they work quite differently from mine.

Analyzing the differences:
- High asymmetric rudder foils are meant to maximize lift until the central hull is raised from the water, when their lift contribution becomes unnecessary. They never generate negative lift. The lift x angle of attack function is discontinuous. They are draggy in light airs.
- Your foils provide a smaller positive lift most of the time that gradually reduces and becomes negative as the pitch attitude requires more and more correction. There is a lot less drag in light air, but extra wetted surface in heavy weather conditions due to the negative lift sinking the stern. This means more drag AND more wetted surface. In other words, it slows down the boat to keep it from pitchpoling. Sacrificing speed for stability is a good trade whenever fore and aft stability is what limits speed. For this reason, it is reasonable to say that your type of foils is a great addition for any boat with more transversal stability than fore and aft stability.

I ignore the rationale behind the choice of each foil shape used in my boat. There are four different formats:

- Symmetric section rudder blade with elliptical tip
- Asymmetric section Bruce foils with elliptical tips.
- Asymmetric section delta shaped rudder's foils with straight tips.
- Swept back asymmetric section rear float foils with straight tips.

All asymmetric foils feature one flat surface and one curved surface. As far as I know, the choice of section was for constructive reasons, convex surfaces being difficult to build both for the plug and to laminate in the mould (for serial construction). I wonder if the tips of the smaller foils are the only straight ones for the same reason (constructive), or if it is because those are the foils that go in and out of the water to keep the boat with a bow up attitude.

More later. Or after tests <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

Hi Darryl,
I'm curious, how did you determine the incidence you should set your foils at so that they are neutral when the boat is level? I've got a Hobie 14 (AKA, Pitchpole Central!!! {And the H-16 guys complain!!!}) that I'd like to add these to, but I'm not sure how to "Keep it level"!!! Have you got any suggestions?
Thanks, Ryan

My guess: he just positioned the foil parallel to the waterline - but this is not zero angle of incidence because the flow is tilted upwards. If you want zero incidence and the rudder is shallow, place the foil parallel to the nearby hull bottom. If the rudder is VERY deep, horizontal is fine. If it is average, place the foils between horizontal and parallel to hull bottom.

Related info: my rudder foils are positioned with the flat face parallel to the waterline. This represents about 1 or 2 deg incidence,if we consider "zero" to be the zero lift flow direction. However, the flow there runs upwards. Assuming the flow being paralel to the hull's bottom, I must add another 11 to 13 degrees, totalling 12 to 15 degrees incidence, which seems VERY HIGH.

The lift must be significant. The price is paid in drag. I wonder if this incidence isn't too much - and plan to try a plain blade as well, just to compare performances.

Ryan, the T foils for a cat that you want to use as a “pitch” control I.E to stop (or dampen) the bows from diving AND rising dramatically, needs to be of a symmetrical profile (Luis’s post goes into a range of effects of different profile foils which could confuse the issue if you all you want from them is for the cat to be more stable fore and aft). Personally I feel that cats that could benefit the greatest of any of those cats “out there” at present are the Hobie 14 and 16.
As a pitch control, you want to ascertain the “ideal attitude” that you would want the hulls to be sailing at if you were sailing on the proverbial dead flat, smooth surface, and the wind was absolutely constant. (No such conditions could ever exist but we can dream), then project a line parallel to the “flat surface” from bow to stern of the hulls. Transpose that line onto the rudders in their fully down, “locked” position. That line then becomes the centreline of the foils, as that is the angle to the water surface that ideally you want the hulls to be sailing at all of the time, regardless of any “outside forces”.
You want symmetrical foils because you want lift to be generated both up or down depending on which way that the hulls are “tending” to pitch, so that the lift acts as a self regulating equal and opposite countering force to that “pitch”
As the bows of a Hobie 14 in particular, are so low in buoyancy, I personally think that I would set the T foils for them with a couple of degrees of positive lift rather than neutral I.E. set them up as described above then before fixing them into their final position angle them front down just a touch (2 or 3 degrees which is very small)

Wouter,

In the Trifoiler article there is only half a paragraph about "L" foils:

What Makes Them Work So Well By Greg Ketterman
Multihulls Magazine May-June 1994

"We have continued to pursue our L-shaped foils for many reasons. They are smooth and simple, and they have no moving parts below the water. Wing tips and "T" connections generally cause turbulence and drag. With our L-shaped foils, the aspect ratio of the horizontal section effectively adds to the aspect raio of the vertical section, and we have only one wing tip that creates losses. Sure, there is more stress in these fois, but modern materials can handle the stress without any problem."

There's another interesting (but unrelated) segment:

"In our research we discovered something that is surprising. The amount of wind required to get onto the foils is not sensitiveto the size of the foils...(supressed)... This is surprising because with airplanes, if you have a larger wing then you can take off at a lower speed and less power is required. Sailboats are unusual vehicles as they have the ability to increase their power as they accelerate. The power of most vehicles is fixed and therefore the thrust decreases as the vehicle accelerates; however, with a sailboat the thrust, or driving force, remains nearly steady as the boat accelerates. Since the thrust is steady and the speed is increasing, the power generated increases, magically. Once this is understood, then it makes sense to make the foils relatively small to yield better high-end performance. The top seed and efficiency of the boat are somewhat sensitive to the size of the foils. Our foils are surprisingly small..."

There is not much about L foils in Cogito's article as well:

The Aussie's Little America's Cup Reign is Sunk by Christian Féurier
Multihulls Magazine Jan-Feb 1996

"As the Australian early summer had been abnormally breezy, th Americans tried new rudders, L-shaped inside, in early January. Probably to try to stabilize hobby horsing in choppy seas, or reduce pitchpoling risks. They woked perfectly, but the cost was certainly an increased drag and they never used them."

PHOTO of Cogito flying a hull to show the L rudder with the following legend:

"The L-shaped rudders workd perfectly in choppy seas to stabilize the boat, but were not used in the races."

These were my sources. Summaries of real life experience. Your comments about L foils effective aspect ratio are very wellcome. Another view of my rudder's foils is attached.

All the best,

Agreed with everything, but you certainly mean "negative lift" (downwards).

2 or 3 degrees is not so small angle of attack. Symetrical Daggerbords work at about this angle of attack.

Rgrds,

Right Luiz when you are looking at the DIRECTION that the HULL transom is moving I.E transom down (negative DIRECTION) – bow up (positive DIRECTION), and visa versa, but - the usable productive lift generated from a symmetrical foil is always positive, (generated on the side that you want the "usable” lift) – it is generated through the inclination of the horizontal motion of the hull through the water and "operates in a direction", either, up or down (positive lift UPWARDS or positive lift DOWNWARDS
In the case of the Hobie 14', I feel that there should be a "static" amount of downward lift generated at the transom when sailing at the, so called, "level" state which will incline the bows slightly up simply to compensate for the lack of bouncy in the bows.
(Basically what is a little confusing is just a case of semantics)
When I said “a small amount” (2 to 3 degrees), it is because, with symmetrical T foils set at or near the bottom of the rudders, there is a certain amount of latitude for the actual angle(s) either side of the “level” which is quite “forgiving”. This is because within a few degrees either up or down of the actual “neutral” setting of the foils, the “real” lift/drag factor becomes progressively very small. (that is untill we look at very high velocities where the percentages are the same but their "effects" become "critical")
(We could make these descriptions REALLY confusing, by including, “pressure variables” into the mix, (I think that we would lose a great percentage of the readers if we did)

Luiz do you have rudders on the transom of the ama's as well as on the main hull, or do you only have a rudder on the central hull?

The theory of the curved “L” foils is very sound (and apparently also in practice as well); the primary problem with them is one of manufacture/construction. There are a LOT of side’s way leverage loads on the vertical part of the foil even under quite small sailing speeds and this alone creates difficulties in constructing a rigid/strong rudder, particularly one that has a high aspect ratio. The “T” foils on the other hand, have only minor sides way, leverage load differences acting on the vertical foil (they tend to balance each other out)
The main reason that I could see for using “L” foiled rudders would be where there is a problem with the “maximum overall beam” of a cat where the T foil would be wider than the allowable beam.
This in itself doesn’t have to be a problem if the T foils are “raked” aft to get the desired surface area and still not extend any wider than the outside of the hull.
By extending the foils back there is also a “hidden” advantage that, as the foils move up and down they also generate a small forward “thrust” to the boat.

The new light-wind weapon, jumping up and down on the bow.. Working the T-foil like a trampofoil. At last we can get to use some kinetics in cats also. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
http://ourworld.compuserve.com/homepages/roberthodgen/tramp.htm

With reference to angles of attack:-

On the Stealth, the rudders are held down by a pin through the top of the stock. Without the pin in the rudder moves up and down with changes in speed. As you sail gently in to/out from a beach you can watch the rudders rise and fall slowly. At quite fast speeds (IMO around 10 knots) the rudders are around threequarters down on my boat. So the loadings can not be particularly high. If you sit forward in this situation, as you'd expect, the rudders sink. When you move aft to put the pins in the rudders rise.

This is a useful trait when landing at a beach because all you need to do is unpin the rudders and then as you are about to land, move right aft and luff at the last moment. With these vertical stocks you retain steerage with even a small amount of rudder in the water at these lower speeds.

Interestingly, at Eastbourne a while back, the locking pin came out of one of my rudders on the downwind blast. This provided huge entertainment for Paul Warren right behind me as my port rudder launched itself out through the bottom of the stock! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
I, though, was not amused! <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />

Both "T" and "L" foils were tried on aircraft. Except for special applications "T" foils were dropped.

Every country that builds transport aircraft, that I know of, controls this information. Try looking up ITAR and Export Control.

Only one rudder on the central hull. It is designed to achieve max speed with the mainhull skiming the surface, so float rudders aren't necessary. It IS a cruising boat, with head, nav station, berths, etc.

Darryl,

Just to clarify:

The goat is to keep the boat from buriyng the bow, so the rudder's foils must generate downwards lift, to bury the stern (raising the bow).

In order to generate lift downwards the foil's leading edge must be positioned lower than its trailing edge.

That's about all one needs to know. The rest are nuances.

Is the situation the same for foils in the middle of the rudder, like mine? (lets call them "cross" foils).

On an aircraft "foils in the middle of the rudder" are called fences and used to control spanwise flow.

"T" foils on planes were not dropped, check out A320 family wingtips

Please forgive my ignorance, but what about the auto kick up feature? Is the a safety system on this set up? you just never know what you might encounter out there on the water.

Hey Luiz, NO boat is a cruising boat, if another one appears within 100 metres of it!! The race is on!!
In relation to the foils on a Hobie, I thought that was what I said - the front (leading edge) of the T foil lower (Pointing down) than the trailing edge, positive lift downwards at the transom??
Both T foils and L foils have their place on the wings of aircraft, If the foil is included as part of the wing in the design then a high aspect "curved" tip ending in an L foil is highly efficient (and desirable). When an existing "standard" straight wing ending in a "squared" off tip has tiplets added, T foils are more effective in “reducing “tip vortex than a single upward pointing foil with a "hard" angle at the transition between tiplet and wing. (Although just one “hard” angled tiplet is still more efficient than no tiplet at all). As I said earlier, the main detraction for an L foil on a cat is the manufacturing “difficulties” to compensate for it’s greater loads, not its undeniable efficiency as a continuation and integral part of the rudder.

I think there are plenty of T-foils on the tails of planes.

--Glenn

THey do not kick up ! You just stop PDQ !!!!!

"T foils on the tail of planes" are an entirely different subject for totally different reasons compared to T foils or L foils on the wings of aircraft.
Although as I think about it, maybe we should be relating the effects of T foils on rudders more to the “T” foils (elevators) on the tail of aircraft as their effects on the plane are much more closely related to the effects of T foils on a boat than any boat rudder foils are related to any foil(s) on the wings.
The elevators (T foils on the tail) control, primarily the forward angle of the aircraft, both nose up or nose down (and every angle in between) and apart from them being “articulated”, their “effect” works in exactly the same way that the T foils on the rudders of a cat work. The L or T foils on the wing tips of aircraft have only the one primary function of improving the efficiency of the wing mainly through reducing the tip vortex effect dramatically, apart from that it has no other “direct” effect on the stability, direction, or trim of the aircraft.
Has anyone seen L foils on the tail section of an aircraft??

Called a phugoid, test of aircraft stability in longitudinal axis, I have carried out this test on various aircraft. Similar to what you are seeing with T foils I guess.


http://en.wikipedia.org/wiki/Phugoid

When skipper-induced oscillation occurs on our boat it is of particular nuisance to my crew! <img src="http://www.catsailor.com/forums/images/graemlins/smirk.gif" alt="" /> <img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" />

There are some similarities between high elevator tail sections and T-Foil rudders. However there are a lot of differences and the tail sections have moveable surfaces which complicates things. Articles from the 1950's and 1960's might have some basic data. I would understand winglet first

No, but has anyone seen an aircraft with two fuselages and two tail rudders?


Has anyone seen what brought an end to A-class development in this? Rules? Drifting conditions downwind when some degree of bow down often is used to reduce transom drag.?
Would be interesting to see what was the reasoning for abandoning it as it seem to be very promesing.

BR
Patrik

Luiz, your rudder is unique. It would not be my solution but it from what I read, a lot of testing has been and it works. My concern would be "if you stall the rudder do you stall the lifting surface". If you push too hard on the rudder at speed do you make things much much worse instead of just worse.

The P-38 Lightning comes to mind when you ask about two fuselages. A very beautiful plane in my opinion: http://www.richard-seaman.com/Aircraft/AirShows/Chino2004/Sampler/P38.jpg
If you look at some of the planes Burt Rutan and Scaled Composites have done, you can find other examples, like Steve Fossets "Global Flyer" and others.

Have the A's even tried this? If they have, I guess their hullshape and length is is such that they dont need it to keep their rigs stable. Much the same reason the C-class dont use them.

Yes:

P38 Lightning http://en.wikipedia.org/wiki/P-38_Lightning

Cessna 337
http://en.wikipedia.org/wiki/Cessna_337

Not sure what this proves other than an unhealthy knowledge of aircraft <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Actually, twin rudder is reasonably common: http://en.wikipedia.org/wiki/Twin_tail

I'll get my anorak.

Paul

http://en.wikipedia.org/wiki/Image:B-25_Flying.jpg

This plane has IMHO something very much like an L form...

So does the cessna and the P-38 although, not fully symetrical anyway.

In A-cats, there is a clear difference due to hull shape from older boats to newer on how much they nod, I believe that is one of the things driving wavepiercing bows and so?

All the best
Patrik

My A is very stable in pitch. I can't see a lot of advantage in that area. If I want to lift the rudders in light air, I sit on the front crossbeam. There are easier ways to handle these problems.

Foiled rudders have been looked at to reduce drag. But, you don't gain that much compared to the pain.

Maybe we need to rethink this. If I build foiled rudders for my 14 you can be certain, that they will fit my A.

The 14's are different. Mine is really unstable in pitch. Anything would help.

Carl, what I meant was that when adopting that bow down attitude a foiled rudder would both hinder (downwards lift) it and, as lift and drag is coupled, slow the boat down.

I'm comparing a Auscat Mk3 with Marstroem boats and to me it seems as there is a clear difference in pitching behaviour.

It would be most interesting if you did try foiled rudders on your A-cat.

I don't think the A's are a good platform for T-foils. Their general make-up is such that gains would indeed be very limited. This also hints at the fact that other cat design, which are significantly different when compared to the A's can most definately benefit alot from application of T-foils.

For example I feel the A's are rather narrow compared to their length and mast height. Much more then other cats. They are therefor much more limited by capsizing then pitching. Wider boats like most of the non-A-class designs are much more limited in pitching the capsizing here the T-foils can be a great advantage. Probably increasingly so with decreasing hull length.

WOuter

Carl,

I guess if my rudder stalls the foil placed on the side where the flow is detached will also stall. I see no reason for the other foil to stall together. Since the stalled foil still generates lots of lift, this is not a reason for concern. Reataching the flow is as easy as placing the rudder in a lower angle of attack. Then, of course, I want to test it in real life.

As far as I know, the A Class initially banned rudder foils similar to mine. They were close to the surface and the concept was that they would increase the effective waterline. They probably worked well, otherwise it wouldn't be necessary to ban them.

I don't remember where I read this, so take it as an unconfirmed rumour.

Carl,

You are focusing on stability only. As I wrote before in this thread, most of the time the T foil provides upwards lift.

When the foil's lift is up, weight must be moved further aft to maintain the same pitch attitude. When lift is upwards the wetted surface is reduced. If this causes a (friction) drag reduction bigger than the foil's drag, their contribution is positive to performance.

Only when the boat pitches down the T foil provides downwards lift. Downward lift increases wetted surface. That adds to the foil drag to slow down the boat. This exchange of speed for stability is usefull when sailing in the limit. The rest of the time moving the weight aft is faster.

It could be seen as unhealthy not to know of the p38...