Rudder ends or T foils are not included in the beam measurement.

I've not done detailed calcs, but if you are saying we can get 40kg per foil, then that is an extra person for virtually no drag. Makes it sound like a no brainer that every one must have them, or we ban them ?

Thanks for the clarification. This is good because T-foils are much easier to build strong enough.

I was about to blow up about my guesses being used as facts but decided to do the calcs instead...lucky...my calcs indicate that a force of about 90kg with a 0.05m^2 foil may be achieved with about 2kg of drag at 20 knots. It's all rough numbers anyway because boats will pitch and heave which will change angles of attack constantly.

I personally think it is going to be exciting being in a class that has this sort of development. I will certainly participate...if it doesn't get banned...

You still haven't explained why you are promoting a banning of rudder foils because of the cost, but then you are promoting a rule which will make expensive carbon masts more favourable, in terms of performance and safety apparently, against the cheaper alternative...?

As I said previously, the rules are good as they are, for the moment. Those that want to develop can do so with very little risk of blowing away those ppl that want to buy a production boat off the shelf. I think it is a good balance at the moment.

If someone doesn't want to be part of a restricted development class, there are other classes more suited to their tastes.

Carbon masts are a known quantity when it comes to cost, but variable pitch T-foil rudders are an unknown. We dont know what they will cost if they are ever implemented, debugged and turned into a race winner. To me it dont make sense to ban then before we know more, but others want to stop the development before it passes from the stage of an idea.

I'm proposing to propose (if that makes any sense) to allow carbon masts to be built down to a level at which they can be built. John P has already confimed that his masts are built to design and not to a weight and so I believe that his masts may need correctors to measure. He has stared that he believes his masts are more than strong enough to withsatnd the loads. Has anyone asked John to quote for a Carbon masts only and compared this with an appropiate Alu section? I'm simply sayinmg that the tip weight rule limits who can sail the boat (yes they can carry righting bags or pole, but would someone want to ?)

I propose to ban variable trim T foils because I believe they will make all current boats obsolete.

Nope. On the trifoiler, both windward and leeward foils seek a fixed depth, thanks to the forward "sensors." In lighter winds, both foils generate positive lift. In high winds that would otherwise capsize the Trifoiler, the windward foil generates negative lift to seek the target depth.



The vertical coupling is meant to be cable, which cannot push, and therefore cannot cause the foil to generate positive lift and bury bows. The feedback system therefore generates only negative lift and cannot lift the sterns. Adjusted properly, it would only increase negative lift (and drag) once the corresponding hull lifts clear of the water, since there is no point in the foil increasing downward lift when the hull is still in the water!

The traditional T-foil property of generating negative lift as bows dive should be maintained in this system not by the feedback system, but by limitting the rotational travel of the horizontal foils. Such as system would always hold the sterns down at least as well as traditional T foils (and better when the windward hull rises).

A valid concern about the system is that that the additional righting moment would mean one could sail much hotter and faster downwind in high wind, but in doing so you risk stalling the windward foil and pitchpoling suddenly at speed. (But this is somewhat true of T-foils in general, I theorize: once the windward one clears the water it suddenly stops down-lifting, and the hull pops and the bows bury.)

I am not sure a foil would generate 90 kgs of lift for that little drag. Can anyone concur that statement as I'm a dummy with maths

At 0.05 m>2 this would mean a practical foil with a modern section and aspect ratio of about 1.25 metres long x 75mm wide. Now the loading would be so high at the tips that a huge amount of carbon would be needed such that I would doubt that you could construct such a wide beastie. OK reduce the width to say 75cms which is still a really wide wing on a rudder, down comes the aspect ratio, up goes the drag, add in a few dings etc and surface impections and up goes the drag even further, mmmmmm not looking so good now.

For all those maths boys, how much force in regards to foward motion does a F16 Spinnaker actually produce, I bet its not that many kilos as one can fairly easily hold on the sheet which is taking probably more than a third of the load. Interesting calculation

Yes Glen on my Stealth when the windward T foil comes out of the water the leeward bow immediately buries, fortunately the Stealths have ample reserve in the bows and generally the boat wants to submarine along its length to such an extent that the drag slows the boat and the sheet loads go so high that one tends to dump the sheet rather than pitchpole.

Still not convinced that in a practical sense adjustiable foils are any worry, if in doubt simply put an upper limit on the foil sq mtr size.

Have a read of the tri foiler manual. I put the link on the last posting. In it Ketterman explains why the leeward foil rises. You will find it interesting. Or maybe have a go on a tri foiler! <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

It would seem to me that unless a person has quite a lot of personal, PRACTICAL, hands-on experience with foils OR they have been involved in AND understand fully the maths, they should be very careful entering into debate on this subject in any way other than subjective curiosity as most of what is being written here concerning foils is pure conjecture and in many ways misleading, which could very easily lead to banning something for entirely the wrong assumptions.

Ok, with T-foils you are making a distinction between variable and fixed foils. So you are only opposed to variable foils.

Still a bit iffy about the mast tip weight rule change but I guess I need to become an F16 association member soon and vote on it. Can I get voting rights before the boat is finished and measured? I may have issues getting measured since there are no class measurers within a days drive of me...that I know of.

Disclaimer: The numbers I generated for T-foil lift are very quick and theoretical based on a set of lift and drag coefficients for a slightly incorrect reynolds number (about twice as much as it should be), so they are technically wrong. I believe the drag only takes into account induced drag; no friction, aspect ratio, etc. drag. It is true, practical foil design is fairly different to theoretical design.

The foil I had in mind was 500mm * 100mm. My mate has a higher aspect ratio foil (about 800 * 75mm) on his moth and I'm not a fan of them for boats, too much fluctuation in angle of attack (due to varying speed, yawing, pitching), which high aspect boards don't like in general. They tend to stall at lower angles of attack than lower aspect ratio foils.

There is a vast difference in the performance (efficiencies) between a “straight” high aspect foil with a small flap on the trailing edge and the same high aspect ratio foils raked backwards with the whole foil “turning” (up and down). Then to complicate matters even more if very small “tip winglets” are added then the efficiencies increase dramatically again. (The adage applies – “There are many more than one way to skin a cat”) Consider that a low aspect ratio foil set “straight” to all intent and purpose becomes a much higher aspect ratio in practice when raked, it’s chord length becomes much smaller in ratio to the surface that it is exposing to the direction of the fluid travelling over it. (If these principles hadn’t been exploited they would still be trying to break the sound barrier in aircraft today)

My assertion that the windward foil can generate negative lift in high wind is based on a vector diagram drawn by Mr. Ketterman himself, which I saw years ago. Nothing in the tri foiler manual contradicts this.

Yes there is all sorts of foils but hydrodynamics has been around a long time now and there is an awful lot known about it. My question is and still hasn't been answered is the following. How much actual drag will there be created from a foil of 0.5 metre sq and how much force can a Spinnaker create in foward motion.

Maths boys, and there are a number of you who regularly post on this forum, get your calculators out and do the sums for us dummies and please don't go all shy on me, show us your credentials. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

There is no answer to you question in the form that it is. For both parts IE foil - the drag is a variable calculatable only with additional criteria. the same applies to the "power" generated by the sinnaker

Very dependent on speed of flow around the spinnaker or foil, angle of attack, etc. etc...The question is too vague.

A vague answer about the force on the spinnaker...

As long as the boat isn't accelerating...

The force from the sails is equal to the force of drag on the hull and appendages, just in the opposite direction. (This is on all points of sail, upwind, downwind, reaching...)

Probably a big percentage of that force is developed by the spinnaker.

Glen, Give it a try and make some foils! I would hate to stop progress! If ever you are in the UK give me a call and come and try the only 2 tri foilers in Great Britain! Good Luck!

David