foils

Anyone care to offer a concise argument for/against foils?

Foils don't hurt as much as sabers (sabre EU)?

Really, how concise? Performance vs. convenience. Concise enough.

Different foil.

If foils improve performance, how? And under what wind conditions and sea states?

When I've tried to follow this subject in the past, clarity suffered almost from the beginning. As with all things F16, there is much angst.

Not sure if I understand your question, you are talking about lifting hydrofoils?
If yes, the pro is
less drag for fast vessels, because the drag due to lift of a foil dimishes with speed (1/v²), while the drag of a non lifting hull increases with speed (v²). Depending on weight and geometry there is a certain speed, above it, foils are a good, below it foils are bad. To achieve this speed you need enough wind and calm see state.
The main cons are impractical handling on beaches with banks and other obstacles and complexity.

At the end the question is: Do we need foils to have fun?

Cheers,

Klaus

I'm not sure I understand my question! I'm wondering if foils added to the rudders of my Blade would reduce the "nose dive" under spin. . . and what are the trade-offs?

I think he is referring to bridle foils that enable you to lower the jib tack without stressing the hulls. The Nacra 6.0 had bridle foils and a huge jib. These are good things but the box rules may prohibit.

Pgp,

think of rudder foils like down force on an F1 car. On the car extra down force will make it easier to go around corners etc making the car quicker around the track, despite having cost you some top end speed.

T foils on your rudders will make it easier/safer to go down wind but this will be at the expence of top end speed both upwind and down due to increased drag.

Look at it like this.. The current top speed of your boat down wind is X, if you fit foils it will be reduced to 0.95X. However because of the risk of capsize you might only sail to 80% of the boat's possible top speed down wind at present and this could increase to 90% with the foils.

So some quick algebra suggests that at present your going 0.8X down wind but if you fit foils you'll be able to do 0.86X.

The real question is what are the actual percentages and is the gain down wind sufficient to make up for to loss upwind?

I had this crazy notion; put a t-foil on a bracket like an out board motor or just lift it like a dagger board.

Pete,

That is the Stealth system. Foils and case done just like that. The only issue with installation would be getting angle correct. Misalignment of the T to the correct sailing plane will be very slow.

They do work to provide pitching resistance. Note canted daggers do the same thing. There is a slight use problem from a kick up standpoint but this is no more of a problem than the daggers.

MY opinion on foils: They try and hold the hull at a set orientation. This would be OK with me if that orientation worked in all conditions. In flat water we sail 1 way, but in rough conditions we may elect to try and run the nose up some to clear the waves. Now I have drag fighting me trying to keep it down. The other thing is that if the foils are working to keep the boat in a particular orientation, you may not be placing your crew weight correctly. It looks right but the foils are "working =drag" keeping the orientation. The other item which bothered me most was when they do let go it is catastrophic. In a big pitch there can be quite a bit of down force on the stern, when it lets go you are gone. It may save you sometimes but that feeling of almost saving it followed by cavitation just did not jive quite right.

M

This is why I don't like them.

". . .when they do let go it is catastrophic."

That's what I was afraid of.

THing is, in 2 years pf sailing my Stealth, in loads of wind at times, I have NEVER had them let go.

Andy,




The F16 rules (as established in 2002) never rule on details like that. Such a thing would be fundamentally against the concept of the F16 class. We only rule on fundamental principles, never on specific details or implementations. For example, we have a rule on mast length or mast tipweight but don't rule in any way on how you satisfy these rules.

By extention the bridle foils are allowed as long as you use this feature to break some fundamental rule by fitting for example an oversized jib or whatever.

Wouter

I agree with Simon and Matt here.

Getting the angle set up right is very important, but in racing with the T-foils I found their advantages to be very convincing.

Personally, I would love to have them on my Taipan F16, especially when singlehanding. The boat calms right down and you have bought yourself heaps of leeway with respect to diving on bear-aways, chop and reaching.

At the Global Challenge 2007 it would have improved my own results dramatically.

Of course nothing is without drawbacks, but that is not the point. Scarecrow also touches on this. The trick is to design them in such a way that the advantages outweight the disadvantages over a wide spectrum of conditions. So in some conditions you may face a drawback but in a disproportionally large remaining spectrum you get advantages, making you overall better.

Personally, I think (kick-up) T-foil rudders are a very good concept for novice and/or recreational F16 sailors. It makes the boat feel like a 20 footer in the dive sense while keeping all other aspects of a nimble lightweight 16 footer.

The best solution would be to have normal kick-up T-foil rudders where the T-foils can be unlocked to allow them to rotate freely. In the light stuff and when leaving/returning to the beach you just let them weathervane to whatever hull (or rudder) attitude you prefer and in the rough stuff you lock them down.

Wouter

Let me jump ahead for a moment.

In reference to the racing rules: If I have a system, permanently mounted to the boat, I can deploy it at will like the chute or dagger boards.

If I have an optional system, like sailing 1-up or 2-up, I must use it for the entirety of a regatta.

If that is true, I can mount a t-foil off the back of the rear cross bar and deploy it like the dagger boards. Up or down as I see fit?

From my reading of the rules all T-foils should be outlawed:

Rule 1.6 (Daggerboards and rudders), paragraph 4 (added by vote in 2007), point d:

"End fences/horizontal appendages below the waterline will not be allowed."

Here you go. The next Stealth with T-foils I'm racing against is going to be protested. Let's see how it goes

Read the full paragraph, that sentence only applies to dagger/centreboards, not rudders.

Pgp, I think your proposed foil would be considered a dagger board and therefore wouldn't be legal.

I read the full paragraph. And I disagree with you, this could be interpreted as applying to both centerboard and dagger board.

Full para is; wih my annotations

1.6.4 (Added by vote, August 2007) For the avoidance of doubt, daggerboards/centerboards will conform to the following :
a) Curved/’Banana’ boards will not be allowed.
b) Assymetrical cross-section profile boards will be allowed.
c) Fore/aft movement of the boards when in the down position will not be allowed.
d) End fences/horizontal appendages below the waterline will not be allowed. The board shall be capable of removal, without tools, via the upper opening of the case.
e) There will be no limitation on the daggerboard/centerboard length

Why hasn't somebody came up with an adjustable T-foil that can be changed on the fly?

A pivot point and a tube running through the rudder with threaded rod and a knob to change the angle.

Doesn't seem that complicated in my head. Biggest problem would be the weight.


Ooooh! or, a rudder that is two pieces. A front part and a back part that slip against each other, so the shape doesn't change too much. Dovetail them together in some fashion. Front half of the T-foil pivots on the front part of the rudder. Back mount of the T-foil slides on a pin on the moveable part of the rudder. Unless they were Aluminum they would probably be heave as well.

If you're interested look at the International 14s. They have the systems you just need to link them.

Hi all,

seems to me the only people that think that, T foils on rudders have drawbacks are those that have not used them.

Mind you I have not used them, but the improvement in performance that I witnessed racing against Barret's F14 with and with out them, has convinced me. Probably the most surprising improvement in performance was upwind, which most people seem to ignore. The reduction in pitching or "Hobby Horseing" allows the flow to stay attached to sails, keeping the boat driving through chop.

Can't see why it wouldn't be the same for F16's most cats hobby horse to some extent, particularly one up when you don't have the weight and power to press the bows through the waves and it rises over them.

Hi twicebitten,


this correct, the other big improvement comes from the fact that if the boat is pitching the T-foil on the rudder generates thrust (e.g. a forward directed force) as well. I don't want to go into the details of this effect, but it is similar to the fin of a dolphin.
However F16 racing results doesn't reflect, that the Stealth F16 are that much superior, so I wouldn't conclude that T-foils are a game changer.
For the downwind benefit of T-foils, I am not sure at all, since there are many other ways to avoid nose diving (more volume in the bows, more aft positioned rear beam to allow crew and helm to be more aft, even water ballast at the sterns) without generating tha much drag as T-foils. If the boat starts to nose dive, you can always sail deeper, a bit slower but same vmg.

But I have no T-foils, so I must see the drawbacks

Cheers,

Klaus

OK then there are those for and against T foils, I count myself definately a convert having sailed with both on the same hulls, for me its the lack of pitching and lack of bow down moments which swings it.

To move on one more stage then what about inclined foils and T foils AKA the A class where inclined or banana board seems mandatory at the moment.

A designer once likened inclined boards as the same advantage as when you rail a windsurfer with a centre board ( OK not so many around these days ) to incline the board and the baord will lift to promote earlier planning, it does seem to work.

yes agreed, for the same hulls. But if you have the choice between a boat with unsufficient bow volume and T-foils or a boat with proper volume distribution and without T-foils, what would you take? T-foils producing 20kg downforce is the same as a boat with 20 kg lead in its sterns. (I should mention that I think that ballast can be something good in some cases)

On a A-class we have lifting foils, which means lifting the bows and reducing the drag, while rudder-T-foils raise the bows and increase drag. There is now doubt about the benefit of lifting foils, once your boat can reach a certain speed. Many designs have shown that (Hobie Trifoiler, Raven, etc.)

Cheers,

Klaus

So how about my bolt on/bolt off question? Is such a system in compliance with current rules?

What if I had two sets of rudders; one with foils one without?

The T foils on the Stealth are symmetrical, when the hull is level it doesn't behave as a foil ( but has some drag ). However when the hull starts to dive the angle of attack increases the lift in a normal conventional way ( basically it tries to keep the hull level ). To check my rudders were working properly and at the right position to the horizontal I simply undid the locating pin, transferring the weight along the boat would raise or lower the rudder ie the rudder was trying to maintain its own level in the water regardless of the hull.

Getting back to the inclined foils, would the class limits give enough benefit on lifting the hull ( less hull in the water means more speed ) versus extra drag caused by the angle of the foil creating lift.

As long as you dont switch rudders during an event (except if you break something etc and apply the RC in writing for the change), I dont see why you can not do that.

Personally, I still think we dont have enough data to decide what pays off, and when tough. Good luck with it if you decide to experiment with it. Dont forget the old "time on the boat" advice

For T-foils on the rudders, perhaps time to take a look at the 14 ft skiffs. They have it higher up the blade. Way of smoothing the transition flow (or something technical like that) of the water leaving the transom. Also adjustable, and removable.

Pix can be found here.

http://www.fastcomposites.ca/gallery/index.php?pid=I14R

But looking at the rules for dagger/centreboards. There are ways in the current rules to make the boards act like hydrofoils. Noone really mentioned any of that yet in the discussion...

Jeez, do you ever think about anything else than trying to find a loophole in the F16 rules. Good luck with your hydrofoils. Let me know when you make it work.

Haha Rolf. The usual bitter reply from you. Was trying to see if anyone had thought of any ways to improve performance. I know I have.

Bitter is your choice of words, tired of the endless harping on topics alread beaten to death is my view on it. Why dont you go and build your ideas and clean up in the next regatta.

I'll have a boat on the line whenever you guys host an event in Singapore (or somewhere in Asia).

But my comments weren't beating to death a topic, and I provided info/link to how another class has adapted T-Foils on their rudders. In the 14s you can easily remove the foil bit (even do between races) and adjust the angle of attack. You just went straight negative as usual.

So go build the thing then instead of tossing up variations on how to "cheat the F16 rules".

Cheat? Yeah right. If it passes the rules, how cheating?

And as i said, when the GC organise something in Singapore or Asia, i will be there.

I'd guess we'd like to come. It's really down to the local club(s) putting a proposal together and presenting it to the GC; which would then suggest options to the membership if more than one local pitched up for an event.