Ground Hog Day

From a bunch of people that don't even own Ground Hogs no less.

Quote :This is going to be a disaster for the class unless the officials starts acting fast. And so far they have done NOTHING!!!

I am very close to the A-class official(s) and i can tell you that there is more debate going on then only on this forum .

Does any one know what the lifting difference is between a banana board, an angled straight board and a straight board in the vertical line with the boat. Calculated in theory.

Cheers,

Hans

Get an A-cat Jake instead of that old F18, then you might get a life <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Hi Hans,
good to hear that things are moving among the officials. Could you post the new rules here or give me a link to the rules. I could only find the old one on the A-cat and ISAF webpage.

I think you could get a lift of roughly 60 kg from a foil that is 0.4 m long and 0.3 meters in width in speeds of 15 knots. The foil is L-shaped in this example which means that only one edge has "end effect problems" of whatevere it is called.

/hakan

Hi Hakan,

I send you a mail.

Cheers,
Hans

Actually I do. I have a very well maintained Boyer Mk IV. <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" />

Your signature still says F18. I know, sometimes it's hard to let go.

I thought they were a "fad" anyway.... <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" />

doh....better now?

Wouter,
I like the Aclass, but the class keeps talking out both sides of their face - are they are developement class or not? They bill the class as a development class and thats whats gotten them this far, but tightening the ruleset goes against this philosophy.

I agree with your comments that the class need to continue to evolve in order to stay fresh and grow.

By the way, I'm on the Acat website, so I guess I'm not a hater.


http://bp0.blogger.com/_mLM5Q9YpULE/RwDy7AZKX7I/AAAAAAAAAA8/fV8EIv1SsoQ/s1600-h/Bill+Vinning.jpg

Harkan,


There was a clarification diagram on the USACA website under rules, under the measurement heading, which has been recently removed.

Absolutely. And that brings us to the core of the hydrofoil issue:

Dynamic lift occurs to all boats in movement. If it wasn't for the existence of static lift (displacement), banning hydrofoils would make as much sense as banning aerofoils from planes.

I believe the only way to eliminate the dynamic lift components is to keep the boat still. This path leads us to reinventing the buoy.

Interestingly, the conceptual evolution of a displacement (hydrostatic) boat follows almost the same path as the lighter than air (aerostatic) craft:

- At rest they are pure displacement vessels.

- When they move, both inevitably generate some dynamic lift, so speed is improved with streamlined forms. (that explains why a buoy and a baloon are spherical and a boat and a zeppelin are streamlined)

- Then, it is natural that both start using the (inevitable) dynamic lift: they receive apendages for steering, stability and damping (rudders and (flippers or boards)).

- Eventually the dynamic lift starts to assist or replace part or all the flotation. The boat shape becomes apropriated to generate lift (plane) and/or receives hydrofoils, deflection strikes and the like, while the zeppelin becomes thinner and receives wings.

- In the end, the baloon becomes an airplane. Motor boats could just follow the same path, but sailboats have a power limitation (wind) that makes positive flotation indispensable.

Conclusion: is it possible to ban dynamic lift? Hardly. Would it make sense? Only if we want to sail streamlined buoys.

All the best,

If the statement is there, you can win a protest against anyone with a daggerboard or rudder. Really.

Anybody got a copy of ISAF Equipment Rules for sailing?

Look up hydrofoil.

Then look up daggerboard and rudder.

I dont have the document, but as it was just explained to its all defined. Daggerboard is defined as being near the centerline of the hull. Hydrofoil is "not near" the centerline of the hull. Rudder is what you would expect.

So Wouter's interpretation of hydrofoil being a "waterborne foil" and Luiz's assertion that "all foils generate lift" are not valid for the sake of this argument. What matters is the ISAF definition.

So if your daggerboard is not in line with the centerline of the hull, it's a hydrofoil according to ISAF's equipement rules of sailing. The ISAF's definitions are what the measurers use, so its that definition that matters.

Under this definition, any boat with a board that is not in line with the centerline of the hull is not an Acat and cant compete. There are boats competing today that are outside this rule, its just not been enforced.

Seems like canted hulls would also be illegal then, depending on the definition of "ceterline of the hull".

you have two hulls and two centerlines...no problem.

Bill,

My comments earlier were a bit tongue in cheek. I was (am) aware for quite some time that we agree on these points.

It was just when I made similar comments about 4 weeks back I was accused of hating the A-class. My recent comments were a sting to those people.

My appologies if I give rise to a misunderstanding.

Wouter

Ohhhh ! Brilliant Jake. Absolutely bleeding sharp. What a way to beat the rule.

Place the daggerboards under a 10 degress inward angle and have the hull both canted outward by 10, ehh voila according to the whigs at ISAF this boat is not using any hydrofoiling effect to lift it out of the water. Because the starboard daggerboard in in line with the port hull centreline.

Wouter

Two non-parallel centerlines? How do you define centerline?

The diffference between a 6 degrees outward canted symmetrical board (hyped up development of yesteryear) compared to an 6 degrees inward canted symmetrical board when the luff board is fully lifted is 30 kg on a doublehanded F16 with crew on trapeze = (20% of the total saildrive perpendicular to the centreline of the boat.)

The A-class has less righting moment and less saildrive byt the ratio of 20% will still hold. Roughly speaking 15 kg lift on the A in the same situation with the crew trapping.

When allowing boards to go to 15 degrees inward angle the difference becomes 50% of the total saildrive perpendicular to the centreline of boat (= 75 kg on 2-up F16 and 37 kg on A)

Calculating the difference between these boards and the banana boards is not easy to do without agreeing on the specs of the banana board first. For all I know the bananaboard can be twisted towards its tips, making it a symmetical daggerboard near the hull and an permanently positively angled lifting foil at its tips. I will need to know the cord and radius of arc of the banana board and the amount of twist or fore-aft angle in its (hull) slot (= gives incidence angle)

Basically a 0.16 sq. mtr daggerboard with a 0.20 mtr cord (aspect ratio = 4) can rather efficiently
create 75 kg force perpendicular to its plane. It can produce even more force by then the lift drag ratio will be less attractive. So if the daggerboard is L-shaped then a horizontal tip of 0.20 by 0.20 can produce 25% force. Of course we have ignored some efficiency effects here but such a L-shape form can be used as a good first approximation of the curve banaboards which tip reaches 0.20 mtr seperation relative to the centreline of the part in the daggerboard well (assuming this one is on the vertical).

It seems to new A-cat anti foiling rule allows up to 0.30 mtr seperation between the vertical and the tip of the banana board = approx 38% of saildrive transformed into vertical lift (= effective weight reduction craft)

It is not hard to calculate these things using theory; it is just that there are so many factors that need to be fixed/chosen for a value can be produced.

Wouter