Hans,

It doesn't say anything about you sailing A classes on your wikipedia page. Someone is going to have to fix that.

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

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

I am not the same guy, he is having the same name but that's not un common i think.
He is good with card tricks.

Cheers,

Hans Klok

[color:"brown"] Ah yes.... Go the Toads [/color] <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Wouter is not even sport any more. I'll leave the mad man to rant to himself for a while now...... Atleast until the next time I am board. <img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" />

Hi Hans.

The boat of Erik is the old version, it doesn't have canted hulls. Marströms new boat has, but the changes from the Marström M4 to M5 are not that eyecatching, it's more in the detail that you see the improvements. But if you see a Marström with a thick strikerless front beam - it's the new version.

Like Landy in this picture:

What a load of crap. We all know who is adressed here and it is simply not truthful.

When we wrote the F16 class rules we specifically DID NOT rule out any hydrofoil devices. We specifically written the rules such that T-Foil rudders and such were allowed. In fact, all the way up to last years ballot (were I voted against the rule change) the F16 class had significantly more open rules regarding foiling then the A's. And indeed, items like T-foils were implemented. During the framing of the rules we regarded it as an attractive refinement on a short hulled boat; much as Luiz is quoting about the ability of angled foils to improve seaworthyness.

So for 6 years we (I) did indeed run the risk and I'm personally still willing to run it now. I feel the F16 ballot last year was heavily inspired by what went on in the A-class rules which I feel is largely based on fear and not technical reality. I'm very much opposed to such crossovers and actually have written a parting brief specifically addressing such a travisty (before the ballot was held).


Hakan, find something else to hit me with because this simply won't fly.

Lets get away from trying to discredit any given person by quoting falsehoods and progess the discussion with scientific arguments.

Wouter

The "and such" is a generalisation which doesn't fit into your squeaky clean technical/factual image.

But had a look through the F16 rules. You don't want to hold a F16 regatta in SE Asia. You don't want to see what kind of boat I would turn up with! Would certainly be an exploiter of those rules.

Give me a break Wouter, everything is not about you.....

The level of competition in A-class is a higher than in F16-class which means that small changes in the performance of the boat makes big changes in the racing results. That's not the case in F16 right now but it could change and I bet that those sailors at the F16 worlds also would like a bit stricter rules so they can focus on sailing.

The international canoe is an example of a class that is divided in three types of boats now with different rules. IC (the original), AC (added a spi) and DC (development). The last worlds had 21 IC, 3 AC and 13 DC but they could have had 37 boats racing together.

/hakan

Interesting thread --thanks .

A general question for any .

Why should the A class be limited to developing radius lifting foils only {banana boards} ?

Wouldn't a simplified A foil type configuration on canted hulls further sailing craft development moreso.

I realize C Class development allows this type of development within its 14 ft beam limititation per C Class rules and some may argue foil development can occur in that very expensive racing class .

Given that and the fact that the A class seems reluctant perhaps it is time to resurect the 18 square class as the foiler class or perhaps a new 20 ft development class for that purpose .

The catamaran version of the Moth class in effect .


What was described previously was a simple version of the A foil that could be built stationary or retractable in 2 slots in each box sectioned canted hull .

This would seem a superior configuration or at least one with greater potenial on box sectioned canted hulls .

pic for any interested

http://www.yachtboutique.com/images/A-foil2.jpg


-

I don't think that we can say in general that the A-class is reluctant to changes. In this thread we have seen examples of sailors from both sides.

The A-class has moved to a bit stricter controlled rules since the type of sailors racing this boat has changed. There are more "racers" than "builders" right now and that is reflected by the rule changes.

/hakan

Hakan
In the USA, I think the growth has been driven by racers joining the class for the racing and the concept of a light singlehanded, single sail performance boat. We are getting new boats from 4 basic builders.

Class growth is not driven by sailors with a better design idea and the skills to go build it.

We are buying boats that are percieved as basically competitive from a domestic builder group that is really quite small.

Within this box, I can think of Ian Lindahl and collaborators and Steve Clark and collaborators building the LR and DK boats on the edge of design. Vectorworks is building the XJ's and Moreeli and Melvin A series. The exchange rate has put a real hurt on the import of Marstroms and Aussie Flyer's 1 and 2 or anything from the EU.

Future growth requires keeping the existing racers and adding new converts. The cat racers moving from 2 man boats or dinghy sailors are choosing between the A class, the single handed spin boats; F16 and F17 spin classes or the traditional Hobie 17 class.

A revolution in design that fractured the class would really change this growth forcast and the dynamics between the single handed cat classes.

How much interest is there in buidling a flying catamaran class?

The case about making the A-Class a flying catamaran is closed. We have a rule stating that Hydrofoils are not allowed, this means adding "something" with the sole purpose of producing vertical lift.

The reason for this is that once you are flying, it really doesn't matter if it's a cat or a monohull.

The box rules about the dagger boards has limited the way you may shape and/or cant your dagger boards, and having the text about measuring the beam of the boat with dagger boards all down and up flush with the bottom, takes care of T-shaped foils - cause they can't be all up flush bottom.

So what we are talking about here is a max beam of 2,30 meters and boards that may not come closer than 1,50 meters from each other. It's fair to assume that the hole for the dagger board at the bottom of the hull is placed approximately 15 cm from the extreme beam, leaving us with 25 cm per side to cant or curve our boards!

It's really not that much if they still have to be able to come up through the dagger board case.

In my opinion this gives enough room for playing around and maybe improve slightly, without being able to create revolutions that will set everybody else out of the competition...

The rules as they are today allow all that and restricts all that, so let's not change anything. (If it aint broken don't fix it)

I think it's marveless to have a class that over 50 years only has seen the need for 9 rules. Let's not change that - having to many and to often rule changes also frustrates the sailors (ask F18 sailors about that...)

I've heard from both Marstrom and Wouter that the curved foils should have a damping effect, but I fail to understand the mechanism behind it? See Wouters text below.

/hakan

/********** From a post from Wouter ***************/
I classify the curved daggerboards much more as a refinement then a breakthrough. This because its effects are far more in the field of damping the boats movements then lowering the overall drag. I also feel the latter is already partly adressed by inward canted straight boards. (whatever happened to outward canted boards guys, the hot and exiting development of a few years back ?) And there are some conflicting design problems that are not obvious at first glance. One of those is that simply curving inwards the boards doesn't do that much to lift the boat when the foils are symmetric. In the way of damping movement they will be effective that way. In order to create meaningful lift (in this case, enough of it to matter) assymmetric profiles are needed or a permanent angle of attack of say 4 degrees. At low speeds or when having two boards down these characteristics are actually a disadvantage. That is why patient lady C-class design, raised one baords and lowered the other after each tack. Patient lady is one of the very few examples of a sufficiently succesful implementation of curved daggerboards as a performance enhancing item.
/***************************************************/

I would love to see (Thread 1) Steve Clark's explanation of this critical element about PL-4 and the apparent success of its NON-SYMMETRICAL banana boards: i.e.: "It lifted at speed".

New Thread for Hakan - Steve told me that the boat he raced in Canada last fall was about 12 years old, basically unmodified and too heavy due to its older construction methods, compared to the new Canadian boats. Maybe the wing was heavy too.

CANTING THREAD: IMHO, having personally raced A-cats, straight boards canted out are useless when doing the Wild Thing. I was there when Charlie Ogletree slalomed through the fleet of other A-cats after the A-mark like a snow skiier--- In not enough air. Note that I was ahead of him at the A-mark, but after that, not so much!

Hakan,

I believe Wouter's quote is exact except for one detail: in my opinion pure pitch damping can be obtained from symmetric foils at zero angle of incidence, like the pitch damping provided to a plane by a symmetric section stabilizer at zero angle of incidence.

It is intuitive that a flat horizontal board damps pitch. It is also intuitive that the flat board (as the hydrofoil) will increase the boat's total drag. I guess the only requirement for a pitch damping board to work is that it is placed fore or aft of the CG.

The mechanics of the pitch damping effect from hydrofoils can be described this way:

When the boat pitches down, the foil moves downwards and its angle of attack increases, also increasing the existing upwards lift force, which counteracts the downwards movement.

Drag usually increases with the higher then normal angles of attack that occur in this case. This is relevant only to understand the difference between a hydrofoil and a flat board.

When the boat pitches up, the foil moves upwards, its angle of attack decreases and lift is reduced or even inverted, counteracting the upwards movement with the reduction of upwards lift or increase of downwards lift.

Added drag is less of a problem in this case, for the angle of attack is being reduced at first. It is only when it becomes negative and relatively large that drag will surpass the levels associated to horizontal motion. This explains the difference between a hydrofoil and a flat board at pitch damping:

The horizontal board forces the boat to decelerate its horizontal motion during pitch up or down damping, regardless the pitch direction. Interestingly, the hydrofoil will allow the boat to accelerate due to less drag while damping the pitch up movement, and force it to decelerate due to increased drag while damping the pitch down movement. There's no magic in it, though: the hydrofoil was sailing with higher drag than the board from the begining, due to its initial angle of incidence or asymetric section.

Hydrofoils work almost exactly like wings on a plane. There is an excelent (and free) online book that teaches a lot about lift, drag, stability and damping from wings (read "foils"). Just follow this link. and enjoy.

Hi there,
I looked into the canted and curved boards and did some math. I'm attaching what I calculated; I tried to make it as clear al possible so it's understandable.

Enjoy!

Cris

Nice work but...for a "same length" board, from what I got out of that, the straight board, at a 25 degree angle creates more lift than the curved board, right?

The first part of your conclusion makes sense. From my personal experience, curved boards are used instead of straight boards for practical reasons: they are easier to insert, lower and lift. Otherwise, straight ones are lighter, easier to build and less draggy.

As for the second part, I would look for benefits in terms of added stability and damping, not in terms of drag reduction. The additional stability and damping improve seaworthiness and may save some energy from unnecessary pitching, heeling and yawing motion. Alternatively, it would allows for a more powerful sail plan.

All the best,
Luiz

Yes. Figure 5 is the 'same length' case. If you match the side force Ly of a 45 degree curved board with a 25 degree straight board your lift Lz will increase from roughly 0.33 to 0.38. The drag will stay very much the same since the board area didn't change. You will exceed the maximum with rule when trying to fit it by a lot!

Since you've done all the math, about how much of an angle would you have to put your daggerboard at to lift the entire weight of an A cat (165lbs) plus say, a skipper of same wt. for a total of 330lbs. clear of the water, at say, 10 knots boatspeed? For computing purposes, figure the two daggers will lift equally, and we will also have T foil rudders which also will (theoretically) lift the same amount as the daggers, or 25% lift on each of the 4 "foils". (so each foil has to lift about 82.5 lbs. at 10 knots boatspeed)

Dave Carlson, did you do similar math when you built the Jackalope foils? <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />

Well, if I did the math right, with the sailor sitting on the windward hull the side force on the sail is roughly 43 Kg (421 N). Each foil will have to supply 10.75 Kg of side force and lift 37.5 Kg (367 N). So your ratio of vertical to side force is 37.5/10.75 or an angle of 74 degree. If you do all the math for alpha=11 degree (gamma of 3 degree), lift coefficient of 0.1 per degree, board aspect ratio of 10 and a speed of 5.1 m/sec you get a cord of 0.1 meter. The board will be one meter long and you would have four of them. Sounds believable...