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Foils & Stuff


Emmessee
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On one of the 18's I sailed, we put a horizontal fin about a third of the way up the bow that stuck out about 100mm each side and were about 400mm long to help prevent us burying the nose going around the top mark.

It worked in some conditions and not in others.

Eventually we used a T rudder and this not only prevented the nose going in at any speed rounding the top mark, it also made the boat absolutely fly down wind.

We also "hollowed" out the rear guts of the hull towards the transom. It was flat for the last 1.3 metres, but then we actually sanded it out so it was concaved inwards about an inch.

This gave us more lift and more speed. as the water flowed along the hull, in reached the hollowed out section and in turn moved upwards creating lift. This worked even better with the T rudder.

The boat did also cost $178,000 to build, but we won everything. At one stage with the winge, the boat was 29 feet wide.

Rules changed and they are pretty much all the same now.

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you guys should go on broad band then the loading isn't a worry, just zaappp and your there.

you have just explained the effects of foils on a boat superbly. The ones forward, to be effective in all conditions needed to have a variable angle of attack. If they were fixed, when the bows pointed down they would drag the hull down further and vica versa, but the rudder or rear foils self compensate for pitch ie when the hull inclines down at the bow the angle of the foils at the rear are trying to pull the rear of the boat down as well and in so doing compensates for the diving of the nose, and the reverse when the nose point to the heavens. Thereby stabilising the pitching effect. Rear foils also have the effect of "tricking" the hull into acting as if it has a few feet extra waterline length.

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I have the entire CBA pipe at my disposal so speed is not an issue for me smile.gif

The forward foils do have the isse of incorrect angles of attack, the T foils deal with the problem before it gets too big, By making small adjustments early in the cycle they are much more efficent. The bow mounted foils have never seemed to work as they only come into play too late in the process and they have way too much drag.

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Guest Simon

Thanks Emmessee, as I was wondering if anyone had tried T foils on an 18teen. Do the rules not allow them? If so they seem a little illogical as making the boats safer and faster with minimal expense would be better for the class. Or maybe not as Awesum Ausie 18teens may never have being realeased without all those cartwheels.

Do you know if anyone has tried concavaties in the hull forward of the mast to create more lift there to keep the bow up?

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As far as I'm concerned, 'T' foils on rudders are a Band-Aid remedy for a more serious design fault in hull shape particularly in cats. I think that when Nils Bunkenberg brought his 'A' to the '99 worlds, his boat rang alarm bells for anyone with sufficient understanding of, and who had any influence on hull form in developing classes. This is why some of the present F18's are so good. It probably explains why the M18 is such a blast too.

What was it about Nils boat which was such a revelation? MMMMMM smile.gif now there's question wink.gif

Bern

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Now! Now! Berny don't be cruel, to say that T foils are a band aid to compensate for hull design faults is a little like saying that centre boards only make you THINK that you suffer less leeward drift with them! when if the hull was designed right you could sail just as high, with advantage, without them? smile.gif They don't hide any design fault, they add to performance, no argument, just fact.

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Forward foils have always had a problem, whether they are part of the hull or "stand alone" as in pure hydrofoils, not in their ability to work, but in the response time to wave oscillations,by responding "late" they can work, but tend to induce much more drag than is desirable, theoretically they should be responding to an oncoming wave face quite a way before the bow reaches it, and this has been a problem for "foilers" since the 50's. Hobie have solved it to a large degree by having their "float" sensors extended forward from of their foils, but they still encounter problems in larger seas. If you are familiar with the work done with hydrofoils since the 50's until now you will be familiar with another quite famous way of trying to overcome this! That was with the "venetian blind foils" multiple foils set parralel to each other in a triangle with the point of the triangle at the bottom. when the greatest lift was needed, most of the foils were in the water supplying great lift at low speed, as the speed increased the foils rose in the water leaving smaller and less foils in the water. It was quite effective, but dead ugly. On a "conventional" hull, where the foils are not used to lift the entire boat out of the water, but as partial lift and as a stabilising effect on the hull, most times it is better to disregard forward foils altogether, relying instead on the bouancy of the bows to "ride the waves" and use only T foils at the transom or on the rudder/s to control excessive pitch. Another viable option is to have the forward foils not so much forward but around the position of the mast step, this gives the natural bouyancy of the hull a chance to come into play and the foils act as assistance to it requiring much less adjustment and giving a time factor for that response that is easier to handle.

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But Darryl what you say presupposes that we know all there is to know about hull form, and foils and the interactions between every variation of each as it applies to one being employed with the other. It would not only cost squillians of $$$$ but ions in time to match each different hull shape with all the various foils in every configuration to evaluate whether or not there exists a hull/hulls with form which has excellent performance characteristics and which is not improved by the addition of foils and I doubt that's what's happened. What we know presently is that a few different foil forms used in few differing ways with a minimal number of differing hull profiles seems to improve performance in some cases and I say seems because the problem with testing on sailboats is you can never replicate the same circumstance for every evaluation and secondly I think we are far from knowing everything there is to know about the various dynamics in this particular area. I still propose that there is a catamaran hull form, possibly already existing or maybe yet to be discovered, which performs without the vices that need to be corrected with the use of foils on the rudders.

I also know that wetted area = drag and adding any additional surface area below the waterline of a displacement hull increases drag and particularly when that additional wetted surface area is in the form of a foil which has it's longest axis not in alignment with the direction of motion and direction of flow of the H2O.

Of course it could also be argued that if a device which marginally slows the boat but makes it less likely to pitchpole is an improvement in performance, given that it's better to finish a race than to sail the fastest, but only over a percentage of the course (DNF).

Also, on the other hand, I'm definitely painting my decks black because one of the guys came to CRSC last week and won with black decks wink.gif.

[This message has been edited by berny (edited 21 May 2004).]

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Simon,

The 18 footers are now pretty much one design, so there is no more experimenting with them.

I do remember Walshie turning up at the start of the season with his Stubbies boat and it had a 20mm step in the hull about two thirds of the way towards the transom, with 5 pipes through the deck and sitting about a foot above it so water could not go down them.

The idea of the step was to seperate the water from the hull and then the 5 holes would suck down air through th pipes and then the boat would be basically sailing on a pocket pf bubbles.

It did work, in about 20 knots downwind, but it was a dog in anything else and only lasted about two months and he then rebuilt the hull.

[This message has been edited by Emmessee (edited 21 May 2004).]

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Guest Michael

Interesting sites. I think they are legal for F18's. My main point is the F18's are 180kg whilst the F10HT's that he has been using them on are only 130kg - i wonder how much extra drag would be created in getting the right angle to lift the extra weight (remember trying 50kg x 9'away requires a lot of force).

Oh yeah - from memory foils of any description (beyond a single plane rudder & centreboard) are banned on the 18' skiffs.

Michael

If you have a look at John Pirece's site http://www.geocities.com/stealthmarine2002/

or http://www.geocities.com/stealthmarine2002/t-foil.html

you will se that he has been using the T foil for a while now. I remember in the mid 90's Andrew Landenberger used the foils on his A class, the fact that he was not so fast is more likley due to other factors than the fault of the rudders. John has done a lot of work with these rudders and they seem to be working very well. John is an ex T sailor and used to do the rounds with me and the guys. If you had any questions about the effectivenes or drawbacks I would suggest emailing him. I am not sure if the T foils are legal in the F18 class, but if you look at the way the boats like the Capricorn are going there would appear to be little need for them.

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I'm sorry if it seems that I presume more understanding of "boats" than the average sailor has berny, that has never been my intention, but if existing knowledge of the subject is never transmitted in one form or another no one will ever know anything other than their own personal experience on the subject, and that makes learning difficult to say the least. (actually I have found that the "average" sailor has a pretty good understanding of the way that it all "works"). On the subject of T foils though, lets keep it simple! and it is simple. Regardless of the hull form, by the addition of T foils on ANY boat there will be a marked improvement in performance, and when it comes to "wetted surface area" drag, for a "small" boat (that includes any hull form up to roughly 28 plus feet) the drag calculation is a "non event". If you start to try reducing wetted surface area in cats up to 20', you can put in hundreds of hours minimising the wetted surface area for such a miniscule gain (or in this case loss of wetted surface area) and achieve such a small percentage of lower drag that a rough equivilent would be that if the crew of that boat were to urinate before they went out sailing the effect of their loss in crew weight would be far greater in reducing drag than ANY reduction in the hulls designed wetted surface area. "Rough water drag" now is an entirely different kettle of fish! and rough water drag only occurs at or near the surface of the water.http://www.catsailor.net/cgi-bin/ubb/icons/icon3.gif

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If any one really wants to test their ideas for different shapes, appendages on hulls, rudder foil shapes in conjunction with their hulls, etc, etc, before actually physically "making" the changes, search the freeware and/or shareware software sites for "modelling test" packages,available for download off the internet. They can then input their ideas in a 3D form and run computer modelling testing on them. Some of these packages are very very good (the main draw back to them as freeware is that although you have full use of them, you usually can't "save" the work or print it). If any one is really serious about designing then probably the best all round package (to purchase) is one called "Mac Surf". You can design, model, and fully test any type of design in it with almost 100% accuracy, many designs in Mac surf give more accurate results than physical model "tank" testing.

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Berny don't get me wrong, I am not proposing that we all go out and put T foils on every boat, - that isn't going to happen regardless of whether they are "the eight wonder of the world" or if they are "just a passing fad", but you refer to then as perhaps a means of correcting existing faults in hull designs that could be corrected by using better design, and thats not what they do. they add to and improve the performance of a hull not "correct" any built in design deficiency. hulls will alway pitch due to wave action alone, when wind variations are added to this through using sail power that pitching will obviously be greater. Thats a fact of the way that boats more over the surface of the water. Although better designed hulls accomodate that movement much better than some lesser designs, that pitching will still always be greater than we would comfortably like in certain curcumstances no matter what the actual hull shape is. By the incorporation of a horizontal "T" foil we are only adding a very small stabilizing foil that reduces that pitch with the minimum of cost, alteration, and with a large positive effect on the overall performance of the boat.

Whats not to like????

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not so unreal as it sounds EMMESSEE, I watched a guy a few years back who made "paper mache" fins for a "planing hull" catamaran, painted them in epoxy resin and used them to test his ideas at sea. His hulls (marine ply) eventually broke up in the shore break but his foils were still as good as the day he put them on. (now there could be the idea for a new "light weight" construction method! lets all make paper mache cats?? - oregami sails???)

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This reminds me of an argument that I witnesed some years back between a group of Prindle 16 and Hobie 16 sailors and a group of mosquito sailors. The Hobie and Prindle guys were saying that the assymetric shape of their hulls provided more lift to windward on a beat, produced less drag than you had to get from a piece of wood stuck down the middle of the hull into the water (centre board) and that they (centre boards) were "an excess drag producing thing of the past" and would never work as well as assymetric hulls! All the mosquito guys said was "why, with heaps more sail area can't any of you ever sail as high as us , or beat us to the windward mark then"????

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Read what they say at Stealth Marine?

Stealth marine is the first company to use T-foil rudders on a production catamaran.

The rudders increase the fore and aft stability of the boat, smoothing out the passage through choppy waves and increasing the resistance against pitch-poling.

They act in the same way as the tail-plane on an aircraft.

When the boat is driven hard and the bows dip, the transom start to rise and the fins on theT-foil start to press the transom down, stopping the bows burying further.

The benefits are particularly noticeable when sailing with the spinnaker, the boat can be driven significantly harder. Also bear aways in strong winds are far less dramatic.

When the wind suddenly drops and the pressure goes off the bows, the transom will drop in the water, again the T-foil will push it back up.

When travelling in choppy water the boat adopts a much more level passage reducing speed sapping pitching back and forth.

The extra drag in light winds on flat water is not noticeable and even small waves from passing rescue boats are enough for the rudders to pay.

These foils have been extensively tested throughout 2001, and we believe that they represent a significant step in catamaran design.

The overall effect of them is that the boat behaves as if it were 2 feet longer.

Click for full size

Click for full size

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I would love to post som epics of the newest way of cat design thinking but this forum wont allow it, if anyone would like some pics of the new Hydraplaner I will galdly email them, this boat has T foils on the rudders but also a stepped hull to get it planing

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I wouldn't mind seeing some pics. How about posting a link to the web page.

OK Darryl I'll concede that 'T' foils on rudders behind a hull will act as a damper to reduce pitching which may improve VMG, depending on how severe the pitching is. smile.gif

Bern

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