Hi Darryl,
Your experience is different from mine. In the early stages of development for the SC20, side by side pitchpole tests were run many times vs the Tornado. Both test teams were told to sail side by side on a broad reach in 20+ knots of wind and make no effort to prevent pitchpole, do not touch the sheets, just hold your couse. The Tornado pitchpoled much more frequently than the SC. Tests were also conducted with sailors switching boats. An interesting observation was made. The SC pitchpole was slower than the Tornado pitchpole. The SC's pitchpole rotation was slower and it took more distance travelled for the pitchpole to actually happen than the Tornado. The SC pitchpole was described as "mushey", happened more slowly, as described by the sailors. The Tornado pitchpole was "quick", it happened fast, in an instant. I think the difference in these characteristics is a reflection of the difference in hull drag once the foredeck is underwater and the pitchpole maneuver is underway.
Another benefit of the highly arched foredeck vs the flat sheet is that the arched shape is inherently stiffer than the flat deck and can carry a greater axial compression loads than the flat sheet. The foredeck of a catamaran hull is loaded primarily in axial compression.
More substantiation: WWII submarines operated at the interface between the air and the water, the surface of the water, during most of their operation. They ran along the surface of the water about half submerged. These boats spent most of their life "punching through waves/chop " just like our catanaran hulls. What hull cross section shape are they and especially what is the foredeck shape? Millions of dollars was spent to develope this optimum, low drag hull shape for this enviroment. What is this shape?? The ellipse, the egg!
Bill
PS Your sailing clubs in Australia were very very smart to teach catamaran sailors "how to right their boats", sailing lesson #1.

I have to add my 2 cents. Firstly, I'm 100% sure that I can't right my Tornado by myself (155 lbs), correct technique or not. On the one occasion we pitch poled, it was indeed VERY quick. Tons of wind, leaned forward to try to force down windward rudder that had popped up with main sheet cleated (big mistake), next instant, swimming, sore a$$ and boat upside down. Non-sealed mast, ALMOST righted using exact technique described (with crew total weight ~330 lbs), but not quite. Due to extreme conditions at the time, we had pre-arranged rescue boat, just for the record.
Never sailed a Supercat unfortunately.
Al

hi all,
I have a problem with calculating the center of effort. I understand that on a boat with a genoa, you work out the centre of the sail area for the mainsail (including the roach) + the genoa (foretriangle), then you use the average distance between the center of the genoa and the centre of the mainsail for the position to measure the distance to the waterline, but what if the cat had a small jib of an area of 2 m2. If you do what you did with the genoa (find the center of genoa) to the jib, the distance between the center of the mainsail to the centre of the jib is huge because the jib is so low down the mast and so small. on the FX-ONE you can have the jib as an option, but if you add or take away the jib won't it have a big affect on the center of effort? can anyone tell me how a professional cat designers work out the the center of effort with a cat with a small jib that sometimes would not be used?
regards
Tom

Hi Wouter,
I am going to respond to some of your comments one last time. I have a request for you. Do not ever use my name again on any of your posts. I do not think your intent is honorable and I do not want to be a part of it.
You know that my training is that of an engineer. Engineers know more than most other professions that there are many solutions to the same physical problem. Some are better than others but there are always many solutions to a given problem. That is part of the fun and pleasure of engineering. Your comment about me and "only one solution" is your invention. I have never said that.
>About pitchpole and H14s and 16s: I did my design work on the SC product line in the mid 1970s. At that time the H14 and H16 were the largest and fastest growing classes in the US. They were the chinning bar at that time and their sailing characteristics were the ones to improve on.
Inter 20 vs Tornado: Why do you think the position you bring forward exists? Let's look at shapes of bodies and drag coefficients. The last piece of the puzzle in the physics of pitchpole is a rapid rise in drag coefficient as the bow of the boat is pushed underwater and the water begins to impinge on the deck. If we look in an aerodynamics text book and find a table of drag coefficients of bodies of various shapes, we see that a flat plate has a very high drag coefficient, flow perpendicular to the surface of the plate. If we take that same flat plate and round/roll the edges with significant radius like the I20 shear line along the foredeck, there is a significant drop in the drag coeficient. This would reduce the I20's tendenct to pitchpole relative to a Tornado. When the deck becomes the bow of the boat, the shape that is parting the water, how draggy the deck is becomes important relative to pitchpole.
Elliptical hulls: When the best and finest F40 one design boat was designed it looked like a scaled up SC20. On the big cats and tris the elliptical hull shapes are the industry standard. In the beach cat business a newer boat cannot look like an older design for fear of being called a copy cat. No one would buy a new boat that looked like an older design even if the older design was superior in some aspects.
>Shared Lift: I first used the shared lift idea on the SC17. Half the lift to counter the side force from the sail was carried by the forward sections of the hull, deep Vee shape, and the other half carried by an oversize rudder. The aft end of the hull was round in cross section and can slide across the water sideways easily and this lets the boat tack much easier than other boardless beach cats. This 17ft boat developed a PN of 73 relative to the 16.5ft long H16 with a PN of 76. This performance improvement shows that the shared lift concept works. The SC17 also tacks much easier and faster than the H16 and is much much more pitchpole resistant.
>Shared lift and spinnakers: The European beach cats are slow to come to S Florida so I haven't sailed any of them. But looking at pictures of them sailing with spinnakers, I see a big difference from the spinnakers I sail with. I look at pictures of these European cats sailing double trap and I notice the leech of these spinnaker sails is just in front of the mast. These are very high aspect ratio spinnakers. The spinnakers I am use to are fairlead to the rear beam or transom. When sailing hot, the leech is only a couple of feet in front of the rear beam fairlead point. Now let's go back to the text book and aerodynamic theory. I see that the short footed, high aspect ratio spinnaker has a much higher lift to drag ratio than the long footed, full size, low aspect ratio spinnaker. This means that the resultant force from the high aspect ratio spinnaker will cross the platform, the boat, at a point, very near the CB trunks, that has little to no effect on helm. The full size spinnaker with its lower lift to drag ratio will generate a resultant force that crosses the boat in front of the CB trunks and this causes lee helm. The high aspect ratio smaller spinnaker will sail higher and faster than the low aspect ratio when sailing high in general. The larger low aspect ratio spinnaker will sail faster and deeper than the smaller high aspect ratio spinnaker when sailing low in general.
So, there you have it, Wouter. If you sail with these short footed, high aspect ratio spinnakers, you can live with the helm with the CB located in the classical position. If you go with a full size spinnaker, the boat requires the CB trunk to be located further forward to balance the helm.
Take a look at Alinghi. This boat has a second daggerboard half way between the main beam and the bow to trim the boat out when large headsails are used.
I'm tired of writing. Goodby Wouter,
Bill

Hello ****

>>Do not ever use my name again on any of your posts.


Okay, ****, I will not use your name anymore.

>>I do not think your intent is honorable and I do not want to be a part of it.

Think what ever you think and then try to stay true to the facts. One more note. if you think the anomymous attacks on you, like the one one the old forum are coming from me then I can garantee you that I will always sign my name to a post. Rest assured there is no comspiracy to "get a ****", these are all people who just want the truth to be told. Differences of opinion ? No problem. False claims ? You will get heat. And beleive me when I say that another other party will get that treatment under similar circumstances. Hell even I received some heat in the past, and often rightly so, when I stepped out of line.



>>Your comment about me and "only one solution" is your invention. I have never said that.

It is true you have never said, but you hint at in in all your other comments. They always go along the lines. "I already knew back in the 70's that .... and still boats today have .... . Of course all ARC and SC product do have .... ever since the first was produced as the only class / product .... etc"


>>>About pitchpole and H14s and 16s: I did my design work on the SC product line in the mid 1970s. At that time the H14 and H16 were the largest and fastest growing classes in the US. They were the chinning bar at that time and their sailing characteristics were the ones to improve on.


Perfectly understandable and that was never the thing I railed against. Point was and still is. That eliptical hulls have since then been replaced be rectangle hull with heavily rounded decks and after that inverted triangular shaped hull where the pointy side is towards the sky. The designed have moved on. I can assure you that an elliptical hulled A-cat or F18 will not be a big hit on today's cirquits. And there is alot of effort and rep going into these designs currently.


>>>Inter 20 vs Tornado: Why do you think the position you bring forward exists?

Simply because the I-20 can get away with a fat flat deck because of teh rounded corners (as you also say) and because the excess volume keeps the bows up. No matter how you put it I-20 hull are not ellipical in shape and do have very good dive resistance. It was an example of a different solution.


>>Elliptical hulls: When the best and finest F40 one design boat was designed it looked like a scaled up SC20.

When was the last F40 designed ? And I know that making a good small airplane goes along different line than a good major jetliner. Large differences in overall size do often alter design problems enough to warrant different solution or tip the balance into a different direction. All the big cats (club med etc) have a 3rd beam in front of the mainbeam. It will be clear enough that this is not a particular smart thing to do on beach cats that are shorter 20 ft.


>>On the big cats and tris the elliptical hull shapes are the industry standard. Even there we see alot of fine entry bows that transform into a high rectangle with rounded corner tehn transition into an ellips or rounded box section and then end in rounded triangular or semicircular sterns. In one hull we go from a flat tall rectangle to a triangle or semicicle via box, rounded rectangle or ellips midsections. We do we want to call these elliptical when they incorporate almost all sections know to man and different station along the date line ?


>>>Shared Lift: I first used the shared lift idea on the SC17. Half the lift to counter the side force from the sail was carried by the forward sections of the hull, deep Vee shape, and the other half carried by an oversize rudder.

There is simply no catamaran that doesn't use shared lift in this sense. With each design part of the resisting sideforce is provided by the hull, sometimes a part is provided by daggers as well and the residue is taking up by the rudder.


>>This performance improvement shows that the shared lift concept works. The SC17 also tacks much easier and faster than the H16 and is much much more pitchpole resistant.


So, all boats designed after 1980 tack better than a Hobie 16 ? And almost none use the same setup as your 17 footer. Big win.


>>>Shared lift and spinnakers: The European beach cats are slow to come to S Florida so I haven't sailed any of them.

Okay , that is fully exceptable and will never cause me to post sceptical comments. Honestly.

But of course even with this fact, "I haven't sailed any of them", you tend to give alot of advice regarding the right construction of these systems to inquiring posters. A favorite claim of you was and is that spinnakers introduce alot of leehelm on cats. Clearly you can't know that when you haven't sailed any of the post 1994 spinnakers; by your own admission. If you don't know then don't comment on it with such displayed certainty.



>>>But looking at pictures of them sailing with spinnakers, I see a big difference from the spinnakers I sail with.

By inquiring posters always ask advice regarding THESE NEW STYLE EUROPEAN SPINNAKERS. I actually think they more Australian in origin but that is a side issue. The gennakers were first developped on the large Aussie skiffs and then jump ship to the F18 class and F20 classes. So you sail with different spinnakers, fine, I have no problem with that. However all modern cat sailors, I-17, I-20 , F18, F18HT, Tornado's, F16's, any new aftermarket spi for any sailor upgrading his cat out of the range H20 to Prindle 15 is getting the new cut spinnakers. Clearly it stands to reason that your experience with old style spis (who did really behave differently) is not really helpful in these situations.


>>>I look at pictures of these European cats sailing double trap and I notice the leech of these spinnaker sails is just in front of the mast. These are very high aspect ratio spinnakers.


They are indeed, and the speeds they are operated in are also alot higher. Most modern spi boats currently sail with an apparent wind at about 80 degrees from the centreline or even less. They are very far apart from true spinnakers; hence the name gennakers.



>>The spinnakers I am use to are fairlead to the rear beam or transom. When sailing hot, the leech is only a couple of feet in front of the rear beam fairlead point. Now let's go back to the text book and aerodynamic theory. I see that the short footed, high aspect ratio spinnaker has a much higher lift to drag ratio than the long footed, full size, low aspect ratio spinnaker. This means that the resultant force from the high aspect ratio spinnaker will cross the platform, the boat, at a point, very near the CB trunks, that has little to no effect on helm. The full size spinnaker with its lower lift to drag ratio will generate a resultant force that crosses the boat in front of the CB trunks and this causes lee helm.


And I think you say a true thing here, it seems to explain what real life sailing shows us. See I have no problem agreeing or honouring your plausible statements when I see them.


>>>The high aspect ratio smaller spinnaker will sail higher and faster than the low aspect ratio when sailing high in general. The larger low aspect ratio spinnaker will sail faster and deeper than the smaller high aspect ratio spinnaker when sailing low in general.


Definately true. The breakthrough in both skiffs and cats was that propulsion using lift and apparent wind allows these crafts to move around the very physical limit of max speed of a mormal spi as this sail try to sail itself in a windless hole it has created itself. Of course this is the very reason we don't see these true spinnakers on high performance sailboats anymore. Actually teh skiff designers found that increases in downwind speed currently have to be sought in reducing the operating angle of attack of the whole rig. Something that was totally weird some 15 years ago. The new line of designs are approaching minimum angle of attack limits. Meaning the luff of the sails start flapping before the craft has reached its top speed on a given course. This is the main reason why the spis are being cut flatter and flatter.


>>So, there you have it, Wouter. If you sail with these short footed, high aspect ratio spinnakers, you can live with the helm with the CB located in the classical position. If you go with a full size spinnaker, the boat requires the CB trunk to be located further forward to balance the helm.

And you are fully correct in this. And as we cat sailors do now exclusively sail with "these short footed, high aspect ratio spinnakers" there is not any reall leehelm problem that needs solving by a daggerboard well in front of the meainbeam. Of course such a setup may have other convincing advantages by that is another discussion.


>>Take a look at Alinghi. This boat has a second daggerboard half way between the main beam and the bow to trim the boat out when large headsails are used.


I think these boards have a different function as well and that that is part of the reason why they are so far forward.


>>I'm tired of writing. Goodby Wouter,


Goodbye ****

Wouter

I think you have explained why our results were different Bill. Yes in the example that you give ie SC versus Tornado, the differences would, I think, (without actually doing the tests) be as you say, but in my opinion, that is not the correct way of conducting an accurate test for "camber deck as compared to flat, or very near flat" To "compare" two different hull forms is just that, a comparison between those two hull forms,on two entirely different characteristic hulls, and the result that you get is a "comparison" between the entire differences of their hull form, not specifically the fore decks. To test whether camber is more efficient to flat, in this instant, the same identical forms must be used in the same controlled conditions with the only difference being the area that is being tested ie the fore decks. As to the anecdotal example of submarines, I think that if you were to research the evolution of the submarine, you will find that the curves over the complete vessel resulted from the need to have the greatest reistance to underwater pressure, and how the submarine travelled at the surface was only of minor secondary consideration. Besides the vast majority of submarines produced through out the second world war all had flat decks. It was only their inner "pressure hull that was curved.

The only thing that I can say AL, is that yes you are right! There are water conditions where, no matter what you do it is very difficult - almost impossible to right any cat (and/or dingy) but those are exceptional conditions where the actual water conditions are the problem, not the righting technique.
In winds up to 18 knots odd (true wind speed) I have personally righted a Tornadoe on several different occasions, and on others I have been unable to right a 14' cat, no matter what I did in winds that came up to over 30 knots with very (very) steep breaking head waves very close together. Every time I looked like getting some where a wave would break and sweep the cat around and slam me down and I had to start again. I don't say that any method is fool froof, but there are methods better than others and if people are going to sail then they should at least "have a fighting chance" of survival.

Besides Bill and Wouter you guys have to remember that "there are thousands of ways to skin a cat" (pardon the pun) and no one, to my knowledge has, as yet, found the best way! It seems that semantics and minor differences create the greatest amount of "heated" argument when most of it won't amount to a "hill of beans" in 50 years time. Perhaps we should all try a little to keep it in perspective. If not lets all move to the middle east to live and continue the arguments. (At least there the one with the biggest gun could have the best argument?)

Bill, on any forum like this one, if you ever try to "explain" principles of Hydrodynamics, aerodynamics, boundary layers, drag coefficients etc, you are going to get yourself into arguments. Most sailors seem, in my opinion, to want "instant" coroboration to their "assumptions" often made by "seat of the pants" so if you try to give any "technical" explaination, your an open target. If you just give them a "reference" where they can read the information themselves, they are satisfied, or at least they won't admit other than satisfaction, as that would show that they couldn't be bothered to look up the reference or that if they did they couldn't understand it or they read it and were enlightened. Which ever applies it has kept you out of the fireing line. Keep it simply, ie some one asks "whats your new design like" answer "real good mate" "no, WHATS it REALLY like" answer "realy, REALY good mate" "OH YOU MEAN that it's GOOD, well that's what I wanted to know!".

Gentlemen,

There is a post elsewhere in this thread that belongs here:



My own two cents come in the form of an old (probably true) story. It's about a great rabi who became crazy and all his disciples left him until only the first disciple - who also was an important rabi - remained. When people asked the disciple why he kept studying with a crazy man, he said that the master might be crazy, but HE was not: "I can tell when the genius is speaking and when the crazy man is, and learn from the genius only".

A wise man can learn from everybody, even from the crazy or stupid. It is up to each of us to separate the good and the bad and react positively to the good only.

It is good to learn from all of you, even when you are all mad , so please keep feeding us with bits of your knowledge.

Take care,

Put in another context.
It's more interesting and makes better reading when parties disagree than if everyone, boringly agreed???

Bill I don't think that anyone has any problems with the "actual principles" that you expound, but I feel that there is an area of doubt in some of the ways that you attempt to explain YOUR application of those principles to hull form.
From all the postings that I have read of yours, I can find nothing wrong with your design criteria, but at times I find debatable the absolutes that it appears that you apply to them. In my opinion you do tend to leave yourself open to disagreement by apparently "shutting the door" to other variants. Nothing at all wrong with that. It takes a large degree of "single mindesness" to be able to even sit down and design a boat, carry it through to fulfillment and fend off the knockers that will always hover, hoping that they can drag it down to a common level. If there wasn't disagreement it would be a boring old place to live in.

BUT how did the second rabbi know that the first one was crazy and HE was sane?? what if the first was sane and he was crazy? OR what if they were both crazy? What if everyone else was crazy and the first was sane and the second one knew it but was catering to the masses? what if - - - - - adfinitum?????? Lots of questions, who knows the answers, OR only THINKS they know???????

He was sane enough to teach us what worked for him, so...



Then we are learning from a crazy man's tale and this in itself is proof of his point - crazy or not.



Then we are learning from a crazy man who learned from another crazy man. This proves the same point.



Then we are learning from a madman teaching madmen what a wise man taught him. This still proves the same point.



Now, what if the second rabi said he could learn from the first one when it was actually impossible and all he wanted was to keep the status quo (home, money, prestige, etc.)?

Then he is even wiser and smarter then we thought - and if a wise and smart man teaches us to learn from everybody, we'd rather follow his advice.

You are right, we could go on forever and still remain in the same place. Have you designed or built any boat with hydrofoils?

Cheers,

Tom a simple, suitable means to most of your needs for ascertaining the combined CE of your sail plan would be to scale out the boat with the mast, sails etc in their relative position, geometrically draw the C of E of each sail, scale the point relative to the combination of all the sails to find the point at which the Cof E of all of them acts then project that down through the hull. For the purpose that it appears that you need it should be accurate enough to assume that all three sails are flat thereby not needing to go into more complicated calculations allowing for the differences in their shape and "drive" positions etc. You can do this with only one sail or with two or with all three, then you can see a good comparison with how the centre of effort of the different combionations will effect the balance.

Hydrofoils? yes but only in half scale models for testing, I decided many years ago that true hydrofoils were fraught with a few very difficult excentricities that made for design difficulties that are still as pertinent today as when they were avidly experimenting with in the 1950's. There have been some very great innovations in recent years, but the draw backs that are present still leave a lot to be desired for a craft to "put out" for general sailing purposes. To put it in another way, the con's, as far as I am concerned, still outway the pro's
I have designed a variation on the "foil borne" sailing craft though, that has passed all testing with flying colors, BUT, although we have sailed a full scale 4.3 test version of it, it has the appearance and out right performance that I feel would completely inhibit it from proving a commercial success at this point in time, and I am afraid that I am a little past the stage in life of producing some thing just to "prove" a point and satisfy my own ego. Still who knows, if interest moves in that direction we may just produce them.
As opposed to "sailing craft" or "hydrofoils" I call this an "Aqu Glider".

Ehhh. One has to remember that the situation is a 3D situation and not merely a 2D one.

Example. In 2D nearly all monohulls will appear to have lee helm when going straight downwind. However as good as all have weatherhelm at this point. This is because the boom is so far out that de CE of the main is so far to the side of the point of drag that the net result is weatherhelm. It is entirely possible to have a boat that can move from weatherhelm to leehelm and back to weatherhelm when going from a beat to straight downwind sailing. In short the 3D pictures is very important and with monohulls even the heel of the boat can give rise to great differences. Another example. A given monohull can have leehelm on a straight downwind run in light air (hardly any heeling) and transition to weatherhelm in a guts (large heeling) when still sailing on the same course.

I agree that Darryls methode is a good grafical methode for finding the CE for the situation where all the sail are sheeting as good as parallel to the centreline but be very careful when extrapolating these result to other course that may have the sails sheeted significantly differently. Of course the spinnaker issue is one of such apparently contradictionary situations. Where the grafical methode suggest alot of lee helm being introduce when in reality this is not really the case.

Regards,

Wouter

Actually the 3D situation on sailboats is a very interesting one.

Even far ago designers knew about this issue/problem. The large schooners and such of two centuries ago were designed to be sailing with a minimal heel. The desired amount of weatherhelm was designed into the craft at that heel. This left the problematic situation where in very light winds (almost no heel) the boat would have leehelm on all courses including going to weather. To combat this the top sails were invented. These are the relatively small sail all the way at the top of the mast. Often tensioned between the mast top and the top Ra (English translation ?). These are not at all intented to provide propulsion but to induce heel so that the craft would return to its design sailing behaviour. Of course any extra propulsion provided would be welcomed by the main goal was extra heel and this was the main criteria of wether to deploy these sails or not.

Also Breaching on a mono hull can only be fully explained by a 3D situation. And as a matter of fact it is a desired characteristic. It is used on mono's as an extra safety mode.

You see how important 3D considerations can be ?

Wouter

lets not get too technical Wouter, if it is kept as a simple two dimensional graphic, it will suit for the purpose of illustration for a "visual" calculation that will show a reasonable representation of where his centre of effort is that will in turn help him to determine it's rtelationship to the centre of lateral resistance of his hulls and from that the understanding of how adjustments can be made to balance the two on different points of sail by all sorts of "set ups" ie mast rake, crew position for different points of sail, cemtreboards raised or lowered for different points of sail and different combinations of sails, etc, etc, and the use of his hulls "shared resistance with his centre boards and rudders, to leeward drift (or shared lift -as Bill may say-)" Or as I tend to say, "keep the leeward hull deep to counter any extravegant lee (or windward) drift, and the windward hull just free of the water.

Greetings,

So what are the practical solutions to the same problems. In your opinion, which is the easiest boardless catamaran to tack? Which boat is the easiest to right after capsizing? Which boat is the most pitch-pole resistant? Which boat is the smoothest sailing or hopping resistant? Which boat is the dryest for the sailor?

SC17, Nacra 5.7/570, G-Cat 5.7 and Prindle 18

Regards,

S. Knapp