So, do we call it a cat or a tri? I'm getting real confused...


Here is one opinion on that question; from the website of Alinghi, whose patron was the leader in developing the D35's:

"With the distinctive feature of three hulls, the outer two acting as floats and the central hull acting as a strengthening structure, this catamaran is well suited to racing."


[www.alinghi.com]


A three-hulled catamaran?

-----------------

From an article by Stuart Alexander yesterday in The Independent:

"Bertarelli's skipper, Coutts' former best buddy Brad Butterworth, recently said that the Alinghi yacht, thought to be a catamaran with a central pod, could finish building within a couple of months."



Edited 1 time(s). Last edit at 04/03/2009 02:16PM by Conrad.

I'm not sure if that text refers to the Alinghi defender for AC, or the Décicion35, or maybe both, but at least the D35 is clearly a cat.

My definition would be simple, and have two parts:
1. Cats have two hulls. Tris have three hulls.
2. A hull is a single separate structure used for buoyancy.

The D35 has a structure that looks like a hull, but isn't, since it'll never float. It's a pure structural component that only gets wet by spray, odd waves or flipping the boat. So, if my definition is a useful one, the Alinghi comment is just misleading. Probably not intended that way though.

I don't know if the D35 concept is a good one for AC, but it seems to be what you'd build if you think tris are better than cats, but really don't want to admit that. The flying central "hull", as mentioned, has one function only: Carrying the longitudinal rig loads; head stay upwards pull, mast downwards compression, main sheet and aft stays upwards pull. It must not flex to banana shape. The loads are huge, and the height available is limited, so this fake "hull" must be built with pretty damn heavy laminates. This will inevitably end up weighing as much as a larger and stiffer proper tri hull, which has other functions as well.

You of course know this, but for the record: A tri centre hull will be the main buoyancy at low speed and should barely touch at high speed. The amas do the opposite. This means the tri hull shapes can be specialized for only low or only high speed. A cat hull must do both, which is hard, but not impossible. The tri also has the advantage of a softer behaviour in flying hulls, since it can "roll over" on the centre hull. So it feels easier to sail, and makes it easier to take out all the power.

On the other hand, there are advantages with cats too of course. One less hull makes for less weight. (Unless you have a D35, which may be heavier than a similar tri.) No extra hull waving in the air on the windward side, gives less windage. Downwind it's more of a sleigh ride, and seems easier to push hard. At max righting moment, a cat has quite much less heel than a tri, giving it a better efficiency at that level, if the righting moment is equal. This is possibly the only point where the D35 has something good: The fake hull makes it easier to make it as wide as a tri, and still support the rig, so it can have the same righting moment.

I think I'd go for a proper tri here.
BUT: I think that if the Alinghi team chooses the right rig, that will be the deciding factor. The right rig then, would be a semi rigid wing, a la C-Class and Connors' Stars & Stripes by Pete Melvin/Gino Morelli (if I remember correctly). No conventional rigged boat would stand a chance, whatever type, size or conditions, unless there's a real storm and dropping most of the sails is necessary, which is a bit more tricky with a complete wing...

Stein

The first quote is an Alinghi description of the basic D35 concept.

The second quote is how Butterworth is said to have described the secret 'Cheezilla' project that is Bertarelli's answer to Ellisons trimaran.

I disagree that the center ... violin case?... on a D35 is not a hull. I'd rather say that it is a full-out hull, in spite of the fact that it does not rest in the water. Recall the construction photo showing the thickness of the center hull carbon laminate? There is a gargantuan amount of carbon there, in comparison to which the outer hull laminates are... merely normal.

These are highly over-rigged light air boats. They can sail on one hull in how much wind? 2.5 m/s or something? Under those circumstances, designed for Swiss lakes, don't they exemplify trimaran principles, optimized for the circumstances?

In my opinion, no.
The centre structure does look like a hull, but on this boat it does not perform the primary functions of a hull, so it isn't one.

Similarly, putting two spare wheels in the trunk of a car, doesn't change it into a six wheel car. To do that, those wheels need to roll on the ground, attached to the car.

The centre "hull" could have been removed and a bracing system with no volume could replace it with no change of the boat caracteristics, apart from maybe being lighter and stiffer than the "hull... :-)

This is a pure cat, but they have correctly noted that cats have a problem with longitudinal stiffness as a platform for the rig. The centre "hull" addresses it well, even though better solutions are thinkable. The main advantage with a tri, apart from lacking the stiffness problem, is its seemingly "softer" handling.

But this cat is obviously well adapted to its environment, as a cat often will be more efficient in light air.

Stein Varjord Wrote:
-------------------------------------------------------
> In my opinion, no.
> The centre structure does look like a hull, but on
> this boat it does not perform the primary
> functions of a hull, so it isn't one.

The 'central structure' does most certainly perform the primary function of a trimaran center hull, and without sitting in the water and creating drag.

> Similarly, putting two spare wheels in the trunk
> of a car, doesn't change it into a six wheel car.
> To do that, those wheels need to roll on the
> ground, attached to the car.

That's so silly, it warrants no further comment. Except that perhaps you think modern supertankers are catamarans too, since both their hulls are in the water?

> The centre "hull" could have been removed and a
> bracing system with no volume could replace it
> with no change of the boat caracteristics, apart
> from maybe being lighter and stiffer than the
> "hull... :-)

Maybe Jo R will show us something like that soon, I never said that Le Black is a trimaran, but the D35's are.

> This is a pure cat, but they have correctly noted
> that cats have a problem with longitudinal
> stiffness as a platform for the rig. The centre
> "hull" addresses it well, even though better
> solutions are thinkable. The main advantage with a
> tri, apart from lacking the stiffness problem, is
> its seemingly "softer" handling.
>

What's this softer landing baloney? The main advantage with a tri, is that you can then make a much wider boat than what catamarans allow.

Look at the Ventilo M2's. 28 feet long, they weigh 375 kilos. But they do not have the beam sufficient to compete with the D35's which weigh 1200.

Here's a recent snapshot of what you call a 'pure cat'.

[4.bp.blogspot.com]

He he.
I'm not willing to move an inch on this! And as you know, baloney and silliness are my favourite hobbies. :-)

As mentioned, a hull is a flotation device. Only objects with that function can be called hulls. The D35 has a structural device sculptured like a hull to look good. That's the only function. The D35 has ONLY 2 hulls and is a pure cat. It has none of the properties of tris, apart from almost the width, which have been done better by other cats before. Like the same Jo Richardson's Full Pelt F28 we both know well. It was much lighter and much wider than the D35s, relatively. It was probably stiffer too, but had a bad sail plan since it was a rebuilt and compressed F30, hampered by the added regulations that in my opinion definitely were the only reason why F28 died.

My sincere opinion is that the D35s are beautiful and fast boats, adapted to their use, but they're not the ultimate speed tool. Way too heavy and a bit too narrow in my opinion. The central structure is definitely a structurally unhealthy solution to get the stiffness they want, but it looks good.

Stein

Happy to read your latest reply, Stein!

This is going to be easy. Like shooting fish in a teapot.


Stein Varjord Wrote:
> As mentioned, a hull is a flotation device. Only
> objects with that function can be called hulls.
> The D35 has a structural device sculptured like a
> hull to look good. That's the only function. The
> D35 has ONLY 2 hulls and is a pure cat.

So, we're just looking at 'structural devices sculptured...to LOOK GOOD'? That's the 'only function'?

Let us then pause for some ART APPRECIATION, and admire more 'sculpture'!

Here's a very sexy photo of (what you stubbornly persist in mislabeling as) a so-called 'pure cat' with 'ONLY 2 hulls':

[ib.myimage.ch]

Isn't it amazing, Stein, how artfully they have sculpted that central structure, to give people the false impression that it somehow has something to do with ...20 TONS OF MAST COMPRESSION ?!?

(and please notice that the crew of 5 are all wearing 'flotation devices', do you suppose we should call it a 'septamaran' then ?)



Another sexy angle in this photo ...and I can't believe you are such a BUOYANCY MORALIST as to deny the HULLISHNESS of this 'central structure' just because it is a couple of INCHES off the surface in calm weather!

[ib.myimage.ch]



Finally, in your obsessive FLOTATIONARY SCROOGELIKE MINDSET, you seem to have entirely overlooked something.... something important...

Here's UNDENIABLE proof of the 'good-looking nonfunctional central device' ACTUALLY PROVIDING CRITICAL BUOYANCY !

To avoid too much mental stress on yourself, please sit down and examine them in the following order;

1) [ib.myimage.ch]

2) [ib.myimage.ch]



... If that is not a conclusive explosion of your FETISH WITH SUBMERSION, then I think we'll have to call in a doctor!


I will take the liberty of paraphrasing the last part of your Archimedean punctiliousness:

> The central structure is definitely a structurally unhealthy central
> solution to get the structural stiffness they centrally want, but it looks good.


Because it looks LIKE A TRIMARAN !


Conrad

He he.
Well, fish or not, just angling (pun intended) for verbal points in a short text never meant to be a complete description, doesn't change my conclusion.

The mentioned "That's the only function" referred not to looking good, but to it being a structural device. Gramatically, I admit, that was a bit too easy to misunderstand, especially on purpose. Writing in a hurry, sometimes gives sub par language. :-)

The same kind of reflections are relevant to the definition of what is a hull. I do not think that flotation is the only property necessary to define a hull. Several others are relevant, BUT: It's clear that no matter what other hull defining properties some object may have, if it's not meant to float while the boat is in a normal operating mode, it's no hull. An example: A hydrofoil operates in the water and carries the weight of the boat, but of course those common properties they have with hulls, still do not make them hulls. The D35 sentral member is not meant to float in any normal situation.

The pictures show exactly what I mean. The central structure is functionally only a load carrying member, which could be argued, is not an entirely good solution. Being hit by wave crests will not slow it down much, but the near pitch pole photo clearly shows that having more resistance in the wrong spot, like in the middle of the boat, rather than to leeward where flotation may be useful, can indeed be critical.

Possibly the pitchpole situation wouldn't have gone as far if the sentral structure had a deck shape and buoyancy distribution like the XOZ and Mirage hulls, (which would have made the D35 into a tri) or if it was much narrower, giving no buoyancy, but also way less drag, like with a tube/wire solution, preferably higher up too. With F28 "Skrik" we had some situations close to that one, but no problem. It popped out quickly and off we went again. Only the proper bows were in the water.

The two ordinary bows buryed deep will try to float up again, but are counteracted by the sails pushing on against a wall of water over all three "bows". The centre "bow" has very little buoyancy, being too shallow, but seemingly even more resistance than the proper bows. The one to leeward is actually the one doing most of the good stuff to save the situation. It's main opponent is the forward push far up in the rig. A good nr two opponent is the immersed centre "bow" resistence.

But beutiful pics they are, with beautiful boats.

Stein

The definition cat versus tri is important if you - as the Texel rating - has different calculations for cats and tri's:
Old IYRU defination: (IOMR)
Catamaran: It has at least 2 hulls, and it is symmetrical about the centreline of the whole structure.
Trimaran: It has 3 hulls, the centre hull displaces not less than 0.34 of the total displacement, and the yacht including its rig is symmetrical about its centreline.
Proa: If the yacht is not classified as either a catamaran or trimaran as above, it shall be considered to be a proa.

This means, that a yacht with 3 identical hulls is a catamaran!

Lars Ou

That definition seems weak and would appear to make a catamaran out of any design with a very light (less than 34% of displacement) center hull.

A number of other cat/tri terminology mixups have caught my attention recently. One of the more notable is in Pierre Yves Jorand's very good D35-related interview in Seahorse, which includes these remarks:
"...we have a central hull, above the water at rest. The thinking behind that is to have stiff load 'loops', meaning when you sheet the mainsail on, it actually tightens the sails rather than just bending the boat! The same applies to sheeting the solent or the drifter on hard; you want the headstay as tight as possible, keeping the sails flat which is vital on a multihull.
"And this centre 'hull' has a secondary use, providing extra buoyancy if the boat pitchpoles – which has helped on several occasions... Having the volume of two hulls, plus the centre one, helps you bounce back up before you go all the way. It also makes the boat very stiff which means you can control the sailplan more accurately. Finally it improves the hydrodynamics in a chop.
In terms of stiffness, while being a cat, the D35 is more like a trimaran..."

(Stein, please note Jorand's opinion about the extra buoyancy!)

The entire interview is here:
[www.alinghi.com]

Hi again Conrad.

I just rediscovered this great silly thread. As we have shared a very large number of hours on the road/autobahn/autostrada/autoroute to races, passing time by this sort of discussions, on any sort of topic, I enjoy the reminder. That was good times. Really.

I also note that I have not answered your last post, so there must be opportunity for a lot of sillyness and baloney at hand. As normal, I will hide this behind pretending to be contextual and presenting the final decicion-ing (pun intended) comment.

The definition you mention Lars, would not necessarily mean that 3 identical hulls makes it a cat. I dont know the complete wording of the definition, but given that this is all, I'd say a vessel vith three exactly equal hulls that are placed on straight beams, so all hulls have exactly the same hight would end up being defined as a cat (but for me that's a tri). This kind of boat would have all hulls displacing one third, or 33,3333...% of the weight on flat water without heeling forces. If the beams were bent, so that the amas could not touch the water simultaneously, the centre hull would displace close to 100%, one ama would touch lightly and the other would be in the air. Then this would be a tri acording to the mentioned definition, even with 3 identical hulls. Actually just a slight bend would be enough to increase the load about 1% on the centre hull and pass the 34% limit.

Mainly Conrad, it seems like you consentrate on the aestethical appearance of the D35 to define it as a tri. That's not enough. Finding others using the word hull about its central structure doesen't make the boat a tri neither. The point is if the vessel has the defining properties of a tri. An easy definition of a tri could be: Watercraft with three hulls. To make that usful, the word "hull" must be defined in a similarly general and simple way. Giving that a try: An object whos main function is to make a vessel float and be controllably moveable while floating.... Seems OK? Probably easy to find loopholes, but the point is it's easy to get what a hull is, and isn't.

Then it's obvious that the D35 has a central structure that is no more a hull than its mast is a hull. When the boat flips, the mast also gives it flotation, temporarily... One of the D35 actual hull shapes could easily be used for an (aerodynamically bad) mast. The the boat would have four pieces looking like "hulls", but would still be a catamaran, not a quadromaran. I guess this qualifies for sillyness and baloney, easily, and might also seem a bit provocative? He he.

Jorands remarks on the centre "bow" helping to prevent pitchpoling, I simply do not believe are correct, apart from some very odd thinkable occation with a convenient narrow wave coming in between the hulls from behind hitting only this "bow". Watching pics and movies of the same boats it's obvious that it's quite the oposite of what Jorand reportedly says. That corresponds with what normal engineering would find. The extra "bow" is too far up, and gives virtually no displacement even at dramatic forward angles, (and the small amount there is, is even in the wrong spot, not to leeward) but at such occations it has the same drag as a full bow. Very bad idea that way. Also it is, as previously mentioned, not a good way to get the stiffness either. Too heavy. Wires and struts would be a better solution.

These conclusions have apparently been reached by the Alinghi guys too, as their number one priority boat at the moment, which looks very much like a D35 on tons of stereoids, has no central "hull" but rather the wires and struts mentioned a number of times. Same thing, but works better, in every way.

Which of the two giants will win though, is a very hard (impossible) question to answer, before they meet. My guess is that the tri will be quite a bit faster and able to point higher due to its wing, but also that it's much heavier (?) and maybe less able to manouvre than the cat. The cat may be more agile generally, and it may be faster downwind... I guess we may se some very agressive sailing and possibly some full on crash. Especially if one of the boats prove clearly faster. This thing may evolve to a circus worthy of the not so nice Emperor Caligula...

Stein

And Happy New Year to you too, Stein!

The Alinghi-BMW Oracle showdown took so much attention for a while, that I plain forgot to check back here for updates.
Now those boats have had their two measly races and apparently are going to be in mothballs forever... what are we going to do for entertainment? (I have an idea below!)

Considering how many references there have been to the BMW-Oracle ~trimaran~ (which when measured for length was treated as if it was a monohull!), this discussion on 'basic math' hasn't been concluded yet?


Here's something interesting... Jo Richards has a new CATAMARAN!

[www.guywhitehouse.com]