Forgive my innocence in this matter, but why do Nacra/HC need an additional 40 kg to build their hulls?
You are forgiven.
But in defense of both Nacra and Hobie builders, they DON'T need an additional 40 kg to build their hulls. Your assumption is incorrect.
I'll give a listing of hull weights for you ;
A-cat : typically around 14 kg / hull (18 foot length)
Prindle 16 : about 30 kg per hull (16 foot length)
F16 : Typically around 25 kg / hull (16 and a halve foot lenth)
FX-one : Around 35 kg / hull (17 foot length)
I-17 : I have no measured data for that hull but suspect also around 35 kg
F18's : about 45 kg per hull as per class rules (18 foot length)
It is wise to understand that the F18 hulls and beams are heavier because of the minimum weight rule that specifies the platform (not the same as a whole boat) to be at least 130 kg. Therefor F18 designers have no insentives to design and produce light hulls, beams and daggerboards/rudder setups.
So in effect an F16 hull is "just" 10kg lighter per hull than its competitors, while being only 6 inches shorter. Not 20 kg per hull.
So in effect the hulls can only explain about 20 kg weight difference between the boats. The other 20 kg is to be found in other items.
Even more interesting is the fact that even old boats like the Prindle 16 and Dart 18's have lighter hulls than the newer "high tech" hulls except the A-cats and F16's. The reason for this is to be found in choice of materials and a decision to optimize for easy and fast production rather then lightweightness. That is a business decision.
So lets continue with the other 20 kg weight difference (although it is probably more than that)
For the sake of simplicity I assume the rigs of the F16 vs I17/FX1 have comparable mass,
This is wrong and therefor all conclusions based on this assumption are wrong as well.
The F16's use the aluminium superwing mast or carbon mast while the FX-one uses what looks like a cut down Tiger mast. There is already 3 kg difference in the overall weight of the mast. We (I) know this thanks to a FX-one sailor who measured his components. The Superwing fittings are also lighter. F16 seal the top of their masts with a block of rubbery foam and a thick layer of sealant. Up till recently the big builders use plug made of cast aluminium or even a stainless steel plate. You'll find significant weight differences here. But the superwing mast is also 0.4 kg per meter lighter than its competitors (except the Swell shadow). It has reinforcing ribs inside the mast section that restore the stiffness and strength of the mast while the wallthickness has been reduced. This is more weight efficient. But we are getting into details.
The sails should weight about the same I'm sure. But the snuffer system of Hobie is again noticeably heavier. Note that when you have several items that weight 1 lbs more then you can quickly build up a significant weight difference.
The weight saving may come from the use of newer materials (e.g. carbon fibre) or a different inner/support structure, but from some reading and talking to the salesmen this last weekend it seems as if the building principles and used material are very comparable.
Indeed, the F16's are largely made with the same basic materials and technics, even though alot of effort is applied to get the max out of them. I'm unsure wether the same effort is made by some others.
The real difference in weight is caused by a simple business decision. Both Nacra and Hobie don't want to have stocks of imcompatible parts. This means that they use all kinds of F18 parts for their singlehanders. As good as all of these are much heavier than needed because of the high minimum weight limits in the F18 class. The F16 builders however decided to optimize all parts for F16 usage.
Examples :
The weight difference between the Tiger F18 rudder setup and the F16 rudder setup is ..... 8 kg's !
The weight difference between the Tiger F18 daggerboards and the F16 daggerboards is .... 3 kg's !
The weight difference between the Tiger F18 beams and the F16 beams is .... 1 kg to 2kg per beam !
Add these differences to those found in the snuffer system, mast and other parts and you'll quickly gether some 20 to 25 kg additional weight.
Does this means that Nacra and Hobie need this weight to build a good boat ? No, not really. It is just that the business director decide to cut cost and increase profibilty but use parts that were orginally designed for the F18 (and their heavy weight limits)
I'm quite sure that both companies could build their singlehanders significantly lighter if they wanted too. But several of us realized a few years back that neither would go that route unless absolutely forced to do so by the competition on the marketplace. And subsequently the F16 class was born, established and grown.
Is it so that the F16 boatbuilders just use less material and use it smarter (but if so how?) and are the boats from HC/Nacra in that sense just old-fashioned? Just curious / interested.
The nacra/hobie boats aren't old-fashioned, the squaretops rigs are just as modern as the ones on the F16's for example. The rudder profiles aren't "old" neither, It is just that the individual parts were never optimized for their "new" usage.
An interesting detail in this is the fact that the One-design Inter-17 class rules (now called F17) allow an I-17 owner to cut shorter his daggerboards. Naturally these board were designed and optimized for the F18 class and doublehanded sailing on the rather heavy platform. This means that they are really too big and too strong for signlehanded use. But they had these F18 daggerboard lying on the shelve and why not use then ? Make alot of sense from a business perspective.
F16 builders were NOT building any F18's at time when they designed their F16's and so they designed the F16 parts to be fully optimized for F16 use. This allowed lighter construction without really sacrificing any strength.
You really feel this difference when sailing these boats. On the F16's you hardly ever pull your daggerboards up while sailing. The boats are calms and balance over a wide spectrum when the boards are fully down. The fact that the boards are significantly shorter and because the sail loads are noticeably smaller allows the daggerboards to be 60 % of the weight of those F18 boards (and FX-one and I-17 boards).
My whole setup of 2 daggerboards, 2 rudderboards, 2 rudder stocks with protectors + tiller and joystick combined weight just 8 kgs ! And it was halve the cost of a comparable F18 setup as well.
So why are these F18 parts so heavy ? Well how else can you get the platform to weight in at 130 kg and the whole boat to weight in at 180 kgs ? As said earlier the sails will all weight very much the same and so to the lines, cleats and blocks. So all that extra weight is concentrated in a few key parts which are the ruddersetup, mast, beams, hulls and fittings like snuffer systems, trampoline etc.
It is my personal hope that in time we can "convince" both Hobie and Nacra to go the -truly fully optimized- route and start designing, building and producing truly optimized boats in addition to the F18's.
I'm sure they can buy several F16 designs and skip the designing face all together if they wanted to.
By the way: At the Nacra dealer I saw a 3D impression of the new Nacra F18 hull. It has the same 'negative' bow as the Blade and Fx One and is even more pleasing to the eye than the current Nacra F18 design.
Forget about the negative bow, that is the least important aspect of these new hullshapes. The truly interesting parts are the shape of the keel line and the volume distribution. Get that right and they are in, get it wrong and you can throw away the design.
Bart, I hope my answers provided some insights.
One more thing. To press home my comments I would like to add that amateur home-builders who are building in Wood-epoxy are producing F16's that are about 110 kg's in overall weight, with the hulls being 25-26 kg. It is a sad time when amateur builders can produce much lighter boats using plain multiplex while the professional builders are giving us 150 kg boats using the "latest technologies". And believe me these darn multiplex boats are way more dent resistant then their glass counterparts. In the of strength and stiffness these multiplex boats are at minimum just as strong and stiff as the glass ones. When build with skill they are both stronger and stiffer. But this is not the topic at hand.
Cheers,
Wouter