With dolphin striker or not? Makes a huge difference. If you have a dominant load direction you would go for box section. Since you want not get injured or cut your trampoline, take something with round edges. CFRP should not be build in to tight curves anyway. Common problem, most people think it is material only, but each material needs it specific design.

Apart from a sagging jib, I am still not convinced why I should look so much for stiffness. I agree about the better feel (see my very first post). But as an engineer, I don't have a problem if one hull drops 40 mm or so, as long as I keep one hull out of the water.
For the jib, I would look for stiffer rigging (i.e. rod or dyform) and stiffer front hulls, before I look for the beams.

For the lost energy theory: the energy loss due to flexing structures is lower than 1% (if you bend something you get 99% or more back). A spring in a watch is a nearly perfect energy storage, ask yourself why. So from the little bit energy which is stored shortly in the structure due to bending, you loos only a liitle bit. A little from a little bit is how much?
The best way to improve speed is to concentarte on the import thinks: Skill, sail shape, foil shape, hull shape, deck layout.

and btw, I like the flexing wings of the B777. It saves tons of structureal weight.

Cheers,

Klaus

"I like the flexing wings of the B777. It saves tons of structureal weight."

That and it makes the ride much smoother for me and the peeps in the back!

http://www.airliners.net/photo/Delta-Air-Lines/Boeing-777-232-LR/1702407/L/

Those that can do "do" those that can't "teach"

I have issue with the way your measuring flex.

your test is measuring the flex of the beam, the beam joints and the supporting structure around the joints. but you completely failing to measure the stiffness of the hulls.

for example, when I press on the side of the capricorn it is very hard to make it flex at all but by comparison my old nacra 5.8 was very flexible in the sides.

not 100% sure on how to measure these stiffness levels but they do contribute to the overall speed of the boat!

I pity the poor students then if this is the standard of tripe you trot out as engineering gospel. I'll be sure to advise my engineering student daughter not to consider the land of the clog in her options for a semester transfer. The crafty old b**tard with 30 years sailing and building experience has some very interesting discussions on these things wth the bright young theory bound student!

Timbo is on to it. He now understands most of the sailing world prefers stiffer platforms and has moved on to consider some ways to achieve them.

Klaus - I like your explanation about beams. I think in isolation a round beam is strongest in all directions but then you have to consider the direction of the greatest forces. I think that is vertical. In A's some have approached that issue by firstly making the beam a larger diameter for overall mechanical advantage then having thicker walls top and bottom. This is easy to do with carbon by filament winding. In alloy of course the dolphin striker does the job. In bigger cats the pelikan striker does the same for forebeams subject to forestay load. I disagree on the amount of energy lost though when the platform twists and returns. Unlike the watch spring that return energy isn't applied to the original job - that is forward motion. I think a substantial amount of it is lost by the platform "wriggling" about in the water rather than applying it to smooth forward motion. I certainly agree with you that there are many other very productive ways to improve speed - probably the most significant for most of us being operaor skill. However the topic of this thread was the merit of varying levels of boat stiffness. I believe a good sailor on a stiffer platform will always beat an equally good sailor on a less stiff platform.

I'm over this now - off to sail on my glued carbon beamed rocketship. Mmmmm - wonder how I can make it stiffer!

Cheers

Feel, think, believe. Theories and anecdotes. That is all thats presented as proof that stiffer is always faster. Question this and closed minds blows their egos all over their keyboards.

A stiff boat feels different and more responsive. It feels easier to sail and it might so. Still no proof that it really is faster or easier to sail. Until proper two boat testing is done under different conditions we dont know ****. Flat earth society mindset lives on.

I`ve read all 7 pages..
I think Macca is trying to say that a stiffer platform is a good thing.
I think Wouter is trying to say that he`s right, but that no-one would double the cost of the boat to get a 2% gain.
I think they`re both right.
Doesn`t the F16 class rules stipulate the boat can`t be glued (ie must be take-apart-able for transport?) I think this sorts out the arms race a bit.

In the quest for ever-diminishing returns :
The Viper seems to have proved (by their results) that higher volume hulls (for 2-up sailing) is beneficial over smaller volume. Of course they must have put the volume in the right places as well.
Now they NEED bigger beams to stiffen a platform which has higher volume hulls, when compared to a boat with lower volume hulls.(This is independent of hull weight, since higher volume boats will be subjected to higher loads.) The bigger beams make the boat heavier once again. So the cycle repeats itself until the boat arrives at it`s weight (which in many folks opinion is way too heavy), but is still as fast as the lightest boats, meaning that the trade-offs seem to have worked slightly in their favour. (I say slightly as they have a highly developed rig and top sailors on their boats, which also gives them an edge).
This is EXACTLY what the F16 class rules are there for, and they seem to be working - Equalising boats that are built differently, but fitting into a boxrule.
If there were NO rules, Playstation would have won the F16 intergalactic champs, as they have taken the above to the other extreme. Bigger truck needs a bigger engine to make it go. Right, the engine is so big it made the truck heavier. "Frank, we need a bigger engine for the now heavier truck." Ok, but the truck will have to be bigger to take the new engine Oh wait...

Now for the case of ever INCREASING returns.
I have no doubt that Darren Bundock on a min. weight Viper would be faster than Darren Bundock on a standard Viper, and the min. weight Viper would cost a LOT more to produce. I won`t argue with Mr. Goodall on this since he seems to have built a boat or two.
If the hulls were built down to 15kg each, they would require a smaller set of (full-carbon) beams, so lighter hulls would require lighter beams, and the whole boat could be built to min. weight, or even 20kg lower, quite easily, if enough money were thrown at it. Min. weight mast with super-light sails that last a regatta or two will help.
Would this cost more than a standard F16 design ?
I think that`s what Macca and Tornado Alive have been trying to say all along. (But I`m not sure).

Excellent synopsis!

Summed up nicely in one post....... Who needed the 7 pages



This is the only part I disagree with.

Well done Steve, excellent sum up.

I would agree with TA, 2% of the population would pay the extra for the 2% gain.

No, we've established that increasing stiffness up to a certain point is better.

Note, that there is an important difference between both statements.

The first statement is open ended where the other is not.






Indeed and therefore the distance between the beams is factor here. In my models the largest component resisting the bows moving up and down independently is flexing of the beams in the up and down plane and not torsion. Torsion resistance is actually only a small component overall.

Therefore box-like (rectangular) beams with lots of material in the top and bottom sides is most efficient. However some shaping is needed on the front to allow for fairing of the beam into the hull. Waves hitting a beam with flat frontsides is not a good idea. Of course, flat backsides and top or bottom sides are desireable; that uses less material (weight savings) and makes it easier to fit blocks, dolphinstrikers and other stuff to the beam. Now look at the Falcon and Aussie Blade beams and you'll see these considerations being implemented. That is the reason why for example the trampoline track (the only things implemented for convenience) is situated in the upper backside corner. Here it allows for easy and clean tramp fitting but also adds the most to the stiffness of the platform. Designs with such tramp tracks halfway up the beam are simply not smart.

From memory those custom made F16 beams are equivalent in stiffness to 90x2 mm round beams but they are smaller and fitted with a more practical overall shape. The rectagular shape also looks the beams better in place in the beamlandings then a round beam that can more easily twist in its beam landings.

Wouter

Not when dealing with non-ideal springs that are submerged in fluids that act as dampers (the water surface or the rig flapping about). In such case the flow of leaked energy (grag) can be significantly greater.

In our case it is not just the spring itself (the beams etc) that we are concerned with. In our case these are attached to large surfaces that flap about in the water or air. Fit a spring to an object with a large surface area (and low weigt) and see whether you can still recover 99% of the stored energy while having it oscillate.

Other then that do this mind experiment.

Lets lay our boat motionless in the water. Then flex the platform, forcing one bow 40 mm down. Let go of the depressed bow and see whether the boats starts to move forward. I say that I see waves being created and the boat and rig shaking about but not much forward motion if indeed any. Now use the same amount of force (and travel) needed to flex the platform to push the boat forward. Spot the difference in the resulting motion ?

So our boats are not designs that recover much of the energy stored in flexing the platform at all.

Wouter

I don't know what kind of **** education you have over there but when I make mistakes students get electricuted, get seriously injured or loose an eye. Ever seen a hydraulic robot go beserk or see a see a steel support wire snap ? I promise you, you'll see people dive for cover and it'll make a big impression on everyone around.


In answer of your other points. I know of no F16 that comes anywhere near the (wall)flexing of the nacra 5.8 hulls. But if they do then that is just another (independed) drag component in the overall picture. At this time we were discussing platform stiffness (not wall stiffness of the hulls) as that is closely related to the choice of beams.

Wouter

Well Ace,

I remember the old geezers saying that a 16 foot High Performance boat would never work and that I was a fool to start such a class back in 2001. It could never be as fast as an F18, just couldn't be. You couldn't offer such a lightweight boat for less then a F18. It could never carry 2 males in a competitive sense. It couldn't ... ... ... etc

But we're here now and the old geezers are still on their fence.

The fruits of my labour are out there for all to see. Yours are, well, what are your achievements exactly ?

I often remember this qoute by Niels Bohr (co-founder of the quantum mechanics theory)

"If you think quantum theory isn't totally insane, then you haven't studied it properly yet."

Still, it is one of the most important theories in town; explaning everything from transistors to the way the universe behaves. Without it we wouldn't have our High Powered computers and mobile phones.

So please forgive me if I put you on the fence next to all the other old "good for nothing" geezers.

I hope your daughter has more brains then that.

Wouter

We know the answer to that question already.

No F16 can be lighter then 107 kg and a standard alu/glass 110 kg Falcon costs 16.000 bucks in the USA. With a 3800 buck carbon mast the boat will be at min. weight.

Now, Macca can build himself a 20 kg lighter F16 using whatever he wants and pay 100.000 bucks but then he can't race it in the F16 class. Not even when putting 20 kg of lead under his mainbeam, thus preventing him from using smaller beams or hulls as refered to in your example. Why ? Because he is only allowed a max of 7 kg of corrector weights and he still needs to design the boat to carry 107 kg + 145 kg of crew weight.

So what he can do is pay 100.000 bucks to basically make a boat that will be identical in specs to say a 19.800 US$ Falcon. Last time I checked, boats with identical specs were also of the same performance.

There is simply no way around that limit.

Wouter

You just don’t get it. Yes, both boats will be same weight and dimensions, but one would be a Glass boat with alloy beams and carbon mast, the other would be a full nomex/honeycomb boat with increased hull volume.
Catamaran designs lately are showing the larger hull volume boats (to a certain point) are proving quicker. A great deal of the reason why the Viper is competitive with boats much lighter boats is because of this and the increased platform stiffness.
If you think a 107kg all carbon /nomex Viper would not be quicker than the current Viper and other F16s, plus significantly more expensive, then you are delusional and this argument will just keep turning a full circle....... However, that is where I feel we are now.

[quote=ACE11I disagree on the amount of energy lost though when the platform twists and returns. Unlike the watch spring that return energy isn't applied to the original job - that is forward motion. I think a substantial amount of it is lost by the platform "wriggling" about in the water rather than applying it to smooth forward motion.
I'm over this now - off to sail on my glued carbon beamed rocketship. Mmmmm - wonder how I can make it stiffer!
[/quote]

A flexing body in a fluid can create propulsion, think of the wings of a bird or a fish swimming in water. I don't say you will recover all the energy. But if your foils are moving around, this is much more efficient as you might think.

The more I think about the stiffness subject, the more I see it is a not explored and understood subject.
Image I am sailing on one hull and a puff hits the boat. What happens. More lift from the sail, which will heel up the boat and create more leeway. The increased leeway increases the forces on the boards, which will heel up more the boat. As a result I open the sheet/change the course to reduce the heeling.
Now, I have a properly designed flexible board:
The puff hits the boat, more forces in the sail, more leeway, but now the board flexes in a c-shape. It produces less sideforce, hence lessheeling moment, but some lift. The lift pushs the hull a bit out of the water, which generates less drag.
Thus with a flexible board I could have less additional heeling moment and less drag, which might be faster...

You can only improve a design if you open your mindset and if you don't get blinded by simplistic and too early conclusions like "stiffer is faster"

Anyway enjoy your sailing on whatever stiff boat.

Cheers

Klaus

Well Wout

It's ACEII - Ace was my boat 30 years ago with many in between. I don't have much imagination with names.

I haven't criticised F16 or F18 in this thread or anywhere for that matter. In fact earlier in this thread I said "I love formula class sailing - that's why I've been sailing and building in it for over 30 years. I wish F16 every success."

Who are these old geezers still on the fence you speak of on this thread?
The debate on this thread has been about platform stiffness not the merits of particular classes of boat.

I have plenty of achievements, the most relevant to this topic being that I sail a lot. Around 100 races in the last 12 months - my wife would say more. I sail in the ultimate development cat class mainly. We are often doing boat on boat testing and always trying things looking for performance improvement. I feel qualified to express a view - take it or leave it.

Cheers

Steve, great summary of the debate.

I would add that the Pink Elephant in the room is the obvious but unstated realization that a One Up F16 and a Two Up F16 require different technical solutions. I think you were referring to this disconnect.


Obviously, the A class (1 up) and the F18 (2 up) are both 18 feet in length but the technical solutions are quite different (very crude comparison). This technical gap is much smaller at the 16 foot scale and one of the key insights of the founders as they looked at the marketability of the F16 concept.

The more important twin of the technical pink elephant that is not explored are the merits of a formula class that believes that fair racing between one up and two up teams is possible.

Assume perfect technical equivalence between a one up and two up F16 boats. Clone a sailor a couple of times and put them on the two boats. The single handed clone would have to magically come up with a lot more skill to get his boat around the course then his two clones on a two up F16 for the desired dead heat. It's damn hard to sail the one-up boat to it's number over the wind range and you have to really be at the top of the game to do this. (Some estimates of F16 1-up racers is that it takes 30% more skill to get back to your spot in the pecking order). Consequently, it would be better to race as two classes

Now you can acknowledge this disparity and deal with it, dismiss the disparity as "so be it", or not deal with it at all but this is simply politics. Without resolving the fundamental disconnects... the debate will continue.

I suspect that if you focused the debate on two up F16' class growth, the winning solutions will be clear. My solution... Follow Bundy and Caroljn.. F16 is a perfect solution for Light weight and mixed teams, Women teams and Youth teams! Hell... the Hobie 16 market was enormous world wide and you can't quibble with the experience of those two and other world class racers who want to develop this niche of the sport.

The single handers need a different solution for growing the single handed class....

Builders will offer their best equipment to meet the TWO needs as the TWO classes develop!

What a load of drivel!!!

That's a hell of a crystal ball you've got there Mark - you haven't even set foot on an F16 have you?

All you've done is made assumptions and drawn further assumptions based on those first assumptions.