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#212001 - 05/27/10 03:21 AM Is over "stiffness" of a boat that desirable  
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waynemarlow Offline
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Over stiffness in structures can lead to more problems than solve, glider design ( who probably lead the world in composite construction ) have now gone away from very stiff structures, it was leading to structural failure at key points ( stress fractures ) and many pilots felt that they were taking such a physical battering, they couldn't cope physically over longer flights. Food for thought and I would guess the super stiff boats must be nearing this point or is boat design still catching up.

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#212002 - 05/27/10 03:37 AM Re: Is over "stiffness" of a boat that desirable [Re: waynemarlow]  
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Mark P Offline
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MP*MULTIHULLS
#212005 - 05/27/10 03:53 AM Re: Is over "stiffness" of a boat that desirable [Re: waynemarlow]  
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Wouter Offline
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I have always seen boat stiffness as a field of diminishing returns. Each progressive step (increase in stiffness) results in less gains and at some point the additional increase is simply not worth the effort (cost).

Therefore, it is my opinion that the best approach is to find a good optimum here. One where the stiffness is sufficient to provide for a nice sailing feel and good performance without going overboard with respect to say weight or costs.

Just to give an example ; a 180 kg F18 can be made very stiff and perform well with that but I doubt that any such stiffness increases are enough to results in more performance then say a slightly less stiff but 30 kg lighter platform of the same dimensions.

Boat design is always a game of balancing one benefit (or drawback) against another. The designer who does this the best will produce the boat that performs the best over a wide range of conditions and thus be most competitive in the long run.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#212006 - 05/27/10 04:02 AM Re: Is over "stiffness" of a boat that desirable [Re: Wouter]  
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mitchellsailor Offline
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in BIG boats there is still a never ending search for stiffness. Punching through waves a volvo 70 will still get a slack forestay.
The latest America's cup multi's were still capable of producing more power than their structure could handle.

So scale up and stiffness becomes more of an issue.

*yes that is very "stiff"


Mosquito 1750 Bonnie-GLYC / Peninsula

The plan was simple.... Like my brother in law Phil, except this plan just might work!
#212008 - 05/27/10 04:04 AM Re: Is over "stiffness" of a boat that desirable [Re: mitchellsailor]  
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Wouter Offline
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Quote

So scaled everything up and stiffness becomes more of an issue.



Now scale everything down (as we did on the F16's) and ... !

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#212013 - 05/27/10 04:43 AM Re: Is over "stiffness" of a boat that desirable [Re: Wouter]  
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waynemarlow Offline
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Nice reposte Mark, your library of videos is uber cool

As an engineer going for the ultimate goal always incurs penalties of some form or other. My worry is that we are totally into trying to get the ultimate platform stiffness but incurring penalties such as weight and cost for what may or maybe not be small incremental gains.

But will we push through the point where it suddenly gives problems to us as humans. I remember flying a pretty state of the art glider in the 90's with carbon wings, it was so stiff that every bit of air turbulence was transmitted into the **** and litterally was jaw chattering at times. Flying the less state of art glider with glass and carbon was like flying a comfy arm chair where you could feel every thermal and puff of uplift. Now myself and others were pretty agreed that over a day the softer platform would be a much more forgiving and hence better aircraft to fly.

#212028 - 05/27/10 06:42 AM Re: Is over "stiffness" of a boat that desirable [Re: waynemarlow]  
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Karl_Brogger Offline
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There is only two downsides to making a platform more stiff.

1. It generally costs you some weight
2. More fatigue on other parts. Something has to give, or at least it will more expose weaknesses in parts.

You get more of a return from stiffening up the platform, than removing weight.

Last edited by Karl_Brogger; 05/27/10 06:44 AM.
#212039 - 05/27/10 07:41 AM Re: Is over "stiffness" of a boat that desirable [Re: Karl_Brogger]  
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Wouter Offline
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Quote

You get more of a return from stiffening up the platform, than removing weight.



You can't state that without including some quantification.

I'm quite sure a F18 that is 50 kg lighter and only "invest" a 1% loss of stiffness is going to be faster overall then the regular F18.

There is always a balance point to be found somewhere. A point where the effects of one change are not enough to counteract the effects of another (but linked) modification.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#212053 - 05/27/10 10:53 AM Re: Is over "stiffness" of a boat that desirable [Re: Karl_Brogger]  
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ok some real life reports about stiffness:

one or two years ago, I tried to use dyneema for the shrouds. Because of the creep, I never could setup the rig as tight and stiff as with wire. It felt different, but it wasn't slow. I run the same speed, the same vmg. But the stiffer rig felt much better, more precise and predictable.

Some years ago, when I did a load of road cycling, there was a huge trend to stiffer frames claiming for a more efficient transmission. I had a stiff bike and a very flexible one. You could really feel the difference, but I could never messure any difference in speed. Funny enough, some time later, there was new trend to new super light weight wheels with 16 or so spokes. Everything you gained with the frame you lost with the wheels. Most people still was convinced that the "stiffer" bike was faster.

I remeber some peolple quoting to must have a low stretch sheet material, and now on some A-class the trend is to use a mid sheeting, supported by the floppy trampoline...

Wasn't the mast section of the Fx-1 too stiff to tune the sail adequately for a single hander? Never sailed one seriouly but was is your expierience with it?

Cheers,

Klaus


#212091 - 05/27/10 06:47 PM Re: Is over "stiffness" of a boat that desirable [Re: Wouter]  
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Karl_Brogger Offline
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Originally Posted by Wouter
You can't state that without including some quantification.


Just repeating what I've been told by some one who knows cats well.

Originally Posted by Smiths_Cat
Wasn't the mast section of the Fx-1 too stiff to tune the sail adequately for a single hander? Never sailed one seriouly but was is your expierience with it?


Yes, it was too stiff, barn pole stiff in fact. I wasn't clear I guess, I was thinking more just the hulls/beams, and not neccessarily the rig. Although a flexible set of blades/rudders doesn't sound too appealling either.

#212092 - 05/27/10 07:16 PM Re: Is over "stiffness" of a boat that desirable [Re: Karl_Brogger]  
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So referring to bikes on a sailing forum.
The stiffness was very important in the bb for power transmission and also solving the down hill wobbles a major problem with some designs.
The wheels are moving so the weight savings in wheels are seen as very important- particulary the rim,tyre,tube combination as they are the furthest away from the centre of rotation. less spokes doesn't solve this problem in many cases as the rim has to be built stronger, but they look nice.
Back to boats, in Australia we have carbon rudder boxes mated with foils that are heavier and more expensive than aluminium but they're popular because they have the "porn" factor


Mosquito 1750 Bonnie-GLYC / Peninsula

The plan was simple.... Like my brother in law Phil, except this plan just might work!
#212101 - 05/27/10 11:44 PM Re: Is over "stiffness" of a boat that desirable [Re: mitchellsailor]  
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And still Eddy Merckx did his one hour record on a ultra flexible frame, and light btw, but he was cycling on flat indoor race track.
Once my friend asked me, if I can give him my new aero wheels (flat spokes, v-shaped rim). After the race he told me, he pushed harder, because of the better wheel. Some weeks later the wheels among others were mearsured by a German university. They had the highest drag and was among the heaviest.
But they look good, I still use them. It is the placebo effect who counts more than 100gr and 1 or 2 drag counts. It is all about believing like religion.

#212102 - 05/27/10 11:52 PM Re: Is over "stiffness" of a boat that desirable [Re: Karl_Brogger]  
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Quote
I was thinking more just the hulls/beams, and not neccessarily the rig. Although a flexible set of blades/rudders doesn't sound too appealling either.

Keep always one hull out of the water, than you don't need to care about stiff beams.
As an aerodynamic specialist, I can tell you that you can neglect the stiffness of the boards and rudders. Catsailor are so stupid and mount tons of lead on tip of a daggerboard.

So it boils down to hull stiffness, which is not a problem for beach cats with sandwich skins. I remember my Dart 18 and early Ts were a bit flexible, but nevertheless fast boats.

Cheers,

Klaus

#212108 - 05/28/10 02:06 AM Re: Is over "stiffness" of a boat that desirable [Re: Smiths_Cat]  
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Wouter Offline
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Quote

Wasn't the mast section of the Fx-1 too stiff to tune the sail adequately for a single hander? Never sailed one seriouly but was is your expierience with it?



Yes, that is my opinion (and another example were using an F18 component on a non F18 design didn't work out). Some consider the Superwing alu mast we have as a noodle but it sails like a dream. Especially when compared to the FX-one setup.

Again, it is in de balancing between the mast and the sailcut. That is the true pathway to success.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#212112 - 05/28/10 03:38 AM Re: Is over "stiffness" of a boat that desirable [Re: Wouter]  
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Bike frames are quite a good example of what I am wondering about. 20 years ago we were building the first of the real MTB ( off road) bikes out of steel, really supple and bendy, gave the really poor first generation suspension a bit of hand and the overall package was a quite supple but user friendly bike. I still have the bike 20 years on and still no sign of frame breakages or stress fractures.

Now I've since had two very stiff aluminium frames with pretty top class suspenders on, great bikes, but already I have broken both frames at the critical stress points.

confused My latest frame is built like a barn door weighs a ton but is considered to pretty bullit proof, and then I look at my skinny little lightweight bendy steel frame and think have we got things right here.

#212236 - 05/29/10 10:10 AM Re: Is over "stiffness" of a boat that desirable [Re: waynemarlow]  
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The Tornado got faster, as they got stiffer.

#212242 - 05/29/10 11:31 AM Re: Is over "stiffness" of a boat that desirable [Re: sail7seas]  
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Originally Posted by sail7seas
The Tornado got faster, as they got stiffer.


Sounds like you are saying that tornados got faster because they were built stiffer. Can you prove it? Tornado teams from the 84 games through 92 are still undecided.

For those who dont know those years were the transition period. State of the art was Gougeon cold moulded hulls and small diam beams. The boats from Goran was not faster in the beginning but they did not break all the time. The boats from sweden might also have been just a tiny bit faster in chop but the difference was probably in the maxed hull volume of those hulls. What killed the woodies and small diam beams were not performance but reliability, and initially price.

Keeping the rig stable is what makes the difference. I have not seen theoretical or real life proof on what is faster. A platform that bends and moves softly in seas or a stiff one bouncing and crashing through waves.
In flat water it makes no difference at all. Sailors are like sheep at times, following the leader instead of asking the whys and hows.

Bundy is smarter than jumping into this. There is no winning game here, only ways to loose business. The rest of the AHPC gang should take note and act as if they had brains.

And by the way. Those cold moulded cedar hulls from 83 are still as stiff if not stiffer than Gorans spaceships and still at min weight.
Talking about carbon masts, carbon hulls and carbon crap is pretty silly. Good engineering and skilled builders is what it takes to build anything good. Even wood can outperform a fresh engineer who throws carbon at whatever challenge he see.
Set untrained farmers to laminate hulls and it takes half a year before they have the skills. Then they are due a raise so they get replaced.
What really is discussed here is how to maximize profits. The rest is smoke, mirrors and spin as Wouter says. Smart butt spin doctors making stir fry to paint a pig.

I would buy US made at min weight.

#212255 - 05/30/10 12:37 AM Re: Is over "stiffness" of a boat that desirable [Re: Wouter]  
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an idea...

drop a state of art F18 rig on a B2 platform and see how far we have really come in platforms.

#212257 - 05/30/10 03:50 AM Re: Is over "stiffness" of a boat that desirable [Re: Stewart]  
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waynemarlow Offline
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Be an interesting test but what would be interesting is to time the boat around successive courses, I think you would be surprised at how little the differnce there would be.

Certainly the Stealth which I have has got stiffer over time, largely due to better reinforcing around the beam areas, is the latest boat any faster than the older boats, certainly they feel different in handling, but around the race course the oldest boats still can win pretty regularly.

My main concern though is to stiffen a structure then you put increased loadings on other areas which then in turn means they have to be beefed up to take the loadings. I would guess it has to be a balance between immediate pleasure ( better handling ) or long term pain ( increased weight and perhaps less long term durability )

#212273 - 05/30/10 01:59 PM Re: Is over "stiffness" of a boat that desirable [Re: 45degApparent]  
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Originally Posted by 45degApparent
Originally Posted by sail7seas
The Tornado got faster, as they got stiffer.


Sounds like you are saying that tornados got faster because they were built stiffer. Can you prove it? Tornado teams from the 84 games through 92 are still undecided.

For those who dont know those years were the transition period. State of the art was Gougeon cold moulded hulls and small diam beams. The boats from Goran was not faster in the beginning but they did not break all the time. The boats from sweden might also have been just a tiny bit faster in chop but the difference was probably in the maxed hull volume of those hulls. What killed the woodies and small diam beams were not performance but reliability, and initially price.

Keeping the rig stable is what makes the difference. I have not seen theoretical or real life proof on what is faster. A platform that bends and moves softly in seas or a stiff one bouncing and crashing through waves.
In flat water it makes no difference at all. Sailors are like sheep at times, following the leader instead of asking the whys and hows.

Bundy is smarter than jumping into this. There is no winning game here, only ways to loose business. The rest of the AHPC gang should take note and act as if they had brains.

And by the way. Those cold moulded cedar hulls from 83 are still as stiff if not stiffer than Gorans spaceships and still at min weight.
Talking about carbon masts, carbon hulls and carbon crap is pretty silly. Good engineering and skilled builders is what it takes to build anything good. Even wood can outperform a fresh engineer who throws carbon at whatever challenge he see.
Set untrained farmers to laminate hulls and it takes half a year before they have the skills. Then they are due a raise so they get replaced.
What really is discussed here is how to maximize profits. The rest is smoke, mirrors and spin as Wouter says. Smart butt spin doctors making stir fry to paint a pig.

I would buy US made at min weight.


This thread is awesome, you are seriously debating if stiffer is slower?


Then we have the theory that wood is as good as carbon to build a boat with?? try building a M20 in wood at the same weight and stiffness...
I heard that Groupama are looking at wood as an solution for their new VO70 and BMWO are planning to limit the use of exotic woods for the next americas cup.... If you seriously think that you can build the same weight for weight stiffness in wood compared to carbon then you are certainly on drugs..


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