Ok, I admit, I have sailed uni rigs for so long, that I forgot about the sagging jib. Well, take higher gauge bridle wires and stiffen the hulls in front of the front beam, and your job is done... or sail uni.

And by the way I touched a X40 boom as much as you sailed on Slingshot .
I would never propose to replace a CFRP boom or mast by wood. But a wooden hull of a small beach cat... as long as you or your builder knows how to build it. Today it is hard to find someone who can.

Oh wow, a boat is a black whole which absorbs energy. Did you ever thought what happens, when structures reflect after removing a load?

Oh wow, a boat is a black whole which absorbs energy. Did you ever thought what happens, when structures reflect after removing a load? [/quote]

I think you may have misunderstood what I was saying. The structure of the platform absorbs the energy as it twists. As it flexes back again not all that energy is transferred to smooth foward motion. Some of it simply results in the boat bobbing up and down in the water. The objective is to not have that twisting and untwisting motion at all so all the energy is applied to forward motion. Much as we try to sail a boat as smoothly as possible in choppy water by such things as footing off a bit, powering the rig up slightly and structural things like lighter masts and sails.
If the theory of not worrying too much about flex in platforms were correct we would all be happy sailing two year old Hobie 16's!

It's only a problem if it lasts over 4 hours!



Stiffness is preferred as long it is not to the extreme. As a reoccurring theme on this forum, we can always come up with examples and analogies that are exceptions. Absolutes are never the rule.

Another view on platform stiffness from someone who might have a clue about these things. This is from a recent published interview with Bob Baier, current German A Class number one and current European champion.

"In my opinion, what is crucial here is simply the honeycomb construction. Here you have much greater stiffness than on a foam boat. Although I am no boat builder, I notice this in the steering. On a stiff boat, one has the feeling that the boat is moving as a single unit. The hulls do not work against one another, rather they move synchronously through the waves, which is how it should be."

The class rules in F16 don't seem to define or measure stiffness. So this seems an area of unrestricted development which would be persued by builders over time. The Viper seems a step ahead in that area. It has certainly provided some impetus for F16 in the so called land of the dog. Before it came along F16 was going nowhere here.
Cheers

Wouter, you either don't know are are not telling the full story with the ORMA 60 issues.

The reason they had to allow the boats to flex was simply that they could not make the entire structure stiff and strong enough without developing a hard spot in which the failures occurred. Generally this was in the float to beam joints. The boats that had this problem were the full nomex cored boats that were stiffer (and faster) than the foam core boats. So then they moved to a mix of nomex and foam to ensure the longevity of the boats. This was a compromise with the speed... I will say this very clearly: The foam (softer boats) were not as quick as the nomex (stiffer) boats.

On a small beach cat where you can build a very stiff platform without the risk of breakage in 10 meter seas.. Stiffness is good, simple as that. But it costs.... I think I have stated many times in here that a full nomex cored, carbon boat will be stiffer and faster than a foam core, carbon boat.

This would appear to be in line with the statement of Bob Baier and I think any of the top level sailors will agree. You can however continue to think otherwise, it makes no real difference to the world of sailing as you are never on the water anyhow..

I love coming to the forum..

I haven't read all the comments but I cant believe people are putting up arguments that a stiff platform is not better.

I would go so far as to say it is impossible to have a F16 platform to stiff.

I'm not a engineer, but practically from testing and testing and a bit more testing.. Stiffer is faster.. no question.. Glue it together... next topic!

Fascinating reading the differences of opinions between groups of people. On one hand we have the professional racers saying that stiffer is better regardless of cost. I guess thats the win at all costs attitude which has made them top racers.

On the other hand we have the guys from engineering backgrounds going OK stiffer maybe better but it is at a cost, usually reliability and lifespan of the structure, that argument looks as though it is supported by the Orma 60's "The reason they had to allow the boats to flex was simply that they could not make the entire structure stiff and strong enough without developing a hard spot in which the failures occurred"

So which is it to be then carry on stiffening the boats until things start to break or allow a bit of flex and get longevity of the structure. Coming from an endurance racing background reliability was more important as soon as my bike was damaged I was out of the race. Damage a part of a boats structure and it can mean weeks and months out of action. And that failure maybe not in say the first year or two of the boats lifespan but further down the road.

I'm still not convinced yet that we have reached the balance of stiffness ( ie more stiffness maybe better ) to reliability that is acceptable to most people, but one only has to look at the problems some of the F18's are getting such as bridle mountings delaminating and I guess the weight ( mass )/ strength / stiffness / reliability question is not far away. Its not to say with a slightly revised engineering solution that those problems wouldn't dissappear at the cost of a bit more weight or investment ( stress analysis ).

Nobody is saying that, it is a retorical trick that is played by the side who favours eternal chaos in the F16 class. By the way, I'm not saying that you are part of that side, Darren.

What is said is that increasingly improving platform stiffness is a project of diminishing returns. At one time a point is reached beyond which additional stiffness is not worth the investments.

Compare it to double glassing in your home. A single layer of glass lets out a sizeable amount of heat from your living quarters. Getting double glazing cuts this loss in half. An errrornous but understandable reaction to this gain could be to get 10-double glassing. Afterall, each time the loss is cut by half, right, so more is "always" better !

Yet, we hardly see any triple glassing in the real world and anything beyond that is unheard off. The reason for this is simple. Triple glassing will only cut in half of what was left after cutting it in half the first time. So if the first time the energy savings amounted to a reduction from say 100 to 50 bucks then the second time the reduction only amouted to a savings of 25 bucks. The fourth and fifth times would result only in respectively 12.5 bucks and 6.25 bucks.

Obviously a reduction of 50 points is easily noticed but a reduction of 12.5 points much less so. Afterall it is only 25% of the the first reduction and 1/8th of the total costs initially incurred with single glassing.

Say the first F16's flexed 64 mm when layed up on their sterns with one hull lifted (note that the standard Hobie Tiger and Nacra F18 flexed in this test by 92 mm !). In fact, my homebuild Taipan F16 (small beams) flexes by about that amount. The first Blade (small 80x2 beams) flexed 40 mm and the newer Blades flexed by about 30 mm. The Falcon with newly designed custom beams is stiffer still and the Stealth always flexed in the order of 20-25 mm (was a very stiff boat from the beginning). Lets say the Viper flexes by about half that amount say 10 mm (on a par with the very best all-carbon A-cats and way better then the modern F18's).

Say my own boat losses 60 seconds per hour bouy racing relative to the Viper due to platform flexing alone. This is a huge amount in my opinion but lets assume a large difference for arguments sake. Note how the Viper is over 6 times stiffer then my own homebuild. Using these numbers we can calculate the relative differences between different F16 makes.


Relative differences (rounded off)

30 seconds / hour gain : Taipan F16 to prototype Blade F16 (80x2 beams)
10 seconds / hour gain : Prototype Blade to Alter cup Blade
5 seconds / hour gain : Alter Blade to Stealth or Falcon :
15 seconds/ hour gain : Stealth/Falcon to Viper :

Absolute differences (rounded off)

30 seconds / hour gain : Taipan F16 to prototype Blade F16 (80x2 beams)
40 seconds / hour gain : Taipan F16 to Alter cup Blade
45 seonds / hour gain : Taipan F16 to Stealth or Falcon
60 seconds/ hour gain : Taipan F16 to Viper F16


So obviously, this example does not disproof that in the F16 situation more platform stiffness makes a boat faster. That is NOT the point. The point is that a gain of 15 seconds between the new generation F16's and the Viper F16 is not much at all. Certainly not when running the numbers on loss of performance by putting 23 kg additional weight on the platform (and get to such a high level of stiffness). Who is not to say that that alone losses 10 seconds of the 15 seconds stiffness gain already, leaving only a negligiable difference of only 5 seconds ! Note that Texel handicap system assumes a 4.752 second performance loss per hour bouy racing per SINGLE kg of added weight; resulting in over 72 seconds per hour (2 points) over 22 kg. So anyone may run the numbers of the example above for any number of minutes the difference is between my home build Taipan F16 and the professionally build Viper F16. The end result will be discouraging every single time.

Therefore many of us here argue that platform stiffness on F16's has already progressed so far that the performance differences are too small to matter. The base line stiffness set by the Stealth, Falcon, Aussie Blade and most likely the AquaRaptor as well is already at such a level such that there is simply not enough performance loss due to flexing left to make a big difference.

The very same reason why no-one is ordering quadriple glassing for his home.

Wouter

I didn't realize that other F16 flexed that much. Where did you get those numbers from? I'm going to measure the flex on my Stealth next Saturday as I'm curious now. I have an original Stealth: narrower than the F16 box rule and designed with a custom front beam with no dolphin striker, I wonder how much difference this makes.

I wouldn't lump the F18 with that label. I believe some F16s (as well as other cats) suffering from structural problems also. Mainly during the early stages of development of a new boat or it is a manufacture error, not common to the class and is rectified through dealer warranty. I could pull some pics of some F16 failures if you like, but that would benefit no one.

As for stiffness, I see your point. Too stiff can cause failure in other areas, however I do not believe OTB cats are even close to that. The Viper is very stiff. It could be made stiffer again and much lighter but that would come at a cost. To some, they would not be willing to explore those limits. To others, if the prize was great enough, then they will go to extraordinary (including financial) lengths to achieve their goals.

The other current F16s are close to minimum weight but could do a lot more work in the platform stiffness department. If the higher volume hulls are more beneficial, then they could do further work there...... however it would come at a great cost.

Raising the minimum weight will not solve this problem (at least alone). The reduced use of exotics is the only way to keep the cost in check. The class has not seen this yet because it is still a very small class produce predominantly by small localised manufactures and are nearly invisible on the sailing scene despite being perhaps the most visible on the internet. If the class really starts to make a strong presence on the water and attract much larger fleet numbers, increase competition, then this will change.

Correct, however this point will vary from person to person. One person may be happy with a standard Taipan 4.9, narrow and small beams. The next person may be willing to make a carbon/nomex min weight Viper. You allow this freedom in the rules and someone or even a few may pursue it.

Pepin,

There are different ways in measuring platform stiffness.

The way we (in F16 land) do it is to lay the boat up on its sterns (check it is perfectly horizontal in both planes) and then lift the boat by one bow only. At some point the other bow will loose contact with its support. When that happens lower the boat a little bit till the bow hanging down is just above its support and then measure the difference of the raised bow above its support.

In the past this measurement was performed by F16 enthousiasts for a series of boats. All the gethered data is useful because we used the exact same procedure for each boat.

The boats were : Hobie Tiger, Nacra F18, Reg White Tornado, Taipan 4.9 (both homebuild and AHPC), (Homebuild) Taipan F16, prototype Blade F16, Blade F16 (both VWM and Aussie), Stealth F16.

Interesting detail here is that the Taipans all flexed by as good as the same amount (only a difference of 2 mm over an average of 64 mm). Therefore my WIDER homebuild F16 flexed by the same amount as the AHPC build standard (narrow width) Taipan 4.9. My boat has only modest reinforcements at the beam landings (a few carefully placed strips of carbon fibre cloth) and a 80x2 mm rearbeam instead of the square rearbeam of the Taipan. That was enough to compensate fully for the "loss of stiffness" that is normally related to making a platform wider (30% stiffness loss). Additionally, my set of beams weight a a fraction less then those on the standard Taipans. The prototype Blade F16 used 2 80x2 mm beams and its set of beams was significantly lighter while also achieving noticeably better stiffness (by 33%) then the Taipans (both versions). A similar improvement was again had by redesigning the F16 beams (used on Aussie Blades and Falcons). 1.5 kg increase in weight against additional 40% stiffess. ... etc.

In the end, it is all about careful engineering. Any knucklehead can make a stiff boat by adding 10's of kg's to the beams. A true boat designer does it by careful analysis and being smart.

Wouter

Indeed, I'm very happy with my 64 mm flexing Taipan F16 (when put to the rather heavy flexing test, this is not the flexing on the water while sailing, mind you !)

I would love to have a modern Falcon, Aussie Blade or a Stealth who all flex three times as little as my poor homebuild.

But I don't delude myself in thinking that I can win anything more then 30 seconds per race that way and I admit that my F16 is not very stiff when compared to the new boats. It still sails like a dream though.

You are also right to "the next person" may persue an all carbon/nomex/diamond inlays F16 and indeed I think that is fine as I can buy a competitive boat to his one-off for just 17.500 bucks.

In the end, his glitter one-off F16 will present the biggest example of how to waste lots of good money on what amounts to a gain of 15 seconds per hour racing. When faced with the same choice I think that I will spend my money on expert coaching and lots of training (lost income).

As such the FORMULA F16 class rules will have done their job. For it is not the responsibility of such class rules to prevent stupidity in its class members but to merely level the playing field and allow normal people with normal budgets to have a fair chance.

Wouter

The fact that you keep saying that doesn't make it true.

I posses several stiffness measurements and these do not support your statements at all.

In fact, the modern lightweight F16's are at their worst on a par with the modern F18's.

Nobody seems to bitch about stiffness there so why do you hold the F16 class to a different benchmark ?

Wouter

F18 is 2 foot longer and a lot heavier, so of course it will flex a bit more. The Viper has the same beams as the Capricorn, is shorter and lighter so should flex less.

Wouter

I don't favour "eternal chaos in the F16 class". Neither I'm sure does the current Australian F16 champion who has posted an opposing view to yourself on the concept of "over stiffness". 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.
However none of the proponents of over stiffness including yourself have defined what you consider is "over stiff" and how that is measured. Of course as platforms are made stiffer in one area failures will occur in other areas. You simply strengthen or change the engineering in that area. Builders and manufacturers do that all the time - even in SMOD classes. You are in a development class so better get used to it. It's called continuous improvement in 90's management speak.
Your measure of stiffness you set out is only valid for platforms of the same weight and length. Anybody with a rudimentary knowledge of engineering will tell you that you can't compare the bow deflection of an A Class with an F18, a Tornado, and an F16. Weight and length have a big influence there. So taking your figures for F16's in isolation, that is a static deflection under only the weight of the boat - not under stress of the rig in sailing conditions. Your extrapolation of times over an hour of sailing is completely erroneous. The differences would be far greater as the deflection is greater under sailing conditions.
I'm sure F16 platforms haven't reached anywhere near over stiffness yet - whatever that is!!!

Cheers

There are no restrictions in any class as to what can be done within their current rule set. A lot of money can be spent to make the ultimately stiff F18 platform (and this is possible within your rules). Carbon is cheap compared what it costs to develop, engineer, manufacture and a product. Judicious use of carbon to achieve what MAY be considered a better product is often a less expensive alternative than restricting yourself to older technology.

More small builders and individual/groups developing “uber” boats on the side can only help the class. This is free development and experimentation that if it works will make the class better. Small builder development of techniques and material use prove in systems that in time become the standard and all classes (should they choose) have the possibility of benefit. Shy of mounting an engine on one, races are still going to be won by the best sailor.

The few F18 and other guys who keep coming to this forum claiming this class is in chaos and doomed because we are not following their rule set, or placing ridiculous restrictions that do nothing, should look at their own classes. Costs keep coming back, if you really want to limit this; then kill all development. Pick your ride and go 1 design. Look at how many new models of boats are being designed, tooled and marketed to keep on top the leader board. Pro drivers being sponsored so their models sit on top. And probably one of the bigger items, sail and rig development. These are the things that are expensive and manufacturers WILL recover these costs if they stay in business.

Yes, but as the overall displacement of the F18 hulls during a dive is ALSO much larger it NEEDS MORE STIFFNESS too. A F16 will typically sail with only 75% the displacement of a F18 [(107+143)kg/(180+15)kg]. Add to that the larger overall rig loads and the fact that it is wider and has longer hulls which both are providing for larger leverage and you'll see why putting F18 beams on a F16 are basically overkill.

For example, those 100 mm of extra width already makes the F18 platform flex 18% more even if it had the same weight and same hull length as the F16's. Now look at any 3.00 mtr wide Tornado or M20 and the flexing will go through the roof unless the beams are made very large. There are several of such factors that all need to be multiplied with eachother and that quickly adds up. That is also why going smaller (with teh F16's) was such a smart idea, because if going bigger and wider has such detrimental consequences then going small will result in equally large ... ... ...

You see, it is very dangerous to make conclusions about these things without doing the physical modelling. It is most definately dangerous to base any such conclusions on your gut (which many people seem to do anyway)

Some people even see proof for the benefits of stiffness in the very sharp feel of the Viper while sailing. It has a very crisp feel to it I'm sure. Sadly, the same comments are also made when such people test sail my own homebuild Taipan F16; and that one flexes 6 times more then the Viper ! Of course, even at that level its stiffness is (relatively speaking) better then any commercial F18 like the Tiger. Hence, I seriously doubt whether the Viper needs that much stiffness at all.

I forgot to give the Tornado flexing last time; it did 45 mm in the described test setup.

Wouter

I teach engineering for a living mate, what's your excuse ?

I guess you also think that a wave treats a F18 bow that flexes 40 mm downward differently then a F16 bow that flexes 10 mm downward. Afterall, the wave is concious and knows that this is caused by the difference in beam length and overall weight, thus forcing him to behave differently.

I say the measurements are surprisingly to the point. A 140 kg F18 platform flexes more in the test then a 70 kg F16 platform, that is true, but its 340 kg displacement (compared to 250 kg or less for F16) will very much put it under higher loads while sailing too. The same in reverse when comparing to A-cats. Such opposing phenomena go a very long way in compensating for eachother, making the test dependable again.

Besides, the whole idea of stiffness in both cycling and sailboat design is to reduce the amount of energy that is "wasted" in flexing the platform. A F16 with 10 mm flex while sailing leaks less energy that way then a F18 that flexes 40 mm; the causes that result in this difference are of no importance what so ever to the wave.

Wouter

OK, so we've decided stiffer is better, now, my question to the Engineers is: Which shape beam would be stiffer in our application, a round beam or a square beam or a trapazoid? I mean, our beams have (at least) two different directional forces acting on them, up and down type flex, but twisting as well.

If there were some way to make them stay perfectly seated to their hulls with zero movement there (glued, like the A cats) would a box beam twist and flex more or less than a round beam, or oval beam, given the same relative size, weight and wall thikness?

I don't see any racing bicycles built with box shaped tubes, or perfectly round tubes any more, most are oval. I know some of that oval shape is for less wind resistance, but we could all use less wind (and water) resistance when we stuff the front beam into a wave, right?