I will be honest about it , I fully expect alu beamed F16's to be stiffer to way stiffer than any carbon beamed A-cat.

I refer to the (vertical) stiffness data that was presented on the various boat makes a while back. I know the stiffness data on the F16's as well and also they came out significantly better than Tigers, Nacra F18 and other designs. Personally I believe A-cats are very much hampered by the low minimum class weight. They need to cut down on weight everywhere; this immediately translates into either less stiffness or the use of increasingly more expensive parts. The only real advantage of carbon is it weight savings.

I will give you all a great example :

A 80x2 round carbon tube of 2.5 mtr length weights 2.15 kg and has 100 % stiffness
A 80x2 round alumi. tube of 2.5 mtr length weights 3.39 kg and has 67 % stiffness => weight loss 1.24 kg
A 80x3 round carbon tube of 2.5 mtr length weights 5.09 kg and has 100 % stiffness => weight loss 2.94 kg
A 92x2 round carbon tube of 2.5 mtr length weights 3.90 kg and has 102 % stiffness => weight loss 1.75 kg

So dumb designers increase wall thickness of an alu beam, smart designers increase the outer diameter. Note how dependent stifness is with respect to outer diameter !

An alu beam that is at 67 % stiffness is only 0.5 kg lighter than one that has the same stiffness as the carbon beam. Who of us is willing to pay 700 US$ more for boat that is equally stiff and that is 0.5 - 1 kg lighter overall. That is when there is NO minimum class limit on overall weight. As that would make the whole comparison mute.

Of course this all holds true only when the beamlandings are made strong and stiff enough to transmit this stiffness to the hulls. We know know full well that this is not always the case. I refer to the Blade F18 data when compared to the other F18's. The Blade was almost 4 times stiffer than its nearest F18 rival. Its beams are certianly not 4 times bigger or heavier. I also refer to Jake Kohls experience that het wrote down in a post a few weeks back. His reseated his beams on his F18 so there was a proper and tight fit and immediately got an noticeable increase in stiffness.

Eventually it all comes down to proper designing and proper building technics. Watering at the mouth over carbon is for believers, not for engineers who know a thing or two about the mechnics of materials and structures

And normal sailors must learn to see the A-cats for what they are. An one-eyed king in the land of the blind.

They are so good, as are the Tornado's because 90 % of the builders simply don't give a damn about proper designing a catamaran. They are only interested in profit margins. That is why certain 17 foot singlehanders are build using F18 optimized parts. In some cases they use a cut down F18 mast that by that action is way to stiff and heavy for its new use. Other components like daggerboards are not even adjusted and make the design badly behaved. What do we expect when they are pitted against A-cats that arguable are fully optimized for their use ?

However we must not make the mistake of attributing all the difference in performance to the superior design of the A-cat. Superior designing, yes, but not to the perceived superior design. As good as halve of the difference is caused by the other side not doing his best.

What about the comparison between A-cats among themselfs ?

Well, this is a very difficult area. The A-cats are really extreme in certain import performance ratios. They are also extreme in the class limits. 75 kg for a 18 foot platform is not a whole lot. So here every 0.5 kg counts. Also each year alot of things are changes on the boats. Who is to say that all the speed increase is caused by a single factor like carbon beams ?

Now Carbon has one advantage. It allows beams of similar specs as an alu beam for less weight and a little smaller dimensions. In the A-cats all weight sayings can be put into other components that are very much on the edge as well. For example; and extra layer of glass on the highly loaded points. Their low minimum weight makes changes like these very attractive. The true question how ever is wether such a thing is still attractive when the basic design was already sufficiently reinforced in these area's ? Compare it too double glasses to save energy costs. When you go from single to double glassing the gain is serious, however when going from double glassing to triple glassing the gains are as good as neglectable.

This is exactly where nearly all sailors go wrong in their appreciation of the A-cat setup. They think that when carbon beams are better in the A-cat class that the same gains can be transposed to other classes when they go for carbon beams as well. These guys will all be proven very wrong. And actually the Blade F18 has proven them wrong allready indeed.

I think Altered problems are more related to the fact that he can't increase the outer diameter of his beams OR improve on the design of his beamlandings. Don't you think it is telling that :



The A-cat design from which Altered was made was supposed to be such a superior design right ? How come the alu beamed Mosquito kicks its butt in the stiffness department ? Both use alu beams as far as I can tell so the cause can only be found in the design of the hulls. In the beam landings specifically.

I know the stiffness specs of the Blade F16 and yes that one too beats F18's and Marstrom Tornado by a significant margin. Blade F18 is still better but than again they had the room to improved the beam landings even more. Blade F16 is actually closer to the Blade F18 in stiffness than it is to its nearest rival that is the Mastrom Tornado. Other F18's could not hold a candle next to the Blade F16.

So again it all comes down to a class stimulating proper designing of the platforms.

I haven't seen any stiffness data on A-cats yet but I fully expect them to be inferiour. Those 30 kg less overall weight do hit them very hard. Especially now that A-cats have doen aways with the dolphin strikers. These things do add alot of stiffness to a platform. Sure you make carbon beams stiff enough to be compare to dolphin strikerless beams but only at the expense of adding alot of weight to the beam, thus decreasing any weight advantage you had before.

Gary ?

Would you do us a favour and measure you vertical stiffness of Altered one time ?

You are in the unique situation to answer some questions permanently for us. Mostly because I have data on a very comparable platform to yours. I have thus the opportunity to filter out the contribution of one very specific factor.

Measure it as follows.

Lay your boat up (about level) on 4 saw horses. Two under the very sterns, as close to the sterns as you dare. And two under the bows. Maybe use a waterlevel stick to get them lined up properly. Than ask your friend to lift one bow still the other bow rises of its saw horse as well. Than slightly lower the lifted bow till the other bow just kissed its saw horse again. Now you measure the distance between the lifted bow and its saw horse. That is all, well expect that you need to make sure your bolts are in tight and the tramp is tensioned. Thus making sure that we get the best read out.

Will you do that for us ?

If you prefer you can send the data privately to me. I will use it to learn and maintain the equalness of the class and when requested will keep the supplied data secret.

Wouter