Hello everyone.
I bought two
sail craft inc
Tornado hulls, and have used an old very stiff alloy mast for the fore beam, and a much flexier alloy beam at the rear. There is some wiggling; If I lift one bow up and down the rear beam will flex a bit so that there is a difference in pitch attitude between the hulls. I think the way to stiffen it is to reinforce the rear beam with a dolphin striker, or exchange it for a thicker one.
The cat is to be used with a windsurf rig, a rowing oar or yuloh, a 6hp outboard and a kite; not at the same time ofcourse. I hope it holds together. I had to cut out and re-make the fore
beam grooves
in the hulls since the mast is so thick.
I have never seen a complete Tornado; How much
pitch stiffness
is to be expected? What effects will too much flex have?
Anybody know of any cheap rudders or centerboards?
Sigurd, Norway.
Dude.....
![[Linked Image]](http://static.flickr.com/71/209061353_c205e8c609.jpg)
But seriously - a dolphin striker under the rear beam will do very little to resist torsion of the platform. Torsion can be reduced by firmly fitting the cross beams to the hulls so they fit in a perfect socket and there is no movement between the hull and the beam. Next, torsional stiffness is a result of the cross section of the beams connecting the hull - that is to resist a twisting motion. There is more coming in to play with the loading of the beams, but strictly speaking you need a really stiff beam to increase the stiffness of the platform. Regardless, you will always get some motion between the hulls.
Flex means that the boat is absorbing some energy as it moves through the water. As we all know, power from sails (or in this case, rowing, kites, and pixie dust), is limited.
The aft beam is very important for platform stiffness. You would probably be better off with the stiffest section as aft beam. The old T's with IYE beam were quite floppy. The newer Marstrøm platforms as quite stiff. If on level ground, and you lift one bow, the other bow follows in about 5cm. I expect at least the double from an older platform.
As the aft beam can 'slam' in steep chop, raising it would be a good alternative to rebuilding the saddles for a larger dimension extrusion. Flexing will slow you down when going trough waves, and if not engineered strong enough, material fatigue will be a concern.
You might check with Geoff Dobbs on the TornadoCat list about rudders, centerboards and other fittings. He might have some spars left from when he ran SailCraft of Canada. http:/
Wow, thanks, you two!
See you found another fellow who appreciates redundant systems. Don't think I'll put a large mast on it, just maybe the windsurf spar for heavy winds. Permanent mast would just foul the kitelines and capsize the boat.
If I am to rebuild the front saddles, and raise the rear saddles, any tips how I should do it? Do I need to raise the side netting rails too?
Do you know how much your platform weights just now? The Tornado is not a lightweight platform, and everything you do add weight. If I was to use it as a platform for sculling, kiting and as a motorboat, I would not have bothered with replacing the rear beam at all. After all, it was designed to have a 9.2m high rig on top, so it is plenty stiff and strong for your application. If you want top performance when sculling and under kite, I think the Tornado has too much wetted surface to be optimal. Likewise, I would not have bothered with getting some original (and likely expensive) Tornado gear for rudders and centerboards. I would have converted the centerboardwells to take high aspect ratio daggerboards. For rudders I would have keept it simple and done rectangular NACA00xx foils in fir+glass housed in a non-kickup rudderhead.
If you go with raised beams, I would have kept the trampoline secured to the beams and the hulls some way. If you re-build the seats, make sure the seats are properly glued/laminated to the bulkheads beneath (there must be bulkheads beneath). Again, contact Geoff as he knows the Sailcraft of Canada platform intimately, and perhaps concider giving him a call as it is usually a lot easier to get information that way.
BTW: If this is the boat I think it is, Haavards platform, what is the dimension of your rear beam and is it extruded from a proper alu alloy or just a 'regular' hardware store alloy?
Please post pictures as you go along!
PS: If you want to have a look at a rigged, competetive, Tornado, we will take part in Røyken Hoot Foot Jollemaraton saturday 19 aug. I think there will be a Taipan 5.7 and possibly some other high performance multis there as well. If you can't make it there, we are based in Molde. Might be a good move to look at how the platform performs before you put too much effort into a kite based boat. It must be really windy before a windsurfing rig on a Tornado platform becomes challenging.
I weighed the hulls, and I think they weigh about 50kg each. The beams probably weigh a bit more than 5kg each - forgot to weigh them. Yes it is a large platform for kiting - I haven't been able to source a kite as large as I want yet. I have a 18m2 and a 12m2, they might be stacked.
Sculling and the windsurf rig are just safety options - I didn't think I would get the motor started, but I did.
Yes it was haavard's.
The rear beam is one of those bars that you can raise and lower across roads to stop cars. (rolf what is the name for
veibom
?) I can't judge how good the alloy is. It's as heavy as the front beam but ten times more flexy (but a lot better than a 2x4"). It has flat sides on the top and bottom, and the short walls are semicircular. There is a shear web - an extra wall - vertically through the center. It is approx 10cm wide and I'll go measure the height when I've eaten.
I was thinking 0012 for dagger, or maybe a bit camber, in a kickup configuration like this: http:/
0012 or 15 for rudder. Most likely they will just be rounded planks for a while.
See my other boat: http:/
http:/
Maybe I'll drop by for the regatta - just monos around here.
Sigurd, Bergen.
As others have said, the raising/twisting of the boat is a torsional stiffness issue, not a bending issue. That said, adding a dolphin striker really won't make much difference. Torsional stiffness is a function of beam material, cross-section, and length. My question is how wide are you making this craft? A Tornado is 10ft wide. Are you planning on making this boat 10ft wide also? You can make the boat a lot stiffer just by making it a little narrower. Also, is torsional stiffness even really an issue? Based on your applications, it doesn't sound like you're going to be putting major stresses on this boat- I don't think your going to break it in half with a 6HP motor or by paddeling it.
sm
look a giant basking shark cometh to eat the silly thing!
srm, you are wrong. The torsional stiffness of each beam is irrelevant. Yes about 3m. About loads - did you ever fly a traction kite?
bob; huh?
Sigurd, I have no idea what a
veibom
would be in english. I dont even know if they have such a word. Road barrier or something like that would perhaps be describing? I was surprised to hear that there is no equivalent to
takk for maten
in the english language, so they are missing some important phrases <img src=
alt=
/>
I dont know if the section you have found for your rear beam is sufficient. If you was to put a Tornado rig on it, I would have said no.. Personally, I would have found a broken monohull rig for the aft crossbeam.
NACA0012 for the rudders sounds good. For the daggerboards I think it's too fat and high drag as you will never go above 3-4 degrees angle of attack, but if you can build them quick they will surely work. The NACA63xxx series might be better as high aspect daggerboards.
A traction kite will not really load up the platform compared to the traditional rig. Imagine the compressions loads put on the platform with a mast, while the kite will mostly pull on the platform. A kite is much 'kinder' than a traditional rig when it comes to loads on the platform, so you can build it lighter.
If would have been fun if you could participate in Røyken Hoot Foot, I wonder what LYS handicap you would receive on your boat <img src=
alt=
/>
veibom
. . .
takk for maten
...they are missing some important phrases <img src=
alt=
/>
That's interesting. There must be some way to translate.
Bob; huh-
Perhaps you could elaborate the mechanics of the hull-beam connection. Please explain how if the torsional stiffness of each beam is irrelevant, what is the mechanism that causes the second hull to raise when the first is lifted? One suggestion, for simplicity, imagine that rather than there being two beams, there is only one.
Regarding the use of a kite, perhaps you are correct, the potential loads generated could be quite high. However, you never stated the size of kite or the conditions in which you would be flying. Thus, based on your original post in which you said you would also be paddeling, motoring (with 6HP), or sailing with a windsurfer rig, I assumed that the power that the craft would be required to handle would be considerably less than the power that could be generated from the full Tornado rig. Additionally, I assumed that the kite would be connected directly to the main beam. Thus, the drive force is substantially lower than that of a full catamaran rig. Resulting in less heeling moment.
Rolf, I didn't realise until now that I have been email corresponding with you.. Embarrassing! <img src=
alt=
/> Thanks for the section recommendation.
The loads may be kinder in many ways but not all. Since there is almost no heeling from the rig, the boards can get very heavily loaded. Also there is this to consider: (check attachment)
srm - you are wrong.
I can't explain it very good but try to attach the beams closer to each other and watch the increased
wigglyness
. Don't take my word for it <img src=
alt=
/>
Look above for kite sizes.
Very fitting name on the boat in the picture <img src=
alt=
/>
To illustrate one of the difficulties with kites: In the winter, often I could hold the kite, stationary, with just a finger. If I sent it through its wind window, attaining its max speed/windspeed, I'd get hurled meters downwind!
By the way the boat is floating but the motor is grumpy.
Frankly, it makes no difference to me, you can believe what you want- it's your boat. You asked for advice, I offered some. I will offer you one insight, other than simply saying you should google the word torsion.
Imagine you have two steel rods of 1
diameter circular cross-section one is 1 foot long, the other is 10 feet long. The rods are each firmly fixed in a vice at one end. At the free end of each rod is another 1 foot long rod firmly fixed at 90 degrees to the first rod (creating an L - shape). Now, using the
L", try to twist the 1-foot rod. Next try to twist the 10-foot rod. Which do you think is going to twist farther (i.e. through a greater angle)?
This is the exact same thing that happens with your boat - TORSION.
good luck
sm
If your boat has only one beam, then it is only the torsional stiffness of that beam that keeps the two hulls in the same plane. With two beams, it is a combination of torsional stiffness and bending stiffness of those beams that keeps the hulls in the same plane, assuming perfectly rigid connections between the beams and hulls.
Imagine it this way - If the hulls are pivoting around the front beam, then the front beam is resisting via torsion only and the rear beam is resisting through both bending and torsion. If they are pivoting around the rear beam, then the reverse is true. If they are pivoting somewhere else then they both will be experiancing some torsion and some bending.
In reality, the nature of the connections to the hulls aw well as the location of the pivot will play a large part in determining how much torsion and how much bending each beam is taking.
If the connections typical in catamarans are less effective in resisting moments about the long axis of the hulls (bending) than moments about the long axis of the beams (torsion), than that would explain why the torsional stiffness of the beams is more important than the bending stiffness of the beams in resisting these sorts of deflections.
Well put Rhino. In mine, the the pitch difference must be way out of whack before the single front beam starts to make a noticeable resistance. It would be different with an extremely thick beam.
I agree totally.
And so going back to the orininal poster's question as to how to make the frame stiffer, I offered the solution, make the boat narrower by shortening the beams. Both linear resistance to bending and axial resistance to torsion are functions of the beam's material of construction, cross-section, and LENGTH. Therefore, shortening the beams would reduce deflection due to both bending and torsion thus making the boat stiffer. But he didn't like that idea.
Not to mention that trying to paddle a 10ft wide boat is probably going to require at least 15ft oars. (
sm
Yeah - if it shows to be an unsurmountable problem I'll shorten the beam. Nice to have the space though.
Next problem is how to lead the kitelines. There are some chainplates in the bows, I assume for the jib tack - how much load do these take under sail you think?