Thanks for you words Brad,
I could pass you the frames ready to print but I do not kows how to post a zip file. Was possible before updating of the site, not anymore so far I knows. Pass me your mail in PM.
Cheers
Claudio
Hi Claudio. I tryed to send you a private message but it seems it was not delivered… So I dare to ask you something in this forum , coying the text. Thanks in advance for your valuable help and opinions.
HI:
I have the drawings for a new hull IOM class. Now i need to find the exact location for the keel and rudder.
1.- Should i first find the center of lateral resistence in the hull with or without the keel/bulb and rudder in place??
2.- After that. Could I keep the distance from the center of lateral resistence in the hull to the center of effort of the sail measured form another IOM?? ( since the rigs are all the same size the center of effort of the sails does not move in the rig) or this distance between keel and mast will vary because of the shape of the new hull??
I just need to have clear the logical steps to achive exact or more eficient location of the mast and keel - rudder
Hope you can comment about it.
Tato Lazo
Hi Tato,
very good question, but I’m not a IOM specialist. Very little I can tell without the complete set of drawings. Each model has specific requirements in termes of Tuning.
To determine the CLR position I personally use the simple method of the balanced carton, other employ other methods .
The “advance” is generally sitting between 6% and 12% of LWL. Actually I use a graph extrapolated from a book dedicated to real boats.
How much will be valid I do not knows yet, but certanly a good point to start a serious Tuning.
In my opinion, the valid contrast surface to the sail power is formed 100% by the Fin and the Rudder surfaces, while the immersed hull and the bulb contribute for a little percentage, less then 30% . Because of that I do not consider the Bulb when making the carton.
So my answers are :
-
- keel and rudder only
-
- Yes, if it is the same model. As a matter of fact, you have made the correct assumption.
To note: As told before each model behave differently in the water, one parameter often ignored, is the ratio between beam and lenght at water level, expecially when tilted.
Just a simple example : take two differents sail models one short and wide and one long and narrow, let manage to tilt them by +/- 30° introducing a mass in the hull.
No Rig, no Rudder, no Fin.
Put them in the water or in a pool is better and give a push to booth. Observe…, very probably the shorter and wider will follow a curve narrover then the one made by the narrow . Assume now that exist an infinity of shapes curves, deepts, etc.
This simple experiment will suggest that the shorter model will requires to be compensated more then the other in order to contrast the tendency to turn . This “tendency” caused by the shape of the hull will be present also when the model will be fully equipped with the Rig and ready to sail.
All that serve to demonstrate that two IOM hulls may requires two differents adjustments and two differents “advance” from CLR to CE.
A small sketch in support of above.
Cheers
Claudio
Claudio:
Thanks for your explanation, very well explained and the drawings make it more clear. So I will need to consider rudder and fin to find the clr and then the better should be trial and error to find the right rig position, forward of afterwards.
Best regards
Tato Lazo
Tato
I have taken a lot of pictures of IOM’s and on most the center of the mast sits about 1 cm forward of the leading edge of the fin. I think that because of the fixed sail plan, the 60mm draft and the 4kg displacement no matter what shape(within reason) you make the hull the mast ends up in that location. Like Claudio said the bulk of the lateral resistance comes from the fin and rudder. If you are out a hair you can adjust it with rudder size. Go surf the net for side on pictures of IOMs and you will see what I mean.
Don
Hi Don:
I know, I have built over 20 sailboats at this time, i am planning to the same proportion of fin and rudder area in the new design, but was told from a design in wich the mast ( i don know if fin too) should be moved 4 cms. forward!!! after few tests.
I want mine to be as perfect as posible at the first try.
I am also thinking to that if I enlarge the ruder to balance the CLR, will have more wet surface too.
The best will be to build one and test the fin and rudder configuration until get satisfying achivements and then produce the final HULL, fin and rudder.
thanks.
Tato Lazo
Hi Tato,
What IOM design are you planning? If the drawing does not have the mast, fin and rudder locations, you could try to e-mail the designer.
John
Hi Claudio and Jhon:
In fact, i am the designer of the hull, my concept was drawed by a naval engeneer with soem hull desgn sofware, but he just sent me the hull frames and side and top view with water lines. In the meanwhile we had many hours talking and conitue the design finding out the rudder area and fin area, wich determined its position. By now, the hull plug is already done and i hope to get the plug for the deck cured next week .
The fin will be with straight trailing edge. The bulb is 31,5 cms. long and weights 2380 grms. melted in a CNC machined mould…what a great investment finally.
The fin will have a carbon honeycomb inside, similar to Bantock concept, while the rudder will be made out of two carbon halves.
Once I finished all this items and start to glue things together i will post them in a new thread.
The problem is that Claudio post so interesting articles I want to build one of his boats too, and replicate what he has been doing!!! don´t you??
Tato Lazo
Very Happy for BMW- ORACLE
No story with the WINGSAIL - non need of a ijb
Looking forward for AC34 !
Claudio
Next race Sunday, weather permitting.
Impossible to comprehend …6-8 knots of wind and 18-20 knots of boat speed !
Hi Dick
Max speed monitored today with BMW-Oracle : 28.8 kt.
Once speeding up, the boat is creating sufficient depression on the sails to create their proper wind . Obviously is more complicated than that , but just to give an idea. Hope some one would explain it better
Cheers
Claudio
I always use a bicycle example. Standing still - no wind, then slight wind from the side. Start riding and slight wind moves forward slightly, bicycle fast and wind from front feels stronger than wind from side. This apparent wind keeps increasing the faster one pedals. It also “moves” forward so it feels more like the wind is coming from the front.
Basically, the bike (and the AC multihulls) are creating their own winds the faster they go. As the apparent wind moves forward as speed increases, the boat must fall off a bit as wind is more from front, Falling off increases speed, and allows sails to be sheeted in tighter, allowing boat to point higher and go faster. This starts the cycle all over again. And obviously, the faster one goes, the fast the wind over the sails and more pressure felt.
Harder for monohull with lead to do this - but a similar but less dramatic “can” be accomplished. Sail downwind with sails at 90 degees to boat center line and boat will"approach" the true wind speed. Sheet in a bit and boat will slow, until you steer off an a broad reach at which time speed increases more than sailing dead downwind. As speed increases wind starts to move from rear boat forward and along the side. This is apparent wind. If on an iceboat with almost zero friction, this wind will quickly move far forward as the boat continues to accelerate. As it moves forward, the mainsail can be trimmed in closer to center-line. Photos of iceboats racing are difficult to tell if reaching or beating, since mainsail is usually always close hauled. For ice boats, land yachts and multihulls, it is seldome required to have a main boom out at 90 degrees except in the very lightest of winds.
These three examples, unlike an older AC monohull, seldom have theoretical hull speeds over which they are unable to overcome. Add in the wave length which also contributes to boat speed and if a boat can exceed that hull speed, it begins to plane, and the hull wave pattern no longer slows the hull down.
Also think of gliders (aircraft) they are kept aloft and can climb higher as long as they can maintain (or increase) wind speed over the wings.
I may have some of this wrong - but it’s the best I can do during my lunch hour which is quickly ending.
Until later.
Dick
A little further search brought this up (Wikipedia) which may further clarify…
"
[edit] Implications on sailing speedsIn sailboat racing, and especially in speed sailing, apparent wind is a vitally important factor, when determining the points of sail a sail-boat can effectively travel in. A vessel travelling at increasing speed relative to the prevailing wind will encounter the wind driving the sail at a decreasing angle and increasing velocity. Eventually, the increased drag and diminished degree of efficiency of a sail at extremely low angles will cause a loss of accelerating force. This constitutes the main limitation to the speed of wind-driven vessels and vehicles.
Windsurfers and certain types of boats are able to sail faster than the true wind. These include fast multihulls and some planing monohulls. Ice-sailors and land-sailors also usually fall into this category, because of their relatively low amount of drag or friction."
and this one …
" Recognizing the difference that speed makes to wind direction
The wind that blows against you as a result of your passage through still air is known as the apparent wind. Boats create their own wind when they’re underway, and if there is a natural wind blowing, it will be modified in force and direction by the boat’s forward movement to become the apparent wind, as observed from the boat. The wind hitting a sailboat’s sails or her steering vane is the apparent wind, and that—not the “true wind”—is the wind by which she is steered.In a dead calm, the apparent wind created by a boat’s movement comes from dead ahead. The faster she goes, the stronger the apparent wind. Conversely, if a boat lies dead in the water when a wind is blowing, the wind she experiences will come from the true-wind direction. However, as soon as she starts moving forward, the apparent wind direction will draw ahead; the faster she moves, the more it will move ahead.As the wind moves ahead, a sailboat must pull off more to keep her sails full; therefore, a boat going to windward at 6 knots cannot point quite as close to the true wind as a boat doing only 4 knots. Luckily, the difference is small, so there is no chance of the slower boat reaching a windward destination ahead of the faster boat because she can point slightly higher.It’s interesting to observe the effect of the apparent wind when you’re sailing dead downwind in a light breeze. If the wind is blowing at 5 knots from astern and your forward speed is 5 knots, the apparent wind will cancel out the true wind. You will fall into dead air until the boat slows down and the true wind can once more overwhelm the apparent wind. This holds true no matter how much sail you raise. The answer is to change course and tack downwind on a series of broad reaches, thereby generating an apparent wind at an angle that provides useful drive instead of merely canceling out the true wind."
Hello,
I want to share images of some new hull in construction:
Fly Emirates New Zealand NZL-92 http://iacc120cup.altervista.org/phpbb/viewtopic.php?f=1&t=166&start=0&st=0&sk=t&sd=a
Alinghi SUI-100 http://iacc120cup.altervista.org/phpbb/viewtopic.php?f=1&t=135&start=10#p1078
http://iacc120cup.altervista.org/phpbb/download/file.php?id=307
Alinghi SUI-104 http://iacc120cup.altervista.org/phpbb/viewtopic.php?f=1&t=156#p1029
America 3 http://iacc120cup.altervista.org/phpbb/viewtopic.php?f=1&t=121&start=0&st=0&sk=t&sd=a
Moro di Venezia ITA-15 http://iacc120cup.altervista.org/phpbb/viewtopic.php?f=1&t=159&st=0&sk=t&sd=a&start=10#p1087
Victory Challenge SWE-73 http://iacc120cup.altervista.org/phpbb/viewtopic.php?f=1&t=159&st=0&sk=t&sd=a&start=10#p1100
Alinghi http://img51.imageshack.us/i/dscf0273.jpg/
Cheers
Matthias
Hey Matthias,
We need the forum passwords to be able to see the content.
Cheers,
Eric
yes sorry, the password is the simple letter “p”.
Matthias
For CHAD,
I would appreciate to, if this tread could be moved to the New Section since it was the Starting Point of all IACC Class discussions.
Notice the number of views !
Many Thanks
Claudio
KIWI,
I need your sail numers of your two boats. I assumed NZL-92 e NZL-84…could be good for you?
Astute Composites,
Do you think you’ll be In Ravenna, Italy, 11-12 september with your boats for the IACC 120 Cup?
Matth
Hi Claudio, I have to say you do very nice work! This build thread has been most informative for anyone thinking about any IACC model design! I spent close to two hours today alone going threw the hole thread! Your truly an artist! And an inspiration to anyone contemplating a build!
Much Thanks!, Juim
Thank you very much Juim, it is my pleasure !
ClaudioD