After half a year of development and construction, the AC45 has shown his performence on his evidence.
The leeward foil makes a tremendous lift to keep the boat in the horizontal.
However, in the coming weeks is still much fine-tuning required.
Finally got a break in the weather to launch new IACC 120 …NZL-32 Blackmagic Ver 2.0
This one is a little special:
Complete carbon construction:
LOA 1200 mm
LWL 1 = 966 mm (light air)
LWL 2 = 985 mm (med/heavy air)
Drop keel = 390 to 420 mm
Made this keel fin hollow and shaved 150 grams off the bulb and put it inside at the bottom of the keel.
Not 100% happy with the current 78 dm2 sail plan at this stage, think it needs to be max’ed out to 80 dm2
I would like to thank ClaudioD for his patience & valuable time in going through seven revisions before we got to this final design … and from what I can gauge she is a screamer !!!
You can see further photo’s in my album [u]here[/u]
Hi Gilligan, thanks for compliment as they say practice makes perfect and since starting scratch building only few years ago I feel I’ve finally got the hang of it now, only need to learn to sail the bloody things as well as I can build’em …:smile_lol
Testing new sails (80 dm2) with new light weight Square head Rig (283 gm)
Mast = 12 mm HM round carbon tube
Main = 1630 mm luff @ 5156 cm2 sail area
Jib = 1300 mm luff (80% of Main) @ 2823 cm2 sail area (54% of main)
Surprisingly CE is 34 mm in front of LE of fin and boat nicely balanced :rolleyes: with slight weather helm in 5 knots, will be now try creeping fin forward to see if improves performance.
indeed is a surprise and I have no answer to that !
What is the distance from the CE to the back face of the Mast %
What is the mast back face distance from transom ?
According to my records and for Sail & Fin configuration generally employed :
Lead % from CLR-CE = 8% average +/-2% (from various books)
Lead CE from Fin Chord = -1/4 to 0.0 of Fin Chord (from Eric)
Lead from Fin CD = 4.0% average +/- 0.5% (from various reading)
If all above criteria are mixed up, you will find very close result within 1% - Tuning being the last sentence !!
All is dependant from the Sail Plan configuration, Main/Jib Surface Ratio and the aspect ratios.
The Fin position play also a big role on the longitudinal equilibrium. Generally, on my models, the Fin CD is positioned at 30-35% of the Fin Chord
Off course, if at the end, you are satisfied with the actual boat behaviour for all sailing conditions, there is no need to change !
Yes, I can’t seem to find a theory which is consistent with reality … feel like I’m missing something, somewhere :rolleyes:
Having applied “the theories” on previous 5-6 builds, found that I’m always have to move the sail plan forward at least 10-15 mm hence on this build decided to compensate in the construction and move mast box forward & it was pretty dam close this time first time on the water.
Here is the sail plan used, max Sail & Jib area.
Note: Vertical mast the C.E was calculated on sail plan @ 42 mm from luff edge. Sailing in 5 knots had mast tilted aft little less than 1 degree which increasing vertical C.E from 42 mm to 47 mm at the deck. As wind speed increases up to 10 knots I’m anticipating need to tilt mast forward to vertical position again.
Here are the dimensions you asked from sailing in max 5 knot winds (well balanced) unfortunately I have not located the actual CLR (unknown) with the boat in the water, I will do this next time on at the lake.
Claudio’s AC120 boat designs generally allow up to 30 degrees heeling angle for maximum hull efficeincy, when exceeded is indicator to canvass down to B or C sail areas.
Agree raking aft in light wind and then decreasing rake to move CE forward as wind speed increases to maintain slight weather helm is the norm, …often thought aft rake angle in light air that has main leech move vertical to water is more efficient for less aero drag than forward angled leech, no idea if it is right or not, just something that has always been stuck in my peanut.
The lead is something again that has lot of influences such hull shape & positioning of LCB, CLR, LCF, Sail Plan CE & drift that ideally should be identified at maximum sailing heeling angle…which is something l have not been able to work out how to with finished boat, calculating on paper using the theories around have not been acurate for myself on RC models, so far.
Interesting opinions, this one summed up my feelings:
"design is the brief interval between figuring out what went wrong on the last one and the joyous anticipation of the next and perfect boat "
Tending toward the thinking the sail plan aspect ratio plays big role in the senstivity of helm balance e.g high aspect sail plans have less lead (sensitive) apposed to lower aspect sail plan has more lead (less sensitve) helm.
Nevertheless I’m not so pessimistic with my settings .
Very often I let the boat leaving from shoreline in a close hauled course.
Interesting fact is that the transmitter is also very often left on ground for a while without any touch to the rudder joystick while the boat is sailing straight away for 50m, 80mt or more…
You have seen this happen at the time of launch of 123 Esterel testing, also with the antenna still collapsed…
Probably all that is suggesting something and I suppose that I’m not far from the correct melting … between CLR, CE, Cd, LCB, CLF, CG , etc. !!
Good to see you’re still plugging away at it, retirement obviously suits!
In terms of the relationships between CLR, CE, LCB, etc,etc …, I believe most of what we know is from anecdotal evidence, the rest, well, I think Donald Rumsfeld summed it up best (although I don’t think he was talking of yacht design in particular) by saying:
‘…as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don’t know we don’t know…’
Yeah, I know, that’s really helpful, but it’s 7.30pm here and I’ve been up since 4.30am so that’s the best I can offer at the moment!!
as they say practice makes perfect and since starting scratch building only few years ago I feel I’ve finally got the hang of it now, only need to learn to sail the bloody things as well as I can build’em …:smile_lol