Boats and foils comparison

erdb

Anarchist
773
562
Thanks for the tip - I installed Fiji.  The thresholding tool is very powerful.  However, I think it may be expecting a cleaner image than is often the case.  This drawing is not AC or hydrofoil related, but it is typical of the kinds of things I'd like to convert to CAD.  I'll play around with it some more, and actually import something into CAD to see how that works.

View attachment 435959
There is another plugin: https://lukemiller.org/index.php/2011/09/digitizing-data-from-old-figures-with-imagej/

With this, you have to click on data points you want to save, so you're back to manual drawing, but the nice thing is you can calibrate your image to export coordinates in the 0 - 1 range right away.

Cool project BTW!

 

Stingray~

Super Anarchist
11,702
3,122
PNW
Apologies for a hopefully brief interruption, but since this great thread is so active I will post the Q here: 

How do you navigate to Private Messages, in this new format please? My ‘theme’ : 
 

4D0B9C12-6531-4DCF-B20D-DFF04DF63C3A.jpeg

 

Rennmaus

Super Anarchist
10,497
2,028
Apologies for a hopefully brief interruption, but since this great thread is so active I will post the Q here: 

How do you navigate to Private Messages, in this new format please? My ‘theme’ : 
 

View attachment 436070


I get the same on my android phone and haven't been able to find away.

Strangely it works on my android tablet as well as my windblows laptop.
Scroll to the very bottom of the page, click "Themes", choose "IPS default", scroll back to the top, click the sandwich and look at the right upper corner. There you'll find the envelope.

 
You might then want to check against the real thing - in the Italian Air Force’s excellent museum in Vigna di Valle, near Rome

I saw the only other surviving plane in the Bandeirantes Museum, São Paulo
Yes, I found a good set of photos from the Brazilian plane taken when it was undergoing restoration.  I thought it was the only intact surviving one.  It's an M model and I'm going with the X model, but lots of good detail.

That's probably enough of a digression from the AC.  There's another forum where I'll be logging the build when I get going on it.

 

Xlot

Super Anarchist
8,694
1,132
Rome
From Max, sequential logic related to small T- foils:

- T-foils work only if they are small

- but then to facilitate take-off, you need to give down rudder for a moment

- the bow goes down, and take-off happens on the rebound

- as a consequence, bow volumes are not ideal for other aspects

 

MaxHugen

Super Anarchist
From Max, sequential logic related to small T- foils:

- T-foils work only if they are small

- but then to facilitate take-off, you need to give down rudder for a moment

- the bow goes down, and take-off happens on the rebound

- as a consequence, bow volumes are not ideal for other aspects
Interesting, except there was an excellent side-on video of NZ's take-off, which clearly showed that they maintained a very level pitch throughout  the maneuver. It would seem that the foil AoI of 2° (my estimate) plus flap angle were quite sufficient to get NZ foiling.

Note that at 0° pitch, NZ's canoe shaped bustle presents a minimal wetted area, and with less total drag, would enable NZ to get onto the foils no slower than any other team. IMO.

As to why "T-foils work only if they are small"...  that claim has me stumped. :unsure:

 
So what would happen if for the next AC the boat was entirely open? No class rules are all!

Would the boats that turned up all be pretty much AC75 anyway? 

There are boats that would beat them in a straight line, but not around a W/L course and not even they have to match race and win starts.

I'm not sure a bigger boat would go much faster as these boats are at cavitation limits anyway.

The costs would probably astronomical, but the results would be interesting.

 

jaysper

Super Anarchist
10,166
1,293
Wellington
Would the boats that turned up all be pretty much AC75 anyway? 
I doubt that.

  • Firstly the sail plan would become open slather.
  • You would have to assume that at least one of the teams would consider different foils for up and down wind - and yes that would mean some mechanism for switching which foil gets submerged.
  • The grinders would be replaced by batteries or an engine.
  • Pumped ballast would become a consideration.
  • The foil trim would be fully automated with a complete set of sensors to optimise this.
  • Plus  whole bunch of other crap that I can't think of right now.


 

gigi

New member
17
6
Do you know of any way to convert SVG to coords, or a different spline-based app that can export to x-y coords?
There is litle program caled CONCORD. Stands for Coordinate- convertter, it is tool for airfoils. If Ibremember it can do dxf, this shoud be close enough. On javafoil website.

 

MaxHugen

Super Anarchist
There is litle program caled CONCORD. Stands for Coordinate- convertter, it is tool for airfoils. If Ibremember it can do dxf, this shoud be close enough. On javafoil website.
Thanks Gigi. 

This appeared to be a very handy tool:
image.png

However, it was written a couple of decades ago, and it can't read newer CAD file formats such as AutoCAD R12 or R14.  :(    These are the options I have of saving an Inkscape SVG file as a DXF file, from which I'd hoped to convert to a 2 column DAT file.
image.png

Still, it might be useful for some other members here?

 

coercivity

Member
63
6
Auckland
One of the issues with the current design is their rather poor or have tricky performance in the marginal light conditions.

I think they could have an out board only foil above the current foil that would lift the boat at a lower speed  say at 10knts once the wetted area declines and the speed builds it would rise above the surface sort of a ladder foil from old.

the benefit would be smaller main foils possibly and much less foil fall of angst. The light wind sailing was great but marred by some wind holes that reversed entire races in what was a bit silly at times.

ETNZ had smaller foils it was an advantage at bigger speeds probably optimized to 30knts if they were 10% smaller and the outboard foil was say 50% of the full area but built for 15knts for max lift these boats would engage more in the starter area and would be game to go slow as a tactic. luffing, or daring a hook it would be fun and light winds with patchy air did extract a good sailing race.     

 
A

Amati

Guest
One of the issues with the current design is their rather poor or have tricky performance in the marginal light conditions.

I think they could have an out board only foil above the current foil that would lift the boat at a lower speed  say at 10knts once the wetted area declines and the speed builds it would rise above the surface sort of a ladder foil from old.

the benefit would be smaller main foils possibly and much less foil fall of angst. The light wind sailing was great but marred by some wind holes that reversed entire races in what was a bit silly at times.

ETNZ had smaller foils it was an advantage at bigger speeds probably optimized to 30knts if they were 10% smaller and the outboard foil was say 50% of the full area but built for 15knts for max lift these boats would engage more in the starter area and would be game to go slow as a tactic. luffing, or daring a hook it would be fun and light winds with patchy air did extract a good sailing race.     
I was talking to a Bell at a pre COVID wedding ( yes, that Bell family, as in Alexander Graham ) who was intrigued with ladder foils, to the point of designing and having some built and tested, and while they did offer lift in lower wind speeds, he felt drag was a penalty, kind of like Willawaw experienced in lighter wind.  Whether that regime lift was more than Archimedes regime hull drag, friction and wave, he wasn’t sure.  Surface tension entered into things, IIRR.  We got into that during the reception, so you’ll forgive a suspect recollection.  :)

 
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