NACRA 20 with Lifting Foils!

Sorry Tom, it was a joke, hence the smiley.. with a reference to all the recent interest in the LAC, wings, foils etc it was interesting to note that Fred Eaton & Magnus Clarke tested full foiling in a 2-boat testing period, and found the non-foiler to be faster than the foiling cat around a race course, and sailed the non-foiler in the previous LAC to victory.
Of course his foiler (Rocker) was a different foiling configuration to this one, which looks similar to Hydroptere in concept.
My comment, though in jest, is still a viable question : Will full foiling actually improve boatspeed that much in an already highly efficient boat design ? Catamarans already have highly efficient hulls, curved boards assist in reducing the drag associated with loading the one hull up more when flying a hull, so will full-foiling catamarans be quicker around a race course ? From Fred & Magnus` observations, the non-foiling cat was already doing speeds that the boat on foils could only seldom match in real sailing conditions.
Foils have been fitted to windsurfers too, and while it acchieves the objective of raising them clear of the water, it is slower than a planing windsurfer - so foiling, while acchieving airborne flight, may not always be the answer to going faster.
Having said that, the pictures of the boat in this thread shows it on foils in virtually glassy conditions, if it can foil with such light winds then it is impressive.
I`d like to hear more about his boat when they are logging their speeds, so we can see..And if it were to race against an equal platform in all respects without foils, then we`d have a comparison to analyse. Although I doubt a 5,5m cat that is 4m wide is a good idea, when not on foils.

 

=================
Steve, the non-success of Rocker follows a long line of small catamarans that have been slow on hydrofoils-particularly fully submerged multiple foils.
Starting with Icarus,a converted Tornado with surface piercing foils, up thru Caliope and others the performance of cats on foils has usually left something to be desired. Exceptions include Spitfire and a few others.
Throughout the history of foiler development most boats have had three to four foils or more which brings in lots of surface piercing drag and the drag from lots of foil tips. In my opinion the biggest development in sailing foilers over the last hundred years has been the Moth with just two foils. Recently a Moth paced Invictus(!) and Moths have beaten every beachcat under 20' and paced a Tornado. I'm convinced that the number of surface piercings and tips will tell a lot about a foilers potential.
The Windsurers on foils are an interesting study. The windsurfer on the Miller foils has proven faster than planing windsurfers according to Miller. The Rush Randall foilboards use a variation on the air chair foil which is a fairly high drag foil that is optimised for re-entry after a jump-which it does spectaculary well.
Foilers that use surface piercing foils where the foil that pierces the surface is also the lifting foil have an advantage in that, properly designed, there immersed foil area is nearly always optimum-not too much not too little(except, maybe, just before takeoff). They have a disadvantage, in most surface piercing incarnations, in that the foils do not generate RM like fully submerged foilers can(Rave ,Long Shot, Hobie Trifoiler). So they have to carry ballast as Spitfire and Hydroptere do. However, Tom Speer has suggested that a system could be devised using surface piercing foils that DO develop RM.....He and Dr. Bradfield have also suggested that carrying ballast may be better than using foils for righting moment.
For future development I think that a large monohull foiler using just two foils and movable ballast(like Hydroptere) could be very, very fast.
See: http://www.boatdesign.net/forums/sa...acing-monofoiler-design-discussion-15143.html

 

This is an analysis I did in another thread-check it out:

Numbers: THE ANSWER!

--------------------------------------------------------------------------------

===========
Mirabaud 26'
--
Foils- two fully submerged foils, one on daggerboard ,one on rudder:
a. mainfoil area= 3.77 sq.ft.
b. rudder foil area= 3.77 sq.ft.
c. mainfoil loading*@ 80% of sailing weight= 191.4lb./sq.ft.
d. rudder foil loading* @20% of sailing weight= 47.85lb./sq.ft.
* rudder foil loading changes in sailing
e. SA/ws on foils including immersed part of struts: 19.1/1
f. W/SA= 2.54
-----------------
Rocker 27'
--
a. mainfoil area=3.34 sq.ft.(two foils at 1.67 sq.ft. each)
b. rudder foil area= 2.6 sq.ft. (two foils @ 1.3 sq.ft each)
c. mainfoil loading*@ 80% of sailing weight= 183.23lb./sq.ft.
d. rudder foil loading* @ 20% of sailing weight= 58.84lb./sq.ft.
e. SA/ws on foils including immersed part of struts: 23.18/1
f. W/SA= 2.55
----------------------------------------
This is the first time I have compared the nearly equal Mirabaud MONOFOILER
with Rocker-the C Class MULTIFOILER and the results are startling.
The two boats are virtually equal in foil loading and SA/ws on foils; both are
better than the Moth in these respects. In racing that has been done in Switzerland we know that the Moth and Mirabaud were virtually equal in speed last year. We know that the top speed of the moth is 30+ knots and that the top speed of a C class cat is 23 knots and that Rocker was generally slower than the top non foiling C Class.
-----------------
Why? When I was first getting in to hydrofoil design I read and was told by Dr. Bradfield that surface piercing drag was a large drag consideration for any foiler. And almost everyone soon learns that the tips of hydrofoils can be a large source of induced drag when the boat is on foils.
Look at this while keeping in mind that the other technical details of Rocker and Mirabaud are nearly the same:

Rocker-
a. number of foil tips= 8
b. number of surface piercing struts= 4
----
Mirabaud-(and any other bi-foiler!)
a. number of foil tips= 4
b. number of surface piercing struts = 2

=============================
This is not a 1.3% difference-this is a 200% difference-Rocker has TWICE these drag producing elements with the other statisics very nearly equal! Very likely a large part of the reason a four foil catamaran is slow......
-------------------
Thanks to Thomas Jundt for the Mirabaud numbers and to Steve Killing for the Rocker numbers that made this analysis possible

 

Doug, that`s an interesting comparison between the cat foiler & the mono, that the figures you show are so similar yet performance is not. I`m not that mathematically inclined but you`ve made it simple enough for me to get the idea.
I believe the windsurfer foil I have seen (only through internet) does not produce a fast craft as the foil is on the fin, while the mastfoot is far forward of it, so if the sailor were to sheet in hard it would just nosedive - there is a youtube video of it where you can see the sailor standing upright and sheeting out in gusts to keep it balanced. Perhaps two foils like the moth would work better ?
Regarding the foils by Mr. Miller (I have not seen these), it`s much easier to claim something than to do it - if this were true then Hydroptere`s record would belong to him, as anything with a marked performance increase over a speed-optimised sailboard is going to do 55-60knots - that would only require a 10% increase on their current speeds. If foiling windsurfers are much faster than non-foiling ones, where are the records ?
Back to the White Dragon cat.. It seems to be flying in absurdly light winds, by appearances it is not more than 5knots on the water in the photos. That is amazing. I would like to see how they go with it on GPS - could this be a moth-killer ? If it can foil in such light wind, it might just be.

 

================
Steve, the Rush Randle air chair foil does have two foils-linked by a tube. Its just that the "main foil" is a delta shape specifically designed for more or less safe re-entry after a jump. Tinho Dornellas(Caleema Windsurfing) and I tried a Moth foil with a rear foil further separated than the air chair foils but the results were inconclusive-mainly because it required too much of Tinho's time to master. I don't think it would jump very well.
I don't know much about Millers foils but some that do think his system works well but that might be within a narrow range-I just don't know.
Brett Burvill(AU) was the first person to win a race using hydrofoils in the Moth class and his foils were surface piercing foils. Both he and John Ilett reckon that arrangement was fast but I don't think it could beat a bi-foiler even given equal development time(but Burvill does). The bi-foiler has some inherent advantages such as being able to be sailed with veal heel that improves upwind vmg and increases RM. But who knows-development of Burvill's system was stopped because the Powers That Be ruled that it was a catamaran configuration.
There is all kinds of potential left in foiler experiments with configurations like that. Look at the MPX-11(12) thread for a "foil assist" + planing hull configuration(in detail) and note that the new "Hydroptere.ch" has a planing catamaran configuration with variable geometry stepped hulls see the Hydroptere thread.

 

-------------------
More info: http://www.facebook.com/pages/Whites-Dragons/145919742107493?v=info

 

Nacra 20

This is cool: you can see the lift from the curved foils!

http://www.youtube.com/watch?v=82CDZcpqyNU&feature=player_embedded#!

 

Nacra 20 with Lifting Foils

Interesting comments about curved lifting foils on USA 17 and on the Nacra 20 including "J" foils vs constant curve foils:

http://www.proboat.com/daggerboard-debate.html

 

Nacra 20

Marstrom 20 being fitted with a wing rig:

http://vimeo.com/23982224

----------------
Provisional results show the NACRA F20c with curved foils beat the M20 with curved foils and a wing.