Sailing Foiler Design: Foil Assist and Full Flying

Hi Doug,
Would you care to elaborate why the Carl Boat would not sail?
Is it because of the hull, or the hydrofoils?
I would also like to ask, are there any boats that use aerofoils to lift the boat rather than hydrofoils?
It appears to me that sail rocket does this.
I can not get out of my head that a boat with both horizontal and vertical wings would somehow be succesful.
Cheers,
Adam

 

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I made the point of saying it was my gut reaction that it couldn't sail-and that is based on seeing and studying many hydrofoils but it is also limited by not having enough information about the boat to make an intelligent comment.
Sail Rocket utilizes airfoil lift and there is another "sail"boat called "V squared" or something similar that was under development. You maybe be able to find info on it in the multihull thread by trying various combinations of the name.
UPDATE: here it is- http://www.boatdesign.net/forums/multihulls/v-44-albatross-world-speed-sailing-contender-34872.html

 

1) Paper I just found on :"The EFFECT Of HEEL ANGLE AND FREE SURFACE PROXIMITY ON THE PERFORMANCE AND STRUT WAKE OF A MOTH SAILING DINGHY RUDDER T-FOIL"----Top pdf below---

2) Another paper just found on the Moth:

 

DLR applied to foil assist performance prediction?

This is a rather brilliant quote(in my opinion, anyway) from Steve Clark today in a thread on DA discussing rudder t-foils on dinghies:
"Finally the lift from the foil relieves the hull from having to carry some of the weight. This lightens the displacement and allows the hull to operate at a lower displacement length ratio, which is less draggy. In effect the L/D of the foil replaces some of the drag of the hull. Lowering the D/L of the hull can be done by lightening the hull or by making it longer, so some of the effect of the t foil again looks like it makes the hull longer or lighter, your choice."
I want to look at this carefully because it is something I never considered-at least specifically relating DLR to lower weight due to foil lift. This can only be true in a monohull(only??) that is using a foil for "foil assist"-partial lift not full flying. The speed length ratio would also be changed due to the shorter waterline.*
The DA thread: http://forums.sailinganarchy.com/index.php?showtopic=143305
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I-14 in Biekers paper sailing weight 583LB.
Waterine=13.89'
DLR(nominal)=97
Lift from rudder foil=90lb
Displ. minus lift = 493lb
DLR recalculated for lower weight=82(assumes same wl length which would not be likely though change would be small-UPDATE_checked drawing and there woud be no shortening of the waterline with 90lb of lift.)
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* UPDATE- waterline length did not change with foil lift on Biekers boat.

 

Rudder t-foil-I-14

We know the following from Bieker and Ellway:
1) energy recovery is possible at speed length ratios of 1.7 to 2.4 for a correctly placed T-foil,
2) Bieker estimates that lift from the foil at 9 knots upwind is 400 newtons or 90lb,
3) That amount of lift reduces the DLR from 97 to 82
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What we haven't looked at is what is the wetted surface reduction when the boat lifts up assuming it maintains the same pitch attitude as before the foil lifts:
a. Bieker says the SA/WS ratio for his 14 is 4.3/1 ; since upwind SA= 200 sq.ft. then wetted surface(hull+foils) is equal to 46.5 sq.ft..
b. An estimate of the lift of the boat from its non-foil waterline assuming the same pitch attitude is .65"(.054') *
c. At .65" lift, factoring in the angle of the hull bottom most of the way around(.054' increases to .094'), an estimate of wetted surface reduced by lift ,assuming a total waterline length of 32', is .094 X 32=3sq.ft..
d. So the reduction in wetted surface due to foil lift is 3/46.5 or 6.5%. twice the max foil area allowed under the rule
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Bieker I-14 specs:
Sailing weight = approx 265 kg
Side force = approx 30% displ (807N)
Sailing Displ/length ratio = 97
SA/WS = 4.3
Approx speed upwind in breeze = 9kts
(S/L ratio = 2.4, Fn = .72)
Max speed = approx 24kts
Lift from foil upwind @9knots=400 newtons/ 90lb.

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--Lift derived from lb.per inch immersion estimated at: 2.375' X 11' X .083'=2.17 cubic ft= X 64= 139lb
lift ==90 lb so 90/139= .65" lift (.054')
-- I-14 rules limit foil area to .14m^2 or 1.5sq.ft
--Using an area of 1.5 sq.ft. and a lift coefficient of .12 at a speed of 9 knots the foil lift comes out at 87LB. Thats just a reference since I have no idea if Bieker uses the max area allowed under the rule(1.5 sq.ft) or not.
-- Definition: Speed-length ratio is the speed of the vessel in knots divided by the square root of the vessel’s waterline length in feet = V/Lwl^0.5.
===========================
Summary:
As shown earlier there are five main elements to what a T-foil can do when used for foil assist:
1) creates lift around 15% of total weight(depending on area /class rules),
2) reduces DLR and therefore hull drag,
3) reduces wetted surface on the order of 6-7% depending on hull shape and improves SA/WS ratio,
4) if properly placed and if used at speed length ratios of 1.7-2.4 can "recover" energy from the stern wave. No energy recovery at faster speeds.
5) enhances pitch control/improves handling

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--See this thread for additional info, particularly the Van Oosanen "hull vane" for power boats, post 12.
--The Ellway pdf below is an excellent explanation how a t-foil can work both with and without "energy recovery". He specifies the speed length ratio where energy recovery will work(change his 2 to 2.4):

 

Foil Design

Foil description of new Moth main foil from Phil S on Dinghy Anarchy-may be worth some study:

Describes the Lister/Damic main foil. 4 are in use by Lister, Damic, Outteridge and I have not caught who has the other one. It can screw onto a Mach2 centreboard in place of the M2 foil. The last 50mm of the tips are bent down about 10deg. The hinge goes out as far as the turn down, but the tip of the flap is not cut away from the main foil, so the flap tip twists slightly when activated, moving more at the centre and nil at the ends.

 

DSS foil assist

See post 16 for more-follow the links there. Here is an excellent video of the Quant 28 going fast and up close with the Infinity 36 foil(picture by James Boyd of The Daily Sail) :
To get a bigger picture with the video click on the url below then on the youtube "expand" icon---
http://www.youtube.com/watch?v=s9ilCx8B0A0&feature=player_embedded

 

Foiling

This is a new site/organization dedicated to foiling go to this post and check it out: http://www.boatdesign.net/forums/boat-design/foiling-week-49189.html

http://vimeo.com/82183128#at=0

 

Doug, how many threads are you going to cross post this in? I thought cross posting was against the rules.

 

AC trickledown

The newest and only cat under 20' to utilize a refined version the foil system pioneered in the 34th Americas Cup-The Flying Phantom is now in production.
A detailed thread on the boat is here: http://www.boatdesign.net/forums/multihulls/flying-phantom-f-18-catamaran-43898.html
The foil system is characterized by a single main foil(windward foil retracted) and two rudder t-foils. The foil is very similar to the TNZ foil in the sketch below and has the characteristic of automatic altitude control through a large range of speeds which results in excellent heave stability/ride height control. In my opinion, the altitude control appears to be at least as good as a wand controlled system. When required, the angle of incidence of the main foil can be adjusted under sail. The foil is a sort of hybrid surface piercing foil and fully submerged "V" foil with great heave and pitch stability under sail.


Pictures-Left, sketch by DL 2012, Right-sketch by Dario Valenza 2013- The curved part of the vertical foil acts as a surface piercing foil creating less lift the more it rises. The "up-tip" "V" foil (a closed version of an "L" foil) has more drag than a "pure" "L" foil but has proven to have significantly better heave stability which is why TNZ , Groupama and the Flying Phantom use it. Hydros used a version of the system but had a much more "open" main foil with the result that it had poor heave stability and required frequent angle of incidence(rake) adjustment. Oracles main foil was closer to Hydros than to Groupama or TNZ. Leeway plays a major role in how the foil works, since it causes an increase in pressure on the low pressure side of the "L" part of the foil reducing lift as the foil rises. A small down side to a more "up-tip" closed foil is that the "L" portion of the "V" has a component of lift to leeward. The tip of the foil can also breach the surface as a backup and interesingly there is no catastrophic loss of lift as a result-the boat just settles down gently. The foil requires some degree of manual angle of incidence control but the more "V" there is, the longer the interval between the AOI adjustment required. This type of foil and the three foil configuration(single main foil and two rudder t-foils) are the major breakthrus of the 34th AC development and were used in the LAC (Groupama), and now on the Flying Phantom and the GC 32 soon to be equipped with them-pictures coming in January 2014.

IMPORTANT-see post 49 for a correction to this and an explanation by Tom Speer.

 

Doug this isn't a "major breakthrough" since l'Hydroptere was foiling with a 3 foil configuration of surface piercing foils with heavy dihedral and offshore tris have been using banana boards to come close to flying for a long time.

In fact Cheeky Monkey in the PNW broke one of her vaka's some 10 years ago because she started flying.

this is an iterative evolution of the technology and it still requires top notch drivers and crew.

 

AC 34 foil design breakthhru

The configuration of the the AC 72's, Groupama, Hydros is 100% different than Hydroptere or any multihull using foil assist* since these boats use a SINGLE main foil and two rudder foils. That configuration is a first in multihull foiler design-never seen before the development work on the AC 72's. This three foil system has been able to produce rock steady flight on several boats with the hybrid single main foil. Heave stability on the most stable applications of this technology rivals a wand controlled foil system(in addition to studying these systems for over 15 years I have many hours sailing a Rave with a dual wand altitude control system-and have designed , built and produced an RC foiler(F3) with dual independent wands similar to the Rave/Osprey). The key to heave stability is the degree to which an "up tip" foil is used. Less "up-tip"(more open--like Hydros and Oracle to an extent)-the poorer ride height control/heave stability and the more frequently manual angle of incidence adjustment has to be used.
More information on the FACT that this is a breakthru never used on any multihull before the development work on AC34 can be found in the Part 1 article by Morrelli and Melvin at the link below(also see the quote below).
* Foil assist is the term used for foil designed to lift a maximum of 70-80% of the weight of the boat while not(hopefully) flying the hull to which it is attached. The tri's(Mod 70's and the earlier 60's) that use them do not intentionally fly the boat because that can lead to a serious crash since most of these boats including BP5(now Spindrift) don't have rudder t-foils for pitch control. A rudder t-foil on the center hull of a foil assist trimaran has proven ineffective in some cases because the boat is still diagonally unstable. They rely on the residual buoyancy of the ama for pitch stability.

Link to Part 1 and Part 2: http://www.cupinfo.com/en/featuresindex.php

Quote from the article,Part 1:

When we were working on the rule, we knew you wanted to get as much lift as possible when you were going fast downwind,” Melvin says. "For instance, in the 2010 America’s Cup, sailed on giant multihulls, the maximum amount of lift we thought we could get was about 50% of the weight of the boat. At that time, we were still relying on the hull to provide pitch control, so what’s come out of this is the boats all now have elevators (the horizontal foils on the rudders).

“At Team New Zealand, we developed a new type of foil that allows you to keep your height above the water more or less steady. No one had been able to do that before, at least not on a course-racing boat that was not going downwind. We developed that mostly on our SL33 test boats -- they came with the stock constant curvature “C” foils and with those kinds of foils, you can generate 50% boat weight lift before they get unstable. But we noticed that when we could get one boat up fully foiling for a few seconds it would really accelerate away from the other boat – and that got the wheels turning. How, with such a huge potential benefit, can we achieve stable flight downwind? So our design team came up with the “up-tip” type of boards. We refined those on the 33s and our 72 is designed to do that and fortunately it worked right of the box.”

 

functionally it doesn't matter if you have a single foil with a physical dihedral joint in the middle of the two dihedral elements or whether your dihedral elements have a projected virtual joint but are otherwise symmetrical.

and since you have not sailed either a moth or a foiling cat, you are hardly in a place to assert that the heave stability is the same. In fact the evidence is to the contrary as one of the best Moth sailors in the world - Nathan Outerridge - who can do foiling gubes in his sleep on a moth and even has about a 66% success rate on foiling tacks - --- struggled mightily to maintain straight line flight on the Prada AC 72.

So you basically are making this part up. And you have been told this before by folks with actual foiling experience.

As to Morelli and Melvin - given that they have been caught out a couple of times with their predictions, I don't think that you citing them proves anything.

Nor would the fact that a "new type of foil" be necessarily "revolutionary" - given that the foil that l'Hydroptere developed allows you to keep height above water more or less steady - as do the foils on the power cat I was on in St. Petersburg earlier this summer

Basically Doug you are making statements that the facts contradict.

 

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This is an outright lie-as I said in my last post I have over 15 years experience studying and working with boats that have wand based altitude control systems and many hours(200+) sailing a Rave with dual independent wands and have designed built and produced multiple RC foilers using dual independent wands so I know what "heave stability of a wand controlled foiler is" and the most stable of the new foilers rival a wand system for heave stability-that is just a fact.
The rest of your post is unbelievable nonsense. Your only retort is to try to discredit me first followed by a trully sorry attempt to discredit Morrelli and Melvin! You're out of your league and simply don't know what you're talking about but have no compunction about making stuff up about me and even ,of all people, Morrelli and Melvin. Trying to throw dirt on their extraordinary contribution to the latest in modern foiler design is one of the most ignorant attempts to besmirch one of the most advanced catamaran design teams on planet earth. You should be ashamed!

 

BB,

I know you like to find fault in every point Doug makes, but you are probably minimizing recent advances more than appropriate.

Prior to the ETNZ SL33, full foiling was either active/dynamic height control (wands, feelers, etc) or in the same category as Hydroptere (surface piercing / ladder).

Foils with passive self regulation for altitude control previously came with a big cost in terms of drag. Cats tried this technology but it was just not fast enough for normal racing. Hydroptere made it work, but only for a very specific use in very specific conditions.

The early ETNZ foils were a major advance over traditional surface piercing in terms usable height stability with much better lift vs. drag. However, note that in the end the OR system that won required constant manual AOA adjustment for the upwind foiling runs. The AC 72 effort by ETNZ was probably responsible for public awareness of a "new" foiling concept (a higher boat results in more leeway and more leeway means less lift), but in the end the AC boats were not using foiling systems that were fully passive self regulating for altitude control.

The better example of where this "new" foil concept was effective was in the C Class. I seriously doubt that any traditional passive arrangement (surface piercing) would have been able to keep up with the better displacement boats.

I am convinced that a C Class with the right active altitude control system could be as fast or faster than what we saw. However, no one has been able to package an efficient active system on cat and win races with it.

So, I would say that this new concept is at least a "significant advance" in foiling. It has the potential of being used to beat displacement or foils-assist cats with no flaps, wands and attendant complexity.

Eventually, I would expect an active altitude control cat to show up that beats all applicable competition. However, if passive altitude control foiling advances enough, the simplicity advantage will still be a big deal.

A "revolution" occurs in a technology when there is a definite change in direction. If passive altitude control foiling cats become a ongoing segment of sailing, we will have had at least a small "revolution".