60'+ or - 20' Ocean Racing Monofoiler Design Discussion

Chris,

I apologize for diverting the thread off topic. Another may be started for stability and control of foil systems.

Now, i do not understand why you have to come into any thread that involve Doug with such childishly denigrating language.

<<<<love in>>>> -- What on earth are you talking about? Do you actually read any of the posts before you publish yet another attack?

 

Touched a nerve there, Cubey?

You said it yourself, you boys pushed the discussion off in another direction, simply because you wanted to. Personally, I dont understand why you have to come into a thread and childishly move it off topic... and then get up on your back legs because someone calls you out on the business at hand.

You want to know why I take such pleasure in dunning the Lord...? Go way, way, back to his first foray into the relentless pushing of the concept of the dead on delivery, People's Foiler. Douglas asked for input from the members here by putting it out there on this Public Forum.

He seemed to do all right as long as everybody just went along with his presentation and had no contrary opinions. The moment that anyone brought up any business of what was outside of his narrow bandwidth of conceptualizing, he'd attack them directly and very personally. The words chosen, the phrasing of said attacks, the pure and utter lack of interpersonal conversational skills in which a member of a dialogue demonstrates the kind of manners that facilitate a good interchange of ideas.... none of these things were being shown by your Love Buddy, Doug. In fact, he went out of his way to make an *** of himself, not just towards me, but towards anyone who disputed his reasoning on the subject. Many, many knowledgeable members took him to task for his poorly constructed positions and his aggressive behavior while supposedly defending said positions.

Your boy lives in a bubble, Cubey. One which he constructs, shuts out all logical thought that disrupts his limited vision and then attacks those who dare to posit a thought in an opposite direction. He has done it here regularly. He did it here last week when I suggested that the load induced bending of a t-foil vertical strut was present in a photo, which he posted. Doug told me that it was not happening, that it had no relevance to the thread and that I should take my interests elsewhere. Yet, he was the one who posted the image showing the bend in the structural member. (Specifically on point... every material on this planet will bend if the induced load exceeds the static properties. If anyone thinks that the foil struts never bend, then poll the vast number of enthusiasts over at Sailing Anarchy and they'll give you an immediate answer.)

He's exhibited his brand of bad behavior on Sailing Anarchy so often and with such vitriol, that he is currently banned from posting on those pages. He has been summarily banned from two other Fora for the discussion of RC boats due to extremely bad behavior on line and abusive interactions with fellow members.

If you find it appropriate to criticize when someone calls you both out for deliberately drifting the conversation off into your personal zone of pleasure, then, at least do your homework when you want to direct your criticism back towards me. Clearly, you have not done your homework on the issue and have a limited background on the magic that is known as Doug Lord and his Internet habits.

And lastly, what is it with you dudes and the cute little fake names such as Tcubed? If you really want to be regarded with anything like a degree of respect for your opinions, (or be exposed for your off-topic forays) then logic would tell you that you should step out from behind the phony curtain and start posting with your real name. Right now, it looks very much like you just want to play at being legit and sincere, while you are really hiding... should things go bad.

 

60' Moth

I very much appreciate the posts by Rick, Mark and T. Any discussion of foiler control systems is appropriate for this thread from models to human powered foilers on up. So thanks guys! Don't stop now....

 

Chris is not only funny, but also right..........

 

F3 etc.

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T, sorry I missed this question. The battery was about a pound and could move about a foot. It was about 13% of the all up boat weight.
Movable ballast either direction was unnecessary on the F3 but on an radio controlled OR full size monofoiler it is critical in both dorections. Movable ballast is also critical on many surface piercing multifoilers with the two biggest examples being the Australian Spitfire and Hydroptere....

 

So that means you were moving the total CG about 4 cM which is not much compared to the size of the model (i suppose the model is in the 1 to 1.5 M range) which is no doubt why you did not see a difference. The concept itself is valid though.

On another note i myself am of the school of thought that if you need to put water ballast in a foiler you're kind of missing the whole point. Not to belittle the engineers of complex projects like L'Hydroptere but if you need downforce you should get it from the foils, not by adding weight. Weight only gets you so far whereas hydrodynamic forces are virtually unbounded.

As for an angle for increasing seaworthiness of foilers i would focus on the more realistic goal of foil assist , rather than fully flying foilers. Scrap the amas as they are very problematic for self righting without complex mechanical systems.

I have some sketches of something along these lines from my teenage years . Basically an ultra slender minimally ballasted monohull that once at speed (as in wind over F1/F2) relies on dynamic righting moment from a continuous twistable foil that loops under the hull. This setup would have very little stability when inverted so the minimal bulb ballast is enough to get it righted again.

 

Vertically moving keel bulb for monofoiler?

I'm working on another solution to selfrighting on this boat. You can see the
original idea if you carefully read the first post: it is to use a 60* degree(each side) canting keel. A post further along shows a sketch by nflutter that
captures the essence of the idea. The canting keel gets the ballast out to each side nicely with the downside being a fairly complex installation.
What about a ballast bulb that slides up and down on the vertical fin? When this boat requires max RM it will be sailed with 20 degrees or so of veal heel and if the bulb was able to slide up the fin it would also move outboard(to windward). It doesn't develop all the RM(about 1/3) of the 60* degree canting keel but it eliminates the canting system and strut and the associated complexity. The system-like the canting keel- would have to work in a pitchpole situation in order to right the boat and has it's own issues with complexity. And the missing RM has to be found somewhere else..
So far, I haven't figured out a 'clean' way to slide the bulb up and down-any ideas?
*Updated version=110 degrees each side.

 

Tcubed
To get a foil to hold a multihull foiler's windward platform assembly down requires a very serious amount of negative angle of incidence, like at least 10-15 degrees and probably a lot more. Sure you'll be able to hold a windward platform area down ...... but only at a huge amount of drag increase, not worth it, spells very slow, the boat would end up crabbing and dragging along always wanting to turn up into the wind. That is only my opinion of course, someone could prove me wrong. However in early foiling days in Auckland there were a number of people who believed a 3-5 degree or so positive angle of incidence on both float/foils would lift the leeward one and hold the windward one down at the same time. Again IMO, the belief in the windward one (at near zero angle of attack) does absolutely nothing, it pops out of the water as if it is just floating there. which it is.
L'hydroptere's innovative scientists (a fairly rare species) would have done the negative thing long ago otherwise, but they have settled for windward (and after end) water ballast.

 

I must say that i cannot follow your logic there .

The way i look at it is as follows;

Picture a tri foiler with Tfoils and a lightly loaded rudder foil ( a pre-requisite for stability) and symmetrical foils for the sake of argument.

The sum of the lift on all three foils must equal the weight of the entire boat in steady state.

The sum of the force moments of all three foils must be equal and opposite to the force moment of the whole rig (Vertical arm is distance between CE and CLR).

So we have a pair of simultaneous EQs and the second EQ can be separated into roll and pitch components.

Before even getting into the mathematical details we can ascertain a few things by inspection alone.

In the case that the rudder foil is taking zero load (apparent CofG at longitudinal position of front/main foils) we see that leeward foil must positive lift MORE than the windward foil negative lifts so that they add up to weight of boat . So (remember symetrical foils) leeward foil must be steady at greater angle of attack than windward one.

Now suppose a larger trimming moment requires negative lift from rudder foil , then that must be compensated for by more positive lift on main foils so leeward foil is at an even higher absolute angle of attack than the windward one.

If the rudder foil positive lifting then it will tend to equalize the angles of attack of the main foils but the leeward one will always be at a greater absolute value of alpha (AoA) than the windward one.

So i cannot understand the thought sequence you use to assert the windward foil has to be at 10 15 negative AoA. Since the EQs show that the leeward foil will always be at greater absolute value than the windward one and 10 degrees is a bad angle and 15 certainly is stalled.

In the case of a foiler with angled surface piercing main foils the situation is very much more complex as the leeway angle will automatically reduce the angle of attack of the windward foil so it lifts less or lifts downward. Regardless they must still produce net lift to equal and oppose total weight so the leeward foil will always work more (more highly loaded) than the windward one.

 

This is what Greg Ketterman says about the windward foil pulling down. Like Bradfield's boats(and the F3) his boat has virtually unlimited RM:

"Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.
From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited."
http://www.hobiecat.com/sailing/TriFoiler History Original/Magazine Articles/Multihulls 1990.htm
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Exactly!

 

The surface piercing set up not only regulatess lift by immersion but controls righting moment by leeway (dihedral effect). The crucial thing is to get all the vectors to point at the same x y z coords. This is in fact not possible due to the rudder foil, but one aims to get as near as possible.

At first sight it seems that as heeling moments keep on increasing there comes a point when the windward foil (surface piercing) will pull down but when this happens that foil becomes unstable in that it now becomes a positive feedback loop , so the windward foil ends up either burying or releasing. This alone puts a limit on what one can expect out of a surface piercing system.

 

Doug , i read the first post entirely , but i must say the moment i see the sailboat needs an engine to function, i lose interest. Kind of defeats the purpose, kind of like putting ballast on a flying foiler.

I have nothing against motorboats by the way, as long as they exhibit intelligent design. What i object to are sailboats that require motors. Imagine you can't go out sailing because there's no gas or a prob with motor....

I think that the entire premise of a large fully flying bifoiler is pretty nebulous, and is an exercise in overcomplexity and uncontrolability.

Much better in my opinion to concentrate on non flying foilers (to meet the self righting monohull criteria) and have a much simpler more full proof machine but with the massive speed potential offered by dynamic stabilty or DLA as Ketterman outlined.

As has been demonstrated with the moths there is not as much of a speed advantage in flying as one might expect when you look at a broad range of conditions, which is precisely what will be encountered when sailing across oceans. F0 to F12 is what i would be designing for, something completely different to the case of the moths and other harbour use foilers which only get used in a pretty narrow range of conditions, hence scaling up these sorts of designs does not make much sense.

Having potentially unlimited righting moments on the other hand, is fairly simple and massively increases the speed potential at the higher end without negatively impacting the performance at the lower end much.

 

Hallelujah, TxTxT's seen the light! Doug isn't going to agree - and you are running the risk of becoming the target of some abuse and derision.

There is no such thing as a free lunch, and no such thing as "simple" unlimited righting moment without complex unavoidable baggage and consequences. Gary Baigent is right that there will be an off-centerline drag increase. Physics is about mathematical balance - you can't change one side of the equation with affecting the other side. Gaining unlimited righting moment without negative consequences is magic, not science.

It is obviously possible to make a three-point foiler work - hence the Hobie Trilfoiler. The increased drag of the foil providing negative lift (the "righting moment" side) must equal the net drag of the positive lift side, allowing the boat to sail in a balanced fashion. To use the foil-generated righting moment, the whole system has to deal with higher drag than would be required in a system not relying on foil-generated righting moment.

Every design has trade offs - it would be entirely possible to make a Trilfoiler that had less drag, but relied on movable ballast - just like Hydroptere.

 

I know full well that the 'potentially unlimited righting moment' has an induced drag cost.

It is still worth while though. One has to analyse the ratio righting moment / total resistance to see what kind of power to drag ratio to expect. Same fundamentals as with any boat.

The thing with ballast systems is they provide a fixed amount of RM (not dependant on V) whereas with the foils it is a function of V^2. So the harder it blows the faster you go , etc till it self destructs.