# Sailing Without Wind.

Discussion in 'Motorsailers' started by Will Gilmore, Jul 21, 2022.

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### Will GilmoreSenior Member

So...
Remember the controversy over the statement made by AC team Artemis about sailing upstream on the Amazon River just from a ten knot current against still air?

I was thinking about how to use that idea on open water. What if you had neither current, nor wind, or current and wind moving together, so no wind across the deck?

Originally, when I was struggling to come to terms with this concept and had accepted the physics of it, I thought, 'could you just motor up to speed and capture that wind?' Answer, 'No'. In such a situation, you are always generating a head wind, so no usable variant is created.

But...

What if you used thrusters? What if you drove your boat sideways to create a beam reach?

Can you picture a sailboat driving along on a heading, under sail, but there is a smaller amount of energy being put into a sideways force that, under sail, moves the generated AW forward by a vector, to create a greater force that drives the vessel forward faster?

Some of the issues to consider:
1). actual sideways speed that can be generated would have to be small, well below the ten knots suggested in the video. There's a lot of lateral resistance to overcome.
2). The heeling force generated by a large underwater thruster. This force would only add to the heel of a powered up sail. (Catamaran might address that issue).

But, is this something, maybe impractical, but doable? What do you think?

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### seasquirtIn the beginning there were waters.

Nice alternative thinking Will, but if there is no 'energy' to be had, what powers the thrusters ? What replaces the lost energy from prop slip, electrical resistance, rolling resistance, and all the other losses ?
I'd suggest procuring the same ACME catalogue that the Coyote uses.

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### Will GilmoreSenior Member

I'm not proposing running thrusters without power. They would be powered in the usual way. I'm just wondering if headway can be achieved through sailing by creating sideways movement. With the aid of sail lift and vector math, maybe a small amount of energy into side slip could translate into a larger amount of forward movement.

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### Robert BieglerJunior Member

All you need to do that is a boat with VMG downwind faster than true wind speed over the water, and these boats have been recorded doing just that. That is also the reason why they sometimes can improve VMG downwind by going into a contrary current, because that increases true wind speed over the water. It helps if you switch between the different frames of reference, like here: DDWFTTW - Directly Downwind Faster Than The Wind https://www.boatdesign.net/threads/ddwfttw-directly-downwind-faster-than-the-wind.25527/page-30#post-911173

That would be a perpetuum mobile and would (unlike VMG downwind faster than true wind speed, or even going dead downwind faster than the wind) violate conservation of energy. You would not be extracting energy from the relative movement between two media, as Team Artemis did, so your proposed scheme is fundamentally different from what they did.

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### Will GilmoreSenior Member

Yes. True, but my issue, I think, is with my use of terminology. Where I wrote,
I'm wondering if a sideways force to create a small sideways movement, might convert to a larger forward movement. My use of the word 'force' was not appropriate in this case. Of course in a system where a given force is applied, a greater force is not retrievable. However, like a small movement with a given force, can be converted to a large movement that may not have the same ability to do the same work over the small distance, but over the whole distance, the same work is done.

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### seasquirtIn the beginning there were waters.

I can visualise a long deep keeler being borne along by a swift river or tidal flow, in perfectly still air (by the land's reference), and making way. With the hull axis greater than 45 degrees to the apparent head wind and current flow, and sails set for sailing close to the wind, the hull would be under some actual wind power and traveling forward, but also sideways to the water flow, and backward according to lee slip, and likely confined by river banks, so tacking regularly. The water flow speed would be faster than the hull, (drag), and every tack would wash off momentum and speed, becoming even slower in the stream, and slow to get going again, that's if you can even steer, with nothing flowing over the rudder . I don't know fancy maths, but I reckon deploying a drogue, sea anchor, or storm sail as substitute, or better - two, and playing them for steering the hull by its attitude, and keeping it at 90 degrees to the water flow, bare sticks against the 'head wind', and go with the flow sideways. Just watch out for river snags and shallows. The air friction above, and hydraulic inefficiency below would wipe out any advantage of an 'apparent' head wind drive, I think, after working so hard to get it.
Sorry if I sounded sarcastic earlier, but I could just see it: Wile E. Coyote, sail up, electric fan blowing from behind a square rig, (mysterious power source), pushing a bow wave and defying logic, perpetual motion with no resistance and perfect efficiency.
Resistance and entropy wins the long game.

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### Will GilmoreSenior Member

Actually, I also had that picture pop into my head. But I'm talking about continuously putting energy into the system with the thrusters. Using mechanical force to create that all important relative lateral resistance and the AW on the beam. Just a thought. It should work, but what kind of energy would one need to transfer that energy from sideways to forward via sail and keel?

I think the short LWL created driving by driving the boat sideways, LWL then equals WWL, would make generating a significant wind, very hard.

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### seasquirtIn the beginning there were waters.

If there must be some type of small input into the system, to gain a greater or different type of output, the slowly rotating column systems may be useful to adapt. Eg. large driven 'mast' drums taking advantage of the high/low pressure differential generated on the outside diameter, and driving a small propeller or paddle wheel directly somehow, avoiding lossy gear and belt drive systems. But then the weight and complexity makes it all come back to greater hull and top sides resistance, which negates the gains.
Also, with delicate light weight. weight/energy saving equipment, a line squall or king wave will see it off in quick time.
Rocket launch a kite up into a higher atmospheric level, and and jet stream it along. ACME rockets of course.

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### Will GilmoreSenior Member

Of course, a name you can trust.

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### Alan CattelliotSenior Member

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### Will GilmoreSenior Member

A curious diagram.

It looks like the sailplane drag force added to the sailplane lift force equals the total sailplane force. The forward component then equals the sailplane drive. The sailplane drive is exactly countered by the addition of the boat side force to the boat resistance to create the boat drag force. I assume this is only true as long as there is no acceleration such that maximum speed is achieved for the forces applied.

But how does the heeling force calculate in? Are the two cyan arrows of the thruster reaction additive or simply split to represent a balance of fore and aft forces?

The navy, yellow, and green arrows are inverted to the diagram?

It does look exactly like what I was speculating about.

Note that the boat trajectory is no where near directly forward. If it were, there would be no lift that could result in foreward force.

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### Alan CattelliotSenior Member

This is a very common representation of a mechanical system @equilibrium (constant speed of its parts). It is a geometric representation that is "analyticalized" in every Velocity Performance Predictor. It is a "visual VPP". As you can see, there is no indications of referential at all. In general, it is assumed to be Galilean. Since any referential moving at constant speed relatively to any Galilean referential is also Galilean, I have attached the referential, choosen here, to the boat, whose movement will be thus investigated at constant speed. Its origin is arbitrary choosen, and maybe the Center of Gravity of the boat. The filled arrows represent speed vectors. The magnitude of these speed vectors are arbitrary choosen. What is important is their composition and direction, that helps drawing the force vectors applied to the mechanical system. These force vectors are represented by the empty arrows. Both their magnitude and direction are important.

(i) Exact. The sailplane lift force vector and the sailplane drag force are, respectively, normal, and, in opposition, with respect to the incoming air flow. Their addition, as vectors, gives the total sailplane force, which is then split into the sailplane heeling force and the sailplane drive, by projections respectively normal, and, on the boat axis.

(ii) Exact, and its lateral component is named "sailplane heeling force", with reference to the definition of heel force, as a force whose momentum makes the boat heel.

(iii) Exact. To be consistent with a static representation of the boat @ equilibrium (constant speed), I firstly draw the boat resistance vector, as being opposed and equal in magnitude to the sailplane drive, assuming that the sailplane only contributes toward the forward movement of the boat, ie in the fore direction of the boat axis. I then determine the boat drag force, being the sum of the hull and deck windage and the hull drag hydrodynamic drag, whose projection on the boat axis should give the boat resistance vector. I neglect other drag forces or other induced lift forces, in this simple representation. The boat drag force has also a component normal to the boat axis, named boat side force.

(iv) Exact. Although this representation can also be used to qualitatively figure out how the boat would make his way, when the changes of speed are slow enough for the movement to be considered as adiabatic. Of course, the magnitude and the direction of the force vectors should have to be changed.

(v) Attempt of answer in (i)

(vi) Because i skip the use of daggerboard or keel, I use the thruster reactions (TR) to balance in top view the sailplane heeling force (SHF) and the boat side force (BSF), imposing -2 x TR = SHF + BSF, where bold notations represent vectors. This side thrust split is not necessary in this representation, but is made forseeing how this boat configuration will be sailed. I have the feeling that only one thruster will not allow, in general, the total momentum to be null ( or almost ), and that a rudder, remplacing the aft thruster, will be hard to steer. Maybe pods would be preferable. Due to symetry of the problem, I also foresee that the shape of a cap will be the most appropriate for the boat to make his way, although it will pose stability and floatability issues. Also, it may be interessant to consider, in concurrent engineering, the pertinence of the use of a square-rigged sail, like the one used on Mirabella V, for instance.

(vii) Exact. I recognize that the words "Boat speed", "Side speed", and "Forward speed" are not appropriate, in this diagram. They should be replace by something like "Apparent Wind", "Side Wind" and "True Wind". As english is not my mother language, I'm often stucked with terms.

(viii) Then, I may also be mistaken with the sailplane lift force vector and the sailplane drag vector. I will give another look. What should then, the boat trajectory, be ?

Thanks for your kind attention. I'm always very interested in this kind of problems, since new solutions may be the clue to overcome our actual bounds, for our new future that desperately need to be built.

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### Alan CattelliotSenior Member

Ok, then I understand your note about the boat trajectory. I agree with you. It is an important note, considering the problem. I sailed this windsurfer, do you know it ?

The funny thing is that, with this board, with no winds, you were able to practically sail, like in the diagram, but with a side current in place of the thruster reactions. Unbeatable. Having tried in the same conditions other windsurf, and discussed with some sailors of my regions, we conclude that the hull shape, very round, made the difference. A sphere cap may be a little extreme (perhaps interesting though), but i guess that very rounded section would be better to sail without wind, but with side thrusters. Just a though.

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### Will GilmoreSenior Member

Thank you for the diagram and explanation. That is what I was thinking. Because of the vector math, the actual headway (boat speed vector) can be greater than the side thrust velocity. Now to get past the lateral resistance that increases resistance to that lateral thrust. Sort of the opposite problem of good sailing.

No, I don't know windsurfing well. I would think a flat bottom with very softly rounded chines would be ideal. The flat bottom would reduce draft, as well as the amount of bending of the flow of the water under the hull, and a high and rounded chine would be needed for better entry and exit at the surface. I don't understand what would be gained, especially for a windsurfer, by having something that looked like half a log roll to balance on.

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### gonzoSenior Member

If you have a thruster, the most efficient way to use its power is to make it push the boat forward. Eliminate the keel, sails and rig, which only create drag,

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