Sailing: The mythical 50 knot barrier

(This post have also been posted under Boat Design & Multihulls).

I have been doing a field study (in terms of hydro and aerodynamics) on G-Class vessels for ocean records, and are about to cover the mythical 50 knot barrier over 500 meters.

Do some of you know of an "A-Z book" that addresses this problem in specific? I want to get an overview of existing articles which I can start of with before digging into the depths to understand why nobody have been able to overcome the relativly low average speed compared to the fastest motorized vessels?

Perhaps some of you also have been philosophizing about this for a while, and even been experiencing with it? I would be happy to listen to your thoughts, and I've also noticed that several of you are widely read and have the knowlegde to hopefully contribute to this post.

All technical perspectives and thoughts about the theme to "demystify" the topic is very welcome.

Thank you,
OAB

 

Simply put 50 knots is about the region where conventional rudders and centreboards start running into cavitation problems. Motorised craft don't need centreboards and have ample power so can use rudders that are high drag at low speed.

 

A vessel designed for breaking the 50 knot average over 500 meter, outright record, I would presume is designed to be ideal around 50 knots. This meaning that centreboards, rudders and so forth is designed for running at high speed and is not ideal for low speeds. Further more looking at e.g. Yellow Pages Endeavour (asymmetrical trimaran), Hydroptere (foil trimaran), Finian Maynard (windsurfing), Alex Caisergues (kitesurfing), you can see that they are using low drag rudders, vessels, foils, fins, boards; all to minimize drag.

However they all have to work against counterforces from the sail / kite. As forces is almost produced perpendicular compared to a motor pushing the vessel forward as you write. To overcome this they either relying on incline rig, foils and / or fins. For G-Class vessels this is of course a larger problem as they are designed for high average speed in the middle range round 30 knots and works optimal at lower speed than the vessels for the 50 knot / 500 meter records such as Yellow Pages Endeavour and Hydroptere, or windsurfers and kitesurfers.

To mention a few: Drag vs Power input / Power output is one of the main issues to overcome since optimal lift is produced at a much wider angel (almost perpendicular) on sailing vessel compared to a motorized vessel having the power from 0 degree utilizing all power for foward thrust. Further more, increased drag as heeling occurs, power (lift from the sail) is produced at an increased negative angel towards surface, and increasing drag doesn't make it better as heeling also reduces "true" sailing area of the sail. The more heel the more drift due to less optimal canting of the hull in the sea, which causes a less (theoretical) optimal speed course as angel from true wind is what defines your theoretical top speed at a given wind speed, before the overall L/D vectors of the vessel and rig is taken into concideration.

What I am curious about is to get a full overview over all these factors, numbers involved, why has it always been 50 knots and not 40 or 60 knots? 40 knots is beaten almost two decades ago, but still challenging the 40 knots the aim have always been 50 knots... There are some many good ideas out there - some have been realzied, most of them not unfortunatly.

So my question and whish is for you to expand my horizon, so that I can better understand why the 50 knot record have not been taken yet. Is there any limitation factors to overcome, or what is it!? The best way to understand is to start discuss it in a forum like this I guess Attaching a parachute to a vessel in 60 knots, in e.g. the French Trench where water is very flat, most likely such a vessel would go faster than 50 knots over the 500 meters... The interesting part, and optimal for the future as we need alternative propulsion devices for hybrid propulsion, is to increase the performance ratio of a sailing vessel so that it is possible to go over 50 knots in e.g. 20 knots of wind.

Thanks,
OAB

 

Hi,

I am new to this forum, and I joined because I was just exploring the same issue. [some of this post is over on the multi-hull section]. The land and ice sailing records are well over 100 mph, it seems to me that, based on my calculations (I am an engineer) it should be possible to do perhaps 60 knots or more on relatively smooth water. Considering that the all-time 500 m record on the water is held by a sail board, which is not particularly stream lined nor is the sail especially efficient, it seems it should be possible to go faster in a craft designed for that particular purpose.

I was toying with the idea of building something for the 10 sq meter category with that in mind. Since the record is held by a small size craft, and I figure I could build a sailing machine that size in my garage pretty inexpensively. I thought it would be a fun design and construction challenge, even if not successful at beating the record. At the very least it would be a kick in the rear to go zipping around on the water in a pocket sized sail powered micro-speedster.

It appears to me there are two issues that has kept it so low. One is that for some reason no one is using a better sail (or "airfoil") designed for the task of getting the most thrust out of that size sail, and the other is control on the water appears to suffer as the speeds go up. Control is certainly possible since powered boats go much faster (even pulling water skiers!). Perhaps no one has looked at it properly, or no one with the required knowledge is interested.

It is an error to think that because powered boats have no lateral sail loads that there are no lateral loads at all. In order to stay in control of a power boat at 300 mph, you must have dynamic stability and control, which means you have to have very efficient foils designed to dynamically balance and that take significant lateral loads to keep it in a strait line. You can not assume static balancing of loads at these speeds, there is a dynamic interaction between water, air and hull that make it impossible to control at high speeds unless they are dynaically stable. At slower speeds the "pilot" can compensate for any instability, it is impossible at higher speeds (a pilot can not react fast enough). You also get structural and fluid dynamic flutter as the forces increase with increasing speed.

To stay in control (to optimize speed) you need a fairly rigid hull and control surfaces, and dynamic directional stability, which means more weight more surfaces penetrating the water (look how many control surfaces for example that aircraft have to maintain stable flight), which mean either more whetted area (on a displacement hull) or higher induced drag on foils. This also means you need to convert the wind force into forward thrust more efficiently, which means a better sail (or airfoil). People trapped in traditional ways of thinking keep using minor modifications to traditional rigs, which has certain disadvantages to produce maximum forward thrust. I know there have been a number of unconventional craft attempted, some quite inventive, but either they had bad luck with wind or conditions or they were overlooking some significant disadvantage to their design. None hold the record.

So I think it will take the right combination of better design concepts in both sail and hull dynamics (stability and control), luck, and a good location with optimal wind conditions.

 

I have thought further on this and came to the realization that the stablity issue a far larger problem than at first I thought. Consider that any craft is free to move in six degrees of freedom, one in each axis of translation, one in axis of rotation. So you would need to model six partial differential equations. This is common with all vehicles, cars aircraft, space craft, etc. and mathematically modeling them you have to analyze these equations to determine if the vehicle is controllable (of course with some vehicle you can ignore some of the expressions since they are not significant). Careful examination of the Youtube clips of the record breaking sail board run tells you they are on the ragged edge of maintain control of their craft!

With a water craft you also have both aerodynamic stability AND hydrodynamic stability to consider, and the interaction between the two. So potentially you could have 36 different partial differential simultaneous equations to solve to verify stability. You can not assume the water surface provides you with a stable platform the way you would with a land vehicle, even with aircraft you only need to consider interaction with the air in most cases. These equations could probably be simplified to only nine equations if you ignore the translation in three axises since roll (heel), yaw and pitch stability are the most critical (if you can keep it strait it will most likely be controllably stable).

This water/air interaction is not insignificant. For example, using a conventional racing catamaran as a model craft, if on your high speed run a sudden gust causes a heeling (rolling) moment, that causes the lee hull to sink slightly to counter the force, this cases a yaw because of the sudden increase in drag on that side and the reduced drag on the windward hull, this causes a reduction in the angle of attack on the sail, that in turn reduces the heeling moment and the forces become unbalanced. This combination could cause an overshoot in the yaw and heel (roll) response, which causes it to overshoot the other way. In addition, the sudden slowing would cause it to pitch forward driving the nose downward slowing it further. Not only do you loose speed, if the increasing overshoot becomes too large too quickly for the crew to respond to, you lose control of the craft and possibly tumble at those speeds.

Compounding this analysis even further is that the aerodynamic hysteresis (lag in response) is usually slower than the hydrodynamic response, when these kind of forces couple because one lags the other, overshoot reaction are inevitable. This is why it becomes easy to lose control of the craft at higher speed.

At lower normal sailing speeds the crew has time to respond a sudden yaw, and/or these secondary effects are small enough to be ignored because the dampening makes them insignificant. To know ahead of time how these interactions affect control, you have to reduce each of these responses to a mathematical expression and do an analysis for dynamic stability.

This all of course is assuming the structure is rigid enough not to affect the components, because this could add another level of complexity to the problem. If hulls, beams, dagger boards and rudders are also flexing and changing the predicted responses you have to included these predicted outcomes in the equations. Usually you just make it as stiff as possible and you hope it is stiff enough not to matter. This usually is good enough on smaller craft, on large aircraft stiffness adds a lot of weight so it gets analyzed alone with the aerodynamic stability. Of course making the sailing craft as light as possible would help you make a new record, so without a lot of fancy mathematical analysis, you just guess at how stiff is "stiff enough". With good judgment AND good design, you might get pretty close to the ideal.

It might be reasonable to ignore some of the possible interation if qualitatively examined and it can be determined they are small enough to not be an issue. But that takes a good understanding of what is actually happening and how it will affect the other responses. Hopefully you cam make reasonable estimates accurately enough before you build it.

And even if you do not do full analysis, understanding all of the possible interactions when you actually start making some speed runs, if you discover some dynamic instability you will more quickly be able to make alterations that solve the problem. Otherwise you could end up chasing your tail not knowing why it becomes uncontrollable as you pick up speed.

This hopefully gives you a better insight into the problems that anyone could be facing when attempting to design a craft to set new speed records.

 

KFD approach

Hi OAB,

KFD (Kitchen Fluid Dynamic) is my prefered approach to address these kind of issue.
I would suggest you to purchase " High Speed Sailing" by Norwood, you will get sound foundations for your project.

It could be interesting for you to think in term of "wind speed factor" ie:
Do you want to achieve your 50 knts speed with 50knts true wind or 25knts true wind ?

The main limit today in windsurf speed potential is probably the "crew aerodynamic drag" .

You can start with your maximum righting moment, which allow you to optimize you sailplan accordingly for your target true wind speed.
look for mini drag configuration including the crew, and compute roughly the global aero drag for everything above the water, and put it in balance with the driving force of your sailplan.
You will see how much newtons remain available to balance hull, board &rudder drag.
The next step will be probably the trade-off between performance and stability.

Good luck for this ultimate project

 

Training opportunities vs space solutions

When considering windsurf speedrecord one generally fails to consider another factor.
With a windsurf when good wind conditions are established you can have many runs in a short time period, instead if you have an asymetric space machine which requires a lot of care and a special trailor to bring it back at the starting line, it is not intensive training.
Ultimatly you will not have enough opportunities to explore the true speed potential of your project.

It is always a tarde-off

Good luck and keep us informed

 

Surely the people who have been trying to break the barrier for decades are not altogether stupid and hidebound and are on the right track?

 

This boat is capable of getting over 50kts if the conditions are right:
http://www.macquarie.com.au/speedsailing/updates.htm

It offers many design cues to someone interested in getting over 50kts with a rigid wing.

The kites are also getting more efficient and I would not be surprised to see a slender hull exceeding 50kts in the right conditions.

Rick W.

 

CT 249,

The point of your post is not clear, what is it your are saying?. I am well aware of all of the record attempts with rigid wing foils. I have been following them since about 1983. Some of the asymmetrical craft using rigid wings have been quite advanced in their designs and construction; I have no doubt that the designers are pretty sharp and inventive. Yet none hold the record. It is even odder when you consider that a sail board, with only incremental design improvements of a traditional and draggy design, holds the record, and has held it for what? almost 20 years, with only brief periods where one of these unconventional device held it.

Why have not the fully faired, rigid wing, asymmetrical craft not gone a lot faster than a sail boarder? It seems to me to a mystery since it must be possible to make a sail more efficient than a floppy fabric sail board rig, and more streamlined than a guy in a wetsuit. Maybe it has just been bad luck. My postings were simply putting my thoughts in writing, it is not an attack on the many inventive people who have made very worthy attempts with unconventional craft. I very much admire unconventional thinking, yet in this case it has not resulted in any records.

Yes the problem does appear quite complex. Even so one would think that even a sail board with a more efficient sail would push the record higher. Yet the record holder uses a fairly conventional looking sail board sail (very nice for a sail, but nothing unusual). At least from what I can tell from the pictures and film clips.

It is also clear why even on racing sailboats, fabric sails predominate. The fully battened fabric sail has certain advantages for sailing, it is able to be lowered, stowed, reefed, it is variable camber, AND it will easily swing to either tack. As advanced as the modern fabric sail is I find it curious that most sailing rigs do not allow full control of the shape of the sail (camber and twist) and why more attention has not been paid to the leading edge (the mast in most instances). I am playing around with ways to do this on my small sloop. I want try a fully developed rig that better controls camber and twist on a lightweight cat I am designing. Which had got me interested in looking at what is setting the speed records currently. I doubt what I am building would set any speed records since I want to be able to sail it in both directions like a normal sailboat. But with a specially designed sail and a few modifications to my original idea, who knows? it might be worth a try. As I posted earlier, at the very least it would be a fun design and building exercise if you keep the craft fairly small so it does not take too much time or budget.

Even so, ISTM that having the sail board rider wear a lightweight streamlined fairing suit should help it go faster, along with a stiffer mast and perhaps a rigid wing sail. Now to improve the control and stability of that tiny board without increasing drag, then we will be getting somewhere with a new record. Could the same thing be done with the pilot in a streamlined pod, and still have control? It seems like it should, but no one has done it yet.

Erwan, I am not overly obsessed with numerical analysis and I prefer the seat-of-the-pants approach (it saves time) and it helps keep what you are building practical. One of my engineering professors used to say that one simple test is worth a thousand expert opinions. But having a good understanding and feel for the kind of interactions involved helps guide one better in which approach (and which tests) will more likely be successful. If you randomly try every possible configuration without a good understanding of what is happening, you will not live long enough to gather any meaningful data. So the calculations just help you reject approaches early that will likely fail before you go to the trouble of building them. The other problem with "kitchen fluid dynamics" there is often many things with fluid mechanics that are not intuitively obvious. Why do you think it took so long to build a man controllable flying craft, even a hang glider could have been built with readily available materials from 2000-3000 years ago, yet it has only occurred in the last 150 years despite thousands of years of attempts.

Along those lines I recently read a joke about this on another forum. An old physics professor was on his death bed and one of his colleagues asked "when you get to heaven are you going to ask God about fluid dynamics?" "no" he said "I do not want to embarrass Him".

 

Speed

As cool as it is to follow the one way ditch sailors, kite sailors and board sailors the speed record program of the Hydroptere team is particularly interesting to me. They may be very close to the magic 50 in a boat that can sail both directions in waves as well as having the potential to set ocean records.
It will be very interesting to see what the boat looks like when it re-emerges in January with the express goal of beating 50. I wish them luck.
All speed sailing is exciting but there is, obviously, a lot left to be learned(or accidently discovered).

 

The point of your post is not clear, what is it your are saying?

The point is that your comment "Perhaps no one has looked at it properly, or no one with the required knowledge is interested" made it sound as if the quest for 50 knots is simple and those chasing it merely lacked the right knowledge. Surely in fact those seeking it tend to be pretty smart and knowledgeable?!

"It is even odder when you consider that a sail board, with only incremental design improvements of a traditional and draggy design, holds the record, and has held it for what? almost 20 years, with only brief periods where one of these unconventional device held it."

The modern windsurfer sail is a huge advance over the traditional design, and it has dramatically lower drag. This can be demonstrated by switching rigs over, which takes just a few seconds. A more conventional style, while still better in many conditions, is knots slower than the flat, hugely twisted modern windsurfer speed sail in terms of high-end speed. The greater sideforce or (AFAIK) induced drag of the older sails is easily shown by the fact that a shortboard struggles to get upwind under a Raceboard sail, yet it points quite well with a modern slalom type sail.


"As advanced as the modern fabric sail is I find it curious that most sailing rigs do not allow full control of the shape of the sail (camber and twist)"

It depends on what rigs you're looking at, I suppose. A Skiff, Canoe, Moth or good cat rig allows a great deal of control over camble and twist. Sailboard rigs (allowing for the use of different rigs in different conditions) offer enormous control over camber and twist, although it's hard to adjust them independently. The rigs can go from maybe 20% depth to zero; from tight leach to the point where the leach is inverting to leeward.

"why more attention has not been paid to the leading edge (the mast in most instances)."

But there has been a great deal of attention played to the leading edge, since the 1920s. There have been wing masted 12 and 18 Foot Skiffs; R Class; Merlins; NS14s; MG14s; IMS boats (sort of); Open boats; Canoes; Renjolle; Finns; and of course most modern cats use wings.

In most cases, wing masts have been abandoned because they aren't a significant improvement. In a few cases, they are widely used when they suit the class (Tasar, NS14, Finn). When they work, they are widely accepted so people are not biased against them.

Same with wing rigs....they've been tried in several classes but only worked in a couple

"Even so, ISTM that having the sail board rider wear a lightweight streamlined fairing suit should help it go faster, along with a stiffer mast and perhaps a rigid wing sail."

It's been tried, many times. It never went well. A wing mast got the record once, and then it was found that the fabric sail with its bendier mast was more efficient. The modern windsurfer sail actually feels (from distant memory) a lot like a wing mast on a board, but the soft sail caters for a much better range.

The masts are already mainly carbon fibre, it's hard to make them much stiffer without making them bigger and that doesn't help the leading edge.

 

Read gg's lips

"Simply put 50 knots is about the region where conventional rudders and centreboards start running into cavitation problems. Motorised craft don't need centreboards and have ample power so can use rudders that are high drag at low speed."

It's why these wildly differnent boats are within a couple of knots of each other.