The America’s Cup
28 September 2013
I watched, with interest, the videos of the 34th America’s Cup. At last we have fast sailboats engaged in a competition that is fun to watch. The virtual images (such as course boundaries, distance grid lines, separation between boats, etc.) overlaid on the real images really helps to keep the race understandable and interesting for almost anyone. Very well done to all those involved with the video presentation.
Larry Ellison is to be congratulated for having the vision that sailboat racing could be fast and fun to watch and for being the driving force that helped to bring this about. I only hope that the AC competition continues to progress in terms of speed and excitement.
Both Team New Zealand and Team USA were class acts and put on a great battle. For perhaps the first time, I’m looking forward with great interest to the next AC competition.
Over the years, as I was developing Sailien, I would mention to someone that I was developing an exotic high-speed sailboat. The non-sailors would often become quite interested and say things like: “Are you going to race it in the America’s Cup?” or “You should enter it in the America’s Cup”. I’d laugh and say: “The AC guys don’t want to see me; they’re not interested in fast or innovative sailboats”. This would shock them, but I would go on to explain that the AC was really the fastest and most expensive examples of the slowest sailboat design. Meanwhile, the windsurfers were going up to 3 times the AC boat speeds. But now, at last, the AC finally got into the 20th Century!
Hey Bob, where you been, sleeping? This is the 21st Century! True, but I like to think that the most prestigious sailing competition should be on the cutting edge of innovation, and the first successful hydrofoil sailboat I know of was the “Monitor” designed by F. G. Baker. It is reported to have sailed at 30 knots and this is in the 1950’s (from the information I have.)
The 1988 AC race featured the catamaran “Stars and Stripes” with a wing instead of a soft sail. I was quite interested in this as I hoped it would open the way to faster more innovative sailboats. But that was not to be as the traditional old sailing geezers must have been having heart attacks watching that much fun happen. They agreed to rule the AC back to slower boats; I fell asleep.
Larry Ellison changed all that by challenging for the 33rd America’s Cup under the “Deed of Gift” rules and specifying a trimaran; I started to wake up! While the legal battles were disliked by most, that’s what it took to get the AC onto fast boats. Resistance to change is often incredibly strong.
The only real error that I think Ellison made is specifying craft that were too expensive for most to build, resulting in too few challengers with only NZ being competitive. However there is hope as Ellison addressed that point immediately following winning the cup. http://www.youtube.com/watch?v=GhQsk16EKtw
I wonder what it would take to get my Sailien design into the AC?
100 Knots for Hydroptere?
31 August 2013
The latest news from Hydroptere is that they have plans for a 100 knot sailboat. This was posted on 26 Aug 2013, so look for that date at this address. http://hydroptere.com/en/the-news/last-news/
And what do I think their chances are for sailing at 100 knots? Actually those of you that have been reading my blog should be able to answer that.... (This is quiz time, lol.)
Take a look at the image of the craft they are proposing. It does look a lot like Sailrocket, but if you look closely, you might notice that they omitted one of the two most key elements for this type of design. (There's your hint; so what is missing?)
Missing is the inclined windward hydrofoil that is needed to counter the force from the inclined wing. I find it hard to believe that the Hydroptere engineers missed that. The essential set-up for roll stability is to place the airfoil and the hydrofoil parallel in such a manner that the centers of effort from the foils are in the same plane.
The craft shown will be forced up in the water by the forces acting on the vertical fins (keel and rudder). Those fins have horizontal foils at the tips which I imagine are meant to raise the hull out of the water similar to other foiling sail craft. The problem with this is that the vertical portion of the fins will raise the craft; therefore the tip foils are going to have to be used for down-force to keep the fins immersed sufficiently to maintain power. This down-force will add needless drag and will limit speed (this is similar to the problem Trifoiler encountered with their set-up.)
Look at my drawing for the post "More drag for VSR2?" (2 Jan 2012) and you will see how the forces relate to the Hydroptere set-up.
In the configuration shown, 100 knots is not going to happen.
Aptly named Sailrocket, blasts off!
17 November 2012
While yet to be ratified, Sailrocket posted an average speed over 500 meters of 59 knots. I will not be surprised if they increase their record into the 60 knot range during this record attempt.
Those of you that have been following this blog know that I’ve been giving Sailrocket the best chance of increasing the sailing speed record, as soon as they got their (earlier) control issues worked out. They’ve done that and it’s obvious! Early in this blog, I stated that stability was the key to high-speed sailing and Sailrocket has proven me out. It’s interesting that when you get a real certainty in an area, you start to wonder why it’s not obvious to others. But the truth is that it took some work on my part to gain that certainty, and not many others have had that opportunity. It takes some time to change people’s understanding of how things work, when a new idea comes along. Bernard Smith started that new idea with his book “The 40 Knot Sailboat”. Sailrocket has proven Smith right – but not just 40 knots, rather 60 knots and beyond!
What is the potential? I believe I stated that earlier and that it is simply a matter of fluid dynamics and structural engineering; fluid dynamics to design the most efficient craft possible (high-power at low-drag) and structural engineering to design the strongest, lightest craft possible. What speeds do I think are possible? I can’t say because I haven’t attempted to compute them. All along, the one thing I have known is that any speed that any sailing craft was able to achieve using weight for stability, (including Innovation, Hydroptere, kite-boarders, and windsurfers, etc.) could be easily beaten by a craft that was dynamically stable, this stability achieved by properly aligning the forces that drive the boat. Sailrocket, as conceived and executed by Paul Larsen, Malcolm Barnsley, and the whole VSR team, has demonstrated this to the Sailing world.
My own certainty of what the potential was came about in 1985 with my first successful model of what Bernard Smith called an “aero-hydrofoil”. A photo of that model is at the top of this blog page. I believe that a better term than aero-hydrofoil is a “force-aligned” craft, a term I’ve heard others use to describe this type of craft.
An interesting problem I encountered early on was that some sailors thought that “an inclined airfoil is inherently unstable”. I already knew from my own experience that that statement was false. I suspect that the flip of “Delta” (follow link “Sailien prototypes (early), Delta, etc” in the sidebar) may have started that false idea. Delta was derived from Smith’s “Monomaran”, a design that violated the concept of a force-aligned craft by putting the leeway resisting (and steering) foils on the lee side of the craft, under the corners of the airfoil. This is a guarantee of a flip -- if the craft ever gets powered up. While my craft looked quite similar in many respects, in function it was essentially the opposite; my steering and leeway resistance was positioned on the windward side of the craft and there was no leeway resistance elsewhere. This is the most important arrangement for a force-aligned craft that does not use down force for roll stability. Note that Trifoiler is a force-aligned craft, but it uses down force from the windward foil to achieve stability.
What’s next? While Sailrocket is a real sailing “rocket”, it is not a practical sailing craft. The next step to getting stable, high-speed sailboats available is to develop practical craft that will sail all points of sailing that a normal sailboat can sail. I actually did that with the 1985 model and with all the later full-sized prototypes. The only real problem has been low wind-speed performance, but this can be worked out without too much difficulty. Anyone interested in working on this contact me.
More drag for VSR2?
02 January 2012
I want to start by pointing out that the whole VSR2 team has done a stellar job and has demonstrated conclusively that the forces that drive a sailboat can be aligned for roll stability without using ballast and without using any down-force. (Trifoiler achieved roll stability by using down-force, but it added too much drag to get past the low 40 knots.)
Now some of you are going to protest and say "Bob, the force from the main foil (inclined keel, etc.) is pointing down on an angle." True, but the "up-force" on the airfoil and the "down-force" on the main foil are equal, opposite, and cancel out (in the plane viewed from fore or aft). There is no net down-force acting on the craft (if it's properly set-up).
I also want to point out that VSR1 had roll stability as well, however many of you may have been tricked by Paul's magnificent aerobatic show. Paul's "airs" were not due to the main airfoil's inclination but rather to a slight miscalculation in pitch control.
In looking over Paul's comment to my last post, I saw another area that appears to be causing un-needed drag. The top section of the main foil is set at a low inclination with the purpose of lifting the tail of the craft clear of the water. The purpose is correct (to get the aft plane out of the water and eliminate its drag) but a low angled foil at the surface is a problem. The problem is that anything we run at the surface generates waves and that causes drag. I've run into this problem with foils quite a bit.
I'd like to offer this as a solution: place the top (lifting) section of the main foil straight up, then angle the anti-drift foil off the bottom of the vertical section. The profile is up to the fluid dynamicist but the part near the bend should probably be cavitating. To avoid a deep foil, the top would need to be low aspect, and should be sized for low speed control (eliminating any supplementing rudder aft) it should taper to the bend where the anti-drift foil starts.
I've included a sketch showing the forces between the airfoil (blue line and arrow) and the upper (vertical) section of the main foil (green line and arrow). Note the resultant red arrow - that'll get the tail up.
I adjust my own craft (inclination of airfoil and hydrofoil) by which end goes up or down, until it's neutral.
My analysis of Sailrocket
18 December 2011
I copied a diagram of VSR2 (wing doesn’t show well) and added in the major force arrows that apply. Be aware that these arrows are not correct in terms of scale (length) and some of their locations are guesses, however I believe I’m correct enough for us to learn something about what VSR2 has been experiencing. Note that as I stated in an earlier post, all sailboats work in the same way, the only difference being the location and shape of the parts, and how those parts are controlled.
Here is the key to the force arrows:
Wt is the true wind
Wa is the apparent wind
Vb is the boat velocity
Fa is the airfoil force (lift)
Fh is the hydrofoil force (lift)
Fr is the resultant force (Fa plus Fh)
Da is the aerodynamic drag
Dw is the hydrodynamic drag
Dt is the total drag (Da plus Dw)
Observe that Fr and Dt are equal, in line, and opposed. This is the force relationship when the craft is in a steady forward motion (Vb). The craft will have neutral helm. If we change the positions or magnitude of the forces on the craft, the crafts motion will change and we can learn something about what changed by observing the motion change. This is what I will discuss, based only on what has been posted on VSR’s website.
If we rotate the wing (airfoil) clockwise, we see that Fa also rotates clockwise, this causes the intersection between Fa and Fh to shift to the left and Fr also shifts left. Fr and Dt are no longer in alignment and the craft will yaw clockwise (round up). This is the problem that VSR 1&2 both have, although VSR2 has better control of this. This yaw problem is an issue while sheeting in (start-up) or sheeting out (stopping). The solution is to swing the arm forward (the equivalent of rotating the hull and foil counter-clockwise) which keeps Fr aligned with Dt. VSR2 is set-up to do this, but Paul explained that it’s too difficult to do on-the-fly; this has resulted in the start-up procedure Paul has been using.
At speed, with neutral helm, Fr and DT are in alignment, but any wind shift or drag change will change their relationship. This shows up as a force on the rudder which is part of the data the team collects and analyses. Since I don’t have access to that data, I can only “see” the major changes that Paul describes on his blog.
One of these changes that Paul mentioned was with relation to the conventional foil in which he stated that VSR2 did a big yaw away to leeward. He goes on to say that he thought something let go and aborted the run. He said that he thought the main foil ventilated causing the yaw. Let’s look at the diagram and see if we can learn anything about this.
If the conventional foil ventilates, one or both of these things will happen: the foil will lose lift and it will likely have a drag increase (the L/D ratio will get worse). Looking at the diagram, we see that if the main foil loses lift (Fh) it will get overpowered by the wing (Fa) and the foil will drift to leeward a bit. That drift will be countered by the forward positioned rudder and VSR2 should yaw to windward. Note that VSR1 had the rudder aft so under the same conditions it would have yawed to leeward. Rudder location in this case makes the difference. If the foil ventilated and drag increased, (Dw at the main foil) we see that Dt would have shifted to the right (the balance between Da and Dw shifted) Fr and Dt are now unbalanced and will cause the craft to yaw to windward.
I see no way VSR2 would yaw to leeward if the main foil ventilated (if anyone knows, feel free to correct me). Note that if the wind drag increased, the increase at Da would have caused the craft to yaw to leeward, but we have no data to suggest that happened. From all the above, I suspect that the drag on the main foil might have decreased (which would cause a yaw to leeward) and I wonder what would have happened if Paul had kept going.
“Hey Bob, the drag should go up with an increase in speed – you’re nuts!” Well Paul gave us a clue that could account for the drag decreasing. In the comments for Paul’s blog post of 9 Dec 11, Paul gave a reply to “Armchair Comments”. Paul: “The upper section of the foil is more responsible for generating vertical lift. If it generates too much then the back of the boat rises until we reach the transition (radius) of the foil where the vertical component lessens. If we go too far then only the bottom section is left in and that is angled so it is pulling down more than the rig is lifting i.e. we will have net negative lift and be pulled back down to the transition. The boat should seek balance around this transition.”
Paul’s quote above sounds like the main foil angle is set wrong. The wing and main foil should ideally be set parallel and positioned such that the forces through the centers of effort are directly aligned and in plane. That will cause those forces to be equal and opposite in that plane (viewed from fore or aft) and there will be no net up or down force (those forces cancel out). If the main foil is over angled (as the above quote suggests) and is producing negative lift, then VSR2 is producing needless drag as the upper section of the foil produces lift and the lower section produces “negative lift”. This drag will increase with the velocity and put VSR2 up against the wall.
Now the times when the conventional foil bore away (which I suggested might mean less drag) I can account for if there was flex in that foil with the increased load caused by the speed increase. If the foil flexed, it would have moved to a more parallel position relative to the wing and the “negative lift” would have decreased and the drag from the upper and lower sections of the foil fighting each other would have decreased.
Sailien yaws when it lifts onto its foils and the direction it yaws is dependent on which side is lifting up (reducing the drag on that side). Ride height should only be controlled by the upper section of VSR2’s main foil in my opinion.
60 is within reach, what’s next?
23 October 2011
I have been watching Sailrocket’s progress with great interest and there’s no question they have a winner. I fully expect to see them reach 60kt in the near future. Sailrocket has now demonstrated what I first learned with my models and again with my full-sized prototypes, that if you get the forces that act on a sailboat in proper alignment, the only limit to your speed is efficiency (for the techies, that’s L/D) and, of course, the conditions you’re sailing in (wind strength, sea state, etc.).
There have been some interesting comments on Paul’s blog including one asking what you call the craft when it’s only contacting the surface at two points (fore plane and aft foil). Paul’s reply was tops -- that’s it’s an aero-hydrofoil in acknowledgement to Bernard Smith. I titled my patent the same way, to show where my own craft derived from.
I’d like to expand on craft stability with reference to the number of points of contact to the surface. If we look at a child’s wagon we note four wheels that support it stably, whether it’s moving or not. Compare the wagon to a catamaran with the two bows and two sterns being the main points of stability, like the wagon wheels. A tricycle is a bit less stable than a wagon, but still quite stable while at rest or in motion. Compare the trike to a proa in which the bow and stern of the proa form two points and the ama, the third. A bicycle, with two points of contact is totally unstable unless in motion and even then balance has to be maintained by active control, however, if we put “trainer wheels” on the bike, it will be stable at rest or in motion as once again we have four points of contact. A mono-hull and a trimaran could both be compared to a bike with trainer wheels (although I risk the ire of mono or tri sailors for this – no belittlement intended). The monohull uses a weighted keel to add stability to a relatively narrow beam, while the tri spaces the amas fairly widely. There is one more possibility to consider, a unicycle (!) as we know this is unstable under all conditions and it takes great balance and skill to ride one successfully. There are a few sail-craft designs aimed at one point of contact. We can’t go below one point of contact, because as soon as we disconnect from the water, we loose all power (check my earlier posts explaining how a sailboat works using the “squeeze” between the wind and the water).
Here are two sites of craft aimed at one point of contact with the water; I believe there are others but I know of none that are active at this time.
There is really no reason one point of contact can’t be quite successful, however, it will take constant, active control (whether manual or automatic) to maintain stability.