I feel the need...
by John Curnow, Editor, Sail-World AUS 28 Dec 2020 09:00 UTC
Q.E.D. really - static draft is significant, but righting arm, well © Vlad Murnikov
It would have to be one of the most oft quoted lines from the movies, and finishes with... 'The need for speed!' (As well as that big high five.) Now it is no stretch to discover that we have used an aviation-based theme here. It is a direct and consequential result of the chase for higher numbers, whether that is plain boat speed, or 24-hour nautical mile disposal, because the aero package becomes more and more important at these elevated speeds.
Of course, the faster you go, the more the water takes on the form of concrete. That can be nice to roll over with the cushioning afforded by tyres and suspension, but a bit ugly either smacking straight into it from above, or appearing more like a distraught icebreaker when trying in vain to go through an ice shelf, only to get locked in for the season.
Now in addition to having these two main media (air and water) to keep front and centre in our minds, we also need to consider hull form. By and large, the faster we wanted to go (and not forgetting land yachts and the spectacular things they do), firstly it meant cats, then later on tris. Primarily this was due to righting arm, which is one of the reasons Comanche is effectively a cat with one bow and the tramp 'fiiled in', as such.
The AC75 represents the first, high-level attempt at seeing if the mono can indeed 'swing' favour back to itself as the preferred platform for all operations over Mach One. So in addition to media, then hull form, we now need to add mass, leverage, and momentum into our consideration set, as we progress deeper into this discussion, which our Managing Editor, Mark Jardine, kindly opened for us in, To foil or not to foil? That is the question.
Ungainly could be used as one adjective for the AC75, but then any new advancement often gets slapped with this title. By way of example, the low hung, preposterously proportioned front wing on an F1 car is not as elegant as that of her vintage counterparts, but it sure is effective! Yet for me, I am still struggling with the fact that you have 1175kg on one side, which is exactly the same as what's hanging on the other side. Where's the advantage? As the Germans would say - Macht nichts.
Accordingly then, is there a better way? Right oh. Disclaimer. I am not a graduate of the University of Southampton's famed school of Naval Architecture, but I am not the only one posing theorems. In the case of Vlad Murnikov, he brings a wealth of knowledge and experience, as well as countless designs, going all the way back to the magnificent, Fazisi.
Straight off the bat, Vlad showed me a concept for a dart shaped vessel, feathers and all. Most notably, it had a fully rotating keel ring around the tube part of the vessel, which allowed the keel ballast at the end of the fin to fly parallel to the water's surface.
So at this point, think of an old swing bridge and the planetary gears that used to drive them. There were not huge electricity supplies or motors back in those days, so this was an efficient way to move a large mass decisively, and swiftly in an overall sense. Importantly for us, you could forget a mere 40 degrees of cant, here was something that could go through 90 degrees, or more, from the vessel's static position.
Additionally, it heeled the boat to windward, just like a Moth or Waszp, thereby gaining lift from the wind pushing up into the sails. This added lift meant you could have smaller hydrofoils, and dragging a scalpel around, rather than a cleaver had to mean you had less chance of hitting something, simply under the laws of probability alone!
Alas, here we were ticking off a whole lot of the wish list we set up earlier in the piece in just about one whole go. Blasphemy I hear you say? Well SpeedDream worked, and if not for political issues in the Ukraine during the last decade, then Yandex may have had more funding available, and SpeedDream may be the current holder of the Jules Verne Trophy.
Murnikov said, "Yes, my initial idea back in 2008/9 was for a monohull to compete for the Jules Verne Trophy. The America's Cup was just switching to multihulls - they were exciting, fast and modern. I wanted to do fast sailing on a monohull. Simply put, the whole thing was torn down by a lot of people back then - they thought it was heresy..."
"When flying, the righting moment = displacement by righting arm. Increase the righting arm, and voila. We got to 40 degrees easily enough with the monohulls, and so the Volvo Ocean 70 ended up being able to attain similar speeds, of say 40 knots, as compared with Banque Populaire V. The difference is that a multi goes through the waves better, maintaining its high speed, and a mono stops when hitting them (sic) per se. But multies do capsize, and monos are much safer. My goal was to combine advantages of both, while trying to eliminate their respective flaws."
Murnikov added, "Cant to 90 degrees and now the central foil is to leeward, and you have the same or better righting moment as the multihull. This latest generation of IMOCA boats are certainly are starting to look like my SpeedDream concept, and not just because of their foils, either. Their hulls are definitely slender, smaller in volume than their predecessors, which reduces resistance when hitting the water after a splash-down."
"I am positive that a 90 degree cant will be 20 to 25% faster again", said Murnikov. Sadly for us, and as mentioned, the loss of the sponsor put paid to living proof. "The foil sticking out of boat has increased, but the boats are much bigger than the foil, and there will always be a nexus point of load, right atop the foil."
"Historically, the Vendée can loose 60-70% of the fleet, and more often than not it's 50%. It is a race of attrition. The problem is one person on board, and being on autopilot. When doing 30-35 knots, especially at night, there's simply not much you can do. The increase in ocean debris is another issue, and certainly the Vendée highlights our ocean of garbage, but you can't hit something at 30 knots, and not expect something to break."
"The Vendée is now a box rule for the IMOCAs, and no longer Open. Lightness is great, but nothing will help when there is a collision. Kito de Pavant on Bastide Otio and the Sperm Whale shows what happens to the entire keel box, but man made waste (and containers) are far more of an issue."
A patent was granted for Murnikov's 'planetary' keel, which was also regenerative, and stored power from lowering, so as to make lifting even easier. The sails aided lift, which meant you foiled on both hydro and aero surfaces, which in turn meant you rode the sea state much easier. Consequently, you thereby needed a smaller hydrofoil. SpeedDream's sponsor, Yandex, is effectively a Google type organisation, and was going to build the control mechanisms to keep the keel parallel at all times, thereby ensuring maximum righting arm was maintained.
"A mono can be as fast as a multi. There is an issue of stability with the AC75. Philosophically, wings are meant to be light, not lead. Moving ballast like that means there is no stability at slow speed. You cannot trim the sails for speed. Stability under way is from the leeward foil, due to equal weight on other side. The ballast is huge in the foils, hence they suffer in the light air. If they had been like SpeedDream, then they would have been 1.5 tonnes lighter to begin with."
"We moved the keel on SpeedDream from side to side in just eight seconds, and who knows, with more money and time we may have been able to complete the foiling tack. As it was, unfortunately we only ever sailed in light airs, but were able to get eight knots SOG from six knots TWS. That was eight years ago - and that's eons in modern times..."
Read all of that? Good. There'll be a test tomorrow. No seriously, all you have to do is simply ponder this... What will the future bring?
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John Curnow
Editor, Sail-World AUS