For the ones that never heard about it is just a wing that goes perpendicularly to the boat hull, near the surface, on the opposite side of the wind and that like an airplane wing provides lift creating RM and pushing the boat up, preventing it to heel. Its efficiency increases with speed. Look at this movie and you will understand how it works:
Recently there have been a lot of interest about it, since 15 October, when it was decided that contrary to the masts and keels, the appendices would remain free on the IMOCA class (Open 60's), with the already existent limitation of a maximum of 5 movable ones. There are several teams considering using DSS on their boats and even some interesting designs:
Hugh Welbourn, the system inventor and developer is working with several teams and even if for me the limitation of the 5 foils (two rudders, a keel and two daggerboards) make the utilization of the system complicated, he presents several solutions. Eventually there are two more that it seems not to have been considered: With a narrower boat the utilization of a single deep rudder that would allow an independent DSS system or a movable rudder, from one side of the boat to another, that would make possible the actual beamy configuration and again an independent DSS system.
But what have been studied by now is a configuration that maintaining the two rudders as they are, modifying the movable foils that assume a double role: Given grip to the boat upwind and creating lift. The drawing makes sense but the foil could not be completely raised out of the water and, as I see it, will create drag on light wind sailing. I am very curious and hoping any of the new boats will go for that, to see the real system potential and if the advantages will be superior to the disadvantages.
Another disadvantage, that has nothing to do with performance, but will be a practical inconvenient, is the impossibility to put the boat along a quay or pontoon. The boat can not go alongside but stay at some distance, with the foil hitting the quay. It will need some BIG fenders LOL.
Very interesting stuff anyway!
Hugh Welbourn and Dynamic Stability Systems Founder Gordon Kay says about all this:
"Dynamic Stability Systems welcomes this week’s decision by IMOCA to place no further restrictions on its class rule. This permits both the six new IMOCA 60s currently under construction, as well as the existing fleet, to be fitted with the lateral lifting foils which DSS has spent the last decade pioneering. ...
“These foils will allow IMOCA 60s to remain cutting edge as well as providing a performance enhancement every bit as significant as canting keels, which IMOCA pioneered during the 1990s,” ...
..Fitting DSS to a typical IMOCA 60 is complicated by the class rules which restrict boats to a maximum of five movable appendages – typically two rudders, a canting keel and two daggerboards.
The daggerboards are necessary to prevent leeway when the keel is canted, but on recent IMOCA 60s they have had a dual function as by being inclined in the hull is such a way that they are angled (ie off vertical) as they pass through the water, they also produce upwards lift. This lift helps reduce hull drag, but – most significantly – as it does not operate to leeward of the hull, it lacks the same lever arm and, in turn, the massive contribution to righting moment of the DSS foil. So while present generation IMOCA 60 boards make little contribution to righting moment, for their new boats teams have been investigating the use of more efficient L-shaped foils. With these one side of the foil prevents leeway while the other creates vertical lift down to leeward, in turn providing a massive boost to righting moment.
Teams have been looking at principally two configurations for these ‘DSS L-foils’:
a) Tip up: This is similar to a conventional daggerboard only its main shaft is vertical in the water when the boat is heeled, while its tip is effectively a DSS foil, close to horizontal in the water when the boat is heeled, to provide vertical lift.
b) Tip down: This is closer to the standard DSS arrangement where the main shaft of the foil protrudes horizontally through the bottom of the topsides providing vertical lift to leeward, while the downward-pointing tip of the board prevents leeway.
Welbourn, who is currently working with IMOCA teams on evolving this technology, says that while DSS is in the process of being accepted by the Class (just as canting keels were in the 1990s), the first designs to incorporate the DSS L-foils will be ‘middle of the road’ options, still retaining most of the familiar IMOCA 60 features. Thus rather than having the maximum permitted beam of 5.85m, he believes that new DSS L-foil equipped IMOCA 60s will end up closer to 4.8-5.2m....
According to Hugh Welbourn, an IMOCA 60 that relied even more on its DSS foil for righting moment would be an entirely different animal but unlike most innovations could represent further cost savings for the Class. The canting keel – along with all its added weight and complexity – could be dispensed with in favour of a simpler fixed keel and as a result there would be no need for additional daggerboards to prevent leeway as the keel foil could provide this (as it does on most yachts). Windward performance could be enhanced by fitting a trim tab to the keel, which is permitted for fixed keels under the present IMOCA rule. This would also allow conventional, straight lateral DSS foils to be fitted, which would be more efficient as their sole functions would be to provide vertical lift and increase righting moment.
Added reliance on the DSS foil would also result in less need for form stability derived from a beamy hull shape and Welbourn envisages the maximum beam of the ‘Ultimate’ DSS IMOCA 60 could be as small as 4.2m – at present the beam constraint is the shroud base required for the newly introduced one design mast, which has a specified size and weight.
A pure-DSS hull shape would also not require the fat bow that features in many modern offshore race boat designs to prevent nose diving when sailing downwind. “When you start supporting a lot of the boat’s displacement on the foil rather than the hull, what you need is something that penetrates waves very nicely at high speed, not a big fat bow. A slimmer type of boat does that,” states Welbourn.
The end result would weigh approximately 6 tonnes, almost two tonnes less than the present lightest IMOCA 60s. And once again, a substantially narrower and lighter boat, with a fixed, rather than a canting, keel and with straight foils, as opposed to L-shaped ones, can all result in a less expensive boat...
DSS foils or L-foils can also ‘turbo’ the performance of older generation IMOCA 60s. Retrofitting this to an existing boat would cost in the order of £50,000 maintains Welbourn. However this represents good value given that his simulations demonstrate they could take as much as five days off a round the world course compared to the same boat without the new foils.
Welbourn concludes: “Ultimately DSS is a way of producing more sea-kindly and safer boats, which are substantially faster for a negligible increase in cost and potentially with a reduction in cost. Almost all the daggerboards ever fitted to IMOCA 60s provide some degree of vertical lift depending upon their inclination in the boat. DSS foils are simply inclined much more and you get a lot more out of them.”
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