The Dynamic Stability System (DSS) is the brainchild of Hugh Welbourn and Gordon Kay. It is the result of over 5 years of research and development and delivers revolutionary innovation to the world of sailing. The DSS increases the stability of the yacht (and therefore the speed) without the risks associated with canting keels. Instead of having a canting keel weighing down the windward side of the boat, the DSS uses a retractable foil to generate stability and progressive dynamic lift on the boat's leeward side. The Dynamic Stability System can be used on both racing and cruising yachts in a range of sizes.
Harken: What inspired this unique concept?
Hugh Welbourn: I had been thinking about how to make boats lighter and faster. In effect I was looking at the canting keels and the benefits and downsides of those systems that led me to reverse my thinking and make the obvious connection.
However, there were many potential downsides, so the idea sat on the back burner for a couple of years, but never really went away. Some other work I was doing in the GBR America' Cup campaign made me rethink some aspects of the idea. Then after the BOLS Super Maxi program, we began the R & D process in earnest.
How will the DSS be secured and watertight within the hull? How does this affect the structural stability of the hull?
HW: With individual swing-out foils the housing is easy to arrange so the major hull structure is on the upper side of the casing. Potential damage from impact of the foil at speed with objects in the water is dealt with by controlled swing-back of the foil.
With the through-hull foil, the casing is the watertight component. Experience with how daggerboards in multihulls and canting keel monohulls respond to impacts is extremely useful in understanding and dealing with the loads on the hull and casing. However, to protect the hull and casing integrity, ultimate over-stress will result in the controlled failure of the foil itself.
In both scenarios, arrangement of the casing will be through the normal side longitudinals/bunk tops so the hull exit itself is further contained within a watertight area.
How does the foil move from side-to-side? Does the system differ in different sized boats?
HW: A simple rope hauler system is more than adequate on boats to 40 ft with plain sliding contact bearing areas. Above that we move into Harken developed roller bearings for the contact areas but still use with rope haulers.
At the top end Harken roller bearings are the favored solution.
Is the DSS something that would be adjusted depending on the TWA, similar to the way one would adjust a centerboard? ?
HW: No. The system is simple in that either the foil is fully deployed or it is not required.
Can you explain what accounts for the dramatic increase in upwind VMG when the wind speed increases from 10-15 knots? Presumably, that is when the boat becomes fully powered up, but why is there such a dramatic increase in stability?
HW: The improvements to upwind VMG are from two separate effects of the deployed foil. the added stability on a correctly configured system gives the boat more power to carry sail and thus speed. This outweighs the cost of additional drag.
One can also see that you can achieve a degree of stability at a lesser angle of heel with the foil deployed, so the boat is being sailed in a more effective trim for speed.
Secondly, the dynamic damping of the boat in both pitch and roll significantly improves the rig efficiency.
This also reduces the amount of corrections required by the helmsman or autopilot – again, less drag and greatly reduced power requirements.
What accounts for the greater performance increase downwind as opposed to upwind?
HW: The lift of a foil is proportional to the square of the velocity, so as soon as the boat is moving faster then the foil effects rapidly mount up. So the added stability comes into play, and also the reduced displacement of the hull as seen by the water further reduces drag.
It appears as though the gains in speed/lift outweigh the added drag of this appendage in most wind conditions, what happens in very light air?
HW: In light airs, then the foil is fully retracted, so there are no negative effects, just benefits from having an overall lighter and more efficient hull/sail plan.
Is this concept tailored more towards racing or cruising yachts and why?
HW: It has been one of the happy discoveries that the benefits of the system are related to the boat type.
For the racing yacht, more speed, lighter and safer boats with more manageable rigs all add up to a major step forward.
For the cruising yacht, any added speed is never unwelcome. But the far more comfortable motion and reduced heel angles, easier control under autopilot, and totally fail-safe nature of the system are the more important features.
On safety – it also dramatically eases recovery of a man overboard as he can get onto the foil, then stand up on it and regain the boat. Good fun for normal swimming off the boat too!
Do you think that this concept is applicable for inshore racing, or do you see it being used more in offshore scenarios?
HW: Both.The simplicity and ease of use of the system lends itself to all disciplines.
Inshore, faster, lighter boats you can control are just more fun. Offshore, the same applies!
On the plus side - unlike canting keels - there is no need for powered systems.
We are not trying to fully fly the boats and the system is designed to be dynamically stable and self-controlling in terms of overloads.
The cost overhead of the foil system is low in terms of both weight and money.
The potential released by the system to reduce the displacements of the boats then transfers into reduced sail plans, less ballast, and ultimately less cost.
Due to the application of DSS developed dynamic stability and with with this lighter approach, we can finally move into a highly desirable spiral of increasing performance.
Could this concept be applied to dinghies or non-ballasted boats?
HW: Yes. We have looked into a range of boats from dinghies up to 190’ to evaluate the physics of the problem and found that scale effects actually work in our favor at all sizes.
Do you feel this could replace the canting keel?
HW: Yes. The distinct shortage of canting keel boats being built other than Open 60s and Volvo 70s is an indication of a market voting with its feet.
The complications of cost, systems, weight overheads and above all the total loss scenario when canting keels fail have been seen to outweigh the benefits.
With DSS, the loss of the foil merely returns the boat to a normal configuration with its stability profile able to pass the relevant standard.
Is this a proprietary system and will other designers be allowed to use it?
HW: We have extensive patents pending in most countries, but we very much encourage further development with other designers and manufacturers on the basis of license fees for boats produced.
Is this a major additional expense?
HW: No. At the small boat end, this is very much a token fee and typically, in the medium and large yachts then it is only approximately equivalent to the cost of a mainsail.
Who is DSS?
HW: This company has been set up by HBW and GK with a small number of highly motivated investors. This has allowed four years of extensive R & D from radio controlled models through tank testing, culminating in the sailing development boat to take place.
Our partnerships, which have contributed significantly to the rapid development of the concepts and system, include Harken, Doyle Sails (NZ), and Pantaenius Insurance.
These companies reflect the confidence we have in developing and promoting this exciting development for yachts of all description.
Welbourn Design Group
Headed by Hugh Welbourn, The Welbourn Design group has been on the leading edge of innovation and yacht design for 30 years.
With its long history of involvement at the top end of yacht racing, the Welbourn Design office is recognized as one of the leading lights in foil development as well as performance optimization.
Links:
DSS Website
