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Old 09-29-2011
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Some more information about the DSS, a system that increases stability dynamically trough the lift provided by a lateral foil. This is taken from an interview made to Hugh Welbourn by Harken that is also a partner in the system development:

Harken : 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!


Harken : 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!


Harkeen : 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.

Harken : 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.

Harken : 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.

Harken : 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.


Harken : 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.

Harken: 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.
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