# Dynamic Stability System

Discussion in 'Hydrodynamics and Aerodynamics' started by willfox, Oct 1, 2011.

1. Joined: Oct 2008
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### willfoxJunior Member

I was recently thinking about how this system works?

Is the curved foil projected into the water on the leward side of the boat producing lift normal to the top surface of the foil. This then adds righting moment to the vessel allowing sail area to be held for longer. It is not the intention for it to produce lift in the plane of the keel therefore adding Keel side force.

I find this very interesting and was thinking about seeing the effects if I added this to my own primative VPP excel spreadsheet. Assuming the assumption I have made about the application of the system. How would you tackle this problem do you think?

I assume any drag that the added foil creates would be added to the resistance of the vessel using the ITTC calculations as per rudder, hull and fin. The sails would then need to compenste for this by being bigger or more efficient to create more drive.

The foil will obviously increase the righting moment but how would you tackle this increase? Would you simply add the lift created multiplied by a lever? If so, where eould you take this lever from? Would this be from the CL of the vessel or do you think it should be the distance from the center of lift generation of the foil to the perpendicular intersection of BM?

Once this increase has been found giving the new RM, it will then obviously be an iterative process seeing the optimum extent of foil being used in different conditions.

Has anyone tried writing this spread sheet?

2. Joined: May 2009
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Location: Cocoa, Florida

Dss

Why don't you try writing directly to Hugh Welbourn at DSS? He's a good guy and answers fairly quickly.
I would think that one of the hardest things to calculate on a DSS system is the L/D ratio because of the proximity of the foil to the surface and the variability of that with heel. Also, whether or not the hull is a planing hull will be a big factor. DSS does not work on all hulls. There are several threads including comments by Welbourn under "sailboats" on this forum. The latest is the Quant 28 thread( http://www.boatdesign.net/forums/sailboats/quant-28-foil-assist-keelboat-dss-38421.html ). You can e-mail me for Welbourns' e-mail address or you can find it on the DSS site.
The righting arm for the DSS segment of righting moment would be the distance from the center of lift of the properly immersed foil to the heeled CB of the boat.
Good Luck!

3. Joined: Oct 2008
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Location: southampton

Thanks Doug,