How effective is DSS?

sailorman44

Member
281
71
CT/FL
I was checking out Thursdays KWRW highlights on youtube when I came across this video of testing two DSS Infinity 36s side by side. I have been following the DSS concept for about 25 years, ever since a young engineer on my crew, Nick Shada, showed me one of his designs. It included a horizontal lifting foil that would slide from side to side to provide righting moment..

There has been a lot of discussion on Sailing Anarchy about DSS, about how effective it is. Lots of questions but not much in the way of answers. So here is an opportunity to get a definitive answer. A side by side test of two identical boats, one boat using DSS and one boat not. Except this is not what is done. Both boats use DSS upwind and downwind. WTF? What does that prove?


www.youtube.com/watch?v=DRMhvR0nOAE
 

Ease the sheet.

ignoring stupid people is easy
19,938
2,161
It proves that different setups are not want the ip owner wants you to see. Or your google skills need improvement.

 

Moonduster

Super Anarchist
4,823
230
The practical problems are two fold:

  1. Nearly impossible to keep the foil in the water in open ocean conditions as there's too much wave action when there's sufficient wind for a boat to go fast enough to derive any benefit.
  2. Rating penalties exceed performance benefits in almost all conditions.
Looking for line honors in a flat water venue? Willing to screw up your boat's interior to do so? Content with complicated mechanisms that are prone to failure? Willing to pay a substantial royalty to avoid lawsuits? Then DSS is for you.

 

fastyacht

Super Anarchist
12,928
2,596
When I first developed and demonstrated what is now called DSS on Randy's 5o5 in 1974, it was clear that while it certainly worked to some degree, its not really the right way to do it.

Lifting foils that are at least one chord length under water generate a lift to drag of about 20:1. Planing hulls and supercavitating foils are about 10:1. High performance multihulls at high speed are about 12:1. Since DSS is an uncontrolled foil, it does not stay at its optimal depth, but rides up to the surface, and loses all its advantage over a planing hull.

So DSS is basically the same as having a little short wide planing surface to leeward. Better than a leadmine, but worse than a multihull. Basically, a waste of time.

Now if one really had a functioning hydrofoil, one that maintained its depth, then we would see Moth like speed increases.

But DSS is not, so we see boats with weird handling problems as this foil moves suddenly from good lift to drag to generating drag way to leeward.

That is why I stopped fooling around with the concept. It seemed like a good idea that is not supportd well by experiment. I mean, it could be worse, but its very far from how one should really do hydrofoils. Sort of like thinking a yawl rig is a good idea, when you really want a multi slotted wing mast.
If you saw this DSS in 1974, then why is there patent protection on it?

I don't understand the patent office any longer. Seems like they hand out patents like candy.

 

Doug Lord

Super Anarchist
11,483
21
Cocoa Beach, FL
When I first developed and demonstrated what is now called DSS on Randy's 5o5 in 1974, it was clear that while it certainly worked to some degree, its not really the right way to do it.

Lifting foils that are at least one chord length under water generate a lift to drag of about 20:1. Planing hulls and supercavitating foils are about 10:1. High performance multihulls at high speed are about 12:1. Since DSS is an uncontrolled foil, it does not stay at its optimal depth, but rides up to the surface, and loses all its advantage over a planing hull.

So DSS is basically the same as having a little short wide planing surface to leeward. Better than a leadmine, but worse than a multihull. Basically, a waste of time.

Now if one really had a functioning hydrofoil, one that maintained its depth, then we would see Moth like speed increases.

But DSS is not, so we see boats with weird handling problems as this foil moves suddenly from good lift to drag to generating drag way to leeward.

That is why I stopped fooling around with the concept. It seemed like a good idea that is not supportd well by experiment. I mean, it could be worse, but its very far from how one should really do hydrofoils. Sort of like thinking a yawl rig is a good idea, when you really want a multi slotted wing mast.
That's a grossly uninformed description of DSS.........

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jonas a

Super Anarchist
The dss foils seems to add about 12 feet(?) to the width on the Quant when in full foiling mode. It certainly would be interesting to see a similar construction on a 100 footer :)

 

bgytr

Super Anarchist
4,994
616
Doug Lord's ideal sailboat..

4 hulls, 19 foils, 8 sails.

Whoopie what fun!

 
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Doug Lord

Super Anarchist
11,483
21
Cocoa Beach, FL
Unfortunately, this guy says the Moth is the only foiling monofoiler because the Q 23 has "catamaran architecture"!! That is so nuts- the very first tunnel hulled scow was Dominion in 1898-followed in 1962 or 63 by the tunnel hulled M20 scow. The Q 23 is a 23' scow with tunnel hulled very forward sections. It is without a doubt the first foiling keelboat scow! And sure as hell is a monohull foiler.

http://m20-scow.com/history.html

"The M-20 must be considered an advanced scow design and will remain so for years to come............ The tunneled hull of the M-20 is her most unique feature and provides increased stability and structural stiffness."

AND

The I20 was "born" from the M20-both have tunnel hulls:
http://scowsailing.com/about/

"The I-20 is the most recent scow class, adapted from the tunnel-hulled M-20 scow designed in 1963 by Harry and Buddy Melges."




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