Design for DSS-Foil Assist for Keelboats

You have to watch the video. Towards the very end, on a downwind course with the asym spinnaker up they are indeed porpoising badly. On a downwind course, that foil should be able to be pulled in entirely. Lack of buoyancy in that fine bow may be more guilty than the foils though.

It looks like they are choosing to keep the foils half extended on each side for the whole video. I wonder if they are even movable at this point.

A more instructive video of the concept would be some video of a close hauled beat, where the alleged benefits of the system would be most pronounced.

 

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Porposing!? No thats called "going over waves"... No way that is porposing which would be a similar movement in the absence of waves!
The "alleged benefits" of the system are clear cut on any point of sail where the foil is active according to those who have sailed a DSS equipped boat.

Quant 28:
http://www.youtube.com/watch?feature=player_embedded&v=DwDGKghV8fU

 

Looks straight and smooth; of course that is almost flat water. Couple more here, in the second one the boat is handling chop and crossing the wake of the powerboat with about the amount of bucking you would expect -

http://www.youtube.com/watch?v=A8A9GIKyqcI

http://www.youtube.com/watch?v=D-ogozAZ24I&feature=related

 

From Hugh Welbourn on the Quant 28 and DSS:

 

Dss

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Thanks for the video's ,AK I loved the one with "Brace, Brace, Brace" passing the multihulls!

 

I did.
I did see smooth and steady sailing.
the bow is a little depressed at times, what is no surprise at all, with all the extra driving force made possible by extra righting moment.

 

Dss

An interesting thing about DSS is that it appears to be applicable to many(but not all) designs from about 10'(mostly downwind) to virtually unlimited. It's going to be interesting to follow developments as time goes by. One thing I'd like to experiment with, at some point, is an application on small planing hulls that will allow the angle of the incidence of the foil to be changed while at the same time giving excellent access to the foil and incorporating a control line system right at the cockpit.

Here is a rough sketch of the potential system:
click on image-

 

That boat is NOT porpoising, riding through waves, yes, but not porpoising - you're reading/seeing what you want to negatively believe ... but it is not so. Another point': all this talk of negative attack when the bow goes down is also fantasy talk: have you ever sailed on any type of foil boat? I would say no ... because even when the bow goes down, you don't get a negative effect operating on the foils (because of rotational movement in waves) - and I'm talking about fixed foils at say, 3 degrees angle of attack, not movable versions - the foils continue to do there job of lifting even when at acute boat angles in waves.
Sorry cobras, the DSS system works and will continue to be refined. I'm waiting to when they discard the bulb keel entirely (maybe have optional water ballast) and rely entirely on the foil. Then you'll start seeing real multihull-like performance.

 

Many of the comments to date are objective - and objectivity mean you look at all aspects of design - not just the superlative. Otherwise we might be better to label this forum BoatHype.net. And your label of anyone presenting other points of view as "cobras" is questionable.

DSS has positive aspects. High density lead bulb keels have positive aspects. Both have negative aspects. Water ballast has limited application to augmenting righting moment - but it does not provide the simple, reliable and failsafe benefits of keel bulbs in recovering a knocked-down hull.

This forum is of very limited value if all the positions discussed and presented are in unquestioned support of whatever the current flavour of the week technology.

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CutOnce

 

Dss

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On the other hand, a few of the comments were not objective or technical in nature but plain rude and/or uninformed: "goofy design" and assesments of DSS based entirely on a video described as showing a boat "porposing" implying that it was doing so(actually it was going over waves,not porposing!) because of DSS. Comments that far from reality accomplish nothing and Gary was right to point it out.
It's important to understand that a boat that gets a heavy gust and gets knocked down will be much quicker to get back on her feet with DSS because the rotation of the boat increases the angle of attack of the foil almost instantly. This is not speculation but rather an observed characteristic of the use of the foil by those that have sailed it and designed it.
Some of the comments seem to ignore the fact that DSS equipped boats(so far) all have lead keels as well! DSS boats equipped with lead keels obviously have two times the benefits of either separately, right?!
It seems to me to criticize this technology you would need to have first person accounts of the failure of the technology by someone sailing it as opposed to uninformed speculation and/or some technical basis for saying that the foil doesn't work backed up in some way that forcefully illustrates the point.
Pure uninformed speculation doesn't cut it in the face of many first person accounts of the foil working well, as well as videos and race results showing the same thing.

 

Cutone (Bill?) is correct that all side of an argument are needed.

If someone thinks it is porpoising then they have the right to express their opinion.

Gary and several previous posters are also correct that the boat is not porpoising.

 

I re-read all the posts on this thread I can't see where anyone posting has enough knowledge of the DSS system to make objective statements about it's performance or benefits. We're all making subjective statements based on what little data is available.

 

That is true, but there are DSS boats that are demonstrably and visibly working for us observe and discuss in order to try to understand the theory and practice.

The DSS in principle moves part of the lift/buoyancy of the hull outboard to leeward. From a RM point of view this is functionally equivalent to moving the weight of the crew outboard to windward by hiking out. Whatever righting moment the DSS provides can be treated as additional to permit increase sail power, traded for reduced crew hiking, or traded for -perhaps a narrower hull for reduced wetted surface. Maybe other options too.

Reducing the need for crew hiking would allow either a smaller crew (longer range with given stores?) or permit the crew to focus more on active sailing. One would like to say that bringing the crew back inboard again is an opportuity for a safety gain, but if performance is driving the design the extra RM will go into a bigger rig.

So we can have improved performance from a given size boat, or less demand on crew and skipper in the interests of more range/more comfort/larger boat-to-crew ratio/ or whatever.

Sorry to ramble - not yet sure where we are supposed to be going in this thread . . .

 

The problem with the observation to date is that what we are seeing is limited to what people want us to see.

No one has even mentioned the elephant in the room. The point of sail where you need the most righting moment is when you are going hardest to windward. This is the slowest point of sail. Given that DSS is dependant on flow across the DSS foil to generate lift, this is the least effective point of sail for the DSS foil, as it is the slowest. And transitions from tack to tack are worse - as they are slower. Given that crew will be busy shuttling the DSS foil from side to side during tacks, I don't suppose tacking will be faster than a non-DSS boat and more speed will be carried throughout. And I sure hope no one blows a tack and gets into irons - that DSS foil is not going to be a help going backward.

The faster the point of sail, the more effective DSS becomes - so videos of broad reaching are showing the technology to it's best advantage.

Every design element is a compromise of benefits and liabilities, and DSS is no different. It's designers and promoters have investors to answer to. I would not expect someone hoping for financial success from a technology to present it's warts and promote it's downsides. This isn't a negative comment, it is a statement of business reality and human nature.

As I tried to outline earlier, the conditions in which sailing occurs contains far more variables than most other "machine-borne" speed sports. What benefits speed on a broad reach may have less effect going upwind. What optimises planing may have a negative effect when in displacement mode. Ultra light weight that helps planing performance may make punching through steep confused chop impossible. Each point of sail effectively is best handled by a different boat design with different choices of technologies. There is no one size fits all perfect solution.

Although DSS appears on the surface to be a great technology, I have to agree with Sean9c in the observation that no one here has enough evidence to draw conclusions. It sure looks great in the promotional material published to date, but Youtube always presents all the facts, don't they?

I'm pretty certain this post will be immediately followed by a damning response (as is every post I make). I'm not disparaging DSS' designers, the effectiveness of the technology in optimal conditions or making judgements - I'm just trying to extrapolate the whole picture from limited (and carefully chosen) evidence.

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CutOnce

 

Dss

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From Post 34 ,Hugh Welbourn:

#2
Upwind - well the thing here is to match the wing parameters to the boat so that the net result - in steady state - is just slightly in your favour. So RM gain outweighs the drag cost.
However, what we then find is that as soon as there's any chop or seaway to move the boat around, then the damped motion in all axes makes a significant improvement that is seen on the VMG - even when you only seem to be sailing maybe a tenth quicker than you might. Now that comes from logged data and was a bit of ( pleasant! ) surprise to me until I figured out the dynamics of what was going on.
And don't forget, you don't need to use the wing at all until you are running out of natural RM, so no draaaag....until its starts to work and then the balance is in the your favour.

Its all a pretty finely balanced configuration but we've got a good handle on thing now from all the r&d and sailing and how to configure the different types of boat to work.