Mini Ocean Racing Scow

[peterchech]

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Peter, the enormous lift provided by the board would reduce the required planing area as well.

Ah. Upwind though, wouldn't the lift of the board increase leeway as well? I mean, if the boat is heeled over, say 20 degrees, then that board would be creating lift at 20 degrees to lee no, so most of the lift would be pushing the boat up out of the water, but a significant amount would be pushing the boat away from the wind wouldn't it?

 

[Doug Lord]

Mini DSS

Ah. Upwind though, wouldn't the lift of the board increase leeway as well? I mean, if the boat is heeled over, say 20 degrees, then that board would be creating lift at 20 degrees to lee no, so most of the lift would be pushing the boat up out of the water, but a significant amount would be pushing the boat away from the wind wouldn't it?

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Peter, if you look at most DSS boards and the one on the Isotop, you'll notice that it is curved so the board will remain level at "X" amount of heel.
It wouldn't be a good idea to exceed the design angle of heel for very long because the board could do just what you say-develop a component of lift to leeward.

 

[ancient kayaker]

Comments:

A Bruce Foil compensates for wind force heeling automatically, no adjustment required, I have tried it out and it is very effective deployed to either leeward or windward, although it does exhibit more leeway. It's lift is always vertical. Additional drag is more than compensated by increased drive from the vertical rig IMHO.

The DSS presumably does the same job as a Bruce Foil. It looks to me like a DSS board must be adjusted on the go matching both speed and wind force in order to work, although it would allow the sailor to optimise heel angle for a particulal hull, but drive is then lost. I assume the board can be used only on the leeward side.

Both DSS and Bruce Foils must be retracted for mooring and marina life. I'm not sure DSS is an advance over the Bruce Foil.

Rebuttals welcome!

 

[Doug Lord]

Mini DSS

Comments:

A Bruce Foil compensates for wind force heeling automatically, no adjustment required, I have tried it out and it is very effective deployed to either leeward or windward, although it does exhibit more leeway. It's lift is always vertical. Additional drag is more than compensated by increased drive from the vertical rig IMHO.

The DSS presumably does the same job as a Bruce Foil. It looks to me like a DSS board must be adjusted on the go matching both speed and wind force in order to work, although it would allow the sailor to optimise heel angle for a particulal hull, but drive is then lost. I assume the board can be used only on the leeward side.

Both DSS and Bruce Foils must be retracted for mooring and marina life. I'm not sure DSS is an advance over the Bruce Foil.

Rebuttals welcome!

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DSS only develops vertical lift whereas about 50% of the lift from a Bruce foil
is lateral resistance, right?

 

[ancient kayaker]

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DSS only develops vertical lift whereas about 50% of the lift from a Bruce foil
is lateral resistance, right?

Correct; the foil is typically mounted at 45 deg to the vertical so the vertical and lateral forces are equal. A different angle can be used which would change the ratio.

For the same total lift per unit area the foil are must be root(2) X that of a vertical foil; to get the same effect using a vertical foil plus a DSS board twice the area of the vertical foil is required. So for that very simplistic point of view the area and hence drag for the DSS system is root(2) X that of a Bruce foil doing the same job.

However, I suspect there is more to it than that and would like to know more, if anyone knows the answer . . .

 

[Doug Lord]

Correct; the foil is typically mounted at 45 deg to the vertical so the vertical and lateral forces are equal. A different angle can be used which would change the ratio.

For the same total lift per unit area the foil are must be root(2) X that of a vertical foil; to get the same effect using a vertical foil plus a DSS board twice the area of the vertical foil is required. So for that very simplistic point of view the area and hence drag for the DSS system is root(2) X that of a Bruce foil doing the same job.

However, I suspect there is more to it than that and would like to know more, if anyone knows the answer . . .

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From a practical standpoint, the boat needs a ballast keel which is generally a canting keel on a mini. The keel fin could also be used to enhance RM(lifting down) . And because it is a canting keel it needs another form of lateral resistance-either a normal daggerboard(s), an angled lifting daggerboard(s),and better yet curved lifting daggerboards.
However, the closest thing I've seen yet to a "Bruce foil" -in terms of how it works- is Vladimir Murnikovs foils for Speed Dream which combine DSS with a vertical fin on the ends of the DSS foil.

 

[ancient kayaker]

Not really a close match to the BF IMHO.

The principle of the BF emerges from vector analysis. The force vector from the foil should intersect the force vector from the rig exactly over the centerline of the hull, then the two forces will resolve into a single vertical force at the centerline with no heeling moment.

AFAIK, unless it is desired to minimise tip vortices, there is no advantage in using a curved foil to achieve this.

FYI, although there is no heeling, there is no reason why the rig has to be upright; I used a canted rig with a lifting sail in my experiment so the vertical force components also cancelled.

 

[Doug Lord]

Mini DSS

Not really a close match to the BF IMHO.

The principle of the BF emerges from vector analysis. The force vector from the foil should intersect the force vector from the rig exactly over the centerline of the hull, then the two forces will resolve into a single vertical force at the centerline with no heeling moment. AFAIK, unless it is desired to minimise tip vortices, there is no advantage in using a curved foil to achieve this.

FYI, although there is no heeling, there is no reason why the rig has to be upright; I used a canted rig with a lifting sail in my experiment so the vertical force components also cancelled.

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You're right but I was only talking about vertical lift and lateral resistance-I was not comparing Murnikovs solution to a boat designed to use Bruce Foils as you describe them being used. I wasn't comparing curved foils to Bruce foils at all-just presented them as a possible vertical lift/lateral resistance solution for Minis. Sorry, I wasn't very clear.

DSS + Vertical fin= Speed Dream:
click on image-

 

[ancient kayaker]

I was trying to understand what advantage it had over the Bruce Foil: it seems to me that the canting keel offsets a significant portion of the wind force's heeling moment - which I hadn't appreciated before - thus reducing the amount of countering moment that the horizontal foil is required to generate. This should reduce drag compared to a Bruce Foil. It doesn't have the deploy-and-forget simplicity of operation of the BF but that counts for little in the search for performance.

 

[Doug Lord]

747 Scow

Raisons website-need to speak French: http://www.teamworkvoileetmontagne....mporte-la-transat-650-sur-teamwork-evolution/

 

[Doug Lord]

Mini Scow vs "normal"

These renderings were done by Yves Tanton and are posted here with his permission. They show ,very clearly, how David Raisons scow compares to a "standard" mini:

 

[peterchech]

Nice rendering Doug thanks for posting it! The scow clearly has far more buoyancy overall, and more interior space. Haha this may have commercial implications at the slip. More boat for the length!

Is there a definitive answer to how a modern scow, like this, performs upwind in a chop? Is it enough of a negative to preclude it from being practical? Or does this work out better under heel, because of a longer waterline or something?

My hunter 25 gets slowed or stopped (depends on how much wind) in any kind of steep chop around new york bay, and it has a standard bow. It tends to ride over the steep stuff, then slam down the other side. I imagine the scow, with its additional buoyancy forward, would ride even higher and slam even more on the other side....

 

[ancient kayaker]

. . . My hunter 25 gets slowed or stopped (depends on how much wind) in any kind of steep chop around new york bay, and it has a standard bow. It tends to ride over the steep stuff, then slam down the other side. I imagine the scow, with its additional buoyancy forward, would ride even higher and slam even more on the other side....

I would think in less space-constricted waters a skipper could select a heading that either optimized comfort or speed on course?

 

[Doug Lord]

747 Scow

Is there a definitive answer to how a modern scow, like this, performs upwind in a chop? Is it enough of a negative to preclude it from being practical? Or does this work out better under heel, because of a longer waterline or something?

....

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Peter, it must work better at an angle of heel like most other scows. There have been several reports during the Transat of the scow encountering just exactly the conditions most people thought would be its undoing-and doing very well. David Raison has done an incredible job of designing this boat and an equally superb job of sailing it in all kinds of conditions.

 

[ancient kayaker]

Of course, the average day sailor skipper might not want to sail his boat on its ear all the time, so the expectation that this design feature might soon appear in commercial "family" boats maybe premature.