Floating Duck

Mega high SA/D's - How high?

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How long is a piece of string huh... But it's a lazy Sunday and I'm wondering;

What are some high SA/D's that you know of for both upwind and downwind scenarios, and under how much wind is this possible?

Ex. a Melges 32 has

  • 46 upwind - usable until mid teens TWS?
  • 115 downwind, usable well into the 20's TWS?

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36 minutes ago, Tito said:

How long is a piece of string huh... But it's a lazy Sunday and I'm wondering;

What are some high SA/D's that you know of for both upwind and downwind scenarios, and under how much wind is this possible?

Ex. a Melges 32 has

  • 46 upwind - usable until mid teens TWS?
  • 115 downwind, usable well into the 20's TWS?

This number all by itself is not as useful as it's comparison to righting moment..... ideally, some sort of RM/disp number.

A boat that lays on it's ear is not fast

FB- Doug

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1 minute ago, Steam Flyer said:

ideally, some sort of RM/disp number.

100% agreed. 

Perhaps we stick to non-canting monohulls (i.e. Most boats) to make this comparison a bit more fair - seeing how RM numbers aren't usually found. 

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How is crew weight being considered, with it being such a big part of both displacement and RM in such a light boat?

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1 hour ago, blurocketsmate said:

How is crew weight being considered, with it being such a big part of both displacement and RM in such a light boat?

I would absolutely consider it, as you are correct it relates to both. In my simple calculations I have always used 185lbs * # of crew - just as a reference point.

This info however is simple to find. What is not so easy is at how much wind speed do these boats start getting overpowered? For ex. With SA/D of 50 upwind, you may only need 12kts TWS until you need to reduce sail. But with SA/D of only 20 you probably don't need a reef till 25kts.

I guess that's my main question.

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I love how the M32 is always the benchmark for ludicrous SA/D ratios.

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1 hour ago, ajbram said:

I love how the M32 is always the benchmark for ludicrous SA/D ratios.

Hahaha 100% agree, but not much information out there on other models that I can find (the t-boats, shaw's, european lake boats, etc).

Or I would say... not any information that I can find and is readable (i.e. in English) lol.

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6 hours ago, Tito said:

Hahaha 100% agree, but not much information out there on other models that I can find (the t-boats, shaw's, european lake boats, etc).

Or I would say... not any information that I can find and is readable (i.e. in English) lol.

It is a lot of sail for a 3700# boat. When it arrived we talked our way into the university field house to measure the sails that came with it... the first kite we stretched out took up a lot more floor space than we anticipated and we were like "Holy shit! How are we going to keep this thing on its feet?" That being said, it's a remarkably well-behaved boat for all its gigantic sail area. Righting moment from crew weight and stability generated by the keel foil means a lot.

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What I was getting at is, figures published on sailboatdata.com, etc., may be just for the boat, w/o counting the crew.  So the real SA/D may not be as ludicrous.

These boats designers are certainly figuring it all in, displ. and RM w/ crew, and at what wind speed they're fully powered.

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18 hours ago, blurocketsmate said:

at what wind speed they're fully powered.

Exactly... when we're not moving fast (e.g. coming out of a maneuver etc.) the blob at the bottom of the keel does next to nothing if we're powered up. Once we are moving, the foiling action of the keel through the water adds a lot oof stability and SA/D doesn't really figure into it.

 

 

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8 hours ago, ajbram said:

Exactly... when we're not moving fast (e.g. coming out of a maneuver etc.) the blob at the bottom of the keel does next to nothing if we're powered up. Once we are moving, the foiling action of the keel through the water adds a lot oof stability and SA/D doesn't really figure into it.

that oof stability must be something I am not familiar with.

 

Are you suggesting that a symmetric non canting keel has righting moment that is due to water flow ? 

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5 hours ago, LionessRacing said:

that oof stability must be something I am not familiar with.

 

Are you suggesting that a symmetric non canting keel has righting moment that is due to water flow ? 

More like "wronging moment" given leeway and the angle of attack of the flow over the keel foil.  

The Melges 32 SA/D number is very high, but less so when you add 1,000# of crew weight.  I suspect that a TP52, which as a downwind SA/D of about 96 is equivalent or more extreme than the Melges when adding crew weight into the equation.  Same with upwind.  

 

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15 hours ago, LionessRacing said:

that oof stability must be something I am not familiar with.

 

Are you suggesting that a symmetric non canting keel has righting moment that is due to water flow ? 

I wouldn't call it righting moment. It's more stability. When the boat is not moving forward, all the crew weight and the weight of the keel bulb cannot counteract the heeling moment of the sails when they power up. When the boat is moving fast, changes in crew position or wind speed are dampened by the keel tracking a straight line through the water.

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3 hours ago, ajbram said:

I wouldn't call it righting moment. It's more stability. When the boat is not moving forward, all the crew weight and the weight of the keel bulb cannot counteract the heeling moment of the sails when they power up. When the boat is moving fast, changes in crew position or wind speed are dampened by the keel tracking a straight line through the water.

So if I understand you, you are asserting that the narrow deep keel (& Rudder) is resisting heeling more when there is significant flow over it than when it's static.

Since it's symmetric, the only "lift" it generates is due to angle of attack not differential camber.

As that angle of attack changes with yaw more than heel, don't you have a coupling; where a puff that causes the boat to start to round up, creates a hydrodynamic lift on the keel due to change in angle of attack (keel now pointing to weather of stream flow) which actually forces heeling? 

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3 minutes ago, LionessRacing said:

So if I understand you, you are asserting that the narrow deep keel (& Rudder) is resisting heeling more when there is significant flow over it than when it's static.

Since it's symmetric, the only "lift" it generates is due to angle of attack not differential camber.

As that angle of attack changes with yaw more than heel, don't you have a coupling; where a puff that causes the boat to start to round up, creates a hydrodynamic lift on the keel due to change in angle of attack (keel now pointing to weather of stream flow) which actually forces heeling? 

I'm not asserting that there is lift. Of course there is lift that is generated due to angle of attack and not camber. 

I'm not an engineer so I won't try to use proper terminology here, but what I'm describing is the same stabilizing effect as the tail fin on an airplane. With a flat angle of attack at speed, a foil tends to just stay put. Think of a dinghy with no ballast in the centerboard (or old ones where the centerboard is wood, and therefore has negative righting moment). When that dinghy is at speed, the centerboard tends to hold its track through the water as long as the angle of attack is flat. 

All I really know is when we are on step with wind at 90 AWA (which ought to be the maximum heeling moment), we are more stable than when we are dead slow with the same TWS at ~130 AWA, even with the exact same crew weight placement etc. I attribute this to the fact that the keel is tracking through the water. Am I crazy?

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14 hours ago, duncan (the other one) said:

Thames A-ratershttps://www.thamessailingclub.co.uk/TSCsailing/thames-a-raters-1

350 sqft / 750lb ~ SA/D 68 upwind

Now we are getting somewhere, nice! 68 upwind SA/D with a very thin B/L. Probably overpowered in... 5kts of wind?

I hate to speak these words on here, but... Does anyone know the SA/D of... THE CONE ?

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Go the Cone

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55 minutes ago, monsters inc said:

Go the Cone

Ah damn I hope this thread only gets briefly derailed what have I done. 

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On 8/9/2019 at 1:14 PM, Tito said:

...    ...

I hate to speak these words on here, but... Does anyone know the SA/D of... THE CONE ?

 

             cone

        cone cone

    cone cone cone

cone cone cone cone

FB- Doug

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On 8/9/2019 at 1:14 PM, Tito said:

I hate to speak these words on here, but... Does anyone know the SA/D of... THE CONE ?

In a previous thread, SA/D for the cone was calculated at 141.1, with the numbers supplied as: displacement 5124 pounds;  jib + main area 721 and downwind SA ~2400

 

previous SA thread: 

http://forums.sailinganarchy.com/index.php?/topic/41412-another-phrf-debacle/&tab=comments#comment-876773

archived website for the cone measurements (but do not seem to show sail areas):

https://web.archive.org/web/20060615034313/http://www.gothecone.com/boat.html


 

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The problem with SA/D debates is that most of the numbers thrown out are made up - i.e. someones own definition of SA/D - making equal comparison difficult - unless everyone agrees to he same methodology.

In the traditional SA/D calculation (there is no such thing as upwind and downwind SA/D) - SA is calculated as .5(IxJ+PxE) - simple as that.  Using that the Melges 32 has a SA/D of 36.7 while an Olson 30 is 26.5

Nothing wrong with making up numbers like downwind SA/D as long as you're not comparing apples with oranges.

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My international 14 clocks in at about 48 upwind, 125 downwind. With crew added of course, lets not get silly.

The 12s would be higher yet.

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I sailed Cherubs in Australia nearly 40 years ago, and did a few races in Twelves.  Twelves then were just silly -- short sprints between crashes.  We were always just  surviving, never really racing.  Modern ones look much better, with lighter rigs and easier handling, more like a modern I-14.

These days it seems more about reducing drag, and with skiffs, keeping the sails full and flowing with flexy rigs that "give".

Do modern Twelves have more, or less sail than they used to?  Are they still unrestricted?

 

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The FAREAST 28R 538 sqft upwind, 1464 sqf downwind, weighs 2866 lb

SA/D=42,6

SA downwind/D=116

Enough power for the top boat to top out at 21.5kn on our National Championships o Sweden.

 

FB_IMG_1566244745126.jpg

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On 8/6/2019 at 12:10 PM, Tito said:

I would absolutely consider it, as you are correct it relates to both. In my simple calculations I have always used 185lbs * # of crew - just as a reference point.

This info however is simple to find. What is not so easy is at how much wind speed do these boats start getting overpowered? For ex. With SA/D of 50 upwind, you may only need 12kts TWS until you need to reduce sail. But with SA/D of only 20 you probably don't need a reef till 25kts.

I guess that's my main question.

Depends on beam and length too, we’re around 24 upwind with Amati (40t and narrow), but we pretty much do at least wind speed  upwind until 5-7 knots, and then we’re looking at ~ 12-14 apparent, and we put in the first reef at 10-12 TW.  Our U20 had IIRR 36 upwind, but almost as much beam as Amati- but  we could carry that until 15-20k easy upwind.  

Roach has a lot to do with it too-  we got tired of reefing in 10k, so I had our sailmaker take off some roach at the top, and we now don’t have to reef as early, but  she’s sticky in the light.  Not as fun.  Next sail gets the roach back, ditch the big assym, go back to a 3/4 rig w blade, 3/4 shrouds, 3/4 running backs only, and 3/4 assym.  This drives me crazy, because you start thinking about how many sails, and running and standing stuff that you really need.  The U20 had 3 sails, and that was nice.  Jay and Pease put such nice twist in those sails-.  

Bombing around in the light is fun.  Bombing around in the heavy is easy...

part of this belongs in  SHA?

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Fwiw, I’ve found that 3:1 SA:WS (sail area :wetted surface) is the point where things get crisp in the light, but prismatic matters too, and then the design fun really gets sporty-

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