Upwind performance of condomarans

[PaulinOz]

Originally Posted by arsenelupiga

Ok, lets do 8 T then. Here is what I will add so wont have reason to go to shops that often. And see who is the fastest !!!

No I am starting to like the way you think.

[savoir]

Originally Posted by PaulinOz

Quote "load with 3T of stuff."

Only going light ship then not very fair.

Does this mean that Australian beer is heavier than regular beer ?

I've been told that it puts lead in your pencil so perhaps that's it.

[rom]

Originally Posted by 44'cruisingcat

Sailing Catamarans - Keels or Daggerboards, the pros and cons


"Unfortunately, using LAR keels results in a slower boat and more pitching. That is because to optimize speed you need a hull with buoyancy in the ends, not in the middle (technically you need a high Prismatic Coefficient - Cp). Clearly adding a LAR keel adds buoyancy in exactly the wrong place. Furthermore the midships buoyancy makes the boat pitch more as the hull is more "diamond-like". "

I am not following here ... Do you think VPLP (lagoon) designed a "perfectly balanced" boat, say like yours, and then decided to add the keels ? If that is the case then I would probably to agree with you about unexpected parasitic behavior.

However I tend to believe VPLP designed the boat around the keels, or at least with the keels in mind. And I suspect those guys know what they are doing.

A condo cat on keels has lower prismatic coef (do we really care ?) ? Not necessarily IMO. Once again because you would compare it with the same cat without keels, and such cat doesn't exist, so the comparison doesn't hold. Well, as far as condo are concerned and IMHO of course.

[django37]

From close under hullspeed to top speed there is only one parameter that really matters to hull-resistance: Length divided by the 3. root of actual displacement (not designers og factory guessings). Forget about primatic coefficients, waterline length to beam ratios etc. My racing friends always aske me: wouldnt you wish your Lagoon only weighed 4 tons instead of 8? No, I answer, that would make the boat dangerous, I would not be sure it could tack away from a lee shore in a gale with all that windage. To overcome the windage - nessecary for comfort in a small cat -, I need the weight and stability to carry enough sailarea to go to windward in a gale/storm. If the boat was lighter, I would need to rebuild her to half the windage. In light winds I can live with using an engine, if I'm in a hurry - which I'm normally not ...

[StuM]

Originally Posted by arsenelupiga

Ok, lets do 8 T then. Here is what I will add so wont have reason to go to shops that often. And see who is the fastest !!!

Loos like you are adding 4 tuns.

[Factor]

Originally Posted by rom

. Once again because you would compare it with the same cat without keels, and such cat doesn't exist, so the comparison doesn't hold.

Seawind 1160 is not a condo cat but its not super high performance racer either, and it is a boat that is available with mini keels and with daggers. And I have sailed both, The dagger boat sails faster and closer to the wind and is also discernibly quicker off the breeze. Its also more expensive.

[Factor]

Originally Posted by django37

From close under hullspeed to top speed there is only one parameter that really matters to hull-resistance: Length divided by the 3. root of actual displacement (not designers og factory guessings). Forget about primatic coefficients, waterline length to beam ratios etc. My racing friends always aske me: wouldnt you wish your Lagoon only weighed 4 tons instead of 8? No, I answer, that would make the boat dangerous, I would not be sure it could tack away from a lee shore in a gale with all that windage. To overcome the windage - nessecary for comfort in a small cat -, I need the weight and stability to carry enough sailarea to go to windward in a gale/storm. If the boat was lighter, I would need to rebuild her to half the windage. In light winds I can live with using an engine, if I'm in a hurry - which I'm normally not ...

Ah I see your reasoning now. So here is an idea how about filling those mini keels with lead. That should help.

[django37]

Originally Posted by Factor

Seawind 1160 is not a condo cat but its not super high performance racer either, and it is a boat that is available with mini keels and with daggers. And I have sailed both, The dagger boat sails faster and closer to the wind and is also discernibly quicker off the breeze. Its also more expensive.

So Factor: You dissagree with QMYC, which in their rating rule -OMR- say that daggerboards only make a multihull 0.5% faster than the same boat with minikeels?

[44'cruisingcat]

Originally Posted by rom

I am not following here ... Do you think VPLP (lagoon) designed a "perfectly balanced" boat, say like yours, and then decided to add the keels ? If that is the case then I would probably to agree with you about unexpected parasitic behavior.

However I tend to believe VPLP designed the boat around the keels, or at least with the keels in mind. And I suspect those guys know what they are doing.

A condo cat on keels has lower prismatic coef (do we really care ?) ? Not necessarily IMO. Once again because you would compare it with the same cat without keels, and such cat doesn't exist, so the comparison doesn't hold. Well, as far as condo are concerned and IMHO of course.

Yes, clearly you're not following. The link and the quoted passage were from Richard Woods, not me.

And if you'd read the article you'd know that he had built and sailed the same designs with minikeels and daggerboards.

[rom]

Originally Posted by 44'cruisingcat

Yes, clearly you're not following. The link and the quoted passage were from Richard Woods, not me.

And if you'd read the article you'd know that he had built and sailed the same designs with minikeels and daggerboards.

Actually I got that, improper quote sorry.

But we are here talking about condos which AFAIK only come with keels. So all that discussion you started about increased pitching is off topic, isn't it ?

[Just Another Sa]

Originally Posted by 44'cruisingcat

So you reckon you know more about multihull design than Richard Woods?

No. I reckon he is a human being just like the rest of us, thus capable of making mistakes. I also believe he is capable of recognizing them when brought up.

[Just Another Sa]

Originally Posted by django37

From close under hullspeed to top speed there is only one parameter that really matters to hull-resistance: Length divided by the 3. root of actual displacement (not designers og factory guessings).

That is indeed the most important nondimensional parameter, but there are also dimensional parameters like weight and wetted area with far more effect on hull-resistance.

Originally Posted by django37

Forget about prismatic coefficients, waterline length to beam ratios etc. My racing friends always aske me: wouldnt you wish your Lagoon only weighed 4 tons instead of 8? No, I answer, that would make the boat dangerous, I would not be sure it could tack away from a lee shore in a gale with all that windage. To overcome the windage - nessecary for comfort in a small cat -, I need the weight and stability to carry enough sailarea to go to windward in a gale/storm.

If you could have 4 ton version with equal strength, you could have 4 tons of seawater as ballast for those high wind upwind conditions. Then you would have a faster boat in lighter winds without any reduced safety.

[Just Another Sa]

Originally Posted by catsketcher

This will be pretty closely related to the prismatic under the water. Fuller ends above the water reflect a higher prismatic underwater.

The subject was if there is an effect on pitching depending on if there are keels or daggerboards with identical hull shapes. If you count appendages as part of midships area, there will be significant change in prismatic coefficient, but no change on how full the ends are. But you could also ignore the keel area when calculating midships area for the prism, no change in prismatic coefficient either if displacement is the same.
You just changed the subject into different hull shapes, nothing to do with what you quoted.

Pitch resistance and nice stern steps are pretty important, more important than smooth water tank tests.

cheers

Phil

Agreed.

[Just Another Sa]

Originally Posted by rom

But we are here talking about condos which AFAIK only come with keels. So all that discussion you started about increased pitching is off topic, isn't it ?

The subject line for this thread reads:"Upwind performance of condomarans"

Pitching has a great effect on upwind performance of condomarans in some conditions in some boats. Obviously not so in calm seas and light steady winds for any of them.

[rom]

Originally Posted by Just Another Sa

Pitching has a great effect on upwind performance of condomarans in some conditions in some boats.

Yes, but their pitching is not related to them having keels as they were designed from the start like this. You & 44C are comparing the same boat with or without keels, which doesn't make sense here, IMHO.