Freeship Discussion Regarding Cross Curves Calculation

The Freeship Crosscurves Calculation Shows As The Righting Lever: Kn*sin(theta). Two Questions: First, What Is 'n'? Second, If The Intent Is To Express The Righting Lever As Seen Passing Through The Keel (since There Is No Kg) Shouldnt The Expression Read Km*sin(theta)???

 

KM is only valid at small angles of heel. At larger angles of heel the metacenter shifts and at those angles it is denoted KN rather than KM.

 

On a related note, although I realize this thread is a couple months old....
In converting Delftship/Freeship cross curves from KN*sin (phi) to the actual righting arm GZ, is it correct to interpret the Delftship/Freeship output as follows: Divide the output value KN*sin(phi) by the sine of the heel angle to get KN, then subtract KG*sin(heel angle) to get GZ? Or am I misreading something....

 

Stability issues

Marshmat,

I hope the attached image clarifies things a bit.

Martijn

 

Hi!
That is right only for small angles (< 5 degrees )
The cross curves (pantacarenes) build for big angles theta.
Formula would be this: l(theta)=Y_theta*cos(theta)+(Zc_theta-X_g)*sin(theta).
Because X_g unknown -> X_g=0 -> l_conditional=Y_theta*cos(theta)+Zc_theta*sin(theta).

 

Thanks Martijn, that makes a lot more sense.

 

If you look carefully you can see that I'm talking about KN, not KM which is indeed only valid for smaller angles. N is the virtual metacenter at larger angles of heel.

 

blagger/gaff

hi,

i'd very much like to hear from you if the project is still alive , , ,

even if the project has stalled temporarily or otherwise, i'd love to catch up and find out how far you progressed, perhaps sneak a preview at your research,

i am now looking to commence restoration with an original hull, very little to go on rig wise,, but hull good basis as a pattern.

if you were looking to make a fibreclass hull , or a light cold molded hull, maybe we should talk.

all the best edward

 

Marshmat you are correct. KN-KGsin(theta) will give you the GZ..