Freeship Discussion Regarding Cross Curves Calculation

[EAP]

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)???

[Martijn_vE]

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.

[marshmat]

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....

[Martijn_vE]

Marshmat,

I hope the attached image clarifies things a bit.

Martijn

[Victor T]

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).

[marshmat]

Thanks Martijn, that makes a lot more sense.

[Martijn_vE]

Hi!
That is right only for small angles (< 5 degrees )
The cross curves (pantacarenes) build for big angles theta.


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.

[despatches]

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

[conceptia]

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