Hydromax and yacht stability

[tomcat]

Hi,
I've been racing IOM R/C yachts for a while and I want to start designing and building my own IOM yacht. I've read few books on yacht building and I was looking at few available software to help me design my yacht. I came across Hydromax which seems nice but I have few questions when it comes to the Large Angle Stability. I understand the concept of Loadcase in Hydromax but I don’t quite know if the LCG that needs to be entered here must be identical with the ones calculated by Hydromax/Maxsurf. Let's take the hull for example, Maxsurf calculates an LCG for hull (via Calculate 3D area option) and I was wondering if that center needs to be entered here along with the weight of the hull.
Also when I run the Large Angle Stability two of the resulting items are "Draft at FP" and "Draft at AP", well, is it correct to say that in order for the yacht to float on DWL these two values need to be the same?

I appreciate your help.

Catalin

[Dutch Peter]

Contact Andrew Mason, he's a member of this forum and involved with this program. You can email him through the Members List, click his name and the rest is peanuts.

Also try searching this forum because a lot of related topics have been discussed.

Good luck

[nico]

About LCG;

The LCG that you get in Maxsurf, is the centroid of your hull surface. Therefore it will be different from your final lcg (hull + bulb + rig ....). The lcg to be entered in hydromax is the lcg of the complete boat. The easiest way to get it, is to assume that Lcg is equal to the LCB of your hull drawn in maxsurf. To float at its design waterline the final yacht will need to have a Lcg equal to the Lcb (hull + rudder+bulb+keel)


About Draft at FP/AP;

Yes this is true for heel=0°, if you dont get both values equal (at heel=0) that means that the lcg (you put in loadcase) is different from lcb (as designed in Maxsurf). At other heel angles, the drafts will be different, and will show the amount of trim.

[MikeJohns]

For Hydromax loadcase you will need the Longitudinal and Vertical Centres of Mass (Gravity) The Longitudinal one will match the Long Centre of Bouyancy that Maxsurf gives you for the defined shape. The hard one is the Vertical Centre of Mass (Gravity) and can only be accurately given by doing a proper mass distribution calculation for all items aboard.