Small hull stability / moment trim /compared

[skiffguy]

I am comparing 2 hull forms and ask for suggestions on comparing stats while at rest.... suggestions ?

[TeddyDiver]

Check this center of flotation calculation and implications?
In the post 305 is a link to download Eric Sponbergs "Design Ratios". Read the Center of flotation and Waterplane coeffiency.. the rest is all good stuff too..
BR Teddy

[DCockey]

Rhino (at least V4) Hydrostatics command calculates a number of useful quantities including displacment, center of buoyancy, center of floatation and waterplane area for a hull surface. Waterplane area translates directly into pounds per inch of immersion.

Create a plane which represents the waterplane of the hull (complete hull, not just one-half) at the waterline. One way to due this is with the CutPlane command, and then trim the resulting plane with the hull surface. The AreaMoments command used with the plane created gives all the moments needed to calculate the trim and roll stiffness/stability for small changes in loading.

[skiffguy]

Thanks, I have the calculations as done in Maxsurf Calcs. I was trying to find a software solution perhaps to doing the compare instead of calculating it all by hand (yea I know Im being lazy) I want to see how a new hull is going to compare to another I designed 10 years ago...

[ancient kayaker]

If you have have the offsets then download FreeShip and input the offsets.

Then you can can get the cross curves, you can also enter a pitch angle to observe how the center of displacement moves. That should give you a good idea of how the hull will behave when loads are moved.

Carenne is another free download which will give you the pitch angle for a given load and position but it does not do cross curves in the free version ASFAIK.

Carenne is limited compared to FreeShip but is easier to use as it has a more intuitive method of developing a hull shape IMHO. I use carenne when I can, export the XYZ data which can then be imported to FreeShip. That gives me access to freeShip's feature without having to mess around with the peculiar NURBS system it is based on.

With Carene you enter actual dimensional data. When working with FreeShip you tweak control points which influence the hull shape as if you were pulling on a rubber sheet with rubber bands ... and if you start with the wrong number of control points you may be doomed to start over.