# Various questions

DELFTship forum Hull modeling Various questions

• Author
Posts
• #34035
Jim
Participant

HEllo, I had a few questions that I am going to throw out all at once.

-IS there any difference between LCB and LCF. IF so what is it?

-What is the lateral area value/curve used for? I am designing a sailboat and I am not sure what I would use this metric for.

-Having said that I would like to get an idea of the projected surface areas of appendages and sails. How do I do that once I have the shapes designed?

-Is there a way to select points/edges by “box selection” where you draw a square with the mouse and anything within it gets selected?

-How do I delete a layer that is not empty?

-In the resistance report, I am assuming that Rf is Froude resistance, as in wave drag. By elimination I assume that Rr is the residual drag ie friction drag. What is Pe?

-Also in the resistance, does it calculate the resistance of all layers or only the ones turned on?

-If I have appendages will they be included in the resistance calculation or does it only include the hull. If so how does it know the difference?

I figured it would be cleaner to ask all the questions at once instead of in multiple posts.

J

• #34037
Marven
Keymaster
1. LCB is the longitudinal center of buoyancy, the volumetric center of effort of the displacement
2. LCF is the center of effort of your water plane area
3. Lateral area is the projeced area of the submerged hull, the part of your hull below the water plane. You’ll need this to properly calculate the position of your sails.
4. The projected area of hull and sails is calculated in the load cases extension only (wind silhouettes)
5. An empty layer can of course be deleted by first deleting the geometry of that layer. I’m not sure whether this will work in v3.20, but in later versions you can simply press the delete button on your keyboard in the layer properties window. The selected layer, including all the geometry is deleted.
6. RF is frictional resistance. RR is residual resistance (caused by waves, pressure differences between bow and stern etc). PE is the power needed at the propeller (effective power) to propel the vessel at that speed
7. The resistance is calculated for all layers which are included in the hydrostatics, whether visible or not. Appendages are only included if included in the hydrostatics, but rudders and keels for example are better calculated separately
• #34042
Jim
Participant

Hello Marven,

I understand you need to match the sail moment with the appendage moment and how to calculate both of these but how do you transfer this lateral area COE into a moment in this whole appendage/hull/sails location conundrum?

Thanks

JB

• #34049
MICHAEL KERR
Participant

you compare the centre of lateral area of the hull with the centre of force of the sails and the difference is the lead. The percentage of the lead will depend on the type of hull and rig. Yacht design is not an exact science so each designers conclusions vary, its best to read a much as you can on the subjust to draw your own conclusions.