Hi I am creating navmesh manually on an exterior cell , a ship deck that crosses two cells , now I almoust made most of the ship but when I reach 2/3 of it the vertices refuse to go past the cell border , and I do not get why couse I can create the vertices on the other side of the cell but not if linked to the original navmesh I was working on so I can't connect the two sides ... hows't that other problem ? a bug or what?

Each navmesh is made for it's own cell. When you finalise it, they will join together and yo'll get get a solid green line at the join.

To get them to join correctly, make sure that they have the same number of points the border edge and make sure the points from 1 cell mesh touch the corresponding point on the other cell mesh.

ok how u generate then exterior navmesh and how I dlete all navmesh done so far ?

Like Tamb0 said, navmesh doesn't cross cell borders. Make the navmesh go right up against the edge on both sides of the border, then finalize the navmesh and a green line should appear, signifying that they are 'joined' navmeshes. If no green lines appears, line the edges up better and finalize again. Repeat this until you get the green line where all navmeshes meet.