Using Autocad 2010, I have done this attached file.  Use the parametric commands.  This profile can be expanded further and revolved to give you what you need.

 

However if you do not have 2010, the profile can still be done using conventional draughting methods.  Look at the drawing that I am attaching.

 

1. I first set up the centre line of the vessel.

2. Using offset - dia / 2 - place the one outside line of the outer dia.

3. Draw a circle with the centre point on the vessel centre line and the radius being the crown radius.

 

Now from here there are 2 routes to take:

First the long one:

4. Offset the outer dia line and the crown circle by the knuckle radius.

5. The intersection of these is now the centre point location for the knuckle arc - using that as reference draw a circle for the knuckle.

6. You now have the construction lines - using that draw the outline, offset to get the thickness, revolve, etc. and you have a 3d model.

 

The quick and short way:

4. Using trim command, trim the crown circle so that only the bit remains between the vessel centre line and the outer dia line - see the drawing.

5. Using the fillet command with the radius set to the knuckle radius, fillet the crown arc and outer dia line.

6. From here if you have some 3d experience it should be easy to create a profile and revolve it into your vessel.

 

Hope this helps, don't know if I understood your question correctly.  Using ellipse and trimming it does not work, to create a 3d you need to join the lines into a polyline and ellipse does not join - even if you trim it.  Its actually a pretty useless command and I very rarely use it.

 

Ciao

Kobus

 

PS. I have tried to upload the file but for some reason I get an access denied message.  Mail me if you need help.