In the attached file I tried to make boolean union between the boat and the seat. No succeed !! Why ?Loft.3dm (920.8 KB)
Your seat is an overly complex polysurface. There is a sliver surface that is creating problems with multiple edges. Deleting it and matching the adjacent surfaces will fix this.
Hi Stratosfear
Thank you very much for your answer.
Sorry but I don’t understand what you mean and what should I do in order to fix the problem.
Can you please try to explain more detailed?
Thank yo very much
Rachel
The close up image of the seat shows the sliver surface. It’s so narrow it looks like a curve. Once you’ve deleted it use the Surface match command to tangent match and join up the adjacent surfaces. If that fails I would recommend that you rebuild the seat. It’s a simple form that does not require so many surfaces to achieve.
Thank you very much… I can see that the seat is very complex…
Actually it is very strange, because it is all taken from the Training Manuel Level 1 of Mcneel,
Exercise 59 page 171…
I did everything which is written there, and with the Video of Rhino level 1…
Strange …
For what it is worth, this has always struck me as a rather peculiar and counter-intuitive portion of the exercise. It makes much more sense, to me. to extrude the original simple curve in the middle in both directions and then trim the resulting object with the sides of the canoe.
My guess is that in lofting, the curve seams are not lining up cleanly in your case. I’d make sure to snap the little direction arrows to the End points of the projected curves.
-Pascal
Thanks, Pascal.
It is a real good idea to extrude the original simple curve in the middle.
I have tried your suggestion, everything is fine, the seat becomes a very simple closed polysurface,
yet boolean union doesn’t work…
Looks like the reason is in the canoe itself, not in the seat…
Yeah, for the BU, you need just the inner bit of the extruded seat - Split the extrusion with the canoe hull, and throw away all but the middle seat bit. BU that to the hull… worked here.
-Pascal
YEAHHHH !! IT WORKS 
Thank you very much for your kind help
Rachel