Loft failure in Rhino

Hi, I am trying to loft a few degree 5 curves (to model a boat keel) which all have the same point count. When I do the loft with the loose setting it works fine and produces a very nice surface, see the first attached picture:

The surface in the picture is lofted as two parts, and the rear part of the loft fails when I switch to “tight” or “normal” loft option. The aftmost curve “reverses” on itself, so the loft fits this curve from the other direction. I have tried rebuilding the curve and also changing the direction, but it does not help. See the picture below for the failed loft:

This is in Rhino 5.1, x64. Do you know how to correct this loft? I have run out of ideas…

Best regads, I am very grateful for any input!
/Adam, Sweden

Adam, can you post the curves here or send them to me (



Oh, I meant to do that, but it somehow slipped out of my mind!
DropBox link below:

Thank you,
Adam Persson

Hi Adam - the problem is you are lofting 5 rational curves- point weights edited to 5+, with one, on the end that is non rational - the rebuilt one at the front. If you can make that front curve more similar to the others- same points and similar weighting, it should work out better.

Test_4_Haven_12_2_PG.3dm (100.0 KB) <a class=“attachment”


Hello Pascal, thank you for looking at this, that was indeed the problem!

Please correct me if I am wrong, but the important thing is that all the curves are rational (i.e weights are modified) and of the same degree? Are there any other important factor for lofting to succeed?

Best regards, and thank you very much,

Hi Adam- ideally, loft will have exactly the same structure in all curves, but of course that is only possible some of the time. My guess is that you can get a reasonable surface if weights are not too dissimilar from curve to curve, but I have not experimented with that.