Changing Position of Aft Perpendicular
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Tagged: Aft Perpendicular, Coordinate System, Rudder Post
 This topic has 1 reply, 2 voices, and was last updated 2 months, 1 week ago by Terrance Egolf.

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July 25, 2023 at 12:40 #44820MarcusParticipant
Hello everybody,
I have got a problem concerning the Position of the Aft Perpendicular or respectively the Position of my laboratory coordinate system. Delft Ship is putting it by default onto the intersection line of my design water line and the hull and not the intersection of the design water line an the rudder post. Is there a possibility to add the information of the position of my rudder post or to change the Position of the aft perpendicular myself?
Thank you very much!
Best regards
Marcus

July 25, 2023 at 23:22 #44821Terrance EgolfParticipant
Hi Marcus.
From your post, I am understanding that the “origin” of your coordinate system is somewhere near the center of your model at the waterline.
Before doing anything else, check the Project Settings, Coordinate System tab to verify that your origin setting is truly the Aft Perpendicular:
If the coordinate system is at the middle, then switch it to the After Perpendicular setting to see if that fixes your problem.
If the model’s AP is truly in the center, that means that all control points below the waterline have negative zcoordinates. You might try selecting one of the control points near the keel and see if this is true. Also, all control point xcoordinates aft of the “AP” are negative and all forward of the “AP” are positive.
If so, you can easily solve this by selecting the entire model and moving it first in the positive zdirection until whatever you want to use as your model’s baseline (keel, rabbet, etc.) corresponds to the z = 0 coordinate. The Control Point Window (see Section 1.5 of the manual) allows you to constrain movement in one of the three principal axes to accomplish this without changing any of the other coordinates. Then use the same process to move the hull forward until the sternpost coincides with the x = 0 coordinate.
To assist with this process, you might consider creating one or more “floating” square faces oriented in the xz plane, then aligning one of their edges to the desired coordinates in relation to where the AP should be (a horizontal edge aligned to the desired baseline (z = 0) and a vertical edge aligned to the longitudinal origin—x = 0). Then you can very precisely align the model to these edges using the zoom feature.
Obviously, you will need to reposition your reference background images if you have them.
Let us know how this turns out!
Terry
Colorado, USA
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