Importing offsets to DelftShip - definitions needed!

[FlyingFish]

I have been trying the learn how to fill in a table of offsets to import into Delftship for a lobster boat build. 

A quick question to those of you familiar with Free Defltship imports - I cannot for the life of me understand what exactly to measure to complete the 'aft contour' and 'forward contour' data shown in the attached. Nor do I understand what to use as the 'origin'.  I've been through the Delftware forum, but can find only other confused threads. Any help or advice greatly appreciated!

[CDR_Ret]

I might be able to assist you. What kind of vessel are you working with? Sorry, had to reread your post again.

 

The DELFTship offset import function is very buggy. If you do a search on the D/S website using "offset import" key words, you will find there is a long history of problems with the function in at least the Free version.

 

To begin with, I would not try to create offsets of the entire hull and keel assembly. I recommend modeling just the hull between the sheer rail and inner rabbets of the stem, keel, and sternpost, as applicable. If the lobster boat has a propeller skeg or other complicated arrangement around the propeller/rudder, I'd leave that off until the hull form is set.

 

The import offsets function also doesn't deal well with tumblehome. The hull shape should more or less flare outward from the keel to the rail for the best success. Otherwise, the program tries to connect the rail to the lower parts of the hull inside the widest parts of the hull. It gets really confusing that way!

 

The DELFTship manual uses a number of terms that may not make sense. I have communicated with the developers about this but nothing has been done. Here are the definitions as I understand them:

• Contour line at each station—This refers to the sheer rail line (top of moulded rail, if applicable) or the outboard deck sheer line if no rail is included.
• Forward contour line—The line described by the x-coordinates of the inner rabbet of the stem at each waterline. Basically, the profile shape of the bow.
• Aft contour line—The line described by the x-coordinates of the inner rabbet of the sternpost (or the centerline, in the absence of an inner rabbet at the sternpost) at each waterline at the aft end of the vessel. Basically, the profile shape of the stern.
• Origin—The origin is the point in 3D space that establishes the zero coordinates of the x-, y-, and z- axes for your model. Normally, the origin is placed at the baseline for the hull at the aft face of the sternpost. For a lobster boat, you may have to choose whether the origin will be at the extreme stern/transom, the extreme bow, or somewhere else that makes sense. The longitudinal coordinate "x" is positive forward of the origin, the lateral coordinate "y" is positive from the centerline outboard; the vertical coordinate "z" is positive upward from the baseline. So, depending on where you place the origin in the setup of your file, you may end up having to deal with negative values (especially x-values).

I would make the baseline the bottom edge of the inner rabbet along the keel. If the keel is raked, then place the baseline at the lowest extent of the inner rabbet of the keel. This permits all moulded hull z-coordinates to be positive.

 

After you are finished with the moulded surface of the hull, then add the rabbet, keel, stem, and other parts of the backbone.

 

If I were you, for a relatively straight-forward hull that probably has a hard chine, I'd simply build the stations one at a time from scratch, setting the control points at each station against the boat's deadflat view in the plans. Alternatively, you could import all three views of your hull plan as "Background" views, then use one of the example hull models that comes with the program and move the control points around until you create what you want.

 

Each method has its pros and cons. And if you haven't worked with the program before, it's got a steep learning curve.

 

For encouragement, here is my DELFTship model of a "naphtha launch" (c. 1905) that I created from scratch to produce plans for a ship's boat carried by a vessel that my grandfather sailed in back in 1906.

 

 

Please feel free to PM me to walk you through any problems you run up against. You may also want to skim through a mini-tutorial on using DELFTship that I made up in my Galilee topic, starting on page 5. That thread as a whole includes lots of photos of my work in DELFTship developing Galilee's hull form.

 

Terry

Edited January 14, 2021 by CDR_Ret

[FlyingFish]

Well - what a great response! Thank you Terry for the time you have taken with this - I'm emboldened to give it another go, and see what I can do. I think the terminology used in DS is a considerable barrier to new users, and can't see the logic of the developer here. Now I see what they are after I can make some progress. 

I'll also try the second methodology you advise; although I had no drawings at all (the boat is Orca from Jaws, build log just started), so one reason for using DS is to fair the hull and adjust the station frames before cutting out. 

A steep learning curve indeed, but I don't mind that at all, and your tutorial is most helpful.

Thanks too for the offer to advise with problems!