Panel Development

[Wayne Grabow]

TANSL: When I first used this technique, personal computers hadn't been invented. I used a slide rule on the first hull; had to do two-step calculations (left and right of the decimal point) to get enough significant figures. Any computer is fine, but a cheap calculator will do. Glad you believe that many curves can be represented by equations; it has worked for me, but I am just a small-time amateur. Working with equations, allows generation of dozens of EXACT points on a curve located only inches apart. A loftman would have a hard time deviating from the correct course. Dozens of exact points allows detailed projections to create hull surfaces. The situation is usually either given two points (conic projection) to define a line, or one point and a slope (parallel projection) to define a line, calculate a third point at an intersecting plane.

 

[smjmitchell]

SMJ: All of my hulls have used parabolic equations and straight lines. I looked at other equations, incl. second degree conic, but found that the parabolic gave me the best results with the least complication.

The equation can also be integrated to calculate the length of the curved chine to any point (or between points).

Thanks for the additional explanation. I understand where you are coming from in terms of keeping the equations simple. I recently tried to derive the equations for arc length integration of a second degree conic and after pages of equations found that there was no solution.

Yes I saw the photo's of your double chine rowing hull. A nice shape.

 

[Wayne Grabow]

I have the integrated equation in my files somewhere, but seldom use it because the build strongback and frames keep everything in such good alignment that chine length is unimportant. I find slope calculation much more useful.

 

[TANSL]

Wayne Grabow, although it is likely that I lose some nuances, overall I agree what you say. All I wanted in my post # 44 was to discuss some aspects.
I also agree that the most suitable for lofting curves are parables, but I prefer the third grade because they allow changes in the convexity / concavity of curve. In addition, integration with parables, is child's play.
I see you know well the mathematical foundations of lofting. This is, in my opinion, a very interesting and very useful topic that few know.

 

[rick gray]

triangulation

i was a lofts man now retired the old saying i was given was PLAN VIEW PL US ELEVATION RISE EQUALS TRUE LENGTH imagine a triangle or simple cone development the three views have to match up a spot can only be in one place!! so find it in the three views . triangulating curved plates is done by finding true lengths on curved frame lines , expanded curved diagonals . now computers do it all .

 

[TANSL]

That triangulation you say may be very inaccurate when it comes to surfaces with pronounced curvatures. Unless you refer to spherical triangulation, which also has its complications.

 

[rick gray]

lofting

That triangulation you say may be very inaccurate when it comes to surfaces with pronounced curvatures. Unless you refer to spherical triangulation, which also has its complications.

we originally did full-size wood lath templates , triangulated on loft floor . the expanded diagonals where estimated in length by curving a batten length stick ,since the diagonals used from frame line to to frame line was done twice to form a cross pattern and you had the expanded seam battens .so all intersection had to cross fairly close or you had an error . the steel plates fitted real good virtually no trimming we advanced to 10th scale with hull mockup unit and then cad

 

[TANSL]

We also used the triangulation method, but when the curvature was stronger, we used other methods such as the geodetic line or the straight base.
We also go through the 1/10 scale models before moving to CAD/CAM. Nice work lofting, right?

 

[rick gray]

lofting

We also used the triangulation method, but when the curvature was stronger, we used other methods such as the geodetic line or the straight base.
We also go through the 1/10 scale models before moving to CAD/CAM. Nice work lofting, right?

I was an apprentice SHIP,S Plater and was given time and experience in drawing office and loft. I was slow to catch on with shell development, but did end up as foreman in loft. the old-timers from world war taught me. i did Ms dos quick part , others abandoned my union for drawing office CAD training so loft was absorbed. we used to do all panel/bulkheads with length and height stick method my foreman finally changed to detailed sketches ,so fitters did layout with tape measure , we showed him what small ship shops were doing. i did one offshore supply vessel from offsets and design drawings . i did a large ice knife 3 part casting for ice breaker ,just from side profile and some section/waterline/buttock sketches no offsets for last 10 or 20 feet of hull at bow put out 3 views full-size and faired it in. see photos of VAN SHIP pin jigs I did pin heights off 10th scale loft scrieve years ago see new English wheel press for plate forming