best way to build very long, non aerodynamic craft?

[Mantis Toboggan]

After spending hours docking modules in orbit for my new interplanetary ship, I fired up its engine and proceeded to make a new circular orbit. Using mechjeb, docking struts, and many other mods, I proceeded to do this, only to learn that even with stabilizing struts, my ship cannot do anything. Worse yet, with even a single docking strut link, my ship starts spiraling out of control. I am now unable to build my behemoth, and I have nothing to do. Any ideas?

[allmhuran]

What parts compose the spine of the craft? Do you have a picture?

Structural girders form pretty strong connections but do have a little bit of flex. I-beams are similarly strong but slightly more flexible than girders.

If you're building a really, REALLY long ship, you might have to consider redesigning the core. Create secondary or even tertiary spines of structural parts.

Build your docking joins using multiple docking ports. The wider spread the ports are the better, but getting things perfectly aligned when spreading the ports across a wide area can be challenging. If using a tricoupler or quad-coupler the ports are easier to align, but being so close together they do not provide as much resistance to wobble.

[Johnno]

Depends on your definition of 'very long'. You could try to pull your ship instead of pushing it. Alternatively, go through every part of the ship individually to see if there's any single piece that makes it act wonky. There are bugs that can result in phantom forces which will make your ship spin, if even a small component of your ship has that it'll end up spinning the whole ship. I had that happen on a recent mission where a small probe had some conflicting pieces (likely cubicstruts) and made the whole ship spin. Removed the probe and the rest of the ship was fine.

[superm18]

This works fine for me:

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Edited August 5, 2013 by superm18

[Mantis Toboggan]

This works fine for me:

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How can you do this without the docking ports making everything wobble around?

[allmhuran]

As mentioned by Johnno, a long structure with the rockets near the front pulling it tends to wobble less than a long structure with rockets at the back pushing it.

[Donziboy2]

Turn off gimbals for one, only run the reaction wheels at the front or back of the craft also. A small wobble gets amplified by all the reaction wheels and gimbals on your engines. I usually use a central engine with gimbals or turn them all off.